Changes of soil carbon in five land use stages following 10 years of vegetation succession on the Loess Plateau, China

Changes in land use caused by natural vegetation succession can enhance the soil organic carbon (SOC) and carbon (C) stock of terrestrial ecosystems, as reported in many studies throughout the world. However, the dynamics of SOC and soil C stocks and their changes in each succession stage are not clearly following restoration age. Additionally, whether litter and fine roots have positive effects on SOC and soil C sequestration is unclear. We simultaneously studied litter and fine root production and SOC and C stocks along a natural vegetation succession - abandoned farmland, grassland, shrubland, pioneer woodland to natural climax forest - in 2005 and 2015 on the Loess Plateau of China. This allowed a better understanding of the variations of SOC and soil C stock in different land use stages in relation to soil layers and effects of litter and fine roots following vegetation restoration. The land use stages and soil layers significantly affected the rates of SOC and soil C sequestration change. The SOC and soil C stocks in the 0-60 cm soil profile rapidly increased over the course of the long-term natural vegetation succession. During 2005 to 2015, the topsoils (0-20 and 20-40 cm) had higher rates of SOC change (from 0.06 to 0.55 and from 0.23 to 0.51 g kg−1 yr−1, respectively) and soil C sequestration rates (from 0.37 to 1.09 and from 0.40 to 1.16 Mg ha−1 yr−1, respectively) than subsoils (40-60 cm, from 0.04 to 0.36 and from 0.05 to 1.16 Mg ha−1 yr−1). The litter and fine root production increased with age of the natural vegetation succession, and had significant positive effects on changes in SOC and soil C sequestration. Therefore, long-term natural vegetation restoration improved the SOC accumulation, and increased litter and fine root inputs were probably the main factors contributing to soil C sequestration.