Objective To elucidate the characteristics of soil nutrients， microbial communities， and microbial necromass carbon， and their contributions to soil organic carbon in moss-dominated biocrusts of karst rocky desertification areas， and to identify the key environmental factors and microbial mechanisms underlying the formation of microbial necromass carbon. Methods The study was conducted in rocky desertification areas in Zhanyi District， Qujing City， Yunnan Province. Soil samples were collected from the moss-dominated biocrust layer （0-1 cm） and the sub-layer （1-5 cm） at sites representing non-degraded， lightly degraded， moderately degraded， and severely degraded conditions. Soil nutrients， microbial community structure， microbial biomass， and microbial necromass carbon were subsequently analyzed. Results The results showed that， in moss-covered soils， soil organic carbon， total nitrogen， microbial biomass carbon， and microbial biomass nitrogen generally increased with increasing rocky desertification severity， reaching their highest values at the severely degraded stage. Vertically， soil organic carbon， total nitrogen， total phosphorus， microbial biomass carbon， microbial biomass nitrogen， and microbial biomass phosphorus were 19.13%， 29.61%， 10.45%， 97.47%， 97.08%， and 36.21% higher in the biocrust layer than those in the sub-layer， respectively. Bacterial necromass carbon， fungal necromass carbon， and microbial necromass carbon increased with increasing rocky desertification severity， and were generally higher in the biocrust layer than in the sub-layer. The contribution of fungal necromass carbon to soil organic carbon was higher than that of bacterial necromass carbon， and the correlation between fungal necromass carbon and soil organic carbon was stronger than that between bacterial necromass carbon and soil organic carbon. Bacterial communities were more sensitive to soil depth， whereas fungal communities were more responsive to the severity of rocky desertification. Random forest analysis showed that the fungal Shannon index was significantly negatively correlated with fungal necromass carbon in the biocrust layer， while the bacterial Shannon index was significantly positively correlated with bacterial necromass carbon in the sub-layer. Mantel analysis showed that microbial necromass carbon in both soil layers was significantly correlated with soil nutrients and microbial biomass. Microbial necromass carbon in the biocrust layer was mainly associated with bacterial life-history strategies， whereas microbial necromass carbon in the sub-layer was mainly related to fungal life-history strategies. Conclusion Moss biocrusts can significantly enhance soil nutrient availability and microbial activities in karst rocky desertification areas， thereby promoting the accumulation of microbial necromass carbon and its contribution to soil organic carbon， with fungal necromass playing a more prominent role in enhancing the stabilization of soil organic carbon. The formation of microbial necromass carbon is jointly regulated by soil nutrients， microbial activities， community composition， and life-history strategies， and differs between the biocrust layer and the sub-layer.