Effects Of AM Fungi Inoculation And Phosphorus Fertilization On Nutrient Competition Between Rhododendron Chinensis And Phyllostachys Edulis In Karst Areas

Plant invasion not only destroys the function of the local ecosystem,but also causes serious harm to species diversity.Arbuscular mycorrhizal(AM)fungi are a class of soil microbes that can form a mutually beneficial symbiotic relationships with80%of the terrestrial plant roots in the world,which can promote host plants to absorption of nutrients such as nitrogen(N)and phosphorus(P)in the soil,and can affect the competition between invasive plants and native plants.A typical karst landform distribution area in Southwest China,which has the characteristics of large area,wide distribution,complex topographical conditions,high rate of bare rock,shallow and discontinuous soil layer,serious soil erosion and nutrient deficiency such as soil N and P.Some studies have shown that a certain level of phosphorus treatment can promote plant growth.However,how do AM fungi and phosphorus addition affect the growth conditions,nutrient and stoichiometric characteristics of invasive plants and native plants,and what is the difference between the two species under different treatments?Therefore,in this experiment,the common invasive plant Eupatorium adenophorum and the native plant Eupatorium lindleyanum DC.(both are Compositae)in the southwest region were selected as plant materials,through with or without AM fungi(M⁺and M^-)treatment,four phosphorus addition treatments(P₀,P₅,P₁₅and P₂₅),and three competitive treatments including non-competition(CK),intraspecific competition(Intra)and interspecific competition(Inter),to study the effects of AM fungi and phosphorus addition on the plant growth,nutrients accumulation and ecological stoichiometry characteristics of the two plants in karst habitats under different competitive conditions,it is of great significance for elucidating the invasion mechanism of Eupatorium adenophorum in karst habitats and understanding the relationship between AM fungi,phosphorus elements and plants competition.In this experiment,we set species factors,AM fungi factors,phosphorus addition factors and competition factors to conduct a four-factor indoor control experiment.Three months after planting,the root mycorrhizal infection rate and biomass,carbon(C),nitrogen(N),and phosphorus(P)nutrient elements were determined,The main results are as follows:(1)The root mycorrhizal colonization rate of the invasive Eupatorium adenophorum was the highest under the CK treatment and reaches to the highest colonization rate in the P₀treatment.The colonization rate of the native Eupatorium lindleyanum DC.was the lowest during intraspecific competition and reached the maximum colonization rate in the P₀treatment,and the native Eupatorium lindleyanum DC.was higher than the invasive Eupatorium adenophorum.In addition,AM fungi significantly promoted the biomass accumulation in the organs of the two plants.In general,the invasive Eupatorium adenophorum had the highest biomass under the CK condition,while the biomass was the lowest when competing with the native Eupatorium lindleyanum DC..The native Eupatorium lindleyanum DC.had the lowest biomass under the Intra condition.The comparison of biomass between species also showed that the biomass of Eupatorium adenophorum root,stem,leaf and total biomass under the P₂₅-CK-M⁺conditions were significantly higher than the native Eupatorium lindleyanum DC.,the native Eupatorium lindleyanum DC.under the other treatments was significantly higher than the invasive Eupatorium adenophorum.(2)In addition to the inoculation of AM fungi under some treatments that reduced the C and P concentrations of the root,stem and leaf of the two plants,in general,the AM fungi treatment increased the C and P concentrations of the root,stem and leaf of the two plants,and reduced the N concentration of the two plants.Competitive treatment only had a significant effect on the C concentration of stem,N concentration of stem and leaf and P concentration of root and leaf.Phosphorus addition treatment significantly affected the concentration of C,N and P in root,stem and leaf.In general,the C concentration in the various organs of the native Eupatorium lindleyanum DC.was higher than the invasive Eupatorium adenophorum,while the N concentration was different among the treatments.The root and stem P concentration of invasive Eupatorium adenophorum was basically higher than the native Eupatorium lindleyanum DC.,and the leaf P concentration of the native Eupatorium lindleyanum DC.was higher than invasive Eupatorium adenophorum.(3)AM fungi generally increased the accumulation of C,N,and P of the invasive Eupatorium adenophorum and the native Eupatorium lindleyanum DC..In general,the invasive Eupatorium adenophorum had the highest accumulation of C,N,and P under CK conditions,while the C,N,and P accumulation was the lowest when competing with native Eupatorium lindleyanum DC.,and the native Eupatorium lindleyanum DC.had lowest C,N,and P accumulation under the intraspecific competition treatment.The comparison of biomass between species also showed that the accumulation of C,N,and P of Eupatorium adenophorum under the P₂₅-CK-M⁺conditions were significantly higher than the native Eupatorium lindleyanum DC.,the native Eupatorium lindleyanum DC.under the other treatments was significantly higher than the invasive Eupatorium adenophorum.(4)AM fungi,competitive,and phosphorus addition treatments all had a regulatory effect on the nutrient element ratio between the organs of the two plants.Different treatments had different effects on the stoichiometric ratio of C,N and P between the organs of the two plants,and the growth of both plants were limited by the N element.The above,our research results show that AM fungi can improve the growth and nutrients accumulation of the of the two plants,and the native plant Eupatorium lindleyanum DC.was higher than the invasive plant Eupatorium adenophorum in growth and nutrients competition;Different phosphorus addition treatment and competition treatment had different regulation on nutrients of the two plants.In addition,AM fungi can adjust the nutrients accumulation of two plants to respond to different competitive treatments and different phosphorus addition treatments.In summary,invasive Eupatorium adenophorum was weaker than the native plant Eupatorium lindleyanum DC.in growth and nutrient competition and the growth of both were restricted by the N element,indicating that the native Eupatorium lindleyanum DC.can be used as an alternative plant to control the invasion of Eupatorium adenophorum in nitrogen-restricted karst habitats.