Abstract:In order to understand the impact of acid rain on soil respiration of Pinus massoniana and Cunninghamia lanceolata, a field study with 3 simulated acid rain levels (pH 2.5, 4.0 and 5.6) were conducted. Measurement of soil respiration was made using a LI-8100 soil CO2 efflux system, the soil temperature at 10 cm depth and soil moisture at 5cm depth also were recorded at the same time. Results show that: (1) The soil pH values for P. massoniana and C.lanceolata decreased with the increase of rain acidity; (2) The soil respiration of P.Massoniana and C.lanceolata under different acid rain levels fluctuated with distinct seasonal patterns and the soil respiration rate was influenced significantly by soil temperature. The mean rate of soil respiration under pH2.5 level were 1.79 and 1.12μmol?m-2?s-1, and increased 14% and decreased 39% under control level (pH5.6) respectively. (3) Significant relationships between soil respiration and soil temperature at 10 cm under different acid rain levels of P. massoniana and C.lanceolata were found, which could be best described by exponential equations. However, the relationships between soil respiration and soil moistures at 5 cm depth were found in all levels are not significant. The relationships between soil respiration and soil temperature at 10 cm and soil moisture at 5 cm depth were described by multiple regression equation. The regression equations had more predicative capability than those using only temperature or moisture as a single independent variable. (4) The Q10 (temperature sensitivity coefficient of soil respiration) values at pH 2.5 and 4.0 levels of P.Massoniana and C.lanceolata were 1.36, 2.01 and 1.51, 2.25, respectively. Compared with which at control level, the Q10 values tended to increase with rain acidity (pH4.0), and then (pH2.5) decreased. The results indicated that acid rain is an important factor in affecting soil CO2 efflux of P.Massoniana and C.lanceolata.