Agriculture, Ecosystems & Environment ( IF 6.6 ) Pub Date : 2022-08-04 , DOI: 10.1016/j.agee.2022.108119 Qing Qu, Juan Zhang, Xuying Hai, Jianzhao Wu, Jiawei Fan, Defu Wang, Jiwei Li, Zhouping Shangguan, Lei Deng
Grassland is the significant composition of the terrestrial carbon pool. Its belowground carbon turnover process is sensitive to land use changes and has a huge impact on atmospheric CO2 contents. However, the interpretation of the vertical distribution of δ13C values of soil organic carbon (SOC-δ13C), the SOC turnover rate (β value) and their changes in the soil profile remain uncertain after fencing (grazing exclusion). Grasslands that have been fenced for 39 years and grazed (as the control) on the Loess Plateau, China were selected to evaluate the vertical distribution of SOC-δ13C and β values and their influencing factors across the 0–100 cm soil profile (0–10, 10–20, 20–40, 40–60, 60–80, 80–100 cm). The results showed that SOC gradually decreased but SOC-δ13C overall increased with soil depths. Fencing significantly decreased the SOC-δ13C in 10–80 cm depth. The SOC-δ13C had a positive correlation with δ13C values of microbial biomass carbon (MBC-δ13C), but negative correlations with root biomass. Besides, the β values of 0–60 cm depth were higher in fencing grasslands (−2.70) than that in grazing grasslands (−11.38). Overall, carbon input, microbial fractionation and soil leaching contributed to the increasing trend of SOC-δ13C with soil depths, and fencing increased the SOC content in the profile but decreased the SOC turnover rate in 0–60 cm soils. The results provide direct evidence for the change of SOC-δ13C and a more comprehensive understanding of SOC-δ13C and SOC turnover dynamics with long-term fencing across the soil profile. The information on SOC dynamics and their feedback to long-term fencing can aid in developing reasonable grassland management measures.