Microbial communities play an important regulatory 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. We combined a number of complementary techniques to investigate the microbial biomass, community composition and diversity, and potential functioning along soil profile (0–70 cm) in two alpine ecosystems (meadow and shrubland) on the Tibetan Plateau. The microbial biomass and fungi:bacteria ratio declined significantly with depth, while the ratio of Gram-positive to Gram-negative bacteria increased with depth in both ecosystems. Microbial community composition showed significant differences among soil depths and between ecosystems. The relative abundance of some phylum of archaea, bacteria or fungi (e.g. Basidiomycota, Bacteroidetes) changed significantly with soil depth and ecosystem type. Bacteria diversity declined with depth, while archaea richness (OTU number) increased with depth and fungi diversity and richness did not show clear trend with depth. 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 enzymatic activities and soil C mineralization rate declined with depth in both ecosystems. We also detected shifts with depth in some functional guilds of bacteria (based on faprotax database) in both ecosystems and fungi (based on FUNGuild database) only in shrubland. The biomass, community composition and diversity, and potential functioning of microbial communities all shifted significantly along soil profile in both ecosystems, and the vertical patterns of diversity varied among different microbial groups. This may have important implications for carbon and nutrient cycling along the soil profile in alpine ecosystems.

中文翻译：

---

青藏高原两个高寒生态系统微生物生物量、群落组成和多样性的变化及其与土壤深度的关系

微生物群落在陆地生态系统的土壤碳和养分循环中起着重要的调节作用。大多数关于微生物群落和生物地球化学循环的研究都集中在表层土壤（0-20 厘米）上。然而，关于微生物群落的结构和功能如何随土壤剖面深度变化的知识相对较少，这对于理解深层土壤中的生物地球化学循环至关重要。我们结合了许多互补技术来研究青藏高原两个高山生态系统（草甸和灌木丛）中微生物生物量、群落组成和多样性以及沿土壤剖面（0-70 厘米）的潜在功能。微生物生物量和真菌：细菌比例随深度显着下降，而革兰氏阳性菌与革兰氏阴性菌的比例随深度增加而增加。微生物群落组成在土壤深度和生态系统之间表现出显着差异。一些古细菌、细菌或真菌门（例如担子菌门、拟杆菌门）的相对丰度随土壤深度和生态系统类型而显着变化。细菌多样性随深度下降，古菌丰富度（OTU数）随深度增加而增加，真菌多样性和丰富度随深度没有明显变化。共生网络分析进一步表明，与深层土壤微生物相比，表层土壤微生物之间的联系和相互作用更多。此外，两个生态系统的总酶活性和土壤碳矿化率都随着深度的增加而下降。我们还仅在灌木丛中检测到生态系统和真菌（基于 FUNGuild 数据库）中的一些细菌功能群（基于 faprotax 数据库）随深度的变化。生物量、群落组成和多样性以及微生物群落的潜在功能在两个生态系统中都沿着土壤剖面发生了显着变化，不同微生物群之间的垂直多样性模式也不同。这可能对高山生态系统中沿土壤剖面的碳和养分循环具有重要意义。