Context dependent effects of two rotational grazing managements on microbial communities in Southern Oklahoma

This study examined the effects of two rotational grazing strategies, adaptive grazing (AD; higher stocking density with variable recovery periods) and prescriptive grazing (PR; lower stocking density with fixed recovery periods), on soil bacterial and fungal communities in two ecologically distinct Southern Great Plains ranch systems: Native Rangeland and Introduced Pasture. Because the two systems differed in vegetation, soils, and management history, grazing responses were evaluated independently for each system. Soil samples (0–15 cm) were collected across 11 sampling events over four years, including three baseline sampling events under similar management (PRE) and eight events after implementation of the differentiated grazing strategies (POST). The POST period coincided with a prolonged drought (Summer 2022 – Summer 2024). In Native Rangeland, POST bacterial alpha diversity showed significantly different temporal trajectories between grazing treatments, whereas fungal alpha diversity showed little evidence of grazing-associated differences. Glomeromycota showed evidence of greater relative abundance under AD during POST under a relaxed false-discovery threshold. In Introduced Pasture, POST bacterial alpha diversity was lower under AD than PR, whereas evidence for different temporal trajectories between grazing treatments was inconclusive. Fungal diversity, fungal community composition, and dominant fungal phyla showed little evidence of AD–PR differences. Actinomycetota showed greater relative abundance under AD than PR under a relaxed false-discovery threshold. Associations between gravimetric water content, microbial diversity, and phylum-level relative abundance provided a possible explanation for how grazing strategy influenced microbial diversity and phylum composition under concurrent grazing and drought. These findings emphasize context-dependent microbial responses to rotational grazing.