Abstract: To evaluate the effects of acid rain on the organic carbon decomposition in different acidity soils, a 40-day incubation test was conducted with the paddy soils of pH 548, 670 and 818. The soils were amended with 0 and 15 g·kg-1 of rice straw, adjusted to the moisture content of 400 g·kg-1 air-dried soil by using simulated rain of pH 60, 45, and 30, and incubated at 20 ℃. The results showed that straw, acid rain, and soil co-affected the CO2 emission from soil system. The amendment of straw increased the soil CO2 emission rate significantly. Acid rain had no significant effects on soil organic carbon decomposition, but significantly affected the straw decomposition in soil. When treated with pH 30 acid rain, the amount of decomposed straw over 40-day incubation in acid (pH 5.48) and alkaline (pH 818) soils was 8% higher, while that in neutral soil (pH 670) was 15% lower, compared to the treatment of pH 60 rain. In the treatment of pH 30 acid rain, the decomposition rate of soil organic C in acid (pH 548) soil was 43% and 50% (P<005) higher than that in neutral (pH 670) and alkaline (pH 818) soils, while the decomposition rate of straw in neutral soil was 17% and 16% (P<005) lower than that in acid and alkaline soils, respectively.

Key words: tiankeng, plant community, species diversity, talus