Abstract:

Soil surface carbon dioxide flux, the sum of plant and microbial respiration, is an important component of the carbon cycle of terrestrial ecosystems. Temperature is a key factor that regulates many terrestrial biogeochemical processes, such as soil respiration. Numerous studies show that soil respiration increases with temperature, creating a positive feedback to global warming. Accurately quantifying the relationship between soil respiration and temperature is necessary, because it will help to develop mechanisms of the feedback, which will aid in predicting the tendency of global change. In order to determine the law of soil respiration dynamics driven by temperature, and to detect the sensitivity of soil respiration in response to temperature in different communities of temperate grassland, in summer and autumn, we measured soil respiration in eleven communities using the alkali absorption method. We examined seasonal patterns of soil respiration, average respiration rate and responses of soil respiration to temperature. All the communities were located in Xilin River Basin, which has a typical temperate and semi-arid climate.The seasonal variations of soil respiration were similar to those of temperature, but were not completely consistent with each other. The highest value of soil respiration was in summer (June to Aug.). Average soil respiration rates of all communities varied from 565.07 mg C·m-2·d-1 to 1 349.56 mg C·m-2·d-1, and the difference was significant (p<0.001). Respiration was greatest in wet mixed grasses community and least in Caragana stenophylla community. There was no notable relationship between average soil respiration and air temperature in all eleven communities, though relation of soil respiration and temperature could be described well by exponential functions for each community (R2 = 0.330 5 - 0.731 2, p<0.000 1-0.022 0). The modeling was better at lower temperature than at higher. Q10 values of all communities were between 1.47 and 1.84, which were similar to or a little higher than the value in global scale. The Q10 value of wheat community was higher than that of other communities, which implied that land use could affect the sensitivity of soil respiration to temperature, and cultivation of the soil in grassland might be a CO2 source for atmosphere along with global warming.