Effects Of Arbuscular Mycorrhizal Fungi On Interspecific Relationship And Nutrient Utilization Between Grasses And Legumes

Arbuscular mycorrhizal fungi（AMF）can colonize roots of host plants and produce hyphal networks,helping plant absorb and transfer nutrients.AMF plays an important role in driving plant interspecific relationships.Accumulated researches addressed the benefits of grass-legume mixtures for crop production.However,the process of AMF on nutrient utilization in vertical niche of mixed grassland is still not clear.Therefore,we conducted a greenhouse experiment,four plant species with different rooting structure and depths were selected to build the grass-legume plant community,and ¹⁵N isotope tracer technique was used to labeled 3 cm and 25 cm soil layers to explore the effects of AMF on interspecific relationships and nitrogen uptake strategies between species.Combined with high-throughput sequencing technology,we also analyzed the response of soil fungal flora to AMF inoculation in different polycultures.The main results are as follows:（1）Compared with non-inoculation treatment,AMF inoculation significantly increased the aboveground biomass,nodule number and shoot nitrogen of Medicago Sativa and Trifolium repens in polycultures,but the aboveground biomass and shoot nitrogen of Dactylis glomerata in polycultures were significantly decreased,AMF inoculation had no significant effect on aboveground biomass and shoot nitrogen of Lolium perenne.Regardless of polycultures or monocultures,the mycorrhizal root colonization of legumes was significantly greater than grasses,and the aboveground mycorrhizal growth response of two legume species was significant greater than grasses in polycultures.AMF inoculation significantly increased the aboveground and belowground relative yield of legumes in T.repens+D.glomerata polycultures,AMF significantly changed the interspecific relationship between shallow root legume T.repens and deep root grass D.glomerata in polyculture,and the aboveground biomass,shoot nitrogen and phosphorus of T.repens+D.glomerata polyculture were higher than other polycultures.（2）Compared with non-inoculation treatment,AMF inoculation significantly increased the nitrogen fixation rate and the ¹⁵N tracer uptake of T.repens.Regardless of the soil layers,compared with monoculture,polycultures significantly improved the nitrogen fixation efficiency of legumes and reduced the soil ¹⁵N tracer uptake by legumes.However,the ¹⁵N tracer uptake by D.glomerata and Lolium perenne in polyculture was significantly higher than each of their monocultures.AMF inoculation had a significant effect on the ¹⁵N tracer uptake in the vertical niche of T.repens.For non-inoculation treatment,T.repens monoculture mainly uptake ¹⁵N tracer from 3 cm soil layer,while the ¹⁵N tracer uptake significantly increased in 25 cm soil layer in AMF inoculation pots.（3）Compared with the uninoculated control,AMF inoculation significantly improved the richness and diversity of soil fungal community,whereas no significant difference on soil fungal diversity and richness were detected between different polycultures Ascomycota and Basidiomycota were the dominant fungi in soil regardless of AMF inoculation.Compared to uninoculated control,AMF significantly reduced the number of plant fungal pathogens in soil.In conclusion,AMF plays an important role in regulating nutrient absorption and interspecific relationship between legumes and grasses in polycultures,determining the coexistence of plants in polycultures,and effectively reduced the number of plant fungal pathogens in soil.