外源氮输入对毛竹林土壤CH4吸收的影响及其微生物机理的研究

Forest soil is the main sink of atmospheric CH4.Compared with N-limited soils in boreal forests, the response of soil CH4 uptake in subtropical Moso bamboo forest to N addition was expected to be more sensitive. However, only one type of N fertilizer was often used in many previous studies. In this study, two different types of N fertilizer and four N application rates will be used to investigate the effects of simulating N deposition on soil CH4 uptake in subtropical Moso bamboo forest. Soil CH4 flux rate and methanotrophic community will be measured simultaneously using nuclear magnetic resonance (NMR) analysis, elemental analysis, closed static chamber technique and gas chromatography method and molecular biology method, in order to: (1) reveal the effects of the type of N fertilizer and N application rates on soil CH4 uptake; (2) clarify the response of the activity and structure of methanotrophic community to the types of N fertilizer and N application rates; (3)explore the internal relationship between soil CH4 uptake and methanotrophic community; (4) investigate vertical distribution of methane oxidation activity; (5) explain the microbiological mechanism of of soil CH4 uptake in soil-atmosphere and veitical distribution to management practices and nitrogen addition. These results would be conducive to evaluating the role of Moso bamboo forests in climate change, and providing scientific support for establishing model of soil CH4 uptake in subtropical forest.

森林土壤是大气CH4的重要吸收汇。相对于有效氮匮乏的北方森林，处于全球氮沉降高值区、土壤氮素相对富集的亚热带毛竹土壤CH4吸收对外源氮输入应更为敏感。本项目综合了不同氮肥类型、不同剂量的外源氮输入对毛竹林土壤CH4吸收的影响，将野外定位试验和室内培养实验相结合，综合应用核磁共振、元素分析、静态箱-气相色谱和现代微生物分子生物学的方法，将毛竹林土壤CH4吸收和甲烷氧化菌同步监测，明确施氮类型和施氮量对毛竹林土壤CH4吸收的影响，阐明毛竹林土壤甲烷氧化菌群落特征对外源氮输入的响应，揭示毛竹林土壤CH4吸收与甲烷氧化菌群落组成的内在联系，明确毛竹林土壤CH4氧化活性的垂直分布特征，全面揭示外源氮输入和经营管理对毛竹林土壤-大气界面CH4吸收和垂直分布的影响及其环境因子和微生物驱动机制。研究有助于全面评估毛竹林在气候变化中的作用，并为构建亚热带森林土壤CH4通量模型提供科学支撑。

森林土壤是大气CH4的重要吸收汇。相对于有效氮匮乏的北方森林，处于全球氮沉降高值区、土壤氮素相对富集的亚热带毛竹土壤CH4吸收对外源氮输入应更为敏感。本研究以典型亚热带地区毛竹人工林为研究对象，综合研究了不同氮肥类型、不同剂量的的外源氮输入（CK、L-NH4Cl、H-NH4Cl、L-KNO3、H-KNO3）对毛竹林土壤CH4通量的影响，探究毛竹林土壤CH4吸收通量对氮素形态及剂量的响应特征及主控因子，结果表明：（1）外源氮输入显著抑制了毛竹林土壤CH4吸收，与对照相比，毛竹林土壤CH4吸收在施加低剂量的NH4Cl与KNO3导致土壤CH4累积吸收量吸收分别减少了82.36%和82.14%，高剂量的NH4Cl与KNO3导致土壤CH4累积吸收量吸收分别减少了87.33%和88.94%，抑制作用随施氮水平增加而增加；（2）土壤CH4吸收通量与土壤含水量呈极显著负相关性，与NH4+-N含量、NO3--N含量、水溶性有机氮（WSON）含量以及蔗糖酶活性之间具有显著的负相关性，而与地下5cm土壤温度、土壤pH、水溶性有机碳（WSOC）含量、微生物生物量碳（MBC）、微生物生物量氮（MBN）含量和脲酶活性无显著相关关系，外源氮输入主要通过影响土壤氮素含量以及酶活性，从而显著抑制了毛竹林土壤CH4吸收；（3）与粗放经营毛竹林相比，集约经营显著降低了土壤CH4吸收，在CK、L-NH4Cl、H-NH4Cl、L-KNO3、H-KNO3 处理中，集约经营毛竹林土壤CH4吸收量分别比粗放经营毛竹林降低了59.7%、89.3%、89.4%、91.4%和93.4%。研究结果可为大气氮沉降增加对我国亚热带森林土壤CH4吸收的影响提供数据支持。