Tree derived soil carbon is enhanced by tree species richness and functional diversity

Aims We assessed the impact of tree species richness (SR) and functional diversity (FD) on soil carbon (C) accumulation in plantations. Methods We selected six mixed plantations established in 1999 on continuous maize field soils. Plantations differed only in the number of species whereas climatic conditions, stand age, tree density and soil type were the same. In each plantation, four random plots of 400 m(2) each were identified. In each plot and in the nearby maize fields, we collected soil cores to quantify organic C content, soil bulk density and delta C-13. We then calculated the proportion of new and old C by using a mass balance approach. Results Total soil C stock significantly increased 19 years after tree planting (+12%). Most of this increase was detected at 0-15 cm and, on average, almost half of the soil C derived from the trees. Both SR and FD had a positive and significant effect on the proportion of C derived from the current forest vegetation. Conclusions Plantations with higher biodiversity, either in terms of SP or FD, enhance the proportion of C derived from trees.