Effects Of Simulated Climate Change On The Interactions Between Entomopathogenic Fungi And Plants In A Farmland Ecosystem

With multi-interspecific interactions in agricultural ecosystems that exert profound effects on crop quality and safety,the mentalism relationships between plants and insect pests and their natural enemies are increasingly focused.As a natural enemy,entomopathogenic fungi（EF）is well-known for killing insects through damaging body tissue,which has been widely used in agricultural pest control.Recent studies found that EF could also cause nutrient depletion with plants,resulting in indirect positive effects.Growing evidences showed that the dual ecological function of EF has been better understood,however,the response of EF to plants is still lacking.In particular,previous studies have ignored the feedback effects of plants on EF and the interaction between them.Additionally,ecologists have little recognition on the plant-microbial interaction in the context of climate change,especially the relationships between EF and plants in agroecosystems.This study will help to better understand the interaction between EF and plants in agricultural ecosystems,and provide a theoretical basis for the theory of species interactions.At the same time,there is a clear understanding of the dual role of EF,which not only promotes crop growth,but also has important practical value in the effective control of crop pest occurrence in agricultural production.A controlled experiment was conducted in our study.The colonization characteristics of EF in plant and its effects on maize growth were observed in an agroecosystem with maize（Zea mays）,endophytic fungal entomopathogen（Beauveria bassiana）,and Asian corn borer（Ostrinia furnacalis）.The effects of two pathways（direct and indirect）of EF on plants were clarified by simulating two major climate change conditions（elevated air temperature and elevated CO₂）through Open Top Chambers（OTCs）.We also tried to reveal the ecological adaptability and potential mechanism between EF and plants in agricultural ecosystem.The study obtained main results as follow:（1）B.bassiana colonized in maize through various inoculation methods（including seed soaking,root irrigating,stem injecting and foliage spraying）and showed bottom-up dispersion in plants.The spores of B.bassiana preferred to leave.Seed soaking and root irrigating were the best inoculation methods for B.bassiana,and the optimum inoculation concentration was 1×10⁷ conidia/ml.There was the highest B.bassiana endophytism rate of 76.7%in root by irrigating method.There were significant differences in the colonization of B.bassiana in different parts of maize tissues.The conidias of B.bassiana were the most abundant in leaf,only a few conidias were observed in the root of maize after seed soaking and root irrigating,but no observation in stem.（2）Our results showed that there was a positive feedback between EF and plants under ambient climate conditions.It was found that colonization of B.bassiana at different application modes and inoculation concentrations promoted the growth and development of maize,with increase in plant height,leaf length,leaf width and leaf area.When the suspension of B.bassiana was 1×10⁷ conidia/mL,the highest mean plant height occurred at the 14th day of maize seedling,with higher by 16.5%than that of the control;at the same time,the leaf length,leaf width and leaf area of maize seedlings also increased significantly in B.bassiana treatments by seed soaking at this concentration,and there was an increase by 29.0%,10.8%,and 21.8%,respectively,compared to control.Moreover,the plant biomass,the activity of resistant enzyme and content of nutrient elements was promoted by B.bassiana.Meanwhile,with comparing the strain isolated from the plant to the original strain,maize also had a positive effect on the biological characters of B.bassiana due to higher spore germination rate,sporulation quantity,growth rate and virulence of B.bassiana isolated from plants.Therefore,it is suggested that there was a mutualism relationship between EF and plants under ambient climate conditions.（3）There was an asymmetric relationship between EF and plant under climate warming,that is,elevated air temperature could shift the interactions between plants and EF,possibly from mutualism to commensalism.EF had no significant effect on plant growth under warmed condition;however,plants still played a positive role in promoting the growth of EF.The results showed the increase in plant height during each plant growth periods,aboveground plant biomass was higher by 6.93%than that of in control.Moreover,there was a significant effect of elevated temperature on two main resistant enzymes in maize plants,the activity of PAL and PPO increased by10.79%,and 10.95%,respectively.The content of N element and K element in the stalk of corn increased by 5.64%and 5.22%,respectively.On the contrary,plants can still provide living space and nutrients for EF,and further enhance fungus activity.These findings revealed that the patterns of interaction between EF and plants may be changed by climatic warming;meanwhile,it is suggested that temperature seems to be a key factor to affect the balance between EF and plants.（4）The strength of the interactions between EF and plants was enhanced by elevated CO2.Maize had positive effects on B.bassiana under elevated CO2concentration,with an increase in sporulation quantity,spore germination rate,and virulence.At the same time,B.bassiana also directly promoted the growth of maize and enhanced plant resistance.Moreover,B.bassiana-maize symbiont had negative effects on Asian corn borer（ACB）.Therefore,the symbiont limited the growth and development of ACB in the first and second generations with lower feed intake,pupation rate,eclosion rate,and spawning amount.Our results indicated that EF could not only directly promote the growth of plants,but also produce superimposed positive effects on plants through indirect regulation of herbivorous insects.In conclusion,B.bassiana could spread regularly（from bottom to up）and colonized in the host plant,and then form a mutualism relationship.The interactive pattern between entomopathogenic fungi and plants could be changed under the condition of elevated air temperature and elevated CO₂,which was based on changes in the biological characteristics of the species and the effects on the surrounding organisms.In this study,we obtained a further understanding of the colonization of entomopathogenic fungi in plants and their effects on plants,and the interactive relationship between them under different environmental conditions.This study provides a new sight for exploring the interaction between microbes and plants under climate change,and it also gives better understanding to the role of multi-nutrient interactions in agricultural ecosystems.Moreover,it is necessary to supplement the traditional biological control concept and provide basis for formulating reasonable and effective agricultural managements.Thus,it is important to protect the biodiversity,ecological environment,and agricultural systems under future climate change.