Effects of forest grazing on soil properties and microbial community in the Northeast China Tiger and Leopard National Park

Long-term forest grazing is a major anthropogenic disturbance in Northeast China Tiger and Leopard National Park, posing great threat to forest ecosystems due to heterogeneous and unpredictable changes in forest structure, function, and biodiversity． Understanding the responses of soil properties and microbial to grazing is useful for forest management and biodiversity conservation． The effects of long-term forest grazing on soil physicochemical properties and soil microbial community composition in the Northeast China Tiger and Leopard National Park were assessed in this study． Soil samples were collected in the summer in 2021, from 47 cattle-grazed forest plots and 53 un-grazed forest plots． High-throughput sequencing technique was used to analyze soil bacterial and fungal communities in two forest areas． Generalized linear mixed model and non-metric multidimensional scaling were used to assess effects of forest grazing on soil properties and microbiome． Continuous forest grazing was found to significantly increase soil bulk density (P = 0.005), soil conductivity (P = 0.045), but decrease soil water content (P = 0.022); livestock grazing may therefore damage soil structure and reduce soil water retention capacity． Soil exchangeable K⁺ (P = 0.015) and Ca²⁺ (P = 0.006), soil total calcium (P = 0.004) were significantly higher in grazed forests than un-grazed forests, grazing disturbance therefore accelerated soil nutrient accumulation in the National Park． A total of 9488 bacterial operational taxonomic units (OTUs) and 5676 fungal OTUs were obtained according to a 97% sequence similarity level． Non-metric multidimensional scaling revealed that composition of soil bacterial and fungal community differed significantly between grazed and un-grazed forests． Soil bacterial community composition was primarily influenced by slope, electrical conductivity, plant richness, whereas fungal community composition was significantly influenced by grazing intensity, elevation, slope, plant richness, electrical conductivity, total nitrogen and available phosphorus． The relative abundance of Proteobacteria was found significantly positively correlated with grazing intensity, elevation and electrical conductivity, but negatively correlated with plant richness． Relative abundance of Actinobacteriota was positively correlated with the electrical conductivity． Relative abundance of Chloroflexi was significantly correlated with electrical conductivity and plant richness． Relative abundance of Basidiomycota was significantly positively correlated with elevation and slope, but negatively correlated with electrical conductivity, available phosphorus and plant richness． Relative abundance of Ascomycota and Mortierellomycota were found significantly positively correlated with electrical conductivity, available phosphorus and plant richness, but negatively correlated with elevation and slope． Relative abundance of Rozellomycota was significantly positively correlated with total nitrogen, available phosphorus and plant richness, but negatively correlated with elevation and slope． These data suggest that forest grazing practices affect soil properties and microbes differently． Given the strong interaction between soil and microbiome, changes in soil microbial community structure can be expected to substantially alter soil function． This will have important ecological service implications, particularly for wildlife habitat and carbon storage in key regional priorities for biodiversity．