Soil nitric oxide emissions from two subtropical humid forests in south China
一氧化氮与臭氧反应 方程
一氧化氮與臭氧反應方程英文回答：Nitric oxide (NO) and ozone (O3) can react with each other to form nitrogen dioxide (NO2) and oxygen (O2). This reaction can be represented by the following equation:2NO + O3 → 2NO2 + O2。
In this reaction, two molecules of NO react with one molecule of O3 to produce two molecules of NO2 and one molecule of O2. The reaction is exothermic, meaning it releases energy in the form of heat.The reaction between NO and O3 is an important processin the atmosphere. It plays a role in the formation and depletion of ozone in the troposphere. When NO and O3 react, they form NO2, which is a key component in the formation of smog. Smog is a type of air pollution that is harmful to human health and the environment.For example, let's say I live in a city with highlevels of air pollution. The air quality index (AQI) isoften in the unhealthy range, and I can see a brownish haze in the air. This is a result of the reaction between NO and O3. The NO emissions from vehicles and industrial sources combine with the O3 present in the atmosphere, leading tothe formation of NO2 and the brownish smog.中文回答：一氧化氮（NO）和臭氧（O3）可以相互反应生成二氧化氮（NO2）和氧气（O2）。
Biochar Effects on Soil Nutrient Transformation
13Biochar Effects on Soil Nutrient Transformations
Tom H. DeLuca, M. Derek MacKenzie and Michael J. Gundale
Introduction
Nutrient transformations are influenced by a myriad of biotic and abiotic factors. However, to date, there have been no attempts to synthesize the literature regarding the influence of biochar on soil nutrient transformations. Although the major focus of this book is to review biochar as a soil amendment in agro-ecosystems, the majority of the literature that addresses the effects of biochar on nutrient transformations has originated from studies in natural forest ecosystems. The addition of biochar to forest soils has been found to directly influence nitrogen (N) transformations in phenol-rich acidic forest soils of both temperate (DeLuca et al, 2006; Gundale and DeLuca, 2006; MacKenzie and DeLuca, 2006) and boreal (DeLuca et al, 2002; Berglund et al, 2004) forest ecosystems. Applying biochar to forest soils along with natural or synthetic fertilizers has been found to increase the bioavailability and plant uptake of phosphorus (P), alkaline metals and some trace metals (Glaser et al, 2002; Lehmann et al, 2003; Steiner et al, 2007), but the mechanisms for these increases are still a matter of speculation. Biochar additions to soil have been found to stimulate mycorrhizal infection (Saito, 1990; Ishii and Kadoya, 1994) and influence P solubility in forest soils (Gundale and DeLuca, 2007), which may be responsible for observed increases in P uptake. The influence of biochar on sulphur (S) transformations has received little or no attention and has not stood out as a dominant effect of adding biochar to natural soil environments. However, biochar applications to mineral soils may have a noted effect on P and S transformations in manure-enriched agro-ecosystems. The mediation of nutrient turnover by biochar has significant implications for organic agricultural systems where biochar may increase stabilization of organic nutrient sources (Glaser et al, 2001) and reduce nutrient leaching losses (Lehmann et al, 2003). The purpose of this chapter is to provide a state-of-knowledge review of the influences of biochar on N, P and S transformations in soil ecosystems and to provide an overview of the known and potential mechanisms driving
氧化亚氮
Annual emissions of nitrous oxide and nitric oxide from a wheat—maize cropping system on a silt loam calcareous soil in the North China Plain氧化亚氮一氧化氮小麦和玉米套作耕作制度粉砂壤土石灰土华北平原在华北平原小麦与玉米轮作体系下粉砂质钙质土年N2O和NO排放量Nitrogen amendment followed by flooding irrigation is a general Management practice for a wheate maize rotation in the North China Plain, 在小麦-玉米轮种的华北平原，尽量减少氮排放一个主要方式是采用漫灌。
which may favor nitrification and denitrification.而这种漫灌的方式很有可能导致硝化作用和反硝化作用。
Consequently, high emissions of nitrous oxide (N2O) and nitric oxide (NO) are hypothesized to occur.因此，在这种条件下，大量的氧化亚氮和一氧化氮排放作为一种假设可能会发生。
To test this hypothesis, we performed year-round field Measurements ofN2O and NO fluxes from irrigated wheat-maize fields on a calcareous soil applied with all crop residues using a static, opaque chamber measuring system.为了验证这种假设，我们运用了一种静态箱检测系统，花了一整年的时间实地测量了石化土上小麦-玉米轮种水浇地里所有作物秸秆释放氧化亚氮和一氧化氮的流量。
光化学污染对城市大气的影响(英文)
Effects of photo-chemical smog on urban airAbstract:Summary: along with the sustained and rapid development of China's economy, fuel consumption is increasing. Atmospheric carbon monoxide, nitrogen oxides and the emissions of pollutants such as hydrocarbons are also growing rapidly, these are raw material for formation of photochemical smog. Photochemical smog, once formed, affected a wide range. Its dangers have been on the urban environment, human health, and ecological balance causing great threat. Carry out energy-saving emission reduction policies, it is imperative to control emissions of air pollutants. This article is about the production of photochemical smog, and briefly describes the hazards and prevention measures.I. The production of photochemical smogOf atmospheric nitrogen oxides and hydrocarbons react to form photochemical smog, UV irradiation. The atmosphereNitrogen oxides are mainly from fossil fuel combustion and incineration of the plant, and the transformation of agricultural soils and animal waste. Among them, with automobile exhaust gas as the main source. [1]Formation of photochemical smog:1. The condition of pollutionIndustrial emissions, vehicle exhaust emissions such as nitrogen oxides and hydrocarbons.2. Meteorological conditions2.1 strong lightNO2 photolysis is a 290~420nm ' light, therefore, likely to in summer than in winter, around noon in the day light most likely to smoke.2.2 low winds, low humidity, weather temperature inversion.3. Geographical conditionsSolar radiation is one of the main conditions, intensity of solar radiation, depending on the height of the Sun, solar radiation angle with the ground and atmospheric transparency. Therefore, the concentration of photochemical smog, except under the influence of the diurnal variation of solar radiation, but also by the latitude, altitude, season, weather and other conditions influence. Studies have shown that at 60 ~ North latitude 60 between some major cities, smog can occur. [2] II.Second, the harm of photochemical smogPhotochemical smog is strongly oxidizing, stimulate the eyes and the respiratory tract Mucosa, injuries, accelerated ageing of rubber plant leaves, and reduced visibility. Harmful to human, animal and plant and materials is mainly ozone, PAN and secondary pollutants such as Acrolein and formaldehyde. Ozone, PAN can cause rubber products such as ageing, embrittlement, makes dyes fade, and damage to paint and coatings, textile fibers and plastic products. [3]Harmful effects is mainly manifested in the following aspects:1. The risk to human and animal health:Major injury to human and animal eyes and mucous membrane irritation, headache, respiratory disorders, abnormal lung function deterioration of chronic respiratory diseases, children and so on.Ozone is a powerful oxidizing agent. In 0.1ppm concentrations, it has a special smell. And can achieve deep stimulation under the mucosa of the respiratory system, causing chemical changes, it acts as a radiation, chromosomal abnormalities, red blood cell aging. PAN, formaldehyde, Carolina and other products for people and animals such as eye, throat and nose have a stimulating effect. Their domain is0.1ppm. Photochemical smog in addition can help asthma patients asthma attack, it can cause deterioration of chronic respiratory diseases, respiratory disorders, damagethe lungs and other symptoms of long-term inhalation of antioxidants can reduce the human cell's metabolism accelerate aging. PAN was reagents may cause skin cancer. In the 1943 United States Los Angeles the first event has attracted more than 400 people dead.2. Effects of plant growth:Ozone affect the permeability of plant cells. High performance can lead to good qualities disappear, even the loss of plant genetic ability. Ozone damage to plants, skin fade at the beginning was wax-like pigment changes over time reddish-brown spots appear on the leaves. Back of PAN leaves silver gray or bronze effect plant growth and reduce the plant's resistance to pests and diseases.3. Material quality:Contributes to formation of acid rain caused by photochemical smog rubber ageing, embrittlement, makes dyes fade paint buildings and machinery from corrosion and damage coatings, textile fibers and plastic products.4. Reduce the visibility:Photochemical smog is one of the most important characteristics of atmospheric visibility--visual range is shortened. This is mainly due to the formation of photochemical smog pollution in the atmosphere caused by aerosol. The aerosol particle size within the General 0.3~1.0 μ m. Due to the size of particles is not easy because gravity deposition can actually migrate long distances suspended in the air for a long time they are consistent with Visual wavelength and scatter sunlight, thus significantly reducing the atmospheric visibility. Thus impaired the car with the safe operation of aircraft, and other transport, leading to increased traffic accidents.5. Other hazards:Photochemical smog will accelerate the aging of rubber products and cracking, corrosion of buildings and clothing and shorten its life. [4]III.The mechanism of photochemical air pollution treatmentFirst of all, to understand the cause of photochemical smogMechanism of formation of photochemical smog: [5](1) The formation of photochemical smog conditions is the presence of nitrogen oxides and carbon dioxide in the atmosphere, atmospheric temperature is low, and there is strong sunlight, this will be a complex series of reactions in the atmosphere, generating some secondary pollutants, such as aldehydes, PAN, H2O2 and O3.Photochemical smog is a chain reaction, in which the key reactions can be simply divided into 3 groups: (1) formation of NO2 photolysis of O3: Chain initiation reaction of NO2 photolysis, reaction is as follows:NO2 +HV→NO +O O +O2 +M→O3 +M NO +O3→NO2 +O2(2) Hydrocarbons (HC) oxidation activity of free radicals, such as HO, HO2, RO2. In photochemical reactions, free radical reaction plays an important role, the free radical reaction is mainly caused by NO2 and resulting from formaldehyde photolysis:NO2 + HV→NO +O RCHO + HV→RCO +HThe presence of hydrocarbons is the root cause of transformation and proliferation of free radicals:RH +O→R +HO RH + HO→R +H2O H + O2 →HO2 R + O2→RO2 RCO+O2→[RC(O)O2]Where: r-n;RO2-alkyl peroxide; RCO-acyl;[RC ((O) O2]-benzoyl peroxide.(3) Through the above channels generated HO2, RO2, [RC ((O) O2] oxidation of NO to NO2.NO +HO2 →NO2 +HO NO +RO2→NO2 +RO RO +O2 →HO2 +RCHO NO + RC(O)O2→NO2 + RC(O)O RC(O)O→R +CO2Where: RO-alkoxy;RCHO-aldehyde①main pollutants of photochemical pollution from internal combustion engineCar ownership in the world has more than 500 million vehicles, vehicle output of more than 50 million vehicles a year. In the advanced industrialized countries, car exhausts constitute the main cause of air pollution. China's rapid growth in recent years, car production, without effective ways to control vehicle exhaust emissions on atmospheric formation of great harm. NOx is the formation of photochemical smog and acid rain pollutants in the atmosphere.Vehicle exhaust is a great mobile pollution sources, management is difficult. Currently recommended is using the method of exhaust gas purification system, it is the use of catalysts reduce exhaust gas phase activation energy in the process, improve the reaction speed. Especially for NOx control. Even though the installation of electronic-controlled air compensation device, also appears cold starts, fill valve not working, slow, prolonged idling, resulting in excessive emissions [6] in response to this situation, many scholars with an atmospheric pressure non-equilibrium plasma method to eliminate pollutants in automobile exhaust NOx. Atmospheric pressure non-equilibrium plasma is fast developing interdisciplinary disciplines, it has great potential and attractive prospects. [7] Japan set Fang Zhengyi, Xiao Tian Zhezhi, Shui Yezhang have been engaged in research on non-equilibrium plasma discharge pollutants, and certain progress has been made. East and tengjingkuanyi reported by discharge plasma beam control automobile exhaust, Ox removal rate of up to 29.2%.