全球氮循环

亚热带盐沼湿地土壤氮循环关键过程对全球变化的响应摘要河口盐沼湿地受到了陆地和海洋相互作用的影响，可以认为是生物活动较为活跃的地区，同时也是地球化学过程最为活跃的地区，对人类和社会有着重要的影响。

氮在大气组分占78%，是大气圈中最丰富的元素，其在环境介质中的含量会直接影响到周围生物的生长。

由于目前大量的人为输入氮源对河口的盐沼湿地已经产生了巨大的影响，河口地带出现赤潮、河口溶解氧含量锐减,以及大量的温室气体从河口溢出等环境效应。

本研究以福州闽江河口盐沼湿地为研究对象，充分的研究了土壤氮循环的关键过程对全球变化的响应，通过野外采集、实验室模拟的方式，定量的研究了闽江河口盐沼湿地土壤-水体界面的氮循环过程，分别研究了盐入侵、植物入侵、酸沉降和盐沼湿地改为养虾塘后，土壤中硝化、反硝化和矿化作用的变化情况，探讨了氮在河口湿地的变化，及其在河口湿地扮演的重要角色。

主要得到的研究结果如下：1、植物入侵对氮循环的影响无机氮和总氮：（1）互花米草入侵改变了土壤NO3--N含量在不同土层含量，可显著降低土壤的NO3--N含量，但整体增加了土壤的NH4+-N含量。

（2）互花米草不同入侵过程土壤TC、TN含量以及C/N比的垂直变化特征均比较一致，入侵整体增加了土壤的碳氮含量和C/N比和土壤的碳氮储量。

（3）闽江口互花米草入侵对短叶茳芏湿地土壤碳氮含量的影响相对于江苏盐城、长江口以及杭州湾湿地的影响可能更为显著，主要与其对闽江口湿地植物群落格局、养分生物循环以及强促淤作用引起的土壤颗粒组成等的显著改变有关。

互花米草入侵亦改变了土壤中陆源和海源有机质的来源比例，使得入侵后湿地土壤养分的自源性增强。

硝化和反硝化：（1）闽江河口湿地土壤的反硝化速率远高于硝化速率，且呈现明显的季节变化，夏季的硝化-反硝化作用最强。

不同季节条件下，土壤硝化-反硝化速率由大到小顺序，硝化速率：夏季>春季>秋季>冬季，反硝化速率：夏季>秋季>冬季>春季；按不同植被类型下土壤硝化-反硝化速率由大到小顺序，硝化速率：入侵边缘>互花米草>短叶茳芏，反硝化速率：互花米草>交汇处>短叶茳芏。

（2）闽江河口湿地不同植被类型下沉积物-水界面N2O交换通量呈现明显的季节变化。

土著物种短叶茳芏的土壤仅春季对上覆水N2O有微量吸收，夏、秋两季均对水体释放N2O，表现为水体中N2O的净源；由于互花米草的入侵，入侵边缘的土壤为春季释放N2O，而夏、秋两季土壤均吸收N2O，与土著物种短叶茳芏完全相反；互花米草入侵成功后的土壤，其夏季的沉积物-水界面N2O交换通量达到最大，表现为向水体释放较多的N2O，而其春、秋两季都为吸收N2O，但吸收总量小于释放量。

（3）闽江口湿地互花米草入侵后，增强了土壤的硝化-反硝化作用，促进了N2O对大气的释放。

矿化作用：（1）实验通过对不同样地不同土层的研究揭示，土壤氮矿化水平随土层深度的增加降低。

这是由于随着土层深度的不断增加，土壤透气性逐渐降低，可供降解的有机质越来越少，微生物数量下降，氮矿化也随之下降。

（2）对于某一土层来说,随着培养时间的变化其矿化速率表现出波动性，有的随培养时间的增加而下降，有的呈现波浪形变化，这可能是由于季节性变化和土壤层的凋落物降解快慢有关。

