AM Fungi Regulate The Soil Properties Of Herbaceous Plants Through PSF In Karst Soil

Plant-soil feedback refers to plant growth that can alter the soil environment.In turn,changes in the soil environment can affect plant growth,thereby altering the composition and dynamics of the plant community.Karst is a widely distributed landscape type in southwestern China,and the early stages of karst vegetation succession are mainly composed of pioneer successional communities with Compositae and Gramineae as dominant species.These pioneer plant species have different impacts on the soil while growing,and it is not clear how the affected soil will have different plant-soil feedbacks on the later plant growth and the settlement and growth of other species.Some functional microorganisms,such as arbuscular mycorrhiza(AM)fungi,can promote plant growth and nutrient utilization,as well as soil nutrient cycling.However,AM fungi usually act together with other microorganisms to affect plants and soils in natural karst habitats.AM fungi may behave differently on plant growth and nutrient functions due to differences in soil microbial conditions and may further influence later community succession.Therefore,based on the plant-soil feedback(PSF)theory,it is a scientific question of interest to investigate how the microbial conditions soil in the presence of AM fungi further affects the changes in soil physicochemical properties caused by the karst pioneer plants themselves and other species.It is important to answer this question to help reveal the microbial action mechanism of AM fungus-mediated karst plant community succession and provide a theoretical basis for ecological restoration of degraded karst vegetation using mycorrhizal biotechnology.In this experiment,the pioneer Gramineae species Setaria viridis vs.Arthraxon hispidus and the Compositae species Bidens pilosa vs.Bidens tripartita were used to carry out the plant-soil feedback experiment in two stages: the feedback conditioned soil culture stage and the plant-soil feedback stage.Plants were cultured for four months to determine soil spore density,mycelial density,soil nutrients and glomalin.The effects of conditioned soil,conditioned species and feedback species on PSF soil properties were analyzed.The main findings were as follows.(1)Under conditioned soil and conditioned plant treatments,the spore density and hyphal density were the highest in sterilized soil inoculated with AM fungi,and the lowest in sterilized soil without AM fungi.The sterilized soil inoculation with AM fungi decreased soil organic carbon and available potassium of conditioned plant Bidens pilosa.However,natural soil inoculation with AM fungi significantly increased soil organic carbon,total nitrogen,alkaline nitrogen,total phosphorus,available phosphorus,available potassium and EE-GRSP of conditioned plants Setaria viridis,Arthraxon hispidus,Bidens pilosa and Bidens tripartita as a whole.Different conditioned plants responded differently to natural soil inoculation with AM fungi,total nitrogen of Arthraxon hispidus,alkaline nitrogen of Bidens tripartita significantly higher than the other three.(2)Under conditioned soil and feedback plant treatments,the spore density was the highest in sterilized soil inoculated with AM fungi,and the lowest in sterilized soil without AM fungi.The sterilized soil inoculation with AM fungi decreased available potassium of feedback plant Bidens pilosa and available phosphorus of feedback plant Arthraxon hispidus.However,natural soil inoculation with AM fungi significantly increased soil organic carbon,total nitrogen,alkaline nitrogen,total phosphorus,available phosphorus,available potassium and EE-GRSP of feedback plants Setaria viridis,Arthraxon hispidus,Bidens pilosa and Bidens tripartita as a whole.Different feedback plants responded differently to natural soil inoculation with AM fungi.Soil organic carbon and total phosphorus of Setaria viridis,and DE-GRSP,T-GRSP,total potassium,and available potassium of Bidens tripartite,available phosphorus of Arthraxon hispidus significantly higher than the other three.(3)Under conditioned plant and feedback plant treatments,soil spore density,hyphal density,soil carbon,nitrogen,phosphorus,potassium and glomalin were observed differences between the same feedback plants when grown on soils cultivated by the same or heterogeneous conditioned plants.Overall,the feedback plants showed higher soil nutrients on heterozygous plants than on conspecific ones.(4)Soil aggregates composition under the feedback plants Setaria viridis,Arthraxon hispidus,Bidens pilosa and Bidens tripartite showed a significantly higher proportion of aggregates >2 mm than those <0.25 mm.And the soil nutrient with the particle size of < 0.25 mm is the highest.With the decrease of soil aggregates size,the overall trend of soil total nitrogen,alkaline nitrogen,total phosphorus,available phosphorus,available potassium showed an increasing trend.Overall,inoculation of AM fungi significantly increased soil spore density and hyphal density,decreased soil organic carbon and available potassium of conditioned plant Bidens pilosa,and decreased available potassium of feedback plant Bidens pilosa and available phosphorus of feedback plant Arthraxon hispidus.However,natural soil inoculation with AM increased soil nutrients.In addition,the feedback plants showed higher soil nutrients on heterozygous plants than on conspecific ones.For soil aggregates under different feedback plants,there was an overall increasing trend of total nitrogen,alkaline nitrogen,total phosphorus,available phosphorus,available potassium with decreasing particle size of the aggregates.It indicates that the PSF-based AM fungi significantly altered soil properties of karst herbaceous plant feedback,and the change characteristics were significantly different depending on plant species and soil conditions.