Dynamics of soil carbon and nitrogen stocks following afforestation in gully region of Loess Plateau, China

Abstract: The effect of vegetation restoration on soil carbon (C) and nitrogen (N) stocks is an important consideration during the remediation of degraded soil. The temporal variation and distribution of C and N stocks in the soil profile were studied in areas with different types of vegetation restoration in the Zhifanggou catchment of China's Loess Plateau. In this area, the "Grain-for-Green" project (GFGP) encouraged landscape scale habitat restoration during the last decade. Results showed that afforestation of degraded cropland significantly promoted CO2 sequestration and restored soil N availability, which consequently reduced N limitation and sustained C sequestration. Above a vegetation age threshold, i.e. 26 years, afforestation significantly improved the linear correlation relationship between soil organic C (SOC) and total N (TN) stocks in the 0~60 cm soil profile. This linear SOC-TN stock nexus decreased with increasing soil depth, and the potential of having improved SOC stock, TN stock and the ratio between them in deeper soil layers increased with increasing time after afforestation. Managed plantations provide superior CO2 sequestration and improvement in the SOC-TN correlation at a relatively short period after afforestation when compared to natural restoration where vegetation is established by natural colonization. So these results indicate that the C sequestration sustainability of afforestation should be assessed at a long-term scale, and a relative great attention should be focused on deeper soil.