（3）互花米草入侵确实影响了原土著种短叶茳芏土壤的矿化规律特征，从整体上来看互花米草入侵加强了短叶茳芏矿化效果。

（4）入侵机制存在的情况下,互花米草的入侵对原土著种短叶茳芏土壤矿化的影响表现为:夏季＞春季＞秋季＞冬季。

土壤温度、湿度等因子在不同季节差异很大，由土壤微生物的活动以及植物的生长周期和生长特性所引起氮矿化强度的季节变化也较大。

2、盐入侵对氮循环的影响(1)道庆州和鳝鱼滩湿地土壤覆水理化性质分析：结果显示鳝鱼滩和道庆州湿地沉积物中电导率和硝态氮随季节变化影响较大；鳝鱼滩和道庆州覆水中各指标均随季节变化而变化较大。

(2)道庆州和鳝鱼滩湿地土壤硝化特征：硝化速率和硝化活性特征曲线看出，不同浓度的盐能够抑制硝化细菌的活性，导致硝化速率降低。

(3)道庆州和鳝鱼滩湿地土壤反硝化特征：道庆州和鳝鱼滩反硝化活性随着培养天数的增加而增加，说明不同盐度胁迫下，对反硝化影响不是很大。

(4)道庆州和鳝鱼滩湿地土壤矿化特征：从矿化特征曲线看，道庆州和鳝鱼滩湿地矿化速率均出现先增加后减少的趋势，对于鳝鱼滩而言，矿化前期，不同盐度的海水能够刺激氨化，使氨化细菌活性增加，其中盐度为5‰对应的矿化速率最大，而随着时间的增加，在第35天时，盐度为0‰对应矿化速率最大，之后矿化速率在不断降低，说明土壤中的有机质不断的减少，不能够满足氨化细菌的需求，氨化能力降低。

道庆州的变化趋势与鳝鱼滩相似，随着时间的变化，出现先增加后减少的趋势，在21天时，盐度为5‰对应的矿化速率最大。

3、酸沉降对氮循环的影响（1）pH 并不是影响土壤硝化作用的唯一因素,不同梯度pH值条件下，硝化速率的变化趋势均随着时间变化呈现出―N‖字曲线，但不同梯度pH值之间的硝化速率变化差异不大.（2）模拟酸雨对土壤反硝化速率随着时间的变化减少。

而土壤反硝化活性则随着培养天数逐渐增加。

原因可能是土壤值降低，会影响到反硝化细菌和反硝化酶的活性，使反硝化作用减弱。

（3）不同pH条件下，其矿化速率都不相同，酸沉降对土壤矿化影响可能受到多个因素的控制。

4、土地利用变化对氮循环的影响（1）不同时期的硝化速率变化趋势基本保持一致，表现为先增加后减少，各个时期的硝化活性变化趋势随着时间变化均呈现先增加后减少的趋势，硝化反应的变化可能与养殖塘的中期和后期硝化细菌的活性受到了水质的影响有关，土地利用的变化也间接或直接引起养虾塘内的硝化作用。

（2）本研究过程中养虾塘初期、中期和末期的反硝化速率及反硝化活性和时间之间的关系均呈现出先增加后减少，最后趋于平衡的趋势。

且各个不同时期反硝化速率大体表现为初期＞中期＞末期。

该结果一方面说明鱼虾等水生生物的生命活动及其对水体或沉积物扰动作用的强度均对水体反硝化过程有着重要作用，土地利用的变化将对反硝化作用及其N2O的生成与释放有着重要作用。

