土壤氮磷失衡条件下热带雨林N2O排放特征及其微生物调控机制

The imbalance of soil nitrogen: phosphorus (N:P) ratio caused by anthropogenic activities can show substantial impacts on forest ecosystems. High amount of increased N deposition and relatively slow increase in P deposition will intensify the imbalance of soil N:P ratio in tropical rainforest, which consequently affect the emission of important greenhouse gas, nitrous oxide (N2O). However, little is known about the characteristics and associated microbial mechanisms regulating N2O emission driving by imbalanced soil N:P ratio in tropical rainforests. The proposed project will be conducted on the first long-term field N and P addition experimental station in tropical rainforest of China. The intensified and alleviated imbalance of soil N:P ratio will be simulated by adding four different levels of N and P nutrient, and the soil will be incubated in situ and in laboratory conditions. We will use N isotopic signature technique to study the generation paths and their relative contributions to soil N2O emission. Meanwhile, using the High-throughput sequencing combined with microbial network analysis, the qualitative and quantitative analyses of amoA，nirK，nirS，nosZ functional genes will be performed, aiming to clarify the responses of nitrifying and denitrifying microbial activities, structure and keystone species to imbalanced soil N:P ratio. These analyses will help us to elucidate the relationships between soil N2O emission characteristics and functional microbial attributes and further explore the microbial mechanisms regulating N2O emission driving by different functional microorganisms. Results of this study can shed lights on the characteristics and microbial regulating mechanisms of N2O emission in tropical rainforest under imbalanced soil N and P nutrient condition, and provide the theory basis for making policies on greenhouse gas emission reduction and forest conservation in tropical rainforests.

由人类活动导致的土壤氮磷养分失衡对森林生态系统影响巨大。全球氮沉降激增而磷沉降增速缓慢将加剧热带雨林土壤氮磷养分失衡，从而影响温室气体N2O的排放，但土壤氮磷失衡条件下热带雨林N2O的排放特征及其微生物调控机制尚不明确。本研究拟利用国内首个热带雨林长期氮、磷添加实验平台，通过4个不同氮、磷添加比例模拟土壤氮磷养分失衡的加剧和改善，开展原位测定与室内培养实验：利用N同位素标记技术，摸清土壤N2O排放路径及所占比重；利用高通量测序技术结合微生物网络分析，通过对amoA，nirK，nirS，nosZ功能基因进行定量与定性分析，研究土壤硝化、反硝化菌群落活性、结构和关键类群对氮磷失衡的响应。阐明土壤N2O排放特征与硝化、反硝化菌群落的关系，解析不同功能微生物对N2O排放调控分异，进而揭示土壤氮磷失衡条件下热带雨林N2O排放的微生物调控机制，为我国温室气体减排和热带雨林的保护管理提供科学依据。

由人类活动导致的土壤氮磷养分失衡对森林生态系统影响巨大。全球氮沉降激增而磷沉降增速缓慢将加剧热带雨林土壤氮磷养分失衡，从而影响温室气体N2O的排放，但土壤氮磷失衡条件下热带雨林N2O的排放特征及其微生物调控机制尚不明确。本研究利用国内首个热带雨林长期氮、磷添加实验平台，通过4个不同氮、磷添加比例模拟土壤氮磷养分失衡的加剧和改善，开展土壤N2O排放通量的原位动态监测，利用高通量测序和功能基因芯片技术结合微生物网络分析；通过对细菌、真菌以及碳、氮、磷转化相关功能基因进行定量与定性分析，研究土壤微生物群落结构、功能以及关键类群对氮磷失衡的响应，重点关注氮转化功能基因；将土壤N2O排放特征与微生物功能变化相结合，初步阐明氮磷添加下调控N2O排放通量变化的潜在微生物过程。研究结果发现：1）氮磷添加对土壤N2O排放通量的影响与森林类型有关，氮添加显著提高了原始林土壤N2O排放通量，而磷和氮磷添加显著降低了次生林土壤N2O排放通量，所有养分添加处理均导致土壤N2O排放产生了更大的季节波动。2）原始林中，氮添加促进了寡营养细菌的生长，同时增加了介导碳磷矿化、硝化和反硝化的功能基因相对丰度，进而导致土壤N2O排放增加了110%；次生林中，磷和氮磷添加促进了富营养真菌的生长，同时提高了微生物生物量和氮转化功能基因丰度，加快了微生物生长过程中对氮的吸收固定，进而导致土壤N2O排放降低了35%。3）养分添加主要通过改变土壤有效氮磷比而影响微生物功能和组成，进而导致土壤N2O排放通量的改变。基于以上结果，本项目初步揭示了土壤氮磷失衡条件下热带雨林N2O排放的微生物调控机制，为我国温室气体减排和热带雨林的保护管理提供了科学依据。