[8]Therefore, I think that the governance of photochemical smog pollution in the atmosphere, first of all, it is necessary to control Pollutants in automobile exhaust.Internal combustion engine exhaust contains a number of components, the basic ingredients are carbon dioxide (C02), water vapor (H20), excess oxygen (02) andkeep left nitrogen (N2), which is the result after the complete combustion of the fuel and air. In addition to these basic ingredients, exhaust also contains incomplete combustion products and combustion reaction intermediates include carbon monoxide (CO), hydrocarbons (HQ), Secretary of nitrogen oxides (Ox), Sulphur dioxide (S02), solid particles and aldehydes. Total quality of these components in the exhaust gas of diesel engine as a proportion of the not less than 1% of the total emissions in a diesel engine, sometimes up to about 5% in a gasoline engine, and most of them are harmful, or has a strong pungent odor, and some still have carcinogenic effects. Exhaust of harmful components, see table 2-1:Table 2-1: all kinds of harmful exhaust componentsInternal combustion engine emission pollutants nitrogen oxides (n Ox), carbon monoxide (CO), hydrocarbons (HC) air pollution is mainly caused by substances, these pollutants on human and environmental hazards are as follows [9]1. A nitric oxide (n Ox)Nitrogen oxides in the combustion chamber under high temperature and high pressure, nitrogen and oxygen. Nitrogen oxides in the exhaust (n Ox) includes NO, N02, N203, N20, N205, and N03 and so on. After combustion, the fuel discharged from the exhaust pipes of the nitrogen oxides in about 90%-95% NO, few N02, NO is a colorless gas that is highly unlikely after the encounter with the oxygen in the atmosphere will be further oxidized to N02. N02 Brown has a strong pungent odor, n Ox react in the atmosphere to form aerosols, oxygen phthalocyanine based nitric acid, nitric acid, nitrous acid, Nitro hydrocarbons as well as highly carcinogenic nitrosamines, directly harm to humans, animals and plants, and the environment. N Ox is the main cause of photochemical smog formation in the ground.2. Carbon monoxide (CO)Carbon monoxide is a product of incomplete combustion of fuel, seriously affecting the combination of hemoglobin in human blood and oxygen, life-threatening, and participate in various chemical reactions in the atmosphere, has an important role in the formation of smoke and methane.3. Hydrocarbon (HC)Hydrocarbons, including unburned hydrocarbons and incomplete combustion of fuel, lubricating oil and its pyrolysis and partial oxidation products, such as alkanes, alkenes, aromatics, aldehydes, ketones, and hundreds of compounds. Some hydrocarbons do not react, such as methane, ethane, propane, carbon and hydrogen and other reaction (NRHC) and so on. The percentage of non-methane hydrocarbons (total hydrocarbon 100%, minus the percentage of methane is non-methane hydrocarbon ratio), the smaller the better. HC contains benzene is considered to be a carcinogen if inhalation of gaseous benzene would reduce the red and white blood cells, reducing the number of platelets, in people exposed to large amounts of benzene can cause leukemia. Of these pollutants, HC, CO and n-Ox is a major exhaust pollutants. CO and HC can improve the structure of internal combustion engine for combustion and EGR and after treatment technology is effectively controlled,advanced countries have reached discharge standards. N Ox oxidation of N2 in the temperature in the cylinder is formed only by machine processing, cumbersome and difficult to governance, become the main object of study.Second common method of controlling internal combustion engine exhaust gasIn general reduce harmful ingredients in the exhaust gas of internal combustion engines, can be solved by two ways: one is the internal purification, the other is discharging to the exhaust pipe of the cylinder exhaust gas after treatment.1. The internal purificationInternal purification consists of the following measures:⑴improved combustion chamber design, compression ratio and spray nozzles, spray to improve the efficiency of combustion.B suction system air intake preheating temperature.C ignition system delayed ignition, after shortening the flame burning time.⑷firing system using lean combustion and high energy ignition.⑸using exhaust gas recirculation system to reduce n Ox.Services implementing secondary air combustion technology of exhaust pipes.2. Treatment after purificationInternal combustion engine exhaust gas purification technology is of NO x, HC, CO gas phase emission purification, usually using oxidation and reduction methods, with the help of catalysts to convert these harmful gases into N2, H20, CO2, this purification technology has been applied to gasoline engines. In addition to the gas in a diesel engine harmful ingredients, there are made up of solid-phase soluble hydrocarbons and soot particles, these substances are not in real time in the exhaust system catalyst for purifying, suitable particulate filter must be placed in the exhaust tube collection device, when soot particles as the main body to collect micro-particles to a certain number of heaters can be used to burn.Post-processing method in internal combustion engine are described as follows: [10] ①the exhaust gas recirculation (EGR)EGR (Exhaust Gas Recirculation EGR for short) is a fraction of the combustion emissions from exhaust pipes to introduce pipe mixed with fresh air, then burn. Exhaust gas recirculation through the following three aspects lower engine combustion temperatures, decrease the formation of n-Ox:A. improving the heat capacity of the heat capacity of the gas because the CO2 is 1.5 times of the O2, more of the mixture of exhaust gas heat capacity is higher.B. reduced O2 concentration in the mixture as part of the air are replaced by exhaust gas, mixture of O2 content was reduced accordingly.C. low combustion rate above two effects that reduce engine combustion speed, increase the heat of combustion chamber, reducing the maximum burning temperature.Ternary Catalysis II [11] such an approach can also purify the three main pollutants in the exhaust of gasoline engine C0, HC and n Ox. Three-way catalytic converter, is mounted in the exhaust system is the most important machine cleaning device, it can exhaust emission of CO, HC and n Ox and other harmful gases by oxidation and reduction into harmless carbon dioxide, water and nitrogen. Dang high temperature of car exhaust through purification device Shi, ternary catalytic device in the of purification agent will enhanced CO, and HC and n Ox three species gas of activity, prompted its for must of oxidation-restore chemical reactions, which CO in high temperature Xia oxidation became colorless, and nontoxic of carbon dioxide gas; HC compounds in high temperature Xia oxidation into water (H20) and carbon dioxide; n Ox restore into nitrogen and oxygen. Three types of harmful gases into harmless gas, purification of vehicle exhaust gas.IV. ConclusionThe World Health Organization (WHO) and the United States, and Japan and many other countries have ozone and photochemical oxidant levels serve as one of the air quality index, and photochemical smog warning was issued. Environmental protection has become an important subject in sustainable economic development, harm has drawn great attention of photochemical smog. While the world's growing environmental awareness, resistance to photochemical air pollution, prevent the occurrence of photochemical smog, is conducting a worldwide reduction of energy and automobile exhaust pollution cleaning revolution.Urban air pollution is closely linked to levels of economic development, and that China is in a period of rapid development, urban air pollution has become a major environmental problem. In order to prevent outbreaks of photochemical smog, in addition to the above methods, the means of interference of executive order must also be taken in order to have better results.V、Reference[1] Kang Xihui, Liu Meiqing, principles and applications of photochemistry, Tianjin: Tianjin University Press, 1984,1~21[2] Zhang Li; Analysis on photochemical smog pollution, Shandong: 1001-3644 (2005)04-0074-03[3] the voyage, Shao kesheng, Tang Xiaoyan, Li Chin; urban photochemical smog pollution in China [j]; Journal of Peking University (natural science Edition), 1998, Z1[4] The State environmental protection administration. Ozone layer damage [DB/OL]./ztbd/gjcyr/jbcs/200408/t20040830_60877.htm, 2004-08-30[5] The concise course of Biochemistry in early Xia Jian, Beijing: higher education press, 1992,56~601[6] Wan Junhua Xia Y unqing combustion theory based Harbin ship Engineering Academy Publishing House, 1992[7] Guo Guangyong. Experimental study on dielectric barrier discharge treatment of internal combustion engine exhaust gas NOx [d]. Dalian Maritime University, 2002.[8] Li Meng. Japan is how to control air pollution [j]. Legal persons, 2014 (4): 27-30.[9] zhoulongbaoliuchangjungaozongying internal combustion engine mechanical industry publishing house, 1999.[10] Guo Guangyong. Experimental study on dielectric barrier discharge treatment of internal combustion engine exhaust gas NOx [d]. Dalian Maritime University, 2002.[11] The Chen Chong. Catalytic converter structure and performance evaluation [j]. Journal of Sichuan industrial Institute, 2001, 20 (4): 1-3.。
2021年牛津英语译林版九年级中考复习英语阅读强化训练 15(含答案)
牛津英语译林版九年级英语阅读强化训练15一、完形填空I never saw my father come home from work late or ill, nor did I ever see my father take a “night out with the boys”. He had no ___1___ but just took care of his family.For 22 years, since I left home for college, my father had called me every Sunday at 9:00 a. m. He was always ___2___ in my life how my family was going. The ___3___ even came when he and my mother were in Australia, England or Florida.Nine years ago, I bought my first house. My father, 67 years old, spent eight hours a day for three days, ___4___ my house. He would not allow me to ___5___ anyone else to have it done. All he asked was a glass of iced tea, and that I hold a paintbrush for him and talk to him. But I was too ___6___ with work, and I could not spend the time holding the paintbrush, or talking to my father.Five years ago, my 71-year-old father ___7___ five hours putting together a swing set for my daughter. Again, all he asked was that I could get him a glass of ___8___ tea and talk to him. But again, I had laundry to do and the house to ___9___ .The morning on Sunday, January 18, 2015, my father telephoned me as usual. This time he ___10___ to have forgotten some things we had discussed the week before. I had to get to church, so I cut the ___11___ short.The call came at 4:40 a. m. which said my father was sent to hospital in Florida. I got on a plane ___12___ . I vowed that when I arrived, I would ___13___ for the lost time, for I owed him a nice long talk.I arrived in Florida at 1:00 a. m. , but my father passed away at 9:12 p. m. This time it was he who did not have time to ___14___ , or time to wait for me.In the years ___15___ his death I have learnt much about my father, and even more about every single day.1. A. money B. sleep C. hobbies D. freedom2. A. interested B. surprised C. excited D. confused3. A. emails B. calls C. letters D. messages4. A. repairing B. keeping C. building D. painting5. A. show B. pay C. explain D. teach6. A. busy B. bored C. pleased D. angry7. A. used B. wasted C. spent D. took8. A. green B. hot C. black D. iced9. A. clean B. build C. repair D. buy10. A. happened B. decided C. proved D. seemed11. A. introduction B. conversation C. meeting D. interview12. A. carelessly B. rarely C. fluently D. immediately13. A. set up B. hang up C. makeup D. lift up14. A. call B. meet C. talk D. work15. A. during B. since C. before D. until二、阅读理解AA. On foot.B. By car.C. By bike.D. By bus.2. Which of the following is TRUE about Ted and Peter?A. They are brothers.B. They look alike.C. They are classmates.D. They are both shy.3. On Ted’s web page, we can see photos of his ______ .A. familyB. roomC. favourite starsD. tennis team4. How many hobbies are mentioned on Ted Smith’s web page?A. Three.B. Four, oC. Five.D. Six.5. From Ted Smith’s web page, we know ______ .A. Ted is a boy with brown hair and blue eyesB. Ted lives in an apartment at the city centreC. Ted’s room is always in a messD. Ted likes horror movies bestBBy converting leftover cooking oil into fuel for vehicles, Shanghai has made big steps in developing the circular economy.The recycled waste fuel, called B5 biodiesel, is a biofuel mixture consisting of 5 per cent biodiesel, which is made from thrown-away oil from restaurants and sewer pipes, and 95 per cent petroleum diesel fuel.B5 biodiesel produces 10 per cent less heavy metal substances and fine particulate matter, and 80 per cent less nitric oxide emissions compared to the exhaust from ordinary diesel. It first entered the fuel market in Shanghai in September 2013 when buses from a bus company hit the road in a trial project. An examination of the vehicles running on B5 biodiesel conducted by Shanghai’s Tongji University showed that the emission standards from the vehicles had improved notably and no malfunctions had been reported.In May 2019, buses from Shanghai Jiushi officially started running on biodiesel. By the end of 2020, the bus company had used up 50. 