| Grassland ecosystem is one of the important components of terrestrial ecosystem,and the normal functioning of its ecosystem function is of significance for maintaining global regional ecological balance.In recent years,overgrazing have led to increasingly serious degradation of grasslands,resulting in a continuous decline in the ecological functions of grassland.To alleviate the pressure of grazing on natural grasslands,we carried out research on the response of vegetation communities,soil properties,and microbial communities in different types of artificial mixture grassland ecosystems to the effects of grazing in order to understand the change patterns of artificial grassland ecosystems under grazing disturbance.This has direct theoretical guidance and practical significance for the restoration,rational development,and utilization of existing grasslands.In this study,we took the artificial mixture grasslands in Yanchi County,Ningxia as the research object,and adopted a single-factor randomized group design to conduct three mixture forage grass combinations:Treatment 1(T1)--Medicago sativa+Psathyrostachys juncea,Bromus inermis,Festuca rubra;Treatment 2(T2)--Medicago sativa+Psathyrostachys juncea,Elymus nutans and Festuca rubra;and Treatment 3(T3)--Medicago sativa+Psathyrostachys juncea,Agropyron cristatum,Agropyron mongolicum.The experiment studied the changes in soil physicochemical properties and vegetation community diversity of three types of artificial mixture grasses after two years of grazing disturbance effects.With the help of phospholipid fatty acids(PLFAs)and high-throughput sequencing technology,we investigated the changes of soil microbial community composition,AM fungal community structure,and diversity characterized by phospholipid fatty acid content after two consecutive years of grazing disturbance effects,and preliminarily elucidated the environmental factors driving the changes of AM fungal communities in different types of artificially mixture soils.The main results are as follows:(1)After two years of grazing,the aboveground biomass,height,density,importance value,and diversity index of grassland vegetation communities in T1,T2 and T3 treatments showed a decreasing trend with the extension of grazing period.As time went on,the decline in aboveground biomass,plant height,density,importance value,and diversity of the three types of mixture grassland plant communities under grazing increased gradually.Under the same grazing intensity,T1 treatment was stronger than that of T2 and T3 treatments,and T1 treatment could maintain relatively higher vegetation community diversity.(2)Compared to the non-grazing period,after one consecutive year of grazing,the soil available phosphorus(AP)and available potassium(AK)increased by 72.86%to 75.76%and 62.30%to 72.58%under the three types of mixture grasslands respectively.The soil pH,organic matter(OM),total nitrogen(TN),and total phosphorus(TP)contents showed an overall decreasing trend.After the end of grazing impact in 2022,soil organic matter content under treatments T1,T2,and T3 increased by 31.82%to 36.44%compared to 2021,and soil pH,AP,AK,and available nitrogen(AN)content showed an increase trend,while TN and TP content showed a decreasing trend.(3)The impact of two-year grazing caused an increase in the microbial biomass of the main soil taxa characterized by the content of PLFAs.Compared with 2021,in 2022,soil bacteria and fungi under the influence of grazing were elevated by 65.87%to 85.67%and 54.01%to 73.42%,respectively,and the total biomass of microbial communities was elevated by 72.93%to 79.81.Under the impact of grazing for two consecutive years,soil bacterial,fungal,and total microbial populations under T2 treatment were significantly higher than those under T1 and T3.However,the phospholipid and neutral lipid contents of soil AM fungi and the total AM fungal biomass were significantly higher under T3 treatment than T1 and T2 treatments.(4)The Monte Carlo test showed that soil pH,C,and N were the main nutrient elements affecting the change of microbial biomass under grazing disturbance.In 2021,soil ammonium nitrogen(NH4+-N)and OM under grazing impact were the main environmental factors driving the biomass of main soil microbial groups,while soil NH4+-N and TN were the main environmental factors driving changes in soil AM fungi and total microbial biomass after the influence of grazing.In 2022,after the impact of grazing,soil TN and pH were the main environmental factors driving changes in biomass of major soil microbial taxa under the influence of grazing,while soil OM and NH4+-N were the main environmental factors driving changes in AM fungi and total microbial biomass.(5)High-throughput sequencing results showed that the sequences of AM fungal OTUs in soil samples from 3 different types of mixture grassland could be clustered into 1 phylum,3 classes,4 orders,10 families,and 10 genera.At the genus level,under two years of grazing impact,the dominant species of AM fungi were Glomus and Paraglomus,and the sum of their relative abundance accounted for 47.0%to 55.9%.There were significant differences in Chaol index and species number among treatments after two years of grazing disturbance,and there were also significant differences in beta diversity of AM fungal community.RDA analysis showed that the environmental factors driving changes in AM fungal diversity and community composition were soil AP and NO3--N under the influence of grazing in the first year of grazing disturbance.Vegetation biomass and NO3--N were the main environmental factors driving changes in AM fungal diversity and community composition after the second year of grazing disturbance.(6)Pearson correlation analysis showed that grazing affected the correlation between plant community characteristics,soil properties,and AM fungal communities in artificial mixture grassland.Except for soil NH4+-N and AN,there were significant correlations between AM fungal taxa and most soil environmental factors.After two years of grazing impact,the soil AM fungal communities of the three types of artificial mixture grassland were significantly affected by changes in soil moisture,nutrients,and plant communities,but the effect of soil moisture on soil AM fungi was more obvious than the effect of soil environmental factors and plant community changes.The related factors have a direct or indirect impact on the composition and diversity of soil AM fungal communities in different types of artificial mixture grasses. |
