Abstract
Responses of terrestrial ecosystems to decreased nitrogen (N) deposition has brought considerable attention. Soil organic carbon (SOC) turnover is an important parameter in the terrestrial ecosystem model and ecosystem management. However, how SOC turnover responds to decreased N deposition has not yet been evaluated. Here we addressed this issue by the comparison of the SOC turnover in the treatment that receiving high N addition for 4 years and then none for 6 years (48 g N·m−2·yr−1, N48-cessation) with that derived from the control treatment (0 g N·m−2·yr−1, N0) in Inner Mongolia grassland, China. In this study, 14C isotope technology was used to directly reveal SOC turnover time. Our results showed that SOC turnover time in the N48-cessation treatment had no statistical difference compared with that in the N0 treatment after 6 years of N cessation, indicating that its SOC turnover had recovered from high N enrichment. The reduction of SOC storage (274 g/m2) in N48-cessation treatment from 2010 to 2014 also proved this recovery. Moreover, we also found that the species richness and Shannon diversity index in the N48-cessation treatment were significantly lower than those in the N0 treatment. It indicated that the recovery of SOC turnover was faster than plant diversity in the grassland when high N addition was ceased. This study suggested that the grasslands experienced high N deposition should reduce grazing and mowing in order to increase soil carbon input and offset the negative effect of the rapid recovery of SOC turnover on soil C storage when N deposition was decreased.