（3）土地利用的变化，引起场地周边环境的变化，包括湿度，尤其微生物活动等的改变，对场地内的矿化作用产生较大的影响。

各不同时期的养虾塘的矿化速率和培养周期之间的曲线变化趋基本保持先增加后减少的趋势。

最大值均出现在中期。

土壤氮矿化随时间的推移而降低。

关键词：闽江河口；氮转换；植物入侵；盐水入侵；酸雨；土地利用变化abstractAffected by the interaction between the land and sea, the salty marsh wetland on estuary can be regarded as an active area of living things, and the most active region of geochemical process, thus having an important influence to the human and society. Nitrogen accounts for 78% in the atmosphere components, and it is the most abundant in the atmosphere. The content in the medium of environment will directly affect the growth of the creatures around. At present, a lot of nitrogen source is entering the salty marshes of the estuary wetland, thus producing huge influence such as red tides , the collapse of oxygen content of estuaries dissolving, and the overflow effect of a large amount of greenhouse gases from the environment. based on Fuzhou Minjiang estuary salty marsh wetland, this research fully studies the effects of the key process of soil nitrogen cycle in response to the global change. Through the way of field sampling and laboratory simulation, the author quantitatively studies the Minjiang estuary salty marsh wetland soil - water interface of the nitrogen cycle, and also studies the salt intrusion, plant invasion, acid deposition and salt marsh wetland to raise shrimps, nitrification and denitrification in the soil and the change of mineralization respectively, and the author also so some research on the change of nitrogen in the estuarine wetland, and the important roles of them in estuarine wetland. The main research results are as follows:1、the influence of plant invasion in the nitrogen cycleInorganic nitrogen and total nitrogen: (1) the invasion of qingjiao rice grass changed the content of soil NO3 -- N in different soil, and it can significantly reduce the content of soil NO3 – N. But it increases the overall content of NH4 + -n in soil.(2) The content of the qingjiao m grass soil TC, TN in the different invasion process , and the vertical variation of the C/N ratio are relatively consistent. The invasion increased soil carbon and nitrogen content, the C/N ratio and the storage of soil carbon and nitrogen. (3) The influence of the minjiang mouth qingjiao rice grass invasion on short leaf cyperus malaccensis wetland soil carbon and nitrogen content is relatively more significant than that of the wetland in Yancheng, Jiangsu province, the Yangtze estuary and Hangzhou bay. It’s mainly related to the plant community structure, the nutrient cycle and strong effect on promoting sedimentation causes significant changes in the composition of soil particles in theMin river mouth wetland. The invasion of grass also changed the rate of the source of terrigenous and the source of organic matter in soil, making an enhancement of the invasion of the wetland soil nutrients.(1)Nitrification and denitrification : the soil denitrification rate in Minjiang estuary wetland is far higher than that of nitrification rate, and presents a obvious seasonal change, and it works best in summer. Under the condition of different seasons, soil nitrification and denitrification rate from big to small order, nitrification rate: summer > spring > autumn > winter, and the denitrification rate: summer > autumn > spring > winter; According to soil nitrification and denitrification rate under different vegetation types from big to small order, nitrification rate: invasion of edge > rice straw > short leaves each cyperus malaccensis, denitrification rate: qingjiao junction of rice straw >intersection > short cyperus malaccensis.(2)The seasonal exchange of the Minjiang estuary wetland sediment and water interface under different vegetation types is obviously. The soil of the indigenous species of short leaf cyperus malaccensis has only tiny absorption to the overlying water N2O in spring, but in summer and autumn it releases N2O to water, characterized by the clean source of N2O in water; due to the invasion of qingjiao rice grass, on the edge of the invasion, of soil N2O release in spring, and soil absorbs N2O in summer and autumn, which if quite opposite to the short leaf of indigenous species cyperus malaccensis; after the successful invasion of Qingjiao meters of grass, the exchange of sediment of the soil and water interface achieve the maximum of N2O in summer, which is characterized by releasing more water of N2O, and in spring and autumn is for the absorption of N2O, but the absorption amount is less than the amount of release.