Effects of tree species on soil carbon and nitrogen stocks in a coastal sand dune of southern subtropical China

Soil carbon (C) and nitrogen (N) cycles can be affected by different plant traits and stand properties through the influence of nutrients release to soil via mineralization. We investigated the soil C and N stocks under secondary forest and plantations of casuarina, pine, acacia and eucalyptus in a coast sand dune of Fujian province, China. Results show that the soil C and N storages, soil microbial biomass carbon (MBC), soil microbial biomass nitrogen (MBN), soil dissolved organic carbon (DOC) and nitrogen (DON) were significantly higher under secondary forest than under plantations. No significant increase was found in soil C and N storages, MBC and DOC under N-fixing trees compared with non-N-fixing trees, but the MBN and DON under acacia were all higher than non-N-fixing trees. No significant difference was found in soil C storage, MBC, MBN, DOC and DON between coniferous and broadleaf plantations. Our findings indicate that the differences in litter quality and quantity, root biomass and turnover rate are the primary cause of soil C and N stocks in coastal sand dunes, and the lack of N fixation ability may be a significant factor influencing soil C and N stocks under N-fixing trees.