85 million litres of B5 biodiesel. Over the past year or more, all bus parking lots under the bus company have adopted B5 biodiesel, using up more than 20 000 tonnes of the fuel. By the end of 2020, the qualification rate of B5 biodiesel was 100 per cent, as showed by examinations carried out by national and municipal quality supervision departments.It took Shanghai 10 years to finally introduce the biodiesel into the market. As a megacity, Shanghai produces more than 30 000 tonnes of discarded kitchen oil each year, while there are 18 recycling companies in the city that refine the gutter oil for production of B5 biodiesel. In 2013 and 2018, the city issued management guidelines to encourage recycling, transportation and processing of discarded cooking oil Shanghai demanded that recycling businesses purchase discarded cooking oil at a price of no less than 3 600 yuan per tonne. In addition, italso provides a subsidy up to 0.24 yuan per litre of B5 biodiesel for oil companies.Now, the fuel is being sold at 5.72 yuan per litre compared with 6.02 yuan for standard diesel. Shanghai’s environmental sanitation department, for instance, could save 100 000 yuan in costs in a year from 30 sanitary vehicles running on biodiesel rather than on standard diesel.1. According to the passage, what does Shanghai do in developing the circular economy?A. Shanghai changes discarded oil into biodiesel.B. Shanghai controls the use of leftover cooking oil.C. Restaurants recycle leftover cooking oil.D. Shanghai reuses 95% of the leftover cooking oil.2. What’s the main idea of Paragraph 3?A. It is more difficult to produce B5 biodiesel than ordinary diesel.B. B5 biodiesel is easier to produce heavy metal substances compared to ordinary diesel.C. B5 biodiesel is better for the environment than ordinary diesel.D. Ordinary diesel is better for the environment than B5 biodiesel.3. Why did Shanghai issue management guidelines in 2013 and 2018?A. To introduce B5 biodiesel into the market in a short time.B. To encourage and carry forward the leftover oil recycling project.C. In order to set the standards for the B5 biodiesel production.D. In order to ask more companies to refine gutter oil for B5 biodiesel.4. What does the underlined word”purchase” mean in the passage?A. Produce.B. Create.C. Collect.D. Buy.5. What can we infer from the passage?A. There will be no leftover oil in Shanghai.B. B5 biodiesel is helpful to the circular economy.C. B5 biodiesel makes vehicles run much faster.D. Gutter oil recycling companies earn more.CHave you ever heard of character amnesia? Amnesia refers to a condition where someone loses all or most of his or her memory. The word may be too strong to use. With character amnesia, however, it means people have forgotten to put the correct stroke (笔画) in a character or have forgotten the character completely.Character amnesia is partly caused by the popularity of electronic communication. Today, most people write using computers or other electronic devices. These devices all have input software. You can easily type in a character even if you don’t know how to form it.Back in 2013, CCTV held an interesting TV contest. Contestants were given a word and then asked to write it on a screen. Some of them had a hard time writing such common words as “癞蛤蟆” and “打喷嚏”. The audience at home were encouraged to try writing these words at the same time. The contest showed how widespread character amnesia had become. It led much discussion. The audience felt surprised. For teachers, however, it was just old news.Su Yunsheng has taught Chinese for more than twenty years. She says, “In recent years, character amnesia has become more and more common among students. I often see students write words incorrectly. The popularity of electronic devices is a major reason.” Su is not the only one complaining. Many experts think not being able to write characters correctly threatens China’s cultural heritage(遗产).“It will take a lot of effort to protect our Chinese characters. It is the same way in which they try to protect these old hutongs,” said Zhu Linfei, a Beijing graduate student, referring to the traditional Beijing roads. Zhu, who was touring the old bookstores of Liulichang with her classmates to buy calligraphy (书法) books, said that she had already forgotten about 20% of the characters she knew in high school. “But it’s not such a big problem,” she said. “If I don’t know a character, I take out my cellphone to check.” But Zhu Linfei is mistaken. It is a big problem that she cannot write 20% of the characters she knew just 5 or 6 years earlier. By relying on her cellphoneto check those characters she can’t recall, that percentage will increase with each passing year. And, every time Zhu Linfei has to stop to take out her cellphone to ask for help to remind herself how to write a character, she is wasting time, and that in itself is a problem.Written Chinese requires a good memory and a lot of hard work. But Chinese characters are a great cultural achievement, Chinese people should be proud of it. It will be a pity if we lose that heritage someday. The threat is nothing to sneeze at!1. If you have character amnesia, you probably ______ .A. cannot write any Chinese charactersB. have lost all or most of your memoryC. have to check some characters on your computerD. don’t know how to write some characters correctly2. From the interesting CCTV contest in 2013, we can infer many of us ______ .A. have character amnesiaB. lose interest in Chinese charactersC. rely on electronic devices to helpD. start to study hard at Chinese characters3. Which of the following about Su Yunsheng is WRONG?A. She asks her students not to write by using computers.B. She has been a Chinese teacher for more than 20 years.C. She has seen many students suffer from character amnesia.D. She thinks character amnesia is mainly caused by electronic devices.4. By writing this passage, the writer probably wants to ______ .A. explore the causes of character amnesiaB. advise people not to write by using electronic devicesC. ask people to pay attention to the threat of character amnesiaD. tell readers the difference between amnesia and character amnesia5. What’s the best title for the passage?A. The benefit of studying ChineseB. The threat of character amnesiaC. Writing Chinese characters correctlyD. Protecting Chinese characters activelyDCurtis Whitson knew the waterfall was coming. He’d rafted down the Arroyo Seco, a river in central California before. He thought he would jump out of his raft into the shallow water, raft down the rocks on either side of the falls, and continue on his way, as he had on last trip.But this year was different. Heavy snow and spring rains had turned the usually manageable falls into something wild. Whitson went rafting with his girlfriend, Krystal Ramirez, and his 13 year-old son, Hunter. As they reached the falls late in the afternoon, Whitson could tell from the increasing water that they were in serious trouble. There was no way they’d be able to raft down the rocks as planned.They could walk to the shore, but would anyone find them there? They had no cell service, and they hadn’t seen a single person in the past three days. And Whitson knew that they’d be sharing the ground there with snakes and mountain lions.As he thought what to do, Whitson hit on a bit of luck he heard voices coming from the other side of the falls, He shouted, but the sound of the rushing water drowned him out. “We have to give these people a message,” Whitson thought. He got a stick and pulled out his pocket knife to carve “Help” on it. Then he tied a rope to it so the people would know it wasn’t just any stick. He tried throwing it over the falls, but it floated away in the wrong direction.“We’ve got to do something!” Whitson shouted to his son. “Have we got anything else?”Then he saw his green water bottle. Whitson took it and carved “Help!” on it. Ramirez also reminded him that he had a pen and paper, which she ‘d brought to play games with, in his backpack.Whitson knew it was a long shot, But he wrote “We are kept here at the waterfall. Help us please.” and put the note into the bottle. This time, his throw over the waterfall was perfect.It took 30 minutes to get back upstream to the beach where they’d had lunch. They made a fire and set up a tent. They were afraid that nobody could find their message in a bottle, so they spelled out SOS in white rocks, which they set on the blue tarp. As the evening wore on, they placed a headlamp with a flashing light on a ledge so that the SOS could be seen from overhead.By about 10:30 p. m. , they decided they probably weren’t going to get rescued that night, so they pulled out their sleeping bags. Before getting in, Ramirez made the fire to keep the mountain lions away.Then, just after midnight, they heard a plane flying above them. Whitson turned to his son and started shaking him. “They re here!” he said. Whitson ran over to the headlamp and started flashing it at the plane. He, Ramirez, and Hunter were waving and shouting when they heard the magic words, “This is Search and Rescue. You have been found.”At this time, the three knew that they were really rescued. It was amazing!文章选自美国著名杂志《读者文摘》(Reader’s Digest)1. From the second paragraph, we mainly know that ______ .A. they were in serious troubleB. there was heavy snow and rainC. the three persons were raftingD. they could raft down the rocks2. To get these people a message, Whitson ______ at first.A. put the note into the bottle and threw it over the fallsB. threw a stick with the word”Help” on it over the fallsC. placed a headlamp with a flashing light on a ledgeD. called 911 and asked them to save them with a plane3. They placed a headlamp with a flashing light on a ledge ______ .A. to keep snakes and lions awayB. to read something with the lightC. to help make a fire to get warmD. to let someone see SOS from overhead4. Which of the following is the CORRECT order according to the story?a. He tried to throw the stick over the falls.b. He put the note into the bottle and threw it.c. They heard a plane were flying above them.d. He heard voices coming from the other side.e. They got to the beach where they had lunch.A. d-b-a-c-eB. b-a-c-e-dC. d-a-b-e-cD. e-a-c-d-b5. What is the ending of the story?A. The three persons were saved.B. The plane didn’t find them.C. The three persons went on their rafting.D. The three persons didn’t hear the plane.三、任务型阅读AOne of the most common questions I am asked is whether, when, and how to follow up after a job interview. Following up in some way is necessary. Yes, you can get a job without it, but if you compete with other top candidates (候选人), following up can sometimes help you when the other candidates don’t. Here’s how to follow up well:Send a thank-you note right away.Email is fine for this and has the advantage of arriving faster, but handwritten notes are still enjoyed. And if there are many interviews, send a thank you note each time.Find out their timeline. Hopefully, you asked about their timeline in the interview itself, but if you didn’t, follow up within a week to strengthen your interest and politely ask what they expect their timeline for a decision to be.Be patient. Commonly, job seekers (求职者) are too worried about the result. You needn’t look worried to express your interest in the job or check in to ask about the timeline.Don’t be nervous if you don’t her from them at once. The hiring process (招聘流程) often takes longer than a candidate would like. Maybe the decision makers are out of town. If you miss the time they told you to hear something, it’s unnecessary to be nervous. Hiring often ends up taking longer than expected. Just politely follow up, explain you re very interested but understand that hiring will take time, and ask if they have the latest timeline.A young lady was driving a family car home with her father when they were caught in a heavy storm. The young lady was a little afraid and asked her father, “What should I do, stop or keep driving?”Her father said, “Keep driving.”After driving a few kilometres, the storm was becoming heavier and heavier. The young lady noticed that some cars and big transport trucks were pulling over on the side of the road. The young lady asked her father again if they should stop. But her father said nothing. So, she had to keep on driving.Ten minutes later, the storm started to become small and she could see a little more clearly. After several kilometres, she drove out of the storm. Moreover, the sun came out and the road ahead was dry.Her father told her to stop and get out of the car. “But why now, Father?” she asked in surprise.Her father said, “When you get out, you can look back at all the people in cars and big trucks that gave up and they are still in the storm. Now, your storm is over because you didn’t give up.”If you keep going, soon your “personal storms” will be over. The sun will shine on you again and the road ahead will be dry and clear. So, never give up and keep moving.根据短文内容, 回答下列问题。
