Trait-based responses of Gram-positive and Gram-negative soil bacteria to grazing intensity in steppe ecosystems

Аннотация

Background and Aim. Steppe pastures of Central Asia are exposed to long-term grazing pressure that can modify soil properties and belowground microbial communities. Soil bacteria regulate nutrient cycling and ecosystem resilience, yet their responses to grazing intensity in steppe ecosystems remain poorly understood. This study evaluated the effects of grazing intensity on soil bacterial diversity, community composition, and functional structure,with particular emphasis on taxonomic richness and on Gram-positive and Gram-negative bacteria.

Materials and Methods. Soil samples were collected from steppe pastures subjected to light, moderate, and heavy grazing. Bacterial community composition was analyzed using high-throughput sequencing of the 16S rRNA gene. Alpha diversity indices (Chao1, observed species richness, Shannon, Simpson, Pielou’s evenness, and Faith’s phylogenetic diversity) were calculated. Beta diversity was assessed using Bray-Curtis dissimilarity, principal coordinates analysis (PCoA), and permutational multivariate analysis of variance (PERMANOVA). Homogeneity of multivariate dispersion was evaluated using the betadisper. Bacterial taxa were additionally classified into Gram-positive and Gram-negative groups to assess functional responses to grazing.

Results. Taxonomic richness indices differed significantly among grazing groups, indicating sensitivity of bacterial richness to grazing intensity. In contrast, Shannon diversity, evenness indices, and phylogenetic diversity did not differ significantly, suggesting structural stability of bacterial communities. Beta diversity analysis revealed significant compositional differences among grazing groups, while dispersion did not differ significantly, confirming that the observed differences reflect true shifts in community composition. Functional analysis demonstrated contrasting responses of Grampositive and Gram-negative bacteria along the grazing gradient.

Conclusion. Grazing intensity in steppe ecosystems primarily affects soil bacterial richness and community composition, whereas diversity evenness and phylogenetic structure remain comparatively stable. Grazing acts as an environmental filter shaping microbial functional structure without causing a pronounced loss of bacterial diversity. These findings highlight the resilience of steppe soil bacterial communities and support the use of microbial indicators in sustainable pasture management.