北方农牧交错带半干旱草地生态系统碳通量对放牧强度的响应

The carbon exchange among plant, soil and atmosphere in grassland ecosystem is an important part of terrestrial ecosystem carbon cycle and the ecosystem carbon sink size is an important indicator to evaluate grassland sustainability. Grazing significantly influences grassland nutrient cycling by changing plant species composition, soil physical and chemical properties, and soil microbial activity, and further affects ecosystem carbon flux. This project is based on the grazing experiment platform established in the semi-arid grassland of northern agro-pastoral ecotone to explore the effects of no grazing, light grazing, moderate grazing and heavy grazing on the ecosystem carbon exchange and soil respiration. The field monitoring experiments focus on gross ecosystem productivity, ecosystem respiration and net ecosystem carbon exchange to clarify the effects of grazing intensity on semi-arid grassland ecosystem carbon flux. To analyze the change of soil autotrophic respiration and heterotrophic respiration, and their contribution to total soil respiration under different grazing intensities, they could reveal the influencing mechanism of grazing intensity on soil respiration. This study is helpful to understand the effect of grazing intensity on semi-arid grassland ecosystem carbon cycling in agro-pastoral ecotone. It provides data for evaluating carbon source/sink in semi-arid grassland, and scientific basis for optimal management of grassland grazing.

草地生态系统植物-土壤-大气间的碳交换是陆地生态系统碳循环的重要组成部分，其中生态系统碳汇大小是用来评价草地可持续性的重要指标。放牧通过改变植被组成、土壤理化性质和土壤微生物的活性等影响草地生态系统的养分循环，并进一步影响生态系统碳通量。本项目拟依托北方农牧交错带半干旱草地已经建立的放牧实验平台，研究不放牧、轻度放牧、中度放牧和重度放牧对半干旱草地生态系统碳交换和土壤呼吸的影响，通过野外监测总生态系统生产力、生态系统呼吸、净生态系统碳交换，阐明放牧强度对半干旱草地生态系统碳通量的影响；分析不同放牧强度下土壤自养呼吸和异养呼吸的变化规律及其对土壤总呼吸的贡献量，揭示放牧强度对草地生态系统土壤呼吸的影响机制。本研究有助于理解放牧强度对农牧交错带半干旱草地生态系统碳循环的影响，为半干旱草地碳源/汇的分析提供数据支持，同时为草地放牧的优化管理提供科学依据。

北方农牧交错带草地生态系统是我国半干旱草地的重要组成部分，研究不同放牧强度对草地生态系统碳通量的影响及其与环境因素之间的关系，对于阐明该区域草地响应的内在机制具有重要意义。本项目依托山西农业大学右玉草地生态系统野外观测研究站已经建立三年的放牧平台，研究不放牧、轻度放牧、中度放牧、重度放牧下草地生态系统碳通量的响应。研究结果显示，不同放牧强度一定程度上提高净生态系统谈交换，显著促进生态系统呼吸和总生态系统生产力，其中重度放牧下均高于中度放牧和轻度放牧。不同放牧强度对土壤异养呼吸的影响显著，轻度放牧下显著低于不放牧和重度放牧。土壤总呼吸和自养呼吸的平均速率的大小区间为3.62～5.92 µmol CO2·m-2·s-1和1.40～2.51 µmol CO2·m-2·s-1，但对不同放牧强度的响应均不显著。另外，实验结果显示土壤异养呼吸对土壤总呼吸的贡献均值为53.18%～72.81%，在轻度和中度放牧下，土壤异养呼吸对总呼吸的贡献均显著低于不放牧和重度放牧，随着放牧年限的增加，土壤异养呼吸对土壤总呼吸的贡献逐渐降低。本研究表明土壤温度和土壤含水量是调节生态系统碳通量最主要的因素，生态系统碳通量对土壤温度的变化更敏感。本研究为半干旱草地生态系统碳源/汇的分析提供数据支持，为草地放牧的优化管理提供科学依据。