土壤溶解性有机碳组分连续分级测定方法
科技创新导报 Science and Technology Innovation Herald83DOI：10.16660/ki.1674-098X.2018.29.083土壤溶解性有机碳组分连续分级测定方法①臧榕 赵海超*黄智鸿 赵海香 乔赵崇(河北北方学院 河北张家口 075000)摘 要：有机碳是土壤中的重要组分，有机碳组分是影响土壤有机碳活性及生态效应的主要内因。
为更好的揭示有机碳组分对生态环境演变的响应规律，系统的分级土壤有机碳是研究的重点。
该研究为获得土壤有机碳多级浸提方法，在前人研究的基础上选择四种浸提剂，确定浸提时间，并对冀北坝上土壤进行测定。
结果表明，浸提方法为：（1）水溶性有机碳，按照土水质量比1:2加入去离子水，振荡浸提12h，获得低分子量活性有机碳，占总有机碳的1.13%～3.35%；（2）热水解有机碳，残渣加入去离子水，在100℃下水浴2h，获得土壤团聚体表面吸附的有机碳等，占总有机碳2.75%～7.14%；（3）酸解有机碳，残渣加入1mol ·L -1的盐酸，浸提2h，获得富里酸等大分子有机碳，占总有机碳2.11%～7.15%；（4）碱解有机碳，残渣加入0.2mol ·L -1的NaOH，浸提6h，获得胡敏酸等稳定态腐殖质，占总有机碳8.17%～51.07%。
浸提方法能较好反映不同溶解性有机碳组分对土地利用方式的响应。
关键词：土壤 有机碳 溶解性有机碳 连续分级方法中图分类号：S153.6 文献标识码：A 文章编号：1674-098X(2018)10(b)-0083-05A bstract: Organic carbon is an important component in soil, and organic carbon components were the main internal factor affecting soil organic carbon activity and ecological effects. The research of the systematic classif ication of soil organic carbon can be to reveal the response laws of organic carbon components to the evolution of ecological environment. This study had obtained a multi-stage extraction method of soil organic carbon, selected four kinds of extractants based on previous studies to determine the extraction time and determined the soil organic carbon in the Weibei Dam. The results showed that the four extraction methods were followed. (1) To extract water-soluble organic carbon. The deionized water was added to soil according to the mass ratio of soil to water 1:2, and oscillated for 12 h to obtain low molecular weight active organic carbon. It accounted for 1.13%-3.35% of total organic carbon. (2) To obtain thermal hydrolysis of organic carbon. The residue was added to deionized water and heated for 2 h by water bath at 100 °C, and obtained the organic carbon adsorbed on the surface of the soil aggregate. The thermal hydrolysis of organic carbon accounted for 2.75% to 7.14% of the total organic carbon. (3) Fulvic acid and other macromolecular organic carbon (2.11-7.15%) were obtained by acidolysis of organic carbon and adding 1 mol L-1 hydrochloric acid to the residue for 2 h. (4) To obtain alkaliolytic organic carbon. The residue was added with 0.2molL-1 NaOH, and extracted for 6h to obtain stable humus such as humic acid, which accounted for 8.17~51.07% of total organic carbon. The extraction method could better ref lected the response of different dissolved organic carbon components to land use method.Key Words: Soil; Organic carbon; Dissolved organic carbon; Continuous grading method①基金项目：河北北方学院国家级大学生创新创业项目(项目编号：2017003); 河北北方学院卓越农林项目;河北北方学 院博士基金(项目编号：12995543);河北省科技攻关项目（项目编号：13226402D ）;河北省科技支撑重点项目 （项目编号：13226402D ）;张家口科技支撑项目（项目编号：1611050C ）。
土壤碳的固持 英语
土壤碳的固持英语Soil Carbon sequestration: An Essential Process for Sustainable Agriculture and Climate Change Mitigation.Soil carbon sequestration, also known as soil carbon storage or soil carbon fixation, is a critical process in maintaining the health and productivity of soil ecosystems. It involves the stabilization and accumulation of carbon in soil organic matter, which can occur through various biological, chemical, and physical processes. This process is crucial for sustainable agriculture, climate change mitigation, and the overall well-being of the planet.The importance of soil carbon sequestration cannot be overstated. Soils are the largest terrestrial carbon pool, storing more carbon than the atmosphere and all plant biomass combined. This carbon is stored in the form of organic matter, which is composed of dead and decaying plant and animal remains, as well as living microorganisms. When carbon is sequestered in soil organic matter, it iseffectively removed from the atmosphere, thus reducing the concentration of greenhouse gases and mitigating theimpacts of climate change.There are several key processes involved in soil carbon sequestration. One of the most important is photosynthesis, which occurs in plants and converts carbon dioxide into organic matter. When plants die and decay, their carbon-rich remains are incorporated into soil organic matter, contributing to carbon sequestration. Additionally, soil microorganisms play a crucial role in decomposing organic matter and releasing carbon dioxide, which can then be re-fixed by plants through photosynthesis.The management of agricultural systems cansignificantly impact soil carbon sequestration. For example, the use of organic matter in soil amendments, such as compost or manure, can increase the amount of carbon insoil organic matter. Conservation agriculture practices, such as no-till farming or crop rotation, can also enhance soil carbon sequestration by reducing soil erosion and increasing soil organic matter content.The benefits of soil carbon sequestration extend beyond climate change mitigation. Healthy soils are essential for sustainable agriculture, providing a foundation for crop growth and yield. Soil organic matter improves soil structure, water retention, and nutrient cycling, all of which are crucial for crop productivity. By sequestering carbon in soil organic matter, farmers can enhance the fertility and resilience of their soils, leading to improved crop yields and reduced dependence on external inputs.In addition to its agricultural benefits, soil carbon sequestration can also contribute to the achievement of global climate goals. The Intergovernmental Panel on Climate Change (IPCC) has identified soil carbon sequestration as one of the most effective and cost-efficient strategies for reducing greenhouse gas emissions and mitigating climate change. By increasing soil carbon sequestration, we can not only reduce the amount of carbon dioxide in the atmosphere but also enhance the resilience and productivity of our agricultural systems.In conclusion, soil carbon sequestration is a crucial process for sustainable agriculture, climate change mitigation, and the overall well-being of the planet. It involves the stabilization and accumulation of carbon in soil organic matter, which can be enhanced through various agricultural management practices. By sequestering carbon in soil organic matter, we can reduce greenhouse gas emissions, improve soil health and fertility, andcontribute to the achievement of global climate goals. As we face the challenges of climate change and sustainable development, soil carbon sequestration remains an essential component of our efforts to protect our planet and ensure a sustainable future for all.。
fundamentals of soil behavior (3)
5CHAPTER 2Soil Formation2.1INTRODUCTIONThe variety of geomaterials encountered in engineering problems is almost limitless,ranging from hard,dense,large pieces of rock,through gravel,sand,silt,and clay to organic deposits of soft,compressible peat.All these materials may exist over a wide range of densities and water contents.A number of different soil types may be present at any site,and the composition may vary over intervals as small as a few millimeters.It is not surprising,therefore,that much of the geoengineer’s effort is directed at the identification of soils and the evaluation of the appropriate properties for use in a particular analysis or design.Perhaps what is surprising is that the application of the principles of mechanics to a material as diverse as soil meets with as much success as it does.To understand and appreciate the characteristics of any soil deposit require an understanding of what the material is and how it reached its present state.This requires consideration of rock and soil weathering,the erosion and transportation of soil materials,deposi-tional processes,and postdepositional changes in sed-iments.Some important aspects of these processes and their effects are presented in this chapter and in Chap-ter 8.Each has been the subject of numerous books and articles,and the amount of available information is enormous.Thus,it is possible only to summarize the subject and to encourage consultation of the references for more detail.2.2THE EARTH’S CRUSTThe continental crust covers 29percent of Earth’s sur-face.Seismic measurements indicate that the continen-tal crust is about 30to 40km thick,which is 6to 8times thicker than the crust beneath the ocean.Granitic(acid)rocks predominate beneath the continents,and basaltic (basic)rocks predominate beneath the oceans.Because of these lithologic differences,the continental crust average density of 2.7is slightly less than the oceanic crust average density of 2.8.The elemental compositions of the whole Earth and the crust are in-dicated in Fig.2.1.There are more than 100elements,but 90percent of Earth consists of iron,oxygen,sili-con,and magnesium.Less iron is found in the crust than in the core because its higher density causes it to sink.Silicon,aluminum,calcium,potassium,and so-dium are more abundant in the crust than in the core because they are lighter elements.Oxygen is the only anion that has an abundance of more than 1percent by weight;however,it is very abundant by volume.Silicon,aluminum,magnesium,and oxygen are the most commonly observed elements in soils.Within depths up to 2km,the rocks are 75percent secondary (sedimentary and metamorphic)and 25per-cent igneous.From depths of 2to 15km,the rocks are about 95percent igneous and 5percent secondary.Soils may extend from the ground surface to depths of several hundred meters.In many cases the distinction between soil and rock is difficult,as the boundary be-tween soft rock and hard soil is not precisely defined.Earth materials that fall in this range are sometimes difficult to deal with in engineering and construction,as it is not always clear whether they should be treated as soils or rocks.A temperature gradient of about 1ЊC per 30m exists between the bottom of Earth’s crust at 1200ЊC and the surface.1The rate of cooling as molten rock magma1In some localized areas,usually within regions of recent crustal movement (e.g.,fault lines,volcanic zones)the gradient may exceed 20ЊC per 100m.Such regions are of interest both because of their potential as geologic hazards and because of their possible value as sources of geothermal energy.C o p y r i g h t e d M a t e r i a l62SOIL FORMA TIONFigure 2.2Geologiccycle.Figure 2.3Simplified version of the rock cycle.from some other area.Sediment formation pertains to processes by which accumulated sediments are densi-fied,altered in composition,and converted into rock.Crustal movement involves both gradual rising of unloaded areas and slow subsidence of depositional ba-sins (epirogenic movements )and abrupt movements (tectonic movements )such as those associated with faulting and earthquakes.Crustal movements may also result in the formation of new rock masses through igneous or plutonic activity.The interrelationships of these processes are shown in Fig.2.3.More than one process acts simultaneously in na-ture.For example,both weathering and erosion take place at the surface during periods of uplift,or oro-genic activity (mountain building),and deposition,sed-iment formation,and regional subsidence are generally contemporaneous.This accounts in part for the wide variety of topographic and soil conditions in any area.e d M a t e r i a lROCK AND MINERAL STABILITY72.4ROCK AND MINERAL STABILITYRocks are heterogeneous assemblages of smaller com-ponents.The smallest and chemically purest of these components are elements,which combine to form in-organic compounds of fixed composition known as minerals .Hence,rocks are composed of minerals or aggregates of minerals.Rocks are sometimes glassy (volcanic glass,obsidian,e.g.),but usually consist of minerals that crystallized together or in sequence (metamorphic and igneous rocks),or of aggregates of detrital components (most sedimentary rocks).Sometimes,rocks are composed entirely of one type