Influences of litter diversity and soil moisture on soil microbial communities in decomposing mixed litter of alpine steppe species

[Display omitted] •Litter composition, rather than species richness, affects soil microbial communities.•High moisture increases Gram-negative bacteria but decreases Gram-positive and fungi.•Effects of litter composition on soil microbial communities were dependent on soil moisture conditions. Many studies have examined the effects of plant diversity and soil water availability on litter decomposition, but little is known about how these two factors interactively influence soil microbial communities, especially in alpine ecosystems. Therefore, the objective of this work was to investigate how litter diversity influences soil microbial communities under different moisture conditions in an alpine steppe ecosystem in Northern Tibet. We collected litter of four abundant plant species (Stipa purpurea, Sp; Carex moorcroftii, Cm; Leontopodium pusillum, Lp; and Artemisia nanschanica, An), and used phospholipid fatty acid (PLFA) analysis to measure soil microbial biomass and community structure. A fully factorial litter mixing experiment under different soil moisture conditions (i.e., 20%, 30% and 40% water holding capacity) was employed. The results showed that litter composition, rather than species richness, significantly affected soil microbial biomass and community composition. The presence of Sp, Cm and An exerted positive or negative effects on soil microbial communities. Litter quality (i.e., C:N ratio) could explain the effects of litter composition on soil microbial communities. High soil moisture facilitated the growth of gram-negative bacteria, while gram-positive bacteria and fungi were more abundant in lower moisture soil. We did not detect any interactive effects of litter species richness and soil moisture on the microbial communities. However, the effects of litter composition on soil microbial communities were dependent on soil moisture condition. These findings indicate that litter composition, rather than species richness, shows interactive effects with soil moisture on soil microbes, and both factors are important in regulating ecosystem functions.