Abstract: The spatial heterogeneity of soil respiration plays an important role in accurately evaluating soil carbon balance. Based on the observations of the soil respiration, soil environmental factors, and fine root biomass in poplar (Populus balsamifera) plantations at three developmental stages in Yili of Xinjiang, Northwest China, this paper analyzed the spatial variation of soil respiration and related affecting factors. In the whole growth period of P. balsamifera, the coefficient of variation (CV) of soil respiration ranged from 5.7% to 42.6%. The average soil respiration rate for 2-, 7-, and 12-year old P. balsamifera stands was 5.74, 5.10 and 4.71 μmol·m^-2·s^-1, and the CV was 28.8%, 22.4% and 19.6%, respectively, with a significant difference in the spatial variation of soil respiration among the three age classes. Multiple regression analysis suggested that the temperature at soil depth 5 cm and the nitrogen content and fine root biomass in upper soil layer were the main factors determining the spatial heterogeneity of soil respiration, responsible for 86% of the variation in soil respiration. In addition, the factors such as soil temperature and fine root biomass changed with the distance from measurement position to tree stem, which could also lead to the spatial variation of soil respiration. It was suggested that the spatial variation of soil respiration at different developmental stages of P. balsamifera should be taken into consideration when evaluating the soil carbon emission in poplar plantations.

Key words: integrated risk, danger, vulnerability, disaster prevention and mitigation capacity., drought