of mineral (say flint or rock salt),but generally they contain many different minerals,and often the rock is a collection or aggregation of small particles that are themselves pieces of rocks.Books on petrography may list more than 1000species of rock types.Fortunately,however,many of them fall into groups with similar engineering attributes,so that only about 40rock names will suffice for most geotechnical engineering purposes.Minerals have a definite chemical composition and an ordered arrangement of components (a crystal lat-tice);a few minerals are disordered and without defin-able crystal structure (amorphous).Crystal size and structure have an important influence on the resistance of different rocks to weathering.Factors controlling the stability of different crystal structures are considered in Chapter 3.The greatest electrochemical stability of a crystal is reached at its crystallization temperature.As temperature falls below the crystallization temper-ature,the structural stability decreases.For example,olivine crystallizes from igneous rock magma at high temperature,and it is one of the most unstable igneous-rock-forming minerals.On the other hand,quartz does not assume its final crystal structure until the temper-ature drops below 573ЊC.Because of its high stability,quartz is the most abundant nonclay mineral in soils,although it comprises only about 12percent of igneous rocks.As magma cools,minerals may form and remain,or they may react progressively to form other minerals at lower temperatures.Bowen’s reaction series,shown in Fig. 2.5,indicates the crystallization sequence of the silicate minerals as temperature decreases from 1200ЊC.This reaction series closely parallels various weathering stability series as shown later in Table 2.2.For example,in an intermediate granitic rock,horn-blende and plagioclase feldspar would be expected to chemically weather before orthoclase feldspar,which would chemically weather before muscovite mica,and so on.e d M a t e r i a l82SOIL FORMATIONFigure 2.5Bowen’s reaction series of mineral stability.Eachmineral is more stable than the one above it on the list.Mineralogy textbooks commonly list determinative properties for about 200minerals.The list of the most common rock-or soil-forming minerals is rather short,mon minerals found in soils are listed in Table 2.1.The top six silicates originate from rocks by physical weathering processes,whereas the other min-erals are formed by chemical weathering processes.Further description of important minerals found in soils is given in Chapter 3.2.5WEATHERINGWeathering of rocks and soils is a destructive process whereby debris of various sizes,compositions,and shapes is formed.2The new compositions are usually more stable than the old and involve a decrease in the internal energy of the materials.As erosion moves the ground surface downward,pressures and temperatures in the rocks are decreased,so they then possess an internal energy above that for equilibrium in the new environment.This,in conjunction with exposure to the atmosphere,water,and various chemical and biological agents,results in processes of alteration.A variety of physical,chemical,and biological proc-esses act to break down rock masses.Physical proc-esses reduce particle size,increase surface area,and increase bulk volume.Chemical and biological proc-esses can cause complete changes in both physical and chemical properties.2A general definition of weathering (Reiche,1945;Keller,1957)is:the response of materials within the lithosphere to conditions at or near its contact with the atmosphere,the hydrosphere,and perhaps more importantly,the biosphere.The biosphere is the entire space occupied by living organisms;the hydrosphere is the aqueous enve-lope of Earth;and the lithosphere is the solid part of Earth.Physical Processes of WeatheringPhysical weathering processes cause in situ breakdown without chemical change.Five processes are impor-tant:1.Unloading Cracks and joints may form to depths of hundreds of meters below the ground surface when the effective confining pressure is reduced.Reduction in confining pressure may re-sult from uplift,erosion,or changes in fluid pres-sure.Exfoliation is the spalling or peeling off of surface layers of rocks.Exfoliation may occur during rock excavation and tunneling.The term popping rock is used to describe the sudden spall-ing of rock slabs as a result of stress release.2.Thermal Expansion and Contraction The ef-fects of thermal expansion and contraction range from creation of planes of weakness from strains already present in a rock to complete fracture.Repeated frost and insolation (daytime heating)may be important in some desert areas.Fires can cause very rapid temperature increase and rock weathering.3.Crystal Growth,Including Frost Action The crystallization pressures of salts and the pressure associated with the freezing of water in saturated rocks may cause significant disintegration.Many talus deposits have been formed by frost action.However,the role of freeze–thaw in physical weathering has been debated (Birkeland,1984).The rapid rates and high amplitude of tempera-ture change required to produce necessary pres-sure have not been confirmed in the field.Instead,some researchers favor the process in which thin films of adsorbed water is the agent that promotes weathering.These films can be adsorbed so tightly that they cannot freeze.However,the wa-ter is attracted to a freezing front and pressures exerted during the migration of these films can break the rock apart.4.Colloid Plucking The shrinkage of colloidal materials on drying can exert a tensile stress on surfaces with which they are in contact.3anic Activity The growth of plant roots in existing fractures in rocks is an important weath-ering process.In addition,the activities of worms,rodents,and humans may cause consid-erable mixing in the zone of weathering.3To appreciate this phenomenon,smear a film of highly plastic clay paste on the back of your hand and let it dry.C o p y r i g h t e d M a t e r i a lWEA THERING9Table 2.1Common Soil MineralsName Chemical FormulaCharacteristicsQuartz SiO 2Abundant in sand and siltFeldspar (Na,K)AlO 2[SiO 2]3CaAl 2O 4[SiO 2]2Abundant in soil that is not leached extensively Mica K 2Al 2O 5[Si 2O 5]3Al 4(OH)4K 2Al 2O 5[Si 2O 5]3(Mg,Fe)6(OH)4Source of K in most temperate-zone soils Amphibole (Ca,Na,K)2,3(Mg,Fe,Al)5(OH)2[(Si,Al)4O 11]2Easily weathered to clay minerals and oxides Pyroxene (Ca,Mg,Fe,Ti,Al)(Si.Al)O 3Easily weathered Olivine (Mg,Fe)2SiO 4Easily weatheredEpidote Tourmaline Zircon Rutile Kaolinite Ca 2(Al,Fe)3(OH)Si 3O 12NaMg 3Al 6B 3Si 6O 27(OH,F)4ZrSiO 4TiO 2Si 4Al 4O 10(OH)8Highly resistant to chemical weathering;used as ‘‘index mineral’’in pedologic studiesSmectite,vermiculite,chlorite M x (Si,Al)8(Al,Fe,Mg)4O 20(OH)4,where M ϭinterlayer cation Abundant in clays as products of weathering;source of exchangeable cations in soils Allophane Si 3Al 4O 12⅐n H 2OAbundant in soils derived from volcanic ash depositsImogolite Si 2Al 4O 10⅐5H 2O Gibbsite Al(OH)3Abundant in leached soils Goethite FeO(OH)Most abundant Fe oxide Hematite Fe 2O 3Abundant in warm region Ferrihydrate Fe 10O 15⅐9H 2OAbundant in organic horizons Birnessite (Na,Ca)Mn 7O 14⅐2.8H 2O Most abundant Mn oxide Calcite CaCO 3Most abundant carbonate GypsumCaSO 4⅐2H 2OAbundant in arid regionsAdapted from Sposito (1989).Physical weathering processes are generally the forerunners of chemical weathering.Their main con-tributions are to loosen rock masses,reduce particle sizes,and increase the available surface area for chem-ical attack.Chemical Processes of WeatheringChemical weathering transforms one mineral to an-other or completely dissolves the mineral.Practically all chemical weathering processes depend on the pres-ence of water.Hydration,that is,the surface adsorption of water,is the forerunner of all the more complex chemical reactions,many of which proceed simulta-neously.Some important chemical processes are listed below.1.Hydrolysis,probably the most important chemi-cal process,is the reaction between the mineral and H ϩand (OH)Ϫof water.The small size ofthe ion enables it to enter the lattice of minerals and replace existing cations.For feldspar,Orthoclase feldspar:ϩϪK silicate ϩH OH ϩϪ→H silicate ϩK OH (alkaline)Anorthite:ϩϪCa silicate ϩ2H OH →H silicate ϩCa(OH)(basic)2As water is absorbed into feldspar,kaolinite is often produced.In a similar way,other clay min-erals and zeolites (microporous aluminosilicates)may form by weathering of silicate minerals as the associated ions such as silica,sodium,potas-sium,calcium,and magnesium are lost into so-C o p y r i g h t e d M a t e r i a l102SOIL FORMA TIONFigure 2.6Solubility of alumina and amorphous silica inwater (Keller,1964b).lution.Hydrolysis will not continue in the presence of static water.Continued driving of the reaction to the right requires removal of soluble materials by leaching,complexing,adsorption,and precipita-tion,as well as the continued introduction of H ϩions.Carbonic acid (H 2CO 3)speeds chemical weathering.This weak acid is formed by the so-lution in rainwater of a small amount of carbon dioxide gas from the atmosphere.Additional car-bonic acid and other acids are produced by the roots of plants,by insects that live in the soil,and by the bacteria that degrade plant and animal remains.The pH of the system is important because it influences the amount of available H ϩ,the solu-bility of SiO 2and Al 2O 3,and the type of clay mineral that may form.The solubility of silica and alumina as a function of pH is shown in Fig.2.6.2.Chelation involves the complexing and removal of metal ions.It helps to drive hydrolysis reac-tions.For example,Muscovite:K [Si Al ]Al O (OH)ϩ6C O H ϩ8H O26242042422ϩϩ0Ϫ→2K ϩ6C O Al ϩ6Si(OH)ϩ8OH 244Oxalic acid (C 2O 4H 2),the chelating agent,re-leases C 2O 42Ϫ,which forms a soluble complex with Al 3ϩto enhance dissolution of muscovite.Ring-structured organic compounds derived from humus can act as chelating agents by holding metal ions within the rings by covalent bonding.3.Cation exchange is important in chemical weath-ering in at least three ways:a.It may cause replacement of hydrogen on hydrogen bearing colloids.This reduces the ability of the colloids to bring H ϩto unweath-ered surfaces.b.The ions held by Al 2O 3and SiO 2colloids in-fluence the types of clay minerals that form.c.Physical properties of the system such as the permeability may depend on the adsorbed ion concentrations and types.4.Oxidation is the loss of electrons by cations,and reduction is the gain of electrons.Both are im-portant in chemical weathering.Most important oxidation products depend on dissolved oxygen in the water.The oxidation of pyrite is typical of many oxidation reactions during weathering (Keller,1957):2FeS ϩ2H O ϩ7O →2FeSO ϩ2H SO 222424FeSO ϩ2H O →Fe(OH)ϩH SO 42224(hydrolysis)Oxidation of Fe(OH)2gives4Fe(OH)ϩO ϩ2H O →4Fe(OH)22232Fe(OH)→Fe O ⅐n H O (limonite)3232The H 2SO 4formed in these reactions rejuvenates the process.It may also drive the hydrolysis of silicates and weather limestone to produce gyp-sum and carbonic acid.During the construction of the Carsington Dam in England in the early 1980s,soil in the reservoir area that contained pyrite was uncovered during construction follow-ing the excavation and exposure of air and water of the Namurian shale used in the embankment.The sulfuric acid that was released as a result of the pyrite oxidation reacted with limestone to form gypsum and CO 2.Accumulation of CO 2in construction shafts led to the asphyxiation of workers who were unaware of its presence.It is believed that the oxidation process was mediated by bacteria (Cripps et al.,1993),as discussed fur-C o p y r i g h t e d M a t e r i a lWEA THERING11Figure 2.7Microogranisms attached to soil particle sur-faces:(a )bacteria attached to sand particle (from Robertson et al.1993in Chenu and Stotzky,2002),(b )bacterial mi-croaggregate [from Robert and Chenu (1992)in Chenu and Stotzky (2002)],and (c )biofilm on soil surface (from Chenu and Stotzky (2002).ther in the next section.Many iron minerals weather to iron oxide (Fe 2O 3,hematite).The red soils of warm,humid regions are colored by iron oxides.Oxides can act as cementing agents between soil particles.Reduction reactions,which are of importance relative to the influences of bacterial action and plants on weathering,store energy that may be used in later stages of weathering.5.Carbonation is the combination of carbonate or bicarbonate ions with earth materials.Atmos-pheric CO 2is the source of the ions.Limestone made of calcite and dolomite is one of the rocks that weather most quickly especially in humid regions.The