Abstract: Microbial necromass plays an important role in the formation of soil organic carbon (SOC). However, the change of microbial necromass along altitudinal gradient remains unclear. In this study, we analyzed the differences of soil physicochemical properties, microbial necromass (topsoil 0-20 cm), and stand characteristics along an altitudinal gradient (1200, 1700, and 2200 m) in a broad-leaved evergreen forest in Yongde Snow Mountain, Yunnan Province, aiming to reveal the regulatory mechanism of microbial necromass accumulation along the altitudinal gradient. The results showed that microbial necromass was 15.36 g·kg^-1 in the broad-leaved evergreen forest and that its contribution to SOC was 24.09%. The contribution of fungal necromass to SOC (20.36%) was higher than that of bacterial necromass (3.73%). Fungal, bacterial, and microbial necromass increased significantly with increasing altitude. There was no significant difference in the contribution of fungal and microbial necromass to SOC along the altitudinal gradient. In addition, woody species composition showed significant effects on fungal and microbial necromass. Microbial necromass increased with increasing soil nutrients, but increased significantly with decreasing woody species richness. Furthermore, higher SOC, soil total nitrogen, soil available nitrogen, and soil water content, and lower soil pH could promote the accumulation of microbial necromass. Soil nutrient, altitude, and woody species diversity were the important factors affecting microbial necromass. Therefore, altitude promoted the accumulation of microbial necromass but did not increase its contribution to SOC.

Key words: amino sugar, fungal necromass, bacterial necromass, soil organic carbon, woody species diversity, altitude