Which is more important in stabilizing soil organic carbon in mountain ecosystems: molecular features, mineral protection, soil nutrients, or elevation?

Abstract

The mechanisms that maintain soil organic carbon (SOC) stability along the elevation gradient has not been adequately explored in mountain ecosystems, though numerous work has been performed to reveal potential impacts of multiple environmental factors on SOC stability. The objective of this study was to decipher the predominant factor and effects that affected SOC stability by linking elevation, soil nutrients, minerals, and chemical molecular composition with SOC thermal stability in Changbai Mountain (CBM), Northeast China. Results indicated that SOC ranged from 2.12% to 17.75% without obvious elevation dependency. SOC stability was evaluated using the temperature at which haft of the exothermic mass loss (TG50). The TG50 decreased with elevation at p < 0.05 level. SOC did not vary significantly across soils from predominant plant communities, which were the mixed coniferous and broad-leaved forests (HJL), mixed coniferous forests (ZYL), birch forests (YHL), and tundra vegetation zones (TYD). Total phosphorus (P) and manganese (Mn) differed significantly among these four zones. Aliphatic, alkanes, alkenes, and aromatics were predominant moieties of pyrolytic products of SOC in all zones. TP, alkanes, Mn, Th, aliphatic, Lg, and Ph were the main drivers controlling SOC in contents and stabilities. Mineral protection in conjunction with soil nutrients could explain 73% of the total variance in SOC stability, while Mn had more importance than Fe in stabilizing organic carbon in CBM. The structural equation model revealed positive effects of both mineral protection and molecular feature on SOC pool and stability.