Meifang YAN^1,2, Xinshi ZHANG^1,2, Yuan JIANG² and Guangsheng ZHOU²

1 State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875

2 State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, the Chinese Academy of Sciences, 20 Nanxincun Xiangshan, Haidian District, Beijing 100093, P.R. China

Abstract：Soil respiration in forest plantations can be greatly affected by management practices. Irrigation is necessary for high productivity of poplar plantations in semi-arid northwest China. Moreover, plowing is essential for improving soil quality and reducing evaporation. In the present study, the influences of irrigation and plowing on soil carbon dioxide (CO2) efflux were investigated in poplar plantations in 2007 and 2008. The experiments included three stand age classes receiving three treatments: control, irrigation, and plowing. Mean soil respiration in irrigation treatment stands was 5.47, 4.86, and 4.43 mmolm_2 s_1 in 3-, 8-, and 15-year-old stands, respectively, during the growing season. In contrast, mean soil respiration in control stands was 3.71, 3.83, and 3.98 mmolm_2 s_1 in 3-, 8-, and 15-year-old stands, respectively. During the entire observation period, mean soil respiration in plowing treatment stands increased by 36.2% compared with that in the control stands. Mean soil respiration in irrigation treatment stands was significantly higher than that in the control stands; this was mainly because fine root growth and decomposer activities were greatly depressed by soil drought, since natural precipitation could not meet their water demands. The results also suggest that plowing management can greatly increase soil CO2 emission by modifying soil structure. After plowing, soil bulk density decreased and soil aeration was greatly improved, leading to greater rates of oxidation and mineralization.

Key words: poplar plantation, soil CO2 emission, soil disturbance, soil moisture.