Distinct patterns of soil bacterial and fungal communities in the treeline ecotone

Abstract

The upward shift of the alpine treeline driven by global climate change has been extensively observed across many mountain ecosystems worldwide. However, variations in belowground microbial communities in the treeline ecotone, as well as the influence of microtopographic factors (e.g., slope aspect) on these changes, remain unclear. Here, we collected soil samples from different aspects above or below the treeline and analyzed the microbial communities using high-throughput sequencing. Our study revealed distinct community characteristics, co-occurrence patterns, and assembly processes between bacterial and fungal communities. Especially, homogeneous selection and dispersal limitation played dominant roles in shaping bacterial and fungal communities, respectively. Keystone bacteria were more critical for maintaining network stability above the treeline, while fungi were the keystone taxa for network stability below the treeline. We also found that oligotrophic species such as Acidobacteriota, Chloroflexi, Verrucomicrobiota, and Ascomycota were predominantly enriched above the treeline, whereas copiotrophic species like Proteobacteria, Gemmatimonadota, Actinobacteriota, and Firmicutes were more abundant below the treeline. Our results uncovered that microbial communities responded greatly to treeline shift than slope aspect, and also imply that the upward shift of the alpine treeline may increase the stochasticity of microbial communities. These findings facilitate our understanding of how microbial communities in the treeline transition zones of alpine ecosystems respond to global warming and their potential effects on soil carbon dynamics.

Graphical abstract

Keywords

alpine treeline / slope aspect / r/K strategy / keystone species / community assembly / Qinghai-Tibet Plateau

Highlight

	● Homogeneous selection and dispersal limitation played dominant roles in shaping bacterial and fungal communities, respectively.
	● Keystone bacteria were more critical for maintaining network stability above the treeline, while fungi were the keystone taxa for network stability below the treeline.
	● Oligotrophic species were predominantly enriched above the treeline, whereas copiotrophic species were more abundant below the treeline.
	● Microbial communities responded greatly to treeline shift than slope aspect.

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