Cell-size-dependent responses of bacterial communities to warming in the alpine grasslands of the Qinghai-Tibet Plateau

Cell size is a fundamental determinant of bacterial ecology, influencing
community dynamics, physiological processes, and ecological interactions.
However, the impacts of climate change—especially warming—on bacteria of
varying cell sizes remain poorly understood, particularly in sensitive
ecosystems such as alpine grasslands. In this study, we conducted an
open-top chamber warming experiment (+1.3 °C) to investigate how warming
affects bacterial communities across four distinct cell size categories
(<0.4 μm, 0.4–3.0 μm, 3.0–5.0 μm, and >5.0 μm) in the alpine
grasslands of the Qinghai-Tibet Plateau. Our results show that warming
differentially impacts bacterial communities depending on cell size. Small
bacteria (<0.4 μm) were more sensitive to warming, with increased
richness and diversity, while larger bacteria (3.0–5.0 μm) experienced a
decline in both diversity and richness. These shifts were accompanied by
compositional changes, particularly within the <0.4 μm fraction,
where phyla such as β-Proteobacteria, δ-Proteobacteria, Bacteroidetes, and
Thermotogae decreased, while Actinobacteria increased. Additionally,
warming decoupled the interactions between large bacteria and soil or
plant components, while enhancing plant-bacterial coupling for small
bacteria. Co-occurrence network analysis revealed that warming reduced the
complexity and connectivity of small bacterial communities, making them
less stable and more influenced by deterministic processes. In contrast,
warming promoted drift and heterogeneous selection in large bacterial
communities, highlighting divergent ecological responses based on cell
size. These findings underscore the critical role of cell size in
determining bacterial vulnerability to climate change, offering new
insights into microbial community dynamics in response to global warming.