Converting cropland to plantation decreases soil organic carbon stock and liable fractions in the fertile alluvial plain of eastern China

Abstract

Soil organic carbon (OC) stocks are well known to change as a result of land use change. However, the early responses of soil OC stock and liable fractions to converting cropland to plantation in the fertile alluvial plain remain unknown. Thus, we evaluated the OC stock, liable OC fractions [easily oxidizable carbon (EOC), light fraction organic carbon (LFOC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC)] and carbon management index (CMI) in the 0-60 cm soil profile of an Anthrosols for three pure plantations (i.e., Metasequoia glyptostroboides, Cinnamomum camphora and Bischofia polycarpa) and the adjacent cropland. The marked reductions in OC stock and liable OC content were observed at the 7th year following converting cropland to plantation, and the smallest of these initial losses mostly occurred in Bischofia polycarpa plantation. The distributions of OC stock and liable OC content at the depth of 0–20 cm were changed following converting cropland to plantation. The CMI, EOC and LFOC are more sensitive than OC in response to the land use change, and are taken as the useful early indicators of soil OC dynamic. Although the losses of EOC, LFOC, DOC and MBC were significantly positively correlated with the OC loss, these liable OC fractions were not major part of soil OC loss. We conclude that the soil OC sequestration was significantly decreased in the short-term following converting cropland to plantation in the fertile alluvial plain, and the deciduous broad-leaved tree species (Bischofia polycarpa) for afforestation can mitigate the soil OC loss. Moreover, further research needs to confirm or not the results presented in the study after a long period of time.