青藏高原草地土壤固碳微生物群落及其固碳能力研究

Tibetan Plateau, representing the highest area on Earth, is one of the most sensitive regions to climate change and the most ecologically fragile zones. Grassland is the dominant lanscape on the plateau with an area of 162 km2, where low temperature, drought and strong UV inhibit plant growth for short growing season and low biomass and subsequently decrease their carbon sequestration capacity. Soil microbes can fix atmospheric CO2, and microbe-dominated biological soil crust could sequestrate carbon in the amount similar to plants in dryland ecosystems. Tibetan Plateau grassland is typical of plant-growth-inhibited ecosystem, its soil CO2-fixing microbes thus could play a big role in sequestrating carbon. The CO2-fixing microbial community and their carbon sequestration potential remains unexplored in the region. We are proposing to characterize the CO2-fixing microbial community abundance, diversity, carbon sequestration potential and their driving factors along a typical precipitation gradient where meadow, steppe and desert grassland transits. Molecular methods and stable isotope probing techniques will be employed for this purpose. This will extensively contribute to understand the carbon cycling process and accurately assess the carbon balance in the alpine grassland soils, which could provide suggestions and solutions for the grassland management and the protection and construction of the national ecological security shelter zone on the Tibetan Plateau.

青藏高原属典型生态脆弱带，其低温、干旱和强紫外等极端条件极大限制草地植被固碳潜力。土壤微生物可固定大气CO2，全球土壤微生物固碳量可高达49亿吨/年。故在青藏高原草地系统中，土壤微生物固碳潜力可能巨大，但尚未系统研究。本项目将沿该地区降水梯度线（东南至西北方向），采集草甸-草原-荒漠草地土壤样品，采用定量PCR测定土壤中4类固碳微生物类群数量，T-RFLP方法研究其群落结构和多样性，克隆测序方法确定固碳微生物组成；利用13CO2标记技术在室内培养条件下测定土壤微生物固碳能力，并在纳木错站和阿里站利用13CO2标记方法野外原位监测草地土壤固碳能力及其季节动态变化，采用DNA-SIP方法确定固碳微生物活跃类群；耦合土壤、植被和气候等环境因子，阐明不同类型草地土壤固碳微生物群落特征、固碳能力及其环境驱动因子。为全面认识青藏高原草地土壤碳循环过程和准确评估草地土壤碳收支平衡提供理论依据。

青藏高原属典型生态脆弱带，其低温、干旱和强紫外等极端条件极大限制草地植被固碳潜力。土壤微生物可固定大气CO2，全球土壤微生物固碳量可高达49亿吨/年。本项目系统研究了青藏高原草地系统中，土壤微生物固碳潜力及其群落结构特征。本项目沿该地区降水梯度线（东南至西北方向），采集草甸-草原-荒漠草地土壤样品，利用分子生态学方法系统研究了青藏高原土壤固碳微生物群落结构，采用室内稳定同位素13CO2标记试验测定了土壤微生物固碳潜力；并依托中国科学院青藏高原研究所纳木错野外台站，采用静态箱法连续4年定位监测了高寒草原土壤微生物群落结构及其固碳潜力季节动态变化特征。受本项目资助，共发表9篇SCI论文，其中部分论文发表在Journal of Applied Ecology, Soil Biology and Biochemistry, Environmental Microbiology等期刊上。本项目研究发现：（1）连续4年野外观测发现，土壤微生物固碳量最高可达植物固碳量的35%，4年平均固碳量占植物固碳量的18.2%；土壤微生物固碳量年际波动大，其变化率可达76.1%；（2）沿青藏高原随草甸-草原-荒漠样带，土壤总有机碳含量逐渐降低，但土壤溶解性有机质（DOM）可降解性显著增加，土壤DOM可降解性主要受土壤微生物活性驱动，后者受土壤碳氮含量驱动；（3）沿降水梯度带，稀有与优势土壤微生物类群空间分布格局一致，二者群落结构均沿草甸-草原-荒漠生态系统逐渐变化，但稀有种群落构建过程主要由随机过程驱动（72%），优势种群落构建过程由随机和决定性过程共同驱动。本研究为全面认识青藏高原高寒草地土壤碳循环过程和准确评估草地土壤碳收支平衡提供理论依据。