冻融交替对温带草原土壤氮素生物地球化学过程的作用与机制

There is growing concern about how freeze-thaw cycles (FTCs) alter soil ecological processes. However, owning to extremly scarce in the data from experiments conducted in situ in winter, our current knowledge on the effects of FTCs are still generally limitted to what we leared from the simplified laboratory incubations. To fully evaluate the ecological effects of FTCs, it is time to conduct a long-term precisely manipulated in situ test with highlights in measurements of processes of soil nutrient cycling from late fall to early spring during which FTCs used to occurr frequently. Here, we propose to conduct a systymatic study on soil N mineralization, nitrification, denitrification, immobilization, soil physical, chemical and biotic properties through out 4 years along a series of the manipulated stock rates of the Sino-Germany Grazing Experiment. The experiment is located in a Leymus chinensis steppe in Xilin River Basin, Inner Mongolia. In this study, a long-term contimous and in situ mesurement, a laboratory incubation system and the 15N dilution technology will be emloyed. Our objectives are 1) to quantitively link the N transformation processes each other as well as to the biotic and abiotic variables. 2) to identify the effects of FTCs on soil N transformations under different stock rates, and effects of frost temperature and frequency of FTCs on N processes, 3) to quantify the contribution of FTCs on soil N cycling and flux of soil available N, 4) to address the mechanisms involved in changing rates in soil nitrogen biogeochemical processes as affected by FTCs. Our basic hypotheses are that that FTCs of soil enhance the N mineralization and change soil properties, therefore FTCs may benefit plant growth in subsequent growing season.

冻融交替对土壤生态学过程的作用越来越受到关注，但由于来自冬季野外原位实验的数据极其稀少,至今对冻融交替作用的认识仍主要局限于简化了的室内培养实验的结果。为了全面评价冻融交替的生态学效应，当前最迫切需要开展的是长期连续、并加强冻融交替频繁季节（晚秋到初春）土壤养分循环过程及其机制的原位精准控制实验研究。本项目拟以内蒙古锡林郭勒羊草草原为研究对象，基于中德联合长期放牧控制实验，应用稳定性同位素15N稀释技术，长期连续野外原位测定与室内培养实验相结合，对不同放牧强度下土壤氮素矿化、硝化、反硝化和固定过程、相关土壤理化与生物学性质开展系统的研究，建立氮素转化过程之间以及它们和生物与非生物因子之间的数量关系，甄别冻融交替与非冻融交替期间的异同，定量分析冻融交替作用对土壤氮素生物地球化学循环的贡献，阐明不同放牧强度下冻融交替对典型草原土壤氮素生物地球化学循环过程的影响与机制。

内蒙古草原约占我国草地面积的70%，地处高寒地带，在非生长季节冻融交替频繁发生。冻融交替对土壤生态学过程的作用越来越受到关注，但由于来自冬季野外原位实验的数据极其稀少,至今对冻融交替作用的认识仍主要局限于简化了的室内培养实验的结果，限制了我们对生态系统土壤养分循环过程及其机制的全面理解，因此为了深入理解冻融交替的生态学效应，当前亟需开展的是长期连续、并加强冻融交替频繁季节（晚秋到初春）土壤养分循环过程及其机制的原位精准控制实验研究。本项目以内蒙古锡林郭勒羊草草原为研究对象，基于中德联合长期放牧控制实验，通过长期连续野外原位测定、室内培养、先进的高通量测序技术相结合，对不同放牧强度下土壤氮素矿化、硝化、反硝化和固定过程、相关土壤理化与土壤微生物特征开展了系统的研究, 建立了典型草原土壤氮素生态过程的季节动态特征。研究结果表明，土壤理化属性、微生物群落结构、土壤氮素转化过程均对放牧和冻融交替有不同程度的敏感性。PLFAs分析发现细菌比真菌对季节的变化敏感，高通量基因测序则表明真菌比细菌对放牧敏感。放牧后变形菌门（Proteobacteria）和拟杆菌门（Bacteroidetes）均有降低趋势，放牧强度达到9.0只羊/公顷时，两个门均显著性降低。非生长季净氮矿化对全年净氮矿化的贡献可达6-25%，放牧提高了非生长季净氮矿化的贡献率。本项目的顺利实施，可为草原生物地球化学循环过程的模型构建、验证和预测提供参数，同时为我国草原生态系统的可持续利用、管理和生态恢复提供重要的基础科学数据。