Precipitation influences on active fractions of soil organic matter in seasonally dry tropical forests of the Yucatan: regional and seasonal patterns

In a transect study involving 15 mature seasonally dry tropical forests growing on uniform geological substrate in the Yucatan Peninsula, Mexico, we analyzed the influence of a large reduction in mean annual precipitation (1,036–537 mm year−1) on carbon (C) and nitrogen (N) pools in soils. We investigated the C content in organic soil and in active fraction pools (organic matter and microbial biomass) and analyzed the dependence of these pools on precipitation. Carbon (total, inorganic and organic, and in microbial biomass) and N (total) concentrations in bulk soil decreased as rainfall increased from 1,000 mm year−1. Additionally, in all organic matter fractions, C and N concentrations generally decreased with greater precipitation. Soil average C mineralization decreased by 61 % from the wettest to the driest region. Reduced precipitation during the dry season increased microbial biomass C and water-extractable C concentrations and decreased the C concentration in organic matter fractions. No other significant changes were observed between seasons in C concentrations, N concentrations or C mineralization. Overall, we conclude that physical (macroclimate) and biological processes are more active in soils in the wettest region, resulting in a faster turnover of organic matter.