模拟氮沉降对桂西南喀斯特次生林土壤N2O排放的影响及其微生物机制

Karst secondary forest in the Southwest of Guangxi was the important natural ecological protective screen and a typically eco-environmental vulnerable area in our country. Now, atmospheric nitrogen deposition are prominent increasingly in recent years , which has a marked impact on the emission of greenhouse gases from the soil and other ecological environmental problems in the Southwest of Guangxi . Nitrous Oxide (N2O) was one of the main greenhouses, which derived from soil nitrification and denitrification primarily. It was the most important to differentiate the relative contributions of nitrification and denitrification to the production of N2O from soil. With increasing of nitrogen deposition, it was very important for us to find the source of soil N2O emission that we slow the growth of nitrogen oxides emission. Therefore, a simulated nitrogen deposition control experiment was designed at a Karst secondary forest in the Southwest of Guangxi．Effects of nitrogen deposition on soil N2O fluxes were measured by the static chamber-gas chromatography method. Soil gross nitrification rates and denitrification rates were determined using the barometric process separation (BaPS) technique, and the contributions of nitrification and denitrification to the production of N2O from soil were differentiated. The source of soil N2O emission in soil would be found by stable isotope techniques (δ 15N，δ 18O).And the same time, the key processes and microbial mechanisms of soil N2O fluxes were also studied through modern molecular biology methods. At last, the possible measures to reduce nitrogen oxides emission and the scientific data for the forest management policy would be suggested for Karst secondary forest regions in the Southwest of Guangxi.

桂西南喀斯特次生林地区是我国重要的生态屏障区和典型的生态脆弱区，近年来大气氮沉降日益突出，是土壤温室气体排放等生态环境问题的一个重要影响因素。氧化亚氮（N2O）是一种重要的温室气体，硝化作用和反硝化作用是土壤产生和排放N2O的主要途径，有效区分土壤硝化与反硝化对N2O产生的相对贡献尤为重要。而氮沉降增加背景下识别土壤N2O排放来源途径对于减缓土壤氮氧化物排放量具有重要意义。本研究基于桂西南喀斯特次生林模拟氮沉降控制试验，采用静态箱-气相色谱法原位监测土壤N2O排放特征；利用气压过程分离法（BaPS）系统分析土壤总硝化和反硝化作用过程，明确硝化作用和反硝化作用对土壤N2O排放的相对贡献，并结合稳定性同位素技术（δ 15N，δ 18O）辨析土壤N2O排放来源，同时借助现代分子生物学手段，阐明土壤N2O排放过程响应的微生物作用机制。为该地区制定相应的氮氧化物减排措施和科学的森林管理政策提供科学数据。

桂西南喀斯特次生林地区是我国重要的生态屏障区和典型的生态脆弱区，近年来大气氮沉降日益突出，氧化亚氮（N2O）是一种重要的温室气体，氮沉降背景下识别土壤N2O排放来源途径对于减缓土壤氮氧化物排放量具有重要意义。基于桂西南喀斯特次生林模拟氮沉降控制试验，采用静态箱-气相色谱法监测土壤N2O排放特征，利用气压过程分离法（BaPS）分析土壤总硝化和反硝化作用过程，并借助现代分子生物学手段，探讨土壤N2O排放过程响应的微生物作用机制。结果表明：1）随着氮沉降的增加，各处理土壤pH值、土壤速效磷、土壤速效钾均呈下降趋势；增加了土壤总有机碳、微生物生物量碳、全氮、微生物生物量氮、土壤总有效氮、铵态氮和硝态氮含量，氮沉降对土壤有效氮的影响表现出累加效应。2）模拟氮增加降低了凋落物氮、磷 含量以及C /N，C /P和N/P 比值，对凋落物分解产生了促进作用，氮沉降降低了喀斯特次生林土壤酸缓冲能力。氮沉降增加了土壤多酚氧化酶、蔗糖酶、酸性磷酸酶和脲酶的活性，抑制了纤维素酶活性，对过氧化物酶的影响不显著。3）随氮沉降的增加，土壤微生物总PLFAs 降低，硝酸细菌数量逐渐减少，表现出抑制作用，氮沉降增加对反硝化细菌影响不显著。氮沉降的增加，使土壤中细菌 16S r RNA 基因和氨氧化菌 amo A 基因的含量下降。增加了 AOB 群落的多样性，氮的累积施加能提高AOB 的群落多样性。4）在氮沉降条件下，土壤-大气界面N2O的排放主要取决于土壤含水量和土壤温度，全年N2O的排放量约为1.23g/(m2.a)，模拟氮沉降增加促进了N2O的排放。土壤N2O通量与土壤可溶性无机氮含量相关性不高，与土壤可溶性有机氮含量有显著相关性，推测真菌的共同反硝化过程可能也是N2O的排放来源之一。随着施氮量的增加，土壤总硝化速率与反硝化速率总体上均呈现加强的趋势。土壤有机碳含量、土壤硝态氮含量、土壤容重是影响土壤总硝化和反硝化作用的主要因素。土壤硝化作用和反硝化作用对土壤N2O排放的贡献率分别为59. 8%，41. 2%。该项目的研究结果，可为该地区制定相应的氮氧化物减排措施和科学的森林管理政策提供一定科学数据。