高寒草地土壤有机质化学对土壤氮转化的影响

Alpine grassland is the widely distributed ecosystem in alpine region which is chartered by high altitude and low temperature. The N transport and transformation within the ecosystem is more complex, sensitive and special than others because it endure extremely harsh natural environment in the long term. In last several years, we found that soil environment factors, including soil temperature and soil moisture, influenced the soil N transformation process to a certain extent, but they were not the most key factors which control soil N transformation process due to long-term limitation of low temperature. It is reported that soil organic matter chemical composition and constituent have significant influence on soil ecological processes, such as soil C transformation, number and activity of microorganism, enzymatic reaction kinetics. Whether the soil organic matter chemistry is the most key factor which control soil N transformation process in this special alpine environment? This study focus on this issue to explore the relationships between soil organic matter chemical composition and constituent and soil N transformation which including gross nitrification, denitrification, net N mineralization, and so on by combining the field investigate and sampling, long-term soil incubation experiment and laboratory analysis. And to reveal the influence extent and pattern of soil organic matter chemistry on soil N transformation. And further to reveal the key factor and its mechanism of affecting the alpine grassland soil N transformation from a soil organic matter chemistry perspective. We hope that providing a new idea to clarify the mechanism of soil N transformation in special alpine environment through this study.

高寒区独特的高海拔、高寒自然地理特征，使该区域分布的高寒草地长期忍受极端气候环境，生态系统内部N 的迁移、转化过程更为复杂、敏感和特殊。过去几年我们研究发现，在高寒特殊环境，由于长期低温的限制，土壤环境因子虽在一定程度上影响土壤N 转化过程，但并不是控制土壤N 转化的最关键因子；近年来，土壤有机质化学被报道显著影响土壤中的C转化、微生物数量和活性、酶动力学等，那么土壤有机质化学是否也是控制土壤N 转化的关键因子呢？本研究就针对这一科学问题，通过野外原位调查和采样、室内土壤长期培养试验和实验室分析相结合的方法，研究高寒草地土壤有机质化学成分和化学组成与总硝化、反硝化、净N 矿化等土壤N 转化过程的关系，阐明土壤有机质化学对土壤N 转化影响的程度和方式，尝试从土壤有机质化学成分和化学组成角度揭示影响高寒草地土壤N 转化的关键因子及其作用机理，并为揭示高寒特殊环境中土壤N 转化机理提供新的思路。

高寒区独特的高海拔、高寒自然地理特征，使该区域分布的高寒草地长期忍受极端气候环境，生态系统内部N 的迁移、转化过程更为复杂、敏感和特殊。利用Py-GC/MS技术获得高寒草地SOM化学组成 “指纹图谱”，同时对土壤样品进行室内恒温培养210天，分析温室气体排放通量、土壤可溶性有机碳、铵态氮、硝态氮、可溶性总氮等动态特征。结果表明：1）通过Py-GC/MS解析出高寒草地土壤和植物中有机质化学成分“指纹图谱”，获得九类62种化学分子，包括烷烃和烯烃、木质素、含氮化合物、多糖、芳香烃、脂肪酸、酚类、多杂环芳香烃和萜烯，主要物质有2-甲氧基-4-乙烯基酚、D-丙氨酸、吡啶、吡咯、糠醛、苯、甲苯、酚、萘和角鲨烯等；2）高寒草甸土壤中解析出的化合物数量多于高寒草原、高寒草甸草原、高寒荒漠草原和高寒荒漠。含氮化合物表现为高寒草甸草原土壤>高寒荒漠草原土壤>高寒草原土壤>高寒荒漠土壤>高寒草甸土壤；芳香烃、木质素和酚类等主要来源于植物根系的物质在高寒草甸土壤中相对含量高于另外四种草地土壤；萜烯类在高寒荒漠草原土壤中相对含量高于其他草地土壤，而烷烃类和多糖类则表现为高寒草甸土壤>高寒草原土壤>高寒草甸草原土壤>高寒荒漠草原土壤>高寒荒漠土壤。3）高寒草地SOM降解过程中，木质素相对含量在SOM化学组成中均呈现为减少趋势；多糖类化合物相对含量则表现为上升趋势；除高寒草甸草原土壤外，其余四种草地SOM化学组成中含氮化合物相对含量呈现上升趋势。SOM中化学成分对土壤碳氮动态特征的影响具体表现为，土壤CO2累积排放量与SOM含量、SOM化学组成中多糖和芳香烃相对含量呈正相关关系，而与含氮化合物呈负相关；土壤N2O累积排放量与土壤DOC含量、SOM化学组成中多糖、芳香烃和木质素相对含量呈显著正相关，与含氮化合物负相关关系但未达到显著水平；土壤培养过程中累积净氮矿化量与SOM含量及其化学组成中烷烃和烯烃类、芳香烃类、木质素和多糖相对含量呈正相关，而与含氮化合物、脂肪类呈负相关关系。本研究阐明了SOM对土壤氮转化影响的程度和方式，从SOM化学组成角度揭示了影响高寒草地土壤氮转化的关键因子及其作用机理，为探索高寒特殊环境中土壤氮转化机理提供新的思路。