| With global temperatures rising,the frequency and intensity of extreme drought events will gradually increase.Extreme drought can inhibit plant growth and affect plant fungal disease infection.While insect herbivore is a key component of the grassland food web which can change the community structure,biodiversity,and plant above-and below-ground interactions.However,there are few studies on the effects of extreme drought and aboveground insects on foliar fungal disease severity,plant performance,and their relationships.In this study,we select eight common plant species on the grassland of Qinghai-Tibet Plateau as target species to construct artificial plant communities.We carried out two common garden experiments at the two elevations(Hezuo a.s.l.2960 m and Maqu a.s.l.3600m)of Gansu Gannan Grassland Ecosystem National Observation and Research Station at the same time.In the early growing season,we measured plant height and flowering numbers of each plant.Then,we conducted experimental(extreme drought and aboveground insect exclusion(insecticide))treatments during the growing season(July).Within,we measured plant height,flowering numbers,aboveground biomass and foliar fungal disease severity.After 30 days treatments,we rewetted mesocosms,and recorded plant survival rates and measured aboveground biomass of each surviving plant after 30 days of rewetting.We found that:(1)Extreme drought increased plant total foliar fungal disease severity to 1.5times than control and the change varied among different elevations and species.At low elevation,total foliar fungal diseases were more serious.Total foliar fungal diseases of three kinds of grasses(Elymus nutans,Deschampsia cespitosa,Koeleria litvinowii)were the most serious,followed by Rumex acetosa,and other species were less.Insecticide treatment had no significant effect on total foliar fungal disease severity.The variation trend of leaf blight disease was almost the same as total foliar fungal disease,but the trend of leaf spot disease was different from them.Extreme drought reduced leaf spot severity,while insecticide treatment increased leaf spot severity of R.acetosa.At high elevation,leaf spot disease severity was higher.Among different species,leaf spot disease of R.acetosa was the highest.(2)Extreme drought can reduce plant height by approximately 3.9cm and growth rate by 45%,and differences exist between elevations and species.Insect exclusion had no significant effect on plant height,but increased plant growth rate.Plant height and growth rate were higher at low elevation and the two indexes of the three kinds of grasses(E.nutans,D.cespitosa,K.litvinowii)were higher than those of forbs.Extreme drought and insect exclusion had no significant effect on aboveground biomass at both species and community levels.Aboveground biomass was higher at low elevation and varied among species.(3)Extreme drought significantly increased the survival rate of Polygonum viviparum to 1.5 times than control.At low elevation,extreme drought and insecticide treatment had interactions on plant survival rate.Among different species,the survival rate of Veronica eriogyne and P.viviparum were significantly lower than that of other species.At low elevation,the plant survival rate and aboveground biomass after rewetting were significantly higher at species and community levels.(4)With the increasing of plant aboveground biomass,total foliar fungal disease severity and leaf blight severity tends to increase on different treatments,elevations and two plant species.While leaf spot disease severity has no relationship with plant aboveground biomass.These results indicate that extreme drought increase total foliar fungal disease severity,among which leaf blight severity increased while leaf spot severity decreased.Aboveground insect decreases leaf spot severity of R.acetosa.Both of extreme drought and aboveground insect can inhibit plant performance.Extreme drought decreased plant height and plant growth rate,while aboveground insect only decreased plant growth rate.Both of extreme drought and aboveground insect had no significant effects on plant aboveground biomass.At low elevation,plants grow better and are infected by more foliar fungal diseases.Moreover,With the increasing of plant aboveground biomass,total foliar fungal disease severity and leaf blight severity tends to increase,while leaf spot disease severity has no relationship with plant aboveground biomass.This study explored the effects of extreme drought and aboveground insect on foliar fungal disease and plant performance,as well as their relationships,and compared their differences at two elevations.Our results are helpful better understanding the effects of extreme drought on plant performance and fungal disease,and the role of aboveground insect in the process and provides theoretical basis for predicting ecological responses under climate change. |
