Changes in microbial biomass, community composition and diversity, and functioning with soil depth in two alpine ecosystems on the Tibetan Plateau

Tianle Xu1, Xiao Chen1, Yanhui Hou1, Ying Chen1, Biao Zhu1

1Peking University, , China

Microbial communities play an important regulating role in soil carbon and nutrient cycling in terrestrial ecosystems. Most studies on microbial communities and biogeochemical cycling focus on surface soils (0-20 cm). However, relatively little is known about how structure and functioning of microbial communities shift with depth in a soil profile, which is crucial to understand biogeochemical cycling in deep soils. Here, we combined a number of complimentary techniques to investigate the microbial biomass, community composition and diversity, and potential functioning along soil profile (0-70 cm) in two contrasting alpine ecosystems (meadow and shrubland) on the Tibetan Plateau. Results showed that microbial biomass (MBC, MBN or PLFA) and fungi:bacteria ratio all declined greatly with depth, while the ratio of Gram-positive to Gram-negative bacteria increased with depth. Microbial community composition, by PLFA or DNA sequencing (archaea, bacteria or fungi), showed remarkable differences among different soil layers. Microbial community diversity (OTU number) also changed with depth – both bacteria and fungi richness declined with depth, while archaea richness showed the opposite trend. The co-occurrence network analysis further showed that surface soil microbes were more connected and interacted among each other compared to deep soil microbes. Moreover, total enzyme activities (per gram soil) declined with depth, while specific enzyme activities (per gram MBC) did not change with depth. Potential C mineralization rate decreased with depth, while net N mineralization rate was higher at deep soils than at surface soils. We also detected shifts in some functional guilds of bacteria (based on faprotax database) and fungi (based on FUNGuild database) with depth in both ecosystems. Taken together, we detected dramatic shifts in biomass, community composition and diversity, and potential functioning of microbial communities with soil depth, which may have important implications for driving soil organic matter dynamics along soil profile in alpine ecosystems.


Tianle is a postdoctor in Peking University. His work focuses on soil microbial community structure and function, especially the influence of soil microbes on soil organic carbon dynamics in grassland ecosystem. He also works on microbiogeography, and explored the key predictors of fungi and arbuscular mycorrhizal fungi communities across a 5000-km transect in northern China. Tianle have published 10 papers as first author or co-author.

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