Different grazers and grazing practices alter the growth, soil properties, and rhizosphere soil bacterial communities of Medicago ruthenica in the Qinghai-Tibetan Plateau grassland

Livestock grazing is a popular land-use activity for grasslands. Over grazing and trampling of livestock impairs ecosystem function by changing vegetation growth, soil nutrients, and soil bacterial communities. However, information regarding the characteristics of those allied with above- and belowground of grazing-resistant host plant species under different grazers and grazing practices in grassland ecosystems is limited. We examined the impact of single-species grazing of yak only (YG), sheep only (SG), and mixed grazing in the ratio of yak to sheep of 1:2 (MG (1:2)), 1:4 (MG (1:4)), and 1:6 (MG (1:6)) on plant growth, soil properties, and soil microbial communities. Plant biomass and soil properties were measured in each treatment, and soil microbial communities in the rhizosphere soil of Medicago ruthenica were analyzed by high-throughput sequencing of the 16 S rRNA gene. The results showed that shoot height, root length, and plant FW (fresh weight) and DW (dry weight) of M. ruthenica under single-species grazing decreased by 5.60 %, 3.30 %, 11.34 % and 9.82 %, respectively; under mixed-species grazing decreased by 35.65 %, 29.68 %, 52.35 % and 55.60 %, respectively, compared to CK (no grazing). Mixed-species grazing decreased soil UR (urease), SC (sucrase), and ACP (acid phosphatase) activities by decreasing soil NH4+-N, increasing soil NO3−-N and soil SOC (soil organic carbon), compared to CK. Grazing further affected core phyla and genera of rhizosphere bacterial communities, such as Bacteroidota, Rubrobacter, and Gaiella under different grazers and grazing practices by altering soil properties. The interaction of soil bacteria under YG was more sensitive than that under SG, and the interaction of soil bacteria under mixed-species grazing was more sensitive than that under single-species grazing. According to Functional Annotation of Prokaryotic Taxa (FAPROTAX) analysis associated with N cycling, and the relative abundance of the rhizosphere bacteria with the functions of nitrogen respiration and nitrite denitrification under MG (1:2), MG (1:4), and MG (1:6) were increased by 40.75 %, 34.74 %, 32.31 %, 40.86 %, 36.17 %, and 48.11 %, respectively, compared to CK. This study demonstrates that the mechanism by which different grazers and grazing practices affect soil bacterial communities and associated soil properties in the rhizosphere soil of the legume forage species M. ruthenica will contribute to the understanding how beneficial microbes interact efficiently with grazing-tolerant plant species under different grazing practices.