Soil carbon dynamics following forest succession along a weathering gradient in a tropical karst area

Abstract:

Land use change can influence soil carbon (C) storage, although the direction and magnitude of change is inconsistent, particularly for transitions between pastures and secondary forests. This inconsistency may be driven in part by different soil properties which can mediate soil C stability and accumulation under changing vegetation and land use. This work uses a chronosequence of forest succession along a soil-weathering gradient in the karst region of Puerto Rico to address the role of soil properties in determining soil C change. Samples were collected from secondary forests from two age classes as well as active pastures on Mollisols and Alfisols derived from the same limestone parent material. Soil organic C (SOC), total C (TC) and nitrogen (N) stocks were measured along with soil pH to assess the relative importance of land cover and soil properties on controlling soil C. Alfisols contained greater SOC stocks to 1 m, primarily due to having deeper profiles on average, indicating a positive relationship between the degree of weathering and SOC stocks. Mollisols contained greater TC stocks than Alfisols, reflecting the contribution of parent material inorganic carbon in more shallow horizons. Despite expected increases in aboveground biomass with forest growth on pastures, there was no difference in SOC or N stocks among pasture soils or forest successional stage at any depth. Soil pH was positively correlated with TC stocks but did not exhibit strong relationships with OC or N, indicating the role of calcareous parent material in contributing to inorganic C stocks. Karst-derived soils are important but relatively understudied in the tropics, and this study provides additional understanding of soil C dynamics in these soils.