Effects Of Nitrogen And Phosphorus Addition And AM Fungi Regulation On Soil Nutrients And Plant Community Characteristics In Songnen Grassland

The effect of nitrogen and phosphorus additions,arbuscular mycorrhizal(AM)fungi on the soil nutrient and plant community composition and productivity in grassland ecosystem is not clear.In this study,a field experiment was conducted with the manuiculated factors nitrogen(N),phosphorus(P)and AM fungi in Songnen meadow.The effects of N,P and AM fungi on soil nutrients and plant community composition and productivity were studied.The main results of research are as follows:(1)The results of three years showed that the additions of N increased the content of soil microbial biomass carbon(C)and N,which reduced the content of soil microbial biomass P.P addition increased the content of microbial biomass P,which reduced content of microbial biomass N.In addition,the additions of N+P increased the content of soil microbial biomass P,and both C/P and N/P reduced significantly the nitrogen application.There was a significant interactive effect of N addition and P addition on soil microbial biomass N and P were observed.Illustrating that N addition and P addition simultaneously can alleviate the lack of P in soil microbes caused by N addition alone.Benomyl addition has no significant effects on microbial biomass C and N,which reduced significantly microbial biomass P,N+benomyl addition increased significantly microbial biomass C and N,reduced the content of microbial biomass P,and C/P and N /P were significantly higher than those of single benomyl addition.There were significant interactive effects of N and benomyl on the microbial biomass N/P.N additions and P additions had some effects on the content of soil microbial biomass C,N and P but it wasn`t significant.N additions and P additions all reduced soil C content,and C/P、N/P all under the N additions.Benomyl addition and N + benomyl addition increased soil C content.N + benomyl addition increased significantly soil N content,reduced soil P content.Benomyl addition increased soil P content.NO significant interactive between N and benomyl on soil C,N and P.(2)N addition and N+P addition increased significantly the total plant community density,P addition had no significant impact on plant density.The effect of N+P additions on plant community was more obvious than that of single plant N addition or P addition.The effect of benomyl addition on plant community density was not significant in the short term time.N addition has a tendency to reduce species richness and diversity,P addition has a tendency to increase species richness and diversity;the abundance and diversity of N+P additions increased higher than the single P addition,and the abundance of N+P additions was significantly higher than that of contrast and N addition.The results showed that the N+P additions could compensate the effect of single N addition on species diversity of plant community.The effect of benomyl on plant community diversity and abundance was not significant.Both N addition and N+P additions increased the plant dominance community biomass,the N+P additions was more obvious than that of N addition alone.The effect of P on biomass was not significant,and N and P had significant interaction with biomass.Benomyl addition had no significant effect on biomass,the rate of biomass of N+benomyl additions increased higher than that of N addition alone.It can be seen that the maintenance of plant community productivity of AM fungi is related to N addition.N addition raised the plant N/P,P addition reduced the plant N/P,both N additions and P additions reduced plant N/P than that of P addition alone.Benomyl had no significant efffect on plant C and N,which reduced the phosphorus content significantly,there was a significant interaction between N and benomyl with plant N content.N addition,N+P addition increased the mycelium density,reduced the spore density,and the effect of P addition on mycelium and spore density was not significant.Benomyl addition reduced the mycelium density significantly,which increased spore density.The interaction of N and benomyl had an significant effect on spore density.The results showed that the change of soil nutrient content affected the number of AM fungi in Songnen grassland.(3)The mycelial structure of Chenopodiaceae plants was dominated by vesicular structure,and the abundance of arbuscule and mycelium was low.There was a significant negative correlation between AM fungi colonization rate and soil water content and soil available phosphorus content in Chenopodiaceae,which had a positively correlated with soil conductivity.(4)In AM fungi suppression treatment,three litter residues were significantly higher than those in AM fungi treatment.Under the conditions of N and P addition,AM fungi accelerated the decomposition of litter,but the contributions of AM fungi on litter decomposition for different plants were different.Under N and N+P additions condition,the mycelium density and spore density in AM fungi suppression treatment were higher than those in the control and P addition treatment.In AM fungi suppression treatment,soil microbial biomass C,N,P content decreased,significantly.Under N and P addition,there were significant differences in soil microbial C and N content between AM fungi and AM fungi suppression treatment.AM fungi significantly increased soil microbial biomass C,N content.In summary,AM fungi could alter plant community composition and productivity,accelerated the transform of carbon from aboveground to belowground under N and P additions.AM fungi altered the soil nutrient content and the stoichiometric characteristics,which played key roles in maitainning plant community composition and productivity,affecting C and N cyclings in the studied meadow ecosystem.The results suggest that AM fungi might alleviate the negative effects of N and P additions on ecosystem stability in grassland ecosystem.