Alpine Steppe Ecosystem Research Articles

Responses of soil microbial respiration to thermal stress in alpine steppe on the Tibetan plateau

Extensive research has focused on the temperature sensitivity of microbial respiration in tundra and alpine meadows. However, the response of microbial respiration to thermal stress in alpine steppe soils, which have less organic matter and greater aeration, has received less attention. We investigated spatial and temporal variations in microbial respiration using an incubation experiment under different temperature (0, 15 and 30°C) and different percentages of water‐holding capacity (WHC) (50 and 100%) conditions in the alpine steppe, and using a subsequent cooling experiment determined the ‘thermal stress' of soil microorganisms in response to increased temperature in the alpine steppe ecosystem. Microbial respiration rates decreased with increasing temperature at both 50 and 100% WHC for three sampling locations. Thermal stress of soil microorganisms under increased temperatures was found in the alpine steppe because subsequent cooling led to an increase in microbial respiration rates. Soil moisture did not affect microbial respiration, but the temperature sensitivity (Q10) of microbial respiration varied with the interactive effect between soil moisture and sampling location. Our findings suggest that the response of microbial respiration to high temperature may not be always positive as bacteria may experience thermal stress in the alpine steppe. Therefore, it is necessary to include thermal stress responses in alpine steppe models, as they may represent an important negative feedback effect on microbial respiration.

Soil water soluble organic carbon under three alpine grassland types in Northern Tibet, China

Water soluble organic carbon (WSOC) is the most mobile and reactive soil carbon sourceavailable. It plays an important role in many biogeochemical processes. In this study, we assessed WSOC in the upper 0 to 15 cm soil layer, during the growing season of three representative alpine grassland types of Northern Tibet, with an average elevation of over 4500 m. We also evaluated the contributions of soil environmental factors on the three types of grassland. We found that the WSOC was typically higher at the first sampling in May and decreased with subsequent samples. Furthermore, over the short growing season, the alpine meadow steppe ecosystem had significantly higher WSOC content than the alpine meadow and alpine steppe ecosystems. Soil WSOC of alpine grasslands also negatively correlated with both soil temperature and moisture. These results indicated that soil WSOC is considerably different among the different types of grassland in the same alpine area, and we conclude that soil environmental conditions including soil temperature and moisture are important influencing factors that control soil WSOC content. Key words: Water soluble organic carbon, soil temperature, soil moisture, alpine grassland, Northern Tibet.

Profile of Methane Concentrations in Soil and Atmosphere in Alpine Steppe Ecosystem on Tibetan Plateau

Abstract The methane concentration profile from –1.5m depth in soil to 32m height in air was measured in alpine steppe located in the permafrost area. Methane concentrations showed widely variations both in air and in soil during the study period. The mean concentrations in atmosphere were all higher than those in soil, and the highest methane concentration was found in air at the height of 16m with the lowest concentration occurring at the depth of 1.5m in soil. The variations of atmospheric methane concentrations did not show any clear pattern both temporally and spatially, although they exhibited a more steadystable state than those in soil. During the seasonal variations, the methane concentrations at different depths in soil were significantly correlated (R2>0.6) with each other comparing to the weak correlations (R2<0.2) between the atmospheric concentrations at different heights. Mean methane concentrations in soil significantly decreased with depth. This was the compositive influence of the decrea...