Key microbial phylum influencing the priming effects of variously degraded alpine meadow soils enriched with animal excrements

Abstract. Tibetan sheep (Ovis aries) and plateau pika (Ochotona curzoniae) excrements are important organic materials that influence soil carbon cycling in the Qinghai-Tibetan Plateau. However, their exact priming effects (PE) on soil and mechanisms of influence in alpine meadows are subject to their health status. To fill this knowledge gap, we carried out a 45-day incubation experiment using alpine meadow soils with differing degrees of degradation that had been enriched with these two types of excrement. Soil PE was assessed via the natural abundance method, while soil microbial communities and their compositions were examined through high-throughput sequencing. The findings indicated that severely degraded alpine meadow soils exhibit significantly stronger positive priming effects (PE) from Tibetan sheep and plateau pika excrements than non-degraded soils (P < 0.05). These excrements restructure soil microbial communities, reducing bacterial α-diversity while increasing β-diversity and microbial biomass C:N ratios. Key microbial drivers of PE include Actinobacteriota (positive correlation, r = 0.70) and Proteobacteria (negative correlation, r = −0.52), whose abundances are modulated by soil properties: the C:N ratio promotes Proteobacteria (r = 0.39), while a lower NO₃^--N:NH₄⁺-N ratio suppresses Actinobacteriota (r = −0.18). Meadow degradation thus indirectly intensifies PE by altering these microbial phylum and stoichiometric balances. These findings support Qinghai-Tibetan Plateau grassland management through: (1) restricting grazing/pika activity in degraded zones to reduce carbon loss, (2) optimizing soil C:N ratios to suppress priming effect (PE)-enhancing microbes, and (3) conserving intact meadows for carbon sequestration—collectively enabling sustainable grassland management.