Biotic and Abiotic Properties Most Closely Associated with Subtropical Forest Soil Respiration Differ in Wet and Dry Seasons: A 10-Year in Situ Study

Forest ecosystems greatly affect the global carbon (C) budget. Because subtropical regions typically have wet and dry seasons that are likely to differ in their effects on soil respiration, our estimates of carbon dioxide (CO2) emissions from subtropical soil would be improved by consideration of both wet and dry seasons rather than wet seasons alone. In this 10-year study, we determined soil respiration rates (SRRs) and soil properties in a typical subtropical forest in southern China, and we quantified the relationships between SRRs and soil abiotic and biotic properties during the dry and wet seasons. During the 10 years, soil organic carbon contents, microbial biomass, and fine root biomass were generally higher in the wet season than in the dry season. Microbial biomass C and fine root biomass were positively associated with precipitation in dry seasons but negatively associated with precipitation in wet seasons. The SRRs of wet season were consistently and significantly higher than the counterparts of dry season, with the average SRR being 5.94 +/- 0.32 mu mol CO2 m(-2 )s(-1) in the wet season and 1.56 +/- 0.41 mu mol CO2 m(-2) s(-1) in the dry season. In the wet and dry seasons, cumulative CO2 emissions were positively correlated with microbial biomass C and fine root biomass, but the abiotic and biotic factors explaining variation in SRR differed in the wet and dry seasons. Most of the variation in SRRs was explained by fine roots in the wet season but by fine roots, microorganisms, and soil pH in the dry season. The results revealed that the precipitation generated significantly positive effects on the cumulative CO2 emissions in the dry seasons and that the fine root was the crucial factor contributing to the SRRs in wet and dry seasons.