Planted forest ecosystem is becoming a key component of the China’s forest resources and timber storage and plays a key role in the context of potential carbon (C) sequestration and sustainable forest management. Information on the effects of tree species composition and diversity on soil nitrogen (N) availability and organic carbon (C) sequestration remains limited. The investigation and long-term manipulation experiment were carried out in typical subtropical planted forests. Soil under Eucalyptus mixed with N2-fixer accumulated more soil organic C and N, and had lower CO2 emission than in pure stands by increasing total organic C and microbial biomass C, as well as through increased soil microbial community diversity and abundance. SOC and N stocks in the Pinus massoniana and Castanopsis hystrix mixed plantation were higher than in P. massoniana monospecific plantation. The admixing with the higher-quality C. hystrix litter hastened mass loss for recalcitrant C chemical compositions and nutrient return of conifer litter. Our results also showed that tree species mixture significantly altered the soil bacterial community composition and structure, compared with single-species plantations. The C/N ratios of soil and litterfall, TOC, NH4-N, litterfall mass and NO3-N were key factors affecting the soil microbial community. There was a negative relationship between SOC mineralization rates and the abundance of K strategists and a positive relationship for r-strategists. These results indicated that N availability plays an important role on enhancing SOC sequestration through changing soil microbial community composition in subtropical plantations.

07 - Role of nitrogen availability on enhancing soil carbon sequestration in typical subtropical planted forests in southern China