(3) After the invasion of the Minjiang qingjiao mouth wetland rice grass, the soil nitrification –denitrification has been enhanced, and the N2O release to the atmosphere has also been promoted.Mineralization: (1) through the studies of soil in different layers, the experiment discovers that, soil nitrogen mineralized level reduces with the increase of soil depth. This is because along with the increase of soil depth, soil permeability is gradually reduced, and the organic matter for the degradation becomes increasingly less, the microbial population declines, and nitrogen mineralization also decreases. (2) for a particular layer soil, as the cultivating time change, the mineralization rate shows the volatility. Some decreases along with the increaseof incubation time, some appears wavy change. This may be due to seasonal changes and the speed of the degradation.(3) the invasion of qingjiao rice grass did affect the mineralization regularity of the original native species of short leaf cyperus malaccensis soil, but on the whole the invasion strengthened short cyperus malaccensis mineralization effect. (4) under the presence of invasion mechanism, the influence of the invasion on the original indigenous short leaf cyperus malaccensis soil mineralization is characterized by: summer > spring > autumn > winter. Soil temperature, humidity and other factors are various in different seasons, and the nitrogen mineralization intensity caused by the activities of soil microbes and plant growth cycle is also significant.2、the influence of salt invasion on the nitrogen cycle(1) the physical and chemical properties analysis of gyeongju and eel beach wetland soil water: the results show that the sediments conductivity and nitrate on the eel beach wetland vary greatly with the seasons change; each indexes of eel beach and the gyeongju overlying water vary greatly with the season changes.(2) the soil nitrifying characteristics of gyeongju and eel beach wetland: according to the nitrification rate and denitrification activity characteristic curve, different concentrations of salt can inhibit the activity of nitrifying bacteria, leading to the reduction of nitrate.(3) the soil denitrification characteristics of gyeongju and eel beach wetland: the denitrifying activity of the gyeongju and eel beach as increases with the increase of the number of cultivating days, and it shows that under different salinity, the influence on denitrifying is not very big.(4) the soil mineralization characteristics of the gyeongju and eel beach wetland: looking from the mineralization characteristic curve, the mineralization rate of gyeongju and eel beach wetland are presented in a trend of increasing after decreasing. For eel beach, at the beginning of the mineralization, the different salinity of sea water stimulates the ammoniation, making ammonifying bacteria activity increases, and the salinity of 5 ‰ corresponding mineralization rate reaches the maximum. With the increase of time, on the 35th day, the corresponding mineralization rate of 0 ‰ salinity rea ches the largest, and after themineralization the rate is on the decrease, showing that the soil organic matter reduced unceasingly, and it will not be able to meet the needs of ammonifying bacteria, ammonifying capacity reduction. The change trend of the gyeongju is like that of the eels beach, with the change of time, first increase and then decrease, and on the 21th days, the mineralization rate of the corresponding 5 ‰ salinity is the largest.3、the influence of the acid subsidence on the nitrogen cycle(1) the pH is not the only factor affecting the soil nitrification. Under different gradient condition of pH, the change trend of nitrification rate presents a "N"curve with the chage of time, but the difference among different nitrification rate pH gradient is not significant.