Abstract:

Owing to the interactions between environmental factors, different conclusions can be drawn about the relationships among soil microbial biomass carbon, nitrogen, and their influencing factors. Thus, it is important to increase research in different ecosystems. To explore the dynamics of soil microbial biomass during the growing season in the Qinghai alpine grassland and the relative contribution of water and heat factors to spatial changes in soil microbial biomass, we conducted studies on the plots set up by the Sanjiangyuan Grassland Ecosystem National Observation and Research Station. The results showed that: (1) The alpine steppes located in the central and western regions of Qinghai Province, especially the Hoh Xil region, had the lowest microbial biomass, while there was relatively high microbial biomass in alpine meadow, alpine meadow steppe, and warm steppe. (2) The seasonal dynamics of soil microbial biomass carbon and nitrogen varied in different regions, and the central western and eastern regions of Qinghai Province exhibited significantly different trends. (3) Using an enhanced regression tree model to quantitatively evaluate the relative contributions of water (soil water content, relative humidity of air, precipitation, and evapotranspiration) and heat (soil temperature, air temperature, and net radiation) factors to microbial biomass changes, it was found that, compared with other water and heat factors, the soil water content (P=0.000) and soil temperature (P=0.000) had the greatest impact on microbial biomass carbon and nitrogen, and both were positively correlated. On the vertical gradient of the soil, the influence of the water factor (63.58%-76.62%) on the change of microbial biomass was greater than that of the heat factor (23.38%-36.42%), but its contribution decreased with depth in the soil layer. Over the whole region, the heat factor (52.11%-81.84%) contributed most to the variation in microbial biomass in the eastern and central regions, while the water factor (66.33%-95.19%) controlled the variation in microbial biomass in the western regions. We conclude that the soil microbial biomass of alpine meadow, alpine meadow steppe, and temperate steppe was significantly higher than that of alpine steppe in Qinghai. The soil water content and soil temperature were the main factors controlling variations in soil microbial biomass. The impact of the factors on the variation of soil microbial biomass across the region showed a transition from the heat factor in the east to the water factor in the west. This study provides a reference for exploring the soil carbon nitrogen cycle and its influencing factors in Qinghai alpine grassland in the context of climate change.

Key words: Qinghai-Tibetan Plateau, Sanjiangyuan, alpine grassland, soil microbial biomass, soil water content, soil temperature

摘要：

由于环境因子之间的互相干扰，土壤微生物生物量碳、氮及其影响因子之间的关系研究存在着不同的结论，亟需在不同的生态系统中加强研究。为探究青海高寒草地生长季土壤微生物生物量动态，以及水热因子对其空间变化的相对贡献，在青海三江源草地生态系统国家野外科学观测研究站设置的监测样地进行了相关研究。结果显示：（1）位于青海省中西部的高寒草原，尤其是可可西里地区土壤微生物生物量最低，而高寒草甸、高寒草甸草原和温性草原则相对较高；（2）不同区域土壤微生物生物量碳、氮存在不同的季节动态，青海省中西部与东部区域表现出明显不同的变化趋势；（3）利用增强回归树模型定量评估水（土壤含水量、空气相对湿度、降雨量、实际蒸散发）、热（土壤温度、气温、净辐射）因子对微生物生物量变化的相对贡献，发现：与其他水热因子相比，对微生物生物量碳、氮影响最大的为土壤含水量（P=0.000）和土壤温度（P=0.000），且均为正相关。在土壤垂直梯度上，水分因子（63.58%-76.62%）对微生物生物量变化的影响均大于热量因子（23.38%-36.42%），且其贡献随土层加深呈下降趋势。从不同研究区看，东中部区域对土壤微生物生物量变异贡献较大的是热量因子（52.11%-81.84%），而到西部区域，则为水分因子（66.33%-95.19%）控制着微生物生物量的变化。结论：青海高寒草甸、高寒草甸草原和温性草原的土壤微生物生物量明显高于高寒草原；土壤含水量和土壤温度是控制土壤微生物生物量变异的主要因子；对土壤微生物生物量变异的影响，在区域上从东到西呈现从热量因子向水分因子的过度。该研究为探究在气候变化大背景下青海高寒草地土壤碳氮循环规律及其影响因素提供参考。

关键词: 青藏高原, 三江源, 高寒草地, 土壤微生物生物量, 土壤含水量, 土壤温度