Effects Of Grazing Intensity And Different Livestock Assemblages On Plant Fungal Diseases In Alpine Grasslands On The Qinghai-Tibetan Plateau

Soil pathogens are an important component of ecosystem,playing an important role in the maintenance of plant diversity and grassland productivity.However,they can affect grassland health and threaten ecosystem security when infecting plants and causing serious diseases.The Qinghai-Tibet Plateau is one of the important natural pastures in China.Due to the increase in human activities,grazing has recently become the most intensive land use pattern in grasslands.Although several studies have reported grazing effects on plant fungal diseases,the causal relationship between livestock grazing and plant fungal diseases remains largely unexplored.In this study,by relying on two grazing experimental platforms established in the Menyuan and Haiyan,we investigated how foliar fungal diseases and soil pathogenic fungi in alpine grassland responded to different grazing intensities(control,light,moderate,heavy;Menyuan and Haiyan)and livestock assemblages(yak alone,Tibetan sheep alone,mixed grazing by yak and Tibetan sheep with different ratios;Haiyan).We also explored the relationships between fungal diseases and environmental factors.We obtained the following results:(1)The effects of grazing intensity on foliar fungal diseases were similar in Menyuan and Haiyan.At the plant community level,light grazing increased disease severity and heavy grazing decreased.With regard to different plant functional groups,heavy grazing decreased the disease severity of grass and sedge.Regarding to different disease types,the disease severity of biotrophs(rusts and powdery mildews)decreased significantly as the grazing intensity increased,while the disease severity of necrotrophs(leaf spots)showed no significant relationships with grazing intensity.(2)Different ratios of livestock assemblages had different effects on foliar fungal disease.At the plant community level,Tibetan sheep grazing alone,yak grazing alone and yak-Tibetan sheep ratio of 1:2 significantly decreased the disease severity.With regard to different plant functional groups,yak-Tibetan sheep ratio of 1:2 significantly decreased the disease severity of sedge,grass and forb,but had no significant effect on disease severity of legume.At the plant species level,the disease severity of dominant Kobresia humilis and Carex aridula were decreased by all livestock assemblages.(3)Grazing intensity had no significant effects on the relative abundance of total soil pathogenic fungi,but significantly influenced the relative abundance of specific pathogenic fungi.Light grazing significantly increased the relative abundance of Alternaria and moderate grazing increased the relative abundance of Fusarium.Moderate and heavy grazing significantly increased the relative abundance of Coniochaeta.Different livestock assemblages had no significant effects on the relative abundance of total soil pathogenic fungi,but Tibetan sheep grazing alone significantly increased the relative abundance of Coniochaeta.(4)The disease severity of plant community is jointly driven by plant community characteristics and soil nutrients.The community pathogen load was positively related to vegetation coverage and soil total nitrogen content,while it was negatively related to species richness and plant biomass.The relative abundance of soil pathogenic fungus Alternaria was positively related to species richness,whereas the relative abundance of Coniochaeta was negatively related to soil total nitrogen and available phosphorus.This study investigated the effects of grazing intensity and different livestock assemblages on plant foliar fungal diseases and soil pathogenic fungi in alpine grassland on the Qinghai-Tibet Plateau,and explored the relationships between the occurrence of plant fungal diseases and plant community characteristics and soil nutrients.The findings provided important theoretical support for the management and sustainable development of the alpine grassland of the Qinghai-Tibet Plateau in the context of human activities.