Moss-dominated biological soil crusts improve stability of soil organic carbon on the Loess Plateau, China

The succession of biological soil crust (biocrust) may alter soil organic carbon (SOC) stability by affecting SOC fractions in arid and semi-arid regions. In the study, the SOC fractions were measured including soil easily oxidizable carbon (SEOC), soil microbial biomass carbon (SMBC), soil water soluble carbon (SWSC), and soil mineralizable carbon (SMC) at the Loess Plateau of China by using four biocrusts. The results show that SOC fractions in the biocrust layer were consistently higher than that in the subsoil layers. The average SOC content of moss crust was approximately 1.3–2.0 fold that of three other biocrusts. Moss crusts contain the lowest ratio of SEOC to SOC compared with other biocrusts. The ratio of SMC to SOC was the highest in light cyanobacteria biocrust and the lowest in moss crust, but no difference was observed in SMBC to SOC and SWSC to SOC in biocrust layers among four studied biocrusts. The results show that the moss crusts increase the accumulation of organic carbon into soil and reduce the ratio of SEOC to SOC and SMC to SOC. Together, these findings indicate that moss crusts increase the SOC stability and have important implications that SOC fractions and mineralization amount are good indicators for assessing the SOC stability.