carbonation of dolomitic limestone proceeds as follows:CaMg(CO )ϩ2CO ϩ2H O3222→Ca(HCO )ϩMg(HCO )3232The dissolved components can be carried off in water solution.They may also be precipitated at locations away from the original formation.Microbiological EffectsSeveral types of microorganisms are found in soils;there are cellular microorganisms (bacteria,archea,al-gae,fungi,protozoa,and slime molds)and noncellular microorganisms (viruses).They may be nearly round,rodlike,or spiral and range in size from less than 1to 100m,which is equivalent to coarse clay size to fine sand size.Figure 2.7a shows bacteria adhering to quartz sand grains,and Fig.2.7b shows clay minerals coating around the cell envelope,forming what are called bacterial microaggregates.4A few billion to 3trillion microorganisms exist in a kilogram of soil near the ground surface and bacteria are dominant.Micro-organisms can reproduce very rapidly.The replication rate is controlled by factors such as temperature,pH,ionic concentrations,nutrients,and water availability.Under ideal conditions,the ‘‘generation time’’for bac-terial fission can be as short as 10min;however,an hour scale is typical.These high-speed generation rates,mutation,and natural selection lead to very fast adaptation and extraordinary biodiversity.Autotrophic photosynthetic bacteria,that is,photo-autotrophs,played a crucial role in the geological de-4Further details of how microorganisms adhere to soil surfaces are given in Chenu and Stotzky (2002).C o p y r i g h t e d M a t e r i a l122SOIL FORMA TIONvelopment of Earth (Hattori,1973;McCarty,2004).Photosynthetic bacteria,cyanobacteria,or ‘‘blue-green bacteria’’evolved about 3.5billion years ago (Proter-ozoic era—Precambrian),and they are the oldest known fossils.Cyanobacteria use energy from the sun to reduce the carbon in CO 2to cellular carbon and to obtain the needed electrons for oxidizing the oxygen in water to molecular oxygen.During the Archaean period (2.5billion years ago),cyanobacteria converted the atmosphere from reducing to oxidizing and changed the mineral nature of Earth.Eukaryotic algae evolved later,followed by the mul-ticellular eukaryotes including plants.Photosynthesis is the primary producer of the organic particulate mat-ter in shale,sand,silt,and clay,as well as in coal,petroleum,and methane deposits.Furthermore,cyano-bacteria and algae increase the water pH when they consume CO 2dissolved in water,resulting in carbonate formation and precipitation of magnesium and calcium carbonates,leading to Earth’s major carbonate forma-tions.Aerobic bacteria live in the presence of dissolved oxygen.Anaerobic bacteria survive only in the absence of oxygen.Facultative bacteria can live with or without oxygen.Some bacteria may resort to fermentation to sustain their metabolism under anaerobic conditions (Purves et al.,1997).For example,in the case of an-aerobic conditions,fermenting bacteria oxidize carbo-hydrates to produce simple organic acids and H 2that are used to reduction of ferric (Fe 3ϩ)iron,sulfate re-duction,and the generation of methane (Chapelle,2001).Microbial energy metabolism involves electron transfers,and the electron sources and acceptors can be both organic and inorganic compounds (Horn and Meike,1995).Most soil bacteria derive their carbon and energy directly from organic matter and its oxi-dation.Some other bacteria derive their energy from oxidation of inorganic substances such as ammonium,sulfur,and iron and most of their carbon from carbon dioxide.Therefore,biological activity mediates geo-chemical reactions,causing them to proceed at rates that are sometimes orders of magnitude more rapid than would be predicted solely on the basis of the ther-mochemical reactions involved.Bacteria tend to adhere to mineral surfaces and form microcolonies known as biofilms as shown in Fig.2.7c .Some biofilms are made of single-type bacteria,while others involve symbiotic communities where two or more bacteria types coexist and complement each other.For example,biofilms involved in rock weath-ering may involve an upper aerobic layer,followed by an intermediate facultative layer that rests on top of the aerobic layer that produces the weathering agents(e.g.,acids)directly on the rock surface (Ehrlich,1998).Biofilms bind cations in the pore fluid and fa-cilitate nucleation and crystal growth even at low ionic concentrations in the pore fluid (Konhauser and Urru-tia,1999).After nucleation is initiated,further mineral growth or precipitation can occur abiotically,including the precipitation of amorphous iron–aluminum sili-cates and poorly crystallized claylike minerals,such as allophone,imogolite,and smectite (Urrutia and Bev-eridge,1995;Ehrlich,1999;Barton et al.,2001).In the case of the Carsington Dam construction,Cripps et al.(1993)hypothesized that autotrophic bac-teria greatly accelerated the oxidation rate of the pyrite,so that it occurred within months during construction.The resulting sulfuric acid reacted with the drainage blanket constructed of carboniferous limestone,which then resulted in precipitation of gypsum and iron hy-droxide,clogging of drains and generation of carbon dioxide.Weathering ProductsThe products of weathering,several of which will gen-erally coexist at one time,include:1.Unaltered minerals that are either highly resistant or freshly exposed2.Newly formed,more stable minerals having the same structure as the original mineral3.Newly formed minerals having a form similar to the original,but a changed internal structure4.Products of disrupted minerals,either at or trans-ported from the site.Such minerals might include a.Colloidal gels of Al 2O 3and SiO 2b.Clay minerals c.Zeolitesd.Cations and anions in solutione.Mineral precipitates 5.Unused guest reactantsThe relationship between minerals and different weathering stages is given in Table 2.2.The similarity between the order of representative minerals for the different weathering stages and Bowen’s reaction se-ries given earlier (Fig.2.5)may be noted.Contrasts in compositions between terrestrial and lu-nar soils can be accounted for largely in terms of dif-ferences in chemical weathering.Soils on Earth are composed mainly of quartz and clay minerals because the minerals of lower stability,such as feldspar,oli-vine,hornblende,and glasses,are rapidly removed by chemical weathering.On the Moon,however,the ab-sence of water and free oxygen prevent chemical weathering.Hence,lunar soils are made up mainly of fragmented parent rock and rapidly crystallizedC o p y r i g h t e d M a t e r i a lWEA THERING13Table 2.2Representative Minerals and Soils Associated with Weathering Stages Weath-ering StageRepresentative MineralsTypical Soil GroupsEarly Weathering Stages12345Gypsum (also halite,sodium nitrate)Calcite (also dolomite apatite)Olivine-hornblende (also pyroxenes)Biotite (also glauco-nite,nontronite)Albite (also anorthite microcline,ortho-clase)Soils dominated by these minerals in the fine silt and clay frac-tions are the youthful soils all over the world,but mainly soils of the desert regions where limited water keeps chemical weathering to a mini-mum.Intermediate Weathering Stages678Quartz Muscovite (also illite)2Ϻ1layer silicates (in-cluding vermiculite,expanded hydrousmica)MontmorilloniteSoils dominated by these minerals in the fine silt and clay frac-tions are mainly those of temperate regions developed under grass or trees.Includes the major soils of the wheat and corn belts of the world.Advanced weathering stages10111213KaoliniteGibbsiteHematite (also geothite,limonite)Anatase (also rutile,zircon)Many intensely weath-ered soils of the warm and humid equatorialregions have clay fractions dominated by these minerals.They are frequently characterized by their infertility.From Jackson and Sherman (1953).glasses.Mineral fragments in lunar soils include pla-gioclase feldspar,pyroxene,ilmenite,olivine,and po-tassium feldspar.Quartz is extremely rare because it is not abundant in the source rocks.Carrier et al.(1991)present an excellent compilation of information about the composition and properties of lunar soil.Effects of Climate,Topography,Parent Material,Time,and Biotic FactorsThe rate at which weathering can proceed is controlled by parent material and climate.Topography,apart from its influence on climate,determines primarily the rate of erosion,and this controls the depth of soil accu-mulation and the time available for weathering prior to removal of material from the site.In areas of steep topography,rapid mechanical weathering followed by rapid down-slope movement of the debris results in formation of talus slopes (piles of relatively unweath-ered coarse rock fragments).Climate determines the amount of water present,the temperature,and the character of the vegetative cover,and these,in turn,affect the biologic complex.Some general influences of climate are:1.For a given amount of rainfall,chemical weath-ering proceeds more rapidly in warm than in cool climates.At normal temperatures,reaction rates approximately double for each 10ЊC rise in tem-perature.2.At a given temperature,weathering proceeds more rapidly in a wet climate than in a dry cli-mate provided there is good drainage.3.The depth to the water table influences weather-ing by determining the depth to which air is available as a gas or in solution and by its effect on the type of biotic activity.4.Type of rainfall is important:short,intense rains erode and run off,whereas light-intensity,long-duration rains soak in and aid in leaching.Table 2.3summarizes geomorphologic processes in different morphoclimatic zones.The nature and rate of these geomorphologic processes control landform as-semblages.During the early stages of weathering and soil for-mation,the parent material is much more important than it is after intense weathering for long periods of time.Climate ultimately becomes a more dominant factor in residual soil formation than parent material.Of the igneous rock-forming minerals,only quartz and,to a much lesser extent,feldspar,have sufficient chemical durability to persist over long periods of weathering.Quartz is most abundant in coarse-grained granular rocks such as granite,granodiorite,and gneiss,where it typically occurs in grains in the mil-limeter size range.Consequently,granitic rocks are the main source of sand.In addition to the microbiological activities dis-cussed previously,biological factors of importance in-clude the influences of vegetation on erosion rate and the cycling of elements between plants and soils.Mi-C o p y r i g h t e d M a t e r i a l。
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Soil nitric oxide emissions from two subtropical humidforests in south ChinaDejun Li,1Xinming Wang,1Jiangming Mo,2Guoying Sheng,1and Jiamo Fu1Received21March2007;revised2July2007;accepted11September2007;published4December2007.[1]Due to the dense population,rapid industrialization,and intensified agriculturalactivities,some regions in Asia are hot spots of airborne nitrogen oxides and also areaswith increasing nitrogen deposition.Therefore the cycling of nitrogen gases in Asia mightbe of increasing importance on both a regional and a global scale for atmosphericchemistry and budgets of nitrogen.Yet,to date,knowledge of soil NO emission is quitelimited in Asia,particularly in forest ecosystems.In this study,soil NO emissions in twosubtropical humid forests,a broadleaf forest in climax successional stage and a pine forestin primary successional stage,were measured throughout the year2005in DinghushanBiosphere Reserve,south China.In the broadleaf forest,mean NO emission in wet season(14.9ng N mÀ2sÀ1)was lower than in dry season(23.8ng N mÀ2sÀ1).In the pine forest,however,mean NO emission in wet season(17.1ng N mÀ2sÀ1)was higher than indry season(7.9ng N mÀ2sÀ1).In both forests,soil water content was the dominant factorcontrolling the seasonal patterns of NO emissions,and soil NO emission was significantlycorrelated to percent water filled pore space(%WFPS)in a quadratic manner(p<0.001).Annual NO emissions in the broadleaf forest and the pine forest were preliminarilyestimated to be6.1–6.9and4.0–4.3kg N haÀ1yrÀ1,respectively,by using threeupscaling methods.Citation:Li,D.,X.Wang,J.Mo,G.Sheng,and J.Fu(2007),Soil nitric oxide emissions from two subtropical humid forests in south China,J.Geophys.Res.,112,D23302,doi:10.1029/2007JD008680.1.Introduction[2]Nitrogen oxides(NO x=NO+NO2)play a crucial role in atmospheric chemistry[Crutzen,1979;Logan et al., 1981].In the stratosphere,NO x mainly from the oxidation of nitrous oxide there could catalyze the destruction of ozone(O3)[Crutzen,1979].In the troposphere,however, NO x act as a key agent in the photochemical production of O3,and are important in regulating many other oxidizing agents,especially hydroxyl radical(OH)[Crutzen,1979; Williams et al.,1992;Intergovernmental Panel on Climate Change(IPCC),2001].Thus they are important in control-ling the oxidizing capacity of the troposphere,and impact the fate of carbon monoxide(CO),methane(CH4)and non-methane hydrocarbons(NMHC)[Logan et al.,1981;Liu et al.,1987].The end photochemical product of NO x,HNO3 and NO3À,contribute to secondary aerosols and to the acidity of clouds and precipitation[Liu et al.,1987]. [3]Soils are a major source of atmospheric NO x[Yienger and Levy,1995;Delmas et al.,1997].Although NO(the predominant form of NO x emitted from soils)may come from abiotic processes(termed chemodenitrification)in acid soils especially those high in organic matter content,it is mainly produced by the biological processes of nitrification and denitrification[Williams et al.,1992],which depend on physical,biological and chemical properties of the soil,e.g., soil porosity,soil water content,temperature and the nutri-ent status[Ganzeveld et al.,2002].Firestone and Davidson [1989]proposed a relatively simple conceptual model, called‘‘hole-in-the-pipe’’,to describe the biogenic emis-sions of NO and N2O in soils.According to this model,their emissions from soils were controlled mainly at two levels. The first level is the magnitude of flow through the pipe, i.e.,rates of nitrification or denitrification.The second level is the size of the hole,i.e.,soil properties such as soil water content,which determine how much of the produced nitrogen oxides can leak out to the atmosphere from soils.