The difference in soil organic carbon distribution between natural and planted forests: A case study on stony soils mountainous area in the Upper Min River Arid Valley, China

Few studies have been conducted on the factors and distribution of soil organic carbon (SOC) in plantation forests in arid mountainous regions, especially in orchards. We aimed to unravel the SOC distribution among land-use types and the effects of altitude gradients and rock fragment content (RFC) on SOC accumulation and sequestration in the Upper Min River Arid Valley, China. The differences in SOC distribution among land-use types were quantified. The correlation analysis of SOC with various factors, such as altitude and RFC, was conducted. The variation percentage in SOC content and stocks was explained by the factors' contribution using mixed-effects models. SOC distribution was characterized by high content and low stocks in native forests and shrubs, high content and high stocks in eco-forest, and low content and high stocks in orchards. At the surface (0-30 cm), SOC content and stocks in orchards (cherry, plum, and apple) were significantly lower than those in eco-forests. There was a significant positive correlation between altitude and SOC content at the surface but not at the subsoil (30-60 cm). With RFC increased, the surface SOC content decreased in native forests, shrubs, and eco-forests, while it increased in orchards. Our results suggest that land management is the main factor controlling the variation in SOC distribution. Enhancing the surface SOC stability in orchards by land management is a priority for soil carbon pool management in the Arid Valleys.