Compositional Shifts and Co-occurrence Patterns of Topsoil Bacteria and Micro-Eukaryotes Across a Permafrost Thaw Gradient in Alpine Meadows of the Qilian Mountains, China

Abstract

Soil microorganisms are pivotal in the biogeochemical cycles of alpine meadow ecosystems affected by permafrost thaw. However, the mechanisms driving microbial community responses to environmental changes, such as variations in permafrost active layer thickness (ALT), are poorly understood. This study utilizes next-generation sequencing to explore the composition and co-occurrence patterns of bacterial and micro-eukaryotic communities in soils along a permafrost thaw gradient. Our findings revealed a decrease in alpha diversity within bacterial communities along the permafrost thaw gradient, while micro-eukaryotic community exhibited an increase. Although shifts were observed in the composition of these communities in both permafrost and seasonally frozen soils, these variations were not statistically significant. Bacterial communities differed more significantly between frozen soil types than within them, a pattern not observed in eukaryotic communities. LEfSe analysis identified more potential biomarkers in bacterial communities than in micro-eukaryotic ones. Furthermore, bacterial co-occurrence networks showed more nodes, edges, and positive linkages compared to those of micro-eukaryotes. Soil texture, ALT, and bulk density significantly influenced bacterial community structures, particularly affecting the abundance of Acidobacteria, Proteobacteria, and Actinobacteria phyla. Conversely, fungal communities (including Nucletmycea, Rhizaria, Chloroplastida, and Discosea groups) were more influenced by electrical conductivity, vegetation coverage, and ALT. This study underscores the differential responses of soil bacteria and micro-eukaryotes to permafrost thaw, highlighting implications for microbial community stability under global climate change.