(2) the soil denitrification rate of the simulated acid rain decreases with the change of time, While the soil denitrification activity gradually increases with the increasing of the cultivating days. The reason may be that the reduction of the soil could affect the activity of the denitrifying bacteria and denitrifying enzyme , thus weakening the denitrification.(3) Under the different pH conditions, the mineralization rate is not the same, so the effect of acid deposition on soil mineralization may be controlled by multiple factors.4、the influence of land use change on the nitrogen cycle(1) the nitrification rate in different periods are almost consistent with the change trends, presenting a first increase and then decrease change. The denitrification activity trends also presents the same trend according to the time change. The change of the nitration reaction may be related to the affection of the water quality on the activity of nitrifying bacteria in middle and late terms. The change of the land use affects the nitrification in shrimp pools directly or indirectly.(2) the denitrification rate in the middle and late process of shrimp raising in this study and the relationship between denitrification activity and time shows the trend of first increasing and then decreasing, and finally tends to the balance. The denitrification rate in different period presents a trend of early period > middle period > late period. The results suggests the great effect of life activities of the fish and shrimps and the aquatic body andits sediment disturbance intensity on water denitrification process, and the great effect of land use change on denitrification and the formation and release of N2O.(3) The change of land use causes the changes in the surroundings, including moisture, especially the change of the microbial activity, which has a relatively large impact on mineralization of the field. The mineralization rate in different periods and training cycle curve keeps a trend of increasing first and then decreasing. The maximum appears in the medium term. The soil nitrogen mineralization decreases over time.Key words: Minjiang estuary; Nitrogen transformation; Plant invasion; Salt water intrusion; Acid rain; Land use change目录第1章绪论 (1)1.1 前言 (1)1.2 研究背景 (2)1.3 国内外研究现状及发展动态 (3)1.3.1 植物入侵对湿地土壤氮循环的影响 (3)1.3.2 盐水入侵对湿地土壤氮循环的影响 (6)1.3.3 酸沉降对湿地土壤氮循环的影响 (7)1.3.4 土地利用变化对湿地土壤氮循环的影响 (9)1.4 本研究的科学问题 (11)1.5 研究内容与意义 (11)1.5.1 研究内容 (11)1.5.2 研究意义 (12)1.6 论文创新点 (12)第2章研究区概况与研究方法 (12)2.1 研究区概况 (12)2.2 样品的采集与实验方法 (12)2.2.1 N2O通量及环境影响因子研究 (12)2.2.2 沉积物N2O产生和释放测定的培养实验 (12)2.2.3 实验样地环境背景值的测定 (12)2.3 数据处理与分析 (12)第3章潮汐湿地土壤氮转换过程对植物入侵的响应 (13)3.1 引言 (13)3.2 研究材料与方法 (14)3.2.1土壤样品的采集与培养 (14)3.2.2 土壤样品分析与测定 (17)3.3 结果 (18)3.3.1入侵不同阶段土壤无机氮、总氮的变化特征 (18)3.3.2入侵不同阶段的土壤硝化-反硝化作用 (19)3.3.3 入侵不同阶段土壤矿化作用 (22)3.4 讨论 (25)3.4.1 硝化-反硝化作用对植物入侵的响应 (25)3.4.2 矿化作用对植物入侵的响应 (28)3.5 总结 (30)第4章潮汐湿地土壤氮转换过程对盐水入侵的响应 (32)4.1 引言 (32)4.2 研究材料与方法 (32)4.2.1 实验样地 (32)4.2.2 培养条件设置 (33)4.2.3 土壤样品的采集与培养 (33)4.2.4 氮矿化速率、硝化与反硝化速率的计算方法 (34)4.2.5 盐水入侵实验条件选择 (34)4.3 结果 (34)4.3.1 土壤理化性质分析 (34)4.3.2盐水入侵对土壤硝化作用的影响 (35)4.3.3盐水入侵对土壤反硝化作用的影响 (36)4.3.4盐水入侵对土壤矿化作用的影响 (37)4.4 讨论 (38)4.4.1硝化-反硝化作用对盐水入侵的响应 (38)4.4.2矿化作用对盐水入侵的响应 (40)4.5 总结 (41)第5章潮汐湿地土壤氮循环过程对酸雨的响应 (42)5.1 引言 (42)5.2 酸雨对湿地土壤氮转换的影响 (43)5.2.1 酸雨对土壤硝化作用的影响 (43)5.2.2 酸雨对土壤反硝化作用的影响 (43)5.2.3 酸雨对土壤矿化作用的影响 (44)5.3 讨论 (44)5.3.1 硝化作用对酸沉降的响应 (44)5.3.2 反硝化作用对酸沉降的响应 (45)5.3.3 矿化作用对酸沉降的响应 (46)5.4 总结 (47)第6章潮汐湿地土壤氮循环过程对土地利用变化的响应 (47)6.1 引言 (47)6.2 研究材料与方法 (48)6.2.1 实验样地 (48)6.2.2 沉积物柱状样的采集与培养 (48)6.2.3 土壤样品分析与测定 (49)6.2.4 计算方法 (49)6.2.5 数据处理与统计分析 (50)6.2 结果 (50)6.2.1 取样地土壤理化性质分析 (50)6.2.2 不同养殖时期沉积物的硝化作用 (51)6.2.3 不同养殖时期沉积物反硝化作用 (51)6.2.4 不同养殖时期沉积物矿化作用 (51)6.3 讨论 (52)6.3.1 硝化作用对土地利用变化的响应 (52)6.3.2 反硝化作用对土地利用变化的响应 (52)6.3.3 矿化作用对土地利用变化的响应 (53)6.4 总结 (53)第七章全文总结 (54)参考文献 (58)第1章绪论1.1 前言氮是大气圈中最丰富的元素，约占在大气组分78%，它也是陆地生态系统生物地球化学循环中最受限制的元素之一（Mooney et al.,1987），因此在环境介质中的含量会直接影响到周围生物的生长。