氮沉降与生物质炭输入的交互作用对毛竹林土壤N2O通量的影响机制

Mitigation of N2O emissions is of great significance for improving the carbon sequestration function in forest soils. Biochar addtion is one of the effective approaches to reduce soil N2O emissions. However, it remains unclear whether nitrogen (N) deposition will weaken the aforementioned biochar-induced effect of emission reduction. Elucidation of the interactive effects of N deposition and biochar addition on soil N2O fluxes in Moso bamboo plantations and associated mechanisms is the key to addressing the above scientific concern. Moso bamboo plantations will be selected as the study object in this project, and nuclear magnetic resonance (NMR), high-throughput sequencing, gene chip and static chamber-gas chromatography methods will be adopted. Field experiments will be conducted to investigate the effects of N deposition, biochar addition, and their interaction on soil N forms and transformations in Moso bamboo plantations with different duration under intensive management. Furthermore, the dynamic changes in soil N2O fluxes, N forms and transformations, organic carbon fractions as well as microbial communities and functions under the synergistic effects of different levels of N deposition and different application rates of biochar will be intensively investigated. In addition, laboratory incubation experiments will be conducted to clarify the effects of biochar type and exogenous N form on soil N2O emissions in Moso bamboo plantations. This project aims to elucidate the mechanisms associated with the interactive effect of N deposition and biochar addition on soil N2O fluxes in Moso bamboo plantations, and advance the development of technology for reducing soil N2O emissions in subtropical forests under the global climate change.

控制N2O排放对于森林土壤碳汇功能提升具有重要意义。生物质炭输入是降低土壤N2O排放的有效途径之一，但氮沉降是否会削弱上述减排作用尚不明确。探明氮沉降与生物质炭输入的交互作用对土壤N2O通量的影响机制是回答上述科学问题的关键。本项目拟以毛竹人工林为研究对象，综合应用NMR、高通量测序、基因芯片以及静态箱-气相色谱法等分析技术，利用野外控制试验，研究氮沉降与生物质炭输入及其交互作用对不同经营历史毛竹林土壤氮素形态与转化的影响；在此基础上，深入研究不同水平氮沉降与不同用量生物质炭输入协同影响下土壤N2O通量、氮素形态与转化、有机碳组分、微生物群落与功能特征的动态变化规律；再通过室内培养试验，明确生物质炭类型与外源氮形态对毛竹林土壤N2O排放的影响；从而系统揭示氮沉降与生物质炭输入的交互作用对毛竹林土壤N2O通量的影响机制，为全球气候变化背景下亚热带人工林土壤N2O减排技术的研发提供科学依据。

本项目研究了氮沉降与生物质炭输入对毛竹林土壤N2O通量的影响及其机制、外源碳添加对毛竹林土壤N2O通量的影响机制以及生物质炭基尿素和普通尿素对毛竹林土壤CO2和N2O通量的影响机制。取得的主要研究结果如下：.1.氮沉降处理显著增加土壤N2O排放，而生物质炭输入则显著降低土壤N2O排放，且抑制氮沉降对土壤N2O排放的促进作用。结构方程模型显示，氮沉降通过增加土壤NH4+-N浓度、蛋白酶活性和AOA基因丰度从而增加硝化速率，通过增加土壤NO3−-N和WSON浓度、硝酸还原酶和亚硝酸还原酶活性、nirK和nirS基因丰度从而增加反硝化速率，最终增加土壤N2O排放。生物质炭输入通过降低土壤NH4+-N浓度和AOA基因丰度从而降低硝化速率，通过降低土壤WSON浓度、硝酸还原酶和亚硝酸还原酶活性、nirK和nirS基因丰度从而降低反硝化速率，最终降低土壤N2O排放。而在氮沉降背景下，生物质炭可通过以上途径显著抑制氮沉降对土壤N2O排放的促进作用。.2.与对照相比，秸秆处理显著增加了土壤N2O累积排放量，而生物质炭处理显著降低了土壤N2O累积排放量。施用秸秆可通过增加土壤WSOC、NH4+-N、NO3−-N和WSON浓度、脲酶、蛋白酶、硝酸还原酶和亚硝酸还原酶活性、AOA、AOB、nirK和nirS基因丰度从而增加土壤N2O排放，而施用生物质炭可通过降低以上指标从而减少土壤N2O排放。另外，秸秆处理增加土壤N2O累积排放量与其增加土壤烷氧碳含量有关，而生物质炭处理降低土壤N2O累积排放量与其增加土壤芳香碳含量有关。.3.普通尿素处理显著增加了土壤CO2和N2O通量，而生物质炭基尿素处理显著降低了土壤N2O通量，对土壤CO2通量无显著影响。结构方程模型显示，施用尿素显著增加了土壤WSOC浓度、蔗糖酶和β-葡萄糖苷酶活性，导致土壤CO2排放增加，而施用炭基尿素显著增加了土壤WSOC浓度从而导致土壤CO2排放增加；施用尿素显著增加了土壤NH4+-N，NO3−-N和WSON浓度以及脲酶和蛋白酶活性，导致土壤N2O排放增加，而施用炭基尿素显著降低了土壤WSON浓度以及脲酶和蛋白酶活性从而减少了土壤N2O排放。