[4]Although soils are a major source of atmospheric NO x,there still exist huge uncertainties and disagreement about the source strength.The existing inventory models of soil biogenic NO emission showed a large range from<5Tg N yrÀ1to>20Tg N yrÀ1[Yienger and Levy,1995;Potter et al.,1996;Davidson and Kingerlee,1997;Ganzeveld et al., 2002].If the soil source strength falls into the lower part of the range,soils might be the third largest source of atmo-spheric NO x[Delmas et al.,1997].Nevertheless,if soils emitted21Tg N yrÀ1of NO,then soil source would be similar in magnitude to fossil fuel emissions of NO x [Davidson and Kingerlee,1997].The probable causes of this huge uncertainty include large variations of soil NO emissions either temporally[e.g.,Garcia-Montiel et al.,JOURNAL OF GEOPHYSICAL RESEARCH,VOL.112,D23302,doi:10.1029/2007JD008680,2007 1State Key Laboratory of Organic Geochemistry,Guangzhou Instituteof Geochemistry,Chinese Academy of Sciences,Guangzhou,China.2South China Botanical Garden,Chinese Academy of Sciences,Guangzhou,China.Copyright2007by the American Geophysical Union.0148-0227/07/2007JD0086802001;Butterbach-Bahl et al.,2002]or spatially(as was clearly demonstrated by Davidson and Kingerlee[1997]), and the uncertain importance of the canopy in absorbing NO x from soil sources[IPCC,2001].[5]Considering the large spatial variation of NO emissions, previous studies are imbalanced in regions under investiga-tion.As to the forests,for example,most studies about NO fluxes were carried out in Europe,USA,tropical America and Africa[Willams et al.,1992,and references therein; Davidson and Kingerlee,1997,and references therein; Holtgrieve et al.,2005],as well as in Australia[Butterbach-Bahl et al.,2004].Only one report on soil NO emission from Asian forests,to our knowledge,is available to date [Purbopuspito et al.,2006].Considering the rather diverse forest types in Asia,more studies are undoubtedly needed.[6]In this study,we measured NO emissions from two forests in different successional stages in Dinghushan Bio-sphere Reserve in south China.Objectives were to deter-mine(1)seasonal patterns of NO emissions in the two forests,(2)controls on NO emissions,and(3)annual NO emission rates from these subtropical humid forests.2.Materials and Methods2.1.Site Description[7]The experiment was carried out in a broadleaf forest (BF)in climax successional stage and a pine forest(PF)in primary successional stage in Dinghushan Biosphere Re-serve(23°0902100–23°1103000N,112°3003900–112°3304100E). The reserve is located in the subtropical humid forest life zone with a monsoon climate.Annual mean relative hu-midity is about80%.The averaged annual rainfall is about 1927mm with a distinct seasonal pattern.Typically the period from April to September is wet season,and that from October to March is dry season.March and October are transition periods from dry season to wet season and from wet season to dry season,respectively.Annual mean air temperature is about21°C,with monthly means the lowest in January(13°C)and the highest in July(28°C).[8]The broadleaf forest,about250–300m above sea level,has been protected without direct human interference for more than400years.The pine forest,about50–200m above sea level,has been evolved under human disturbance, like collecting litters,since pine trees were first planted in 1930s.The two forests vary not only in their stages of succession,but also in their species composition.The major species in the broadleaf forest are Castanopsis chinensis, Schima superba,Cryptocarya chinensis, C.concinna, Machilus chinensis in the tree layer and Hemigramma decurrens in the understory layer.Tree heights range from 4to30m and diameters from5to163cm.The pine forest is dominated by P.massoniana with densities of100–1000 trees haÀ1,diameters of4–32cm and heights of3–11m. Understory species included grasses,ferns,vines and shrubs for a total of43species[Mo et al.,2006].[9]The soil in the two forests is lateritic red earth formed from sandstone,but the soil depths vary in each site.Some important characteristics of the two forests were presented in Table1.[10]Since the reserve is in the north edge of the Pearl River Delta,one of the most densely populated and indus-trialized regions in China,annual total N input from atmosphere is relatively high;N deposition through rainfall alone reached38.4kg N haÀ1yrÀ1in1998–1999[Zhou and Yan,2001].2.2.NO Flux Measurement[11]At the beginning of the experiment,three1mÂ1m plots(the aims to enclose three plots in each forests were to fix the sampling areas and to protect them from human disturbance)in each forest were chosen and marked.Dis-tance between plots was about10m.Field measurements were conducted in the three plots in March(1),April(1), May(1),June(2),July(6for broadleaf forest and4for pine forest),August(4for broadleaf forest and7for pine forest), September(2)and December(3)in2005(numbers in the parentheses denoted sampling days within that month).At each sampling date,flux measurements were conducted from0800to1800,during which3–6fluxes per plot were obtained at each forest.[12]NO fluxes were measured by a dynamic flow-through chamber technique,which was similar to that used by Pilegaard et al.[1999].Briefly,the chambers were made of stainless steel(inner walls coated with Teflon films),each covering an area of30cmÂ30cm with a total volume of 9L.Each chamber has one inlet port,one exhaust port and one outlet port for sampling.Inside each chamber,a thermo-sensor was fixed to measure air temperature,and a fan attached to ensure sufficient mixing of air within theTable1.Characteristics of the Broadleaf Forest and Pine Forest (Means±S.E.)Pine Forest Broadleaf Forest Biomass,a Mg C haÀ140.6147.8SOC,a Mg C haÀ1105.2164.1Fine root biomassin topsoil,a Mg C haÀ11.9±1.1 4.9±3.0Litter input,aMg C haÀ1yrÀ11.8 4.2Microbial biomass,bm g C gÀ1soil551±127763±73Microbial amount,b106gÀ1dry soil1.172.09pH b 4.3±0.3 3.7±0.2Bulk density,b g cmÀ3 1.50±1.150.91±0.12 Total C,c mg gÀ122.7±3.132.1±2.7 Total N,c mg gÀ1 1.3±0.1 2.5±0.2C/N c17.01±1.3512.84±2.27 Available P,c mg kgÀ1 3.59±0.28 4.96±0.16 Leaf area index(LAI)d 3.4±0.6 6.1±0.2NH+-N,e m g N.gÀ1dry soil 3.1±0.36W3.2±0.49D2.3±0.41M 2.9±0.20W 4.0±0.57D3.0±0.59MNO3À-N,e m g N.gÀ1dry soil 2.6±0.19W5.9±1.34D6.4±4.10M 6.1±0.42W 11.5±2.22D 14.1±6.45MNet mineralization rate,em g N.gÀ1dry soil dayÀ10.5±0.06W 1.6±0.12W Net nitrification rate,em g N.gÀ1dry soil dayÀ10.4±0.04W 1.4±0.11Wa Tang et al.[2006].Fine root in topsoil refers to root(diameter less than 6mm)biomass in0–20cm depth of soil.b Yi et al.[2007].c Mo et al.[2006].d LAI was measured at a height of about80cm above forest floor.(These data were provided by Yuanwen Kuang from South China Botanical Garden,the Chinese Academy of Sciences.)e This study.W,D,and M represent wet season,dry season,and March, respectively.chamber.During field measurement,the sampling chambers were put onto the forest floor without soil frames to avoid disturbing the soils.Instead they were sealed against the outward atmosphere with Teflon foil pinned down by sand bags[Gut et al.,2002].An additional reference chamber, closed at the bottom with Teflon sheet,was employed for in situ quantification of chemical reactions and chamber wall deposition effects[Kirkman et al.,2002].Ambient air was pumped into the chambers at a rate of4L minÀ1 through10m long Teflon tubes with inner diameters of 4.8mm,and the sample air was taken in through tubes of the same dimension.The residence time of air in the chambers was about2.25min.After about15min(over 5cycles of residence time)when a steady state was reached inside the chambers,NO was analyzed by a model42C chemiluminescence NO-NO2-NOx analyzer(Zero noise 25ppt and detection limit50ppt,Thermo Electron Corpo-ration,USA).By the contrast of sampling chambers and the reference chamber,net fluxes from the soils could be obtained[Pilegaard et al.,1999].[13]No corrections were made for the possible removal of NO by chemical reactions taking place in the chambers or by absorption on the chamber wall due to reasons also described by Pilegaard et al.[1999].First,measurements with zero-air and ambient air showed no difference in the calculated fluxes,probably due to low concentrations of O3at the forest floor;In addition,very small changes in the concentrations of NO2were observed,and on average there was a deposition of NO2to the soil,and the NO2 flux was found to be independent of the NO emission, which indicated that the NO+O3reaction did not play a significant role in the chambers.2.3.Soil Parameter Measurement[14]When measuring NO fluxes,soil temperatures at 5cm depths,and volumetric soil water content at0–5cm depth were also determined.Soil temperature was measured with soil temperature probes(TES,Ltd.,China).V olumetric soil water content was measured with MPA-160Moisture Probe Meter(ICT international,Australia).In this paper,the volumetric water content was converted to percent water filled pore space(%WFPS)on the basis of averaged soil bulk density in each forest[Davidson,1993].[15]At selected sampling days,soil samples(0–5cm) were collected with a2.5cm diameter soil corer at each plot for determination of KCl-extractable NH4+-N and NO3À-N (plus NO2À-N)[National Standard Bureau of China,1987],net rates of N mineralization and nitrification[Piccolo et al., 1994].In each forest inorganic N pools were analyzed for 11samples,and net rates of N mineralization and nitrifica-tion were analyzed only for9samples.2.4.Statistics and Data Analysis[16]The statistical software package SPSS10.0(SPSS A)was used for ANOVA testing(post-hoc LSD analysis)of NO fluxes of different months,and for inde-pendent-samples t testing between NO fluxes in the two forests,or between NO fluxes in dry season and wet seasons within a forest.The statistical software package SigmaPlot 9.0(SPSS A)was used for regression analysis. 3.Results and Discussion3.1.Measured NO Fluxes and Their Temporal Patterns[17]Measured NO fluxes were listed in Table 2.As mentioned above,in this region the period from April to September was wet season and that from October to March was dry season,among which March and October were transition period between wet and dry seasons.In the broadleaf forest,mean flux in wet season(14.9ng N mÀ2 sÀ1)was lower than that in dry season(23.8ng N mÀ2sÀ1) (p<0.05);in the pine forest,however,mean flux in wet season(17.1ng N mÀ2sÀ1)was higher than that in dry season(7.9ng N mÀ2sÀ1)(p<0.05).In wet season,soil NO emissions from the two forests had no significant difference,while in dry season NO fluxes in the broadleaf forest were significant higher than those in the pine forest (p<0.05).[18]The seasonal pattern of NO emissions from the broadleaf forest(Figure1)was similar to those observed in some tropical rain forests[Kaplan et al.,1988;Bakwin et al.,1990;Keller and Reiners,1994;Verchot et al.,1999; Garcia-Montiel et al.,2001].In a primary rain forest in eastern Amazonia,Verchot et al.