Abstract:

 Four soil samples of highaltitude permafrost from the QinghaiTibet Plateau were incubated in the laboratory for 90 days at 5 ℃, 15 ℃, 25 ℃ and 35 ℃ temperatures. The results showed that with increasing temperature, the soil respiration rate and cumulative amount of organic carbon decomposition presented a trend of increasing; during the incubation, the soil respiration rate reached a peak at first, then decreased continually, and tended to be steady after 15 days. At the same temperature, the soil respiration rate showed the following order: Tuotuohe (meadow marsh soil)>Wuli (alpine meadow soil)>Wudaoliang (alpine steppe soil)>Geermu (greybrown desert soil), but the last three soil samples had no significant difference. Through the methods of density separation, acid hydrolysis, and chloroform fumigation, the soil organic carbon fractions were divided based on physical, chemical and biological views, respectively; meanwhile decomposition dynamic of organic carbon was simulated using the kinetic equations in two pools and three pools. It showed that dividing soil carbon fractions with different methods had significantly different results, and the proportion of active organic carbon accounting for total organic carbon was as follows: microbial biomass carbon 1.26%10.31%, lightfraction organic carbon 9.13%20.22%, easily oxidized organic carbon 28.35%49.35%; that the results of model fitting through  by dividing two or three pools were 0.50%3.65% and 0.51%3.26%, respectively, and MRT were 856 d and 850 d, respectively, which were close; and that in addition, the proportion of active carbon from model approaches was significantly lower than that from experimental methods. Using linear, exponential and Gaussian models, the rule of change of soil respiration rate with temperature was analyzed. It was found that all of the three models can describe this relationship well, and Gaussian model was the best; the Q10 values from Gaussian model was also more agreed with that from incubation experiment. And Q10 decreased with increasing temperature, indicating that the response of the QinghaiTibet Plateau permafrost to climate warming will be more sensitive.

Key words: Tibetan Plateau permafrost, soil respiration, temperature sensitivity coefficient Q10, organic carbon fractions dividing