Influence of grazing and arbuscular mycorrhiza fungal infections on vegetative growth and powdery mildew incidence in Elymus sibiricus grown in the eastern margin of the Tibetan Plateau in summer

We established a greenhouse experiment to study the influence of arbuscular mycorrhiza (AM) fungal infections on plant growth and powdery mildew incidence in the grass species Elymus sibiricus. Soil was collected from Gansu Maqu alpine grassland and used as follows: no treatment, sterilized to eliminate all microorganisms, sterilized and microorganisms returned except for AM fungi, sterilized and inoculated with a mix of Rhizophagus intraradices and Claroideoglomus etunicatum. E. sibiricus was grown on each of the treated soils and subjected to light grazing (LG), moderate grazing (MG), or heavy grazing (HG). Our analyses showed that growth and powdery mildew incidence in E. sibiricus was influenced by grazing and AM fungal colonization. Powdery mildew incidence varied among grazing intensities and soil treatments. Compared with the intensity in LG, in MG and HG, E. sibiricus had a lower powdery mildew incidence and higher total dry weight, total P content, and photosynthetic rate. The rate of powdery mildew was the highest (59.83%) in plants on soil without any treatment and the lowest (44.73%) in plants on sterilized soil. The rate of E. sibiricus powdery mildew disease decreased 13.15% and total plant dry weight increased by 56.46% after inoculation with AM fungi compared with no treatment. Grazing intensities and soil treatments had interaction effects on total P content, chlorophyll content, and PPO activity.