摘 要(英文)：Aims：The aim of this study was to investigate the effects of elevated CO2 concentration and nitrogen addition on soil organic carbon fractions in subtropical forests where the ambient N deposition was high.
Methods：Seedlings of typical subtropical forest ecosystems were transplanted in ten open-top chambers and grown under CO2 and nitrogen treatments. The treatments included: 1) elevated CO2 (700μmol mol-1); 2) N addition of 100 kg NH4NO3 ha-1 yr-1; 3) combined
elevated CO2 and N addition; and 4) control. We measured soil total organic carbon (TOC), particulate organic carbon (POC), readily oxidizable organic carbon(ROC), and microbial biomass carbon (MBC).
Results：Results showed that elevated CO2 alone did not significantly affect soil TOC, POC and ROC after 4 years of treatment, but increased soil MBC and soil respiration compared to the control. N addition alone had no significant effect neither on soil TOC, POC and ROC, but decreased MBC and soil respiration over
time. However, the elevated CO2 and N addition together significantly increased soil POC and ROC,and had no significant effect on soil MBC.
Conclusions：This study indicated that even in N-rich subtropical forest ecosystems, inputs of N are still needed in order to sustain soil C accumulation under elevated CO2.
Effects of elevated CO2 and nitrogen addition on soil organic carbon fractions in a subtropical forest