Table 1_Structures and determinants of soil microbiomes along a steep elevation gradient in Southwest China.xlsx

Soil microbial communities play a vital role in accelerating nutrient cycling and stabilizing ecosystem functions in forests. However, the diversity of soil microbiome and the mechanisms driving their distribution patterns along elevational gradients in montane areas remain largely unknown. In this study, we investigated the soil microbial diversity along an elevational gradient from 650 m to 3,800 m above sea level in southeast Tibet, China, through DNA metabarcode sequencing of both the bacterial and fungal communities. Our results showed that the dominant bacterial phyla across elevations were Proteobacteria, Acidobacteriota and Actinobacteriota, and the dominant fungal phyla were Ascomycota and Basidiomycota. The Simpson indices of both soil bacteria and fungi demonstrated a hollow trend along the elevational gradient, with an abrupt decrease in bacterial and fungal diversity at 2,600 m a.s.l. in coniferous and broad-leaved mixed forests (CBM). Soil bacterial chemoheterotrophy was the dominant lifestyle and was predicted to decrease with increasing elevation. In terms of fungal lifestyles, saprophytic and symbiotic fungi were the dominant functional communities but their relative abundance was negatively correlated with increasing elevation. Environmental factors including vegetation type (VEG), altitude (ALT), soil pH, total phosphorus (TP), nitrate nitrogen (NO3−-N), and polyphenol oxidase (ppo) all exhibited significant influence on the bacterial community structure, whereas VEG, ALT, and the carbon to nitrogen ratio (C/N) were significantly associated with the fungal community structure. The VPA results indicated that edaphic factors explained 37% of the bacterial community variations, while C/N, ALT, and VEG explained 49% of the total fungal community variations. Our study contributes significantly to our understanding of forest ecosystems in mountainous regions with large elevation changes, highlighting the crucial role of soil environmental factors in shaping soil microbial communities and their variations in specific forest ecosystems.

土壤微生物群落在森林生态系统的养分循环加速与功能稳定中发挥着至关重要的作用。然而，山地生境中土壤微生物组（soil microbiome）的多样性及其沿海拔梯度分布格局的驱动机制，目前仍未得到充分解析。本研究通过对中国西藏东南部海拔650米至3800米梯度下的细菌与真菌群落开展DNA宏条形码测序（DNA metabarcode sequencing），探究了沿线的土壤微生物多样性。研究结果显示，各海拔梯度下的优势细菌门类为变形菌门（Proteobacteria）、酸杆菌门（Acidobacteriota）与放线菌门（Actinobacteriota），优势真菌门类则为子囊菌门（Ascomycota）与担子菌门（Basidiomycota）。土壤细菌与真菌的辛普森指数沿海拔梯度均呈现中空型趋势，在海拔2600米的针阔混交林（CBM）中，细菌与真菌多样性出现骤降。土壤细菌的主导生活型为化能异养型，且其丰度随海拔升高呈降低趋势。就真菌生活型而言，腐生真菌与共生真菌为优势功能类群，但其相对丰度随海拔升高呈负相关关系。包括植被类型（VEG）、海拔（ALT）、土壤pH、总磷（TP）、硝态氮（NO3−-N）以及多酚氧化酶（ppo）在内的环境因子，均对细菌群落结构具有显著影响；而植被类型（VEG）、海拔（ALT）与碳氮比（C/N）则与真菌群落结构显著相关。变异分解分析（VPA）结果显示，土壤因子解释了37%的细菌群落变异，而碳氮比（C/N）、海拔（ALT）与植被类型（VEG）则解释了49%的真菌群落总变异。本研究显著增进了学界对海拔跨度较大的山地森林生态系统的认知，凸显了土壤环境因子在塑造特定森林生态系统中土壤微生物群落及其变异的关键作用。