AM Fungi Regulate The Inter-specific Competition And Phosphorus Transfer Between Poisonous Plants And Grasses In The Tibetan Plateau Alpine Medow

The degradation of ecological system in the Tibetan Plateau alpine medow results in gradual replacement of dominant position of grasses by poisonous plants,which compete with grasses in light,nutrition and water,etc.,and alter the under-ground microbial communities.AM fungi can regulate inter-specific competition,but whether it can influence the inter-specific competition between poisonous plants and grasses has not been revealed.Based on the above discussion,in order to better understand the inter-relationship between poisonous plants,AM fungi and grasses,this study adopts split-compartment facility,and simulates the non-degradation and severe degradation of Tibetan Plateau,to discuss whether AM fungi regulate population distribution of poisonous plants in the succession process of the ecological system in the Tibetan Plateau alpine medow.Whether AM fungi influence the co-existence and inter-specific competition of poisonous plants and grasses,and the diversity of plant community structure? After removal of poisonous plants,whether composition of rhizosphere AM fungi have secondary effects on re-establishment of grasses.And,under split root chambers,whether different AM fungi and P elements have influence on the growth of Elymus nutan? Moreover,it reveals the regulation mechanism of AM fungi on inter-specific competition between poisonous plants and grasses,demonstrates the dynamic development of poisonous plants in ecological system in the Tibetan Plateau,and provides scientific evidence for degradation and restoration of Tibetan Plateau.This study consists of four parts: 1)Split-compartment facility is used to probe into whether the native AM fungi in non-degraded soil ecological system in Tibetan Plateau alpine medow distribute P differently,enhance inter-specific competition between Elymus nutan or Poa pratensis and the poisonous plant Saussurea japonica.2)Split-compartment facility is used to simulate how the native rhizosphere AM fungal mycelia of poisonous plants(donor)in degradation soil ecological system have influence on the growth of Elymus nutan or Poa pratensis(receptor).3)This study discusses the secondary effects of species diversity of rhizosphere AM fungi in poisonous plants on the establishment and growth of grasses after degradation of Tibetan Plateau;4)Split root chambers is used to discuss how different AM fungi improve the growth of Elymus nutan,whether AM fungi can balance plant growth,and whether AM fungi can serve as transfer channel for P.Main results are as follows:1)Severed/non-severed treatment of common mycorrhizal networks(CMNs)is used to find the the influence of CMNs on P uptake and plant growth.Compared with spontaneous establishment and severing of CMNs,pre-establishment of grasses and non-severed CMNs can significantly restrain the growth of Saussurea japonica(P<0.05);however,when the above-ground grasses is cut off(simulating livestock feeding),it can be found that CMNs distribute more P to Saussurea japonica and improve its growth.Therefore,CMNs regulate P distribution,and thus enhance the inter-specific competition between grasses and poisonous plants,with low P level increasing the competition between Elymus nutan or Poa pratensis and Saussurea japonica and inhibitting growth of Saussurea japonica seedlings;high P level is beneficial to co-existence of Elymus nutan or Poa pratensis and Saussurea japonica,and CMNs enhance the competitivity of Saussurea japonica seedlings for P.Besides,photosynthesis of host plants can significantly regulate the influence of CMNs on plant inter-specific competition(P<0.05).The results show that livestock‘s selective feeding can not only influence the structure of above-ground plant community but also regulate the nutrition uptake by AM fungi in underground soil microorganisms,and even reverse the positive influence by AM fungi,intensifying the degradation of Tibetan Plateau alpine medow.2)Gentiana macrophylla,or Ajuga ovalifolia,or Anaphalis lactea,or Polygonum viviparum is pre-established in a compartment,when extraradical mycelium has traversed the 40μm nylon net(only traversable by mycelium)and extended to the other compartment,where Elymus nutan or Poa pratensis is cultivated,which indicates that extraradical mycelium of poisonous plants significantly inhibits growth of grasses,and colonization level of extraradical mycelium is negatively correlated with growth of grasses(P<0.05).It is indicated that the proliferation of poisonous plants may have selectively cultivated favorable native AM fungi species,and inhibitted the establishment and growth of other plants in the rhizosphere.3)Tibetan Plateau alpine medow is divided into two periods,non-degraded and severely degraded,to investigate the relative coverage,relative density,relative biomass,relative height etc.of 8 poisonous plants and important values(IV)is calculated,indicating that IV of non-degraded grassland is significantly different from that of severely degraded grassland(P<0.01),especially Ligularia virgaurea(IV=3.27),demonstrating that the degradation of alpine medow has promoted the spread of poisonous plants.Rhizosphere soil is collected and the density of AM fungi spores in the soil is measured,and then,with Elymus nutan and Poa pratensis as plant materials and 9 rhizosphere soils(20g)as inoculants,either sterilized or non-sterilized,which indicates that compared with the soil inoculated with sterilized rhizosphere soil of poisonous plants,inoculation with non-sterilized rhizosphere soil of poisonous plants more significantly inhibits growth of Elymus nutan and Poa pratensis,especially rhizosphere soil of Lamiophlomis rotata,Ligularia virgaurea and Gentiana macrophylla.With inoculation of sterilized rhizosphere soil,the influence of rhizosphere treatment of poisonous plants on growth of grasses is not significantly different from that of rhizosphere treatment of grasses(P>0.05),and Elymus nutan and Poa pratensis are mycorrhizal dependent plants.Results demonstrate that the degradation of Tibetan Plateau alpine medow can intensify the proliferation of poisonous plants,which alters density and diversity of native AM fungi in Rhizosphere soil,significantly inhibits the establishment of other grasses in its rhizosphere,and provide favorable conditions for the establishment of individual population.4)With split root chambers,this study shows that AM fungi can promote the growth of Elymus nutan,and have significant influence on fresh biomass,biomass,root length,height,tillers and number of leaves(P<0.05);while Elymus nutan is differently mycorrhizal dependent on different AM fungi,and is more dependent on Glomus intraradices than on Acaulospora laevis.Besides,under different P levels,inoculation with the same or different AM fungi in both compartments can significantly promote the growth of Elymus nutan(P<0.05),but under high P level(200mg/kg),Glomus intraradices has more promotion for growth of Elymus nutan than Acaulospora laevis(P<0.05),which indicates that Glomus intraradices is more tolerant against Phosphorus stress.Under treatment of two different nylon nets(40μm or 10μm),mycelium can traverse 40μm nylon net,alleviate high Phosphorus stress,promote the growth of the host plant,with balanced root growth in two compartments and no significant difference in P content,and a significant increase in above-ground P content(P<0.05);mycelium can not traverse 10μm nylon net,with a significant difference in root growth in two compartments and P content(P<0.05),and its above-ground P content is lower than that of 40μm nylon net treatment.Under the same P level,the colonization rate and spore density of AM fungi in 10μm nylon net treatment are significantly lower than that in 40μm nylon net treatment(P<0.05).In addition,in the 40μm nylon net treatment,different AM fungi are inoculated in two compartments,and two AM fungal spores are collected.