Arbuscular Myccorrhizal Fungi Alters The Plant Interspecific Interaction Under The Application Of Nitrogen

Human activities have increased the amount of nitrogen in the world.The eutrophication of nitrogen in the soil led to increase the productivity of the plant community,by reducing the plant diversity and affecting the plant community composition.Arbuscular mycorrhizal fungi(AMF)is one of the important soil microorganisms,which form symbiotic relationship with 80% of terrestrial plants.AM fungi help plants to absorb phosphorus,nitrogen,magnesium,and other inorganic minerals,and water from the soil.Plants also provide photosynthetic products to support the growth of AM fungi.The available nitrogen and AM fungi in the soil can directly or indirectly affect the plant's own growth,thus affecting the plants interspecific interactions.However,in the long-term nitrogen fertilized environment,the changes of ecological function of AM fungi community have yet to be studied.Moreover,the interaction between non-biological(nitrogen fertilizer)and biological factors(AM fungi)on plant interspecific interactions also needs to be further explored.In this study,we selected Vicia faba L.,Hordeum vulgare L.and Brassica napus L.as a study material,which were local crops in the Qinghai-Tibet Plateau.We systematically studied the effect of individual plant growth and plant interspecific interaction by using pot experiment.The experiment was designed by using multiple treatments including nitrogen treatment,different cropping patterns and growth stages(two harvests)and AM fungi treatments.The main experimental results are as follows:(1)Under the condition of without fertilization,AM fungi had no significant effect on the growth of broad bean,barley and rapeseed.The effect of AM fungi on the growth of broad bean and barley was not significant,but the total biomass and total phosphorus content of rapeseed were significantly decreased(P< 0.05).(2)In the case of non-fertilization,AM fungi was not symmetrical,and the growth of barley was inhibited.The application of nitrogen fertilizer increased the competitiveness of barley,and the growth of barley was weakened after inoculation with AM fungi,so AM fungi significantly inhibited the growth of rapeseed,weakened the competitiveness of rapeseed and had no effect on the growth of broad bean.Inoculation of AM fungi significantly reduced the competitiveness of broad bean that was the dominant plant under the condition of nitrogen fertilizer.Mixed highland barley with rapeseed,AM fungi increased the competitiveness of highland barley under the condition of non-fertilizer;Inoculation of AM fungi significantly reduced the competitiveness of dominant plant(barley)after nitrogen fertilizer.(3)When broad bean mixed with highland barley and rapeseed,inoculation of AM fungi significantly weakened the competitiveness of broad bean under non-fertilization.Under the condition of fertilization,the highland barley was the dominant plant,and the inoculation of AM fungi significantly weakened the competitiveness of the barley.(4)The response of each plant to AM fungi was time heterogenised,which was inconsistent during the plant growth period at different times.The function of mycorrhiza was related to the nutritional status of the plant R= 0.22(P = 0.04).Therefore,the mycorrhizal function was affected by the vegetative state of the plant and might be related to soil nutrient.In conclusion,the AM fungi community had differences in the function of soil with different nitrogen contents.Under non-fertilization conditions,AM fungi had no significant effect on single broad bean,barley and rapeseed.After fertilization,AM fungi showed weak response to broad bean and barley,while the growth of rapeseed showed a negative response.Under non-fertilization conditions,the growth of each plant that planted with another plant was inhibited by nitrogen.Inoculation with AM fungi supported the growth of plants with high mycorrhizal dependency.The AM fungi community structure after long-term fertilization had changed to a certain extent.The AM fungi in the environment showed a tendency to inhibited dominant plants in different cropping patterns,weakened the negative effects caused by the increase of nitrogen content,and further promoted the coexistence of plant species.When mixed plants were planted,AM fungi could weaken the competitive trend of dominant plants in the community,and maintain the stability of plant communities to a certain extent.