[1999]measured mean net NO flux of3.3±0.4ng N mÀ2sÀ1in the wet season and 5.9±0.7ng N mÀ2sÀ1in dry season.In a humid tropical forest,Garcia-Montiel et al.[2001]observed mean NO fluxes of1.4and9.2ng N mÀ2sÀ1in wet and dry season of 1998and1999,respectively.However,opposite seasonal pattern was also observed in some rain forests[Serca et al., 1994,1998]and seasonally dry tropical forest[Davidson et al.,1991],just similar to the case in the pine forest (Figure1)of this study.Table2.Monthly Averaged NO Fluxes,Percent Water Filled Pore Space,and Soil Temperature at5cm Depth aBroadleaf Forest Pine ForestNO Fluxes%WFPS T5N NO Fluxes%WFPS T5N Mar45.0±12.252.0±0.717.0±0.1926.7±8.643.5±1.620.9±0.79 Apr8.5±0.560.2±0.924.4±0.41517.2±1.139.8±1.726.7±0.415 May15.7±1.151.0±1.325.9±0.23620.5±0.940.3±1.926.7±0.215 Jun20.7±0.545.1±1.125.1±0.31518.6±0.758.5±1.228.0±0.333 Jul17.8±0.639.8±1.527.1±0.17511.9±0.817.6±1.229.9±0.348 Aug13.2±0.752.7±1.327.3±0.23618.2±0.636.9±1.929.6±0.263 Sep13.3±0.956.1±1.127.4±0.21816.4±0.544.6±2.028.8±0.318 Dec23.8±1.226.5±0.618.8±0.4367.9±0.59.3±0.521.9±0.336a NO fluxes are in ng N mÀ2sÀ1.%WFPS,percent water filled pore space.Soil temperature at5cm depth,T5,is in°C.Values in the table are means±standard errors,and N denotes the number of NO flux measurements.[19]Relatively higher NO fluxes observed in March (Figure 1)in the present study should be largely caused by ‘‘pulsing’’emission,which was characteristic for the transition period from dry season to wet season.Just the day before the sampling day there was a 33mm rainfall after a long time of dryness.These NO emission pulses had been also observed previously in other forests [Bakwin et al.,1990;Davidson et al.,1991;Davidson ,1993;Meixner et al.,1997;Garcia-Montiel et al.,2003;Butterbach-Bahl et al.,2004],and they were probably resulted from a quick use of the accumulated inorganic N during the prolonged soil dryness by soil microbes when wetting soils [Garcia-Montiel et al.,2003].3.2.Soil Moisture and NO Fluxes[20]Averaged soil %WFPS in the broadleaf forest was greater than in the pine forest either in wet season or in dry season (Table 2).In wet season,monthly averaged %WFPS varied from 39to 60%with a mean value of 51%in the broadleaf forest,and from 17to 59%with a mean value of 40%in the pine forest.In dry season,the averaged %WFPS in the broadleaf forest and the pine forest lowered to 26.5%and 9.3%,respectively.[21]When excluding the fluxes measured in March (they were probably pulses as discussed above),NO fluxes were found to be significantly correlated with %WFPS in a quadratic manner in both forests (Figure 2).For the broad-leaf forest r 2=0.48,p <0.001,n =230;and for the pine forest,r 2=0.56,p <0.001,n =228).The fitted regression equations for the two forests were as follows:For BFF NO ¼À1:55Â10À2ÂW 2þ1:05ÂW þ4:08ð1ÞFor PFF NO ¼À6:66Â10À3ÂW 2þ0:670ÂW þ2:82ð2Þwhere F NO is the soil NO emission flux (positive value means flux direction from soil to atmosphere),and W is the %WFPS.According to the above equations,there existed optimum soil moistures for NO emissions in the two forests,and they were calculated to be about 34%WFPS for the broadleaf forest and 50%WFPS for the pine forest.[22]Due to the strong correlation between NO fluxes and soil %WFPS,NO fluxes can be predicted on the basis of the above equations using available moisture data.The pre-dicted NO fluxes in comparison with those field measure-ments in the two forests were presented in Figure 3.We can see that large deviations only occurred in March due to pulseemissions.Figure 2.Correlation of soil NO emission fluxes and %WFPS based on field measurements in (a)the broadleaf forest (r 2=0.48,p <0.001,n =231)and (b)the pine forest (r 2=0.56,p <0.001,n =228).NO fluxes in March were excluded as they werepulses.Figure 1.Monthly averaged NO fluxes (vertical bars),percent water filled pore space (open circles),soil tempera-ture at 5cm depth (solid circles)for (a)the broadleaf forest and (b)the pine forest.Each value is the mean of fluxes from the three plots within a month,and error bars represent standard errors.[23]Soil moisture regulated NO production through its role in the stimulation of microbial activity,in the delivery of electron donors (NH4+,dissolved organic carbon)and acceptors (O 2,NO 3À),and in the diffusion of NO from soils [Firestone and Davidson ,1989;Stark and Firestone ,1995;Holtgrieve et al.,2005].Soil moisture,especially %WFPS,as an important regulating factor on soil NO emissions has been observed in quite a few studies [Davidson et al.,1991;Keller and Reiners ,1994;Yang and Meixner ,1997;Otter et al.,1999;Verchot et al.,1999;Butterbach-Bahl et al.,2004],although the effects of increased soil moisture on soil NO emissions were diversified in these studies.However,there were studies,in which no clear relationship between soil moisture and NO emissions was observed [Ludwig et al.,2001].[24]Many studies also showed that optimum soil mois-ture existed for soil NO emissions [Yang and Meixner ,1997;Otter et al.,1999;Verchot et al.,1999],but the value varied according to soils.For example,a laboratory study showed the optimum soil moisture of about 20%WFPS by Yang and Meixner [1997],but in another study conducted in a seasonally dry forest of eastern Amazon,maximum NOfluxes was observed at approximately 50%WFPS [Verchot et al.,1999].In our study,optimum soil moisture for the two forests significantly varied,which was probably due to their different soil properties.The different seasonal patterns of NO emissions in the broadleaf forest and pine forest of this study were also largely to be resulted from their different responses to the seasonal variations of soil water contents.[25]Due to its higher content of soil organic matter and clay,the soil in the broadleaf forest had a better water holding capacity (Table 1),which is defined as the ability of a soil to retain water against the pull of gravity and is positively correlated with content of soil organic matter and clay [Khaleel et al.,1981;Zhang and Zhuo ,1985];on the contrary,water is easier to be drained out of the soil due to its coarse particles in the pine forest.For this reason and other properties like much more developed root systems in the broadleaf forest (Table 1),during the dry season,the broadleaf forest still kept a considerably higher soil water contents,but water content in the pine forest become so low that microbial activity was reduced for restricted substrate supply.As pores within solid matrices drain and water films coating surfaces become thinner,diffusion path lengths become more tortuous,and the rate of substrate diffusion to microbial cells declines [Stark and Firestone ,1995].Therefore the soil NO emissions would be influenced much more by the dryness in the pine forest than in the broadleaf forest.During wet season,for the broadleaf forest,frequent rains would cause a much higher percent of water-filled pore space,so NO emissions decreased due to the reduced NO diffusibility [Ludwig et al.,2001],and also due to the increasing consumption of NO by denitrifying bacteria under more anoxic conditions [Kra ¨mer and Conrad ,1991;Ye et al.,1994].For the pine forest soil,however,increased soil water content in wet season would benefit the microbial activity and thus increased the production of NO;and due to its poorer water holding capacity %WFPS would not reach a high level at which NO diffusion would impeded as it did in the broadleaf forest.NO emissions from the pine forest floor were thus greatly raised during the wet season while those from the broadleaf forest decreased.So the impacts of water content on soil NO emission depend on the balance between its role in NO biogenic production and its role in NO diffusion from soil to the atmosphere.3.3.Soil Temperature and NO Fluxes[26]Monthly mean soil temperature at 5cm depth ranged from 17to 28°C in the broadleaf forest and from 20to 30°C in the pine forest,respectively (Table 2).Exponential relationship existed between NO fluxes and soil temperature at 5cm depth in the pine forest (F NO =3.48exp 0.05T ,r 2=0.19,p <0.001,n =228),but no significant relationship was found between NO fluxes and soil temperature in the broadleaf forest.[27]Many previous studies observed that soil temperature was an important regulator on soil NO fluxes [Williams and Fehsenfeld ,1991;Otter et al.,1999;Gut et al.,2002].However,other studies found no obvious effects of soil temperature on NO fluxes [Cardenas et al.,1993;Pilegaard ,2001].Considering the dominance of soil microbial pro-cesses for the production of NO,the dependence of NO emissions on soil temperature is reasonable,sinceenzymaticFigure 3.Observed NO fluxes (solid circles)versus predicted NO fluxes by soil moisture alone (red lines)or by both soil moisture and temperature (green lines)for (a)the broadleaf forest and (b)the pine forest.I,March;II,April;III,May;IV,June;V ,July;VI,August;VII,September;VIII,December.processes generally increase exponentially with temperature within a certain range,as long as other factors (substrate or moisture availability)are not limiting [Ludwig et al.,2001].The lack of correlation between soil temperature and NO fluxes in the broadleaf forest was probably because the effect of soil water content greatly overrode that of soil temperature.bined Effects of Soil Moisture and Temperature[28]As biogenic NO production and emission were affected by soil moisture,temperature and many other factors,fitting NO emission with these factors within an acceptable range of confidence would benefit prediction of NO emission.Soil moisture and temperature are mostly available among soil parameters;in the present study they are combined to see their relations to the NO ing measurements in the two forests,NO emission fluxeswere found to be significantly related to soil %WFPS and temperature in a quadratic way (for the broadleaf forest,r 2=0.52,p <0.001,n =231;for the pine forest,r 2=0.58,p <0.001,n =228):For BFF NO ¼51:9þ1:41W À4:40T À1:90Â10À2W 2þ8:41Â10À2T 2ð3ÞFor PFF NO ¼4:62þ0:585W À0:390T À5:63Â10À3W 2þ1:33Â10À2T 2ð4Þwhere W is the %WFPS and T is the soil temperature (°C)at 5cm depth.These relations are also shown in Figure 4.Predicted NO fluxes based on equations (3)and (4)in comparison with those measured in the field are presented in Figure 3.In the two forests,incorporating T into the formulation of fluxes does not significantly improve the prediction of fluxes,implying the dominant influence of soil moisture.3.5.Soil N Availability and NO Emission[29]Throughout the year,total soil inorganic N pools,especially NO 3À-N pools,were greater in the broadleaf forest than in the pine forest (Table 1).NO 3À-N pools in both forests were greater in dry season than in wet season,implying accumulation of NO 3À-N during dry season.For example,the NO 3À-N pools in the broadleaf forest during the dry season were nearly 2times those during the wet season (Table 1).[30]In the broadleaf forest NO fluxes were significantlycorrelated with NO 3À-N pools (r 2=0.73,p <0.001,n =11),net rates of N mineralization (r 2=0.75,p <0.01,n =9)and nitrification (r 2=0.67,p <0.01,n =9).However,no significant relationships were found between NO fluxes and NH 4+-N pools in the broadleaf forest,or between NO fluxes and indices of N availability in the pine forest.[31]Previous studies also found strong correlation be-tween soil NO emissions and indices of N availability in temperate forests [Regina et al.,1998;Stark et al.,2002]and tropical forests [Davidson et al.,1991;Verchot et al.,1999;Garcia-Montiel et al.,2001].The existence of strong correlation between NO emission and soil N availability may be explained by the fact that available N serves as substrate for nitrifying and denitrifying bacteria,which are responsible for soil NO production [Ludwig et al.,2001].Stark et al.[2002]concluded that net rates,rather than gross rates of N cycling might be better predictors of soils NO fluxes.But other studies failed to find any significant relationships between soil NO fluxes and indices of N availability [Keller and Reiners ,1994;Veldkamp et al.,1999].The lack of clear correlation between soil NO fluxes and N availability in the pine forest in the present study also confirmed that N availability might do a poor job of predicting the fluxes of individual NO or N 2O,although it was probably a good predictor for the combined N oxide emissions [Verchot et al.,1999].3.6.Preliminary Estimates of Annual NO Emissions [32]Many previous studies estimated annual NO emission from a specific site by extrapolating the meanfluxesFigure 4.NO emission as a function of soil moisture (%WFPS)and temperature (°C)in (a)the broadleaf forest (r 2=0.52,p <0.001,n =231)and (b)the pine forest (r 2=0.58,p <0.001,n =228).。