Effects Of AM Fungi On Plant Growth And Community Structure Under Different Soil Nitrogen Fertility

Global N deposition has nearly doubled in a short period of 30 years,posing a serious threat to global biodiversity and ecosystem stability.Arbuscular mycorrhiza(AM)fungi are an important type of soil micro-organism that can form reciprocal symbiosis with the root system of most terrestrial plant species.AM fungi can provide plants with mineral elements such as nitrogen(N)and phosphorus(P),which have important regulatory effects on plant growth,element cycling,and ecosystem sustainability.Studies have shown that an increase in fertility of soil N will change the symbiotic relationship between AM fungi and plants,but how does AM fungi affect plant growth and community composition in the situation of increasing soil N? This issue is still poorly understood.This study based on a long-term N(0,5,10,and 15 g N m-2 yr-1;corresponding to N0,N5,N10,and N15)and mycorrhizal inhibition(with and without benomyl)interactively treats plots in the alpine meadow ecosystem,and combined a short-term experimental treatment with N(0,50,and 100 mg N kg-1 soil;corresponding to N0,N1,and N2)and AM fungus inoculation(inoculation and non-inoculation of Funineliformis coronaturm)in the greenhouse(The plant under test: Sorghum haipense),which studied the effects of arbuscular mycorrhizal fungi on plants under different soil N fertility.The main results are as follows:(1)The total length colonization,vesicle colonization,and extraradical hyphal length density were significantly decreased in field-applied N and benomyl addition for 6 consecutive years.Both N application and benomyl treatment significantly increased the above-ground biomass and plant N content of plant communities,but both treatments had no significant effect on plant biomass and plant P content.The mycorrhizal growth effect(MGR)of plant community was significantly negative in N5 treatment,Nitrogen uptake effect(MNR)was a significant negative effect in N5 and N10 treatments,and the phosphorus uptake effect(MPR)was not affected significantly by N treatments.Both nitrogen application and benomyl treatment significantly reduced the species richness of plant communities and had a significant impact on the species composition of plant communities.(2)After 4 months of greenhouse treatment,the results showed that applying N significantly reduced the total length colonization and vesicle colonization of AM fungi in sorghum roots;at the same time,N application significantly increased the aboveground biomass of Sorghum,however,it reduced the underground biomass.In the three N treatments,inoculation of AM fungi significantly increased the above-ground biomass,plant total N and plant total P content of sorghum,and there was a significant interaction between N and AM inoculation on sorghum biomass and total N content.The mycorrhizae growth effect(MGR),nitrogen uptake effect(MNR),and phosphorus uptake effect(MPR)of sorghum exhibited positive effects in most N treatments(only N1 had no significant positive effect on MNR),and with the increase of soil N fertility,it showed the tendency of falling first and then rising.In summary,the study found that the increase of soil N fertility will significantly reduce the root length colonization of AM fungi;At the individual plant level,AM fungi promoted the increase of plant biomass and the absorption of N and P elements,and the mycorrhizal effect(MR)of plants showed a tendency of falling first and then rising.with the increase of soil N fertility.At the community level,although the soil N fertility had no significant effect on the mycorrhiza growth and N,P uptake response of plants,the presence of AM fungi could alleviated the negative effect of N on plant species diversity,indicating that AM fungi have a certain effect on the maintenance of plant diversity under N deposition.