| In the process of dynamic change of aeolian sand land,the community structure and species composition change greatly.It is important to study the ecological stoichiometric characteristics of plant and soil elements for understanding the biogeochemical cycle of ecosystem.Exploring the relationship and feedback mechanism between plant and soil elements is the core issue of ecosystem restoration in alpine sandy land.Therefore,this study takes the main line of "plant-soil-microbe-extracellular enzyme" system in different restoration stages of aeolian sand land,starts with C,N and P ecological stoichiometry,and takes soil microbial community as the core point.The plant-soil ecological stoichiometric characteristics and microbial mechanism of Sophora moorcroftiana shrub in the middle reaches of Yarlung Zangbo River in different restoration stages were studied in a watershed scale system,in order to provide scientific basis for the restoration and management of alpine fragile valley sandy land system.In this study,traditional analytical methods,phospholipid fatty acid analysis and high-throughput sequencing techniques(16S r RNA gene and ITS gene)were used.To investigate the community structure,life form composition,distribution pattern,dynamic equilibrium relationship of ecostoichiometric characteristics of C,N,P in plant-soil system and its relationship with microbial community in different restoration stages of aeolian sandy land(fixed sandy land,semi-fixed sandy land,mobile sandy land)in watershed scale(the middle Yarlung Zangbo River Basin).The stoichiometric ratio dynamic balance of elements C,N and P of S.moorcroftiana shrub in alpine fragile sandy land ecosystem and the mechanism of microbial regulation were investigated.The following results are obtained:1.The community structure of S.moorcroftiana shrub is relatively simple,and the species diversity level is low.The species composition of Compositae,Gramineae and Leguminosae were predominant.The plant life forms are mainly ground budding plants and annual plants.With the recovery of the shrub community,the proportion of Compositae,Gramineae,Legumes and Boraginaceae in the community gradually increased,while the proportion of Amaranthaceae in the community decreased.2.With the restoration of shrub communities,N and P content of plants showed an increasing trend on the whole,while C content had no significant difference in different restoration stages.At the same time,the difference of C,N and P nutrients in different plant components led to the difference of C:N ratio,C:P ratio and N:P ratio.The N:P ratio >16 and P content >1.0mg/g in leaves of S.moorcroftiana shrub at different recovery stages,indicating that S.moorcroftiana population as a whole may be more restricted by P element.In addition,the C:P ratio and N:P ratio of S.moorcroftiana leaves were higher than that of herbaceous plants under the canopy due to the low P content.In vegetation system,N:P is most closely related to leaves,understorey herbs and litters,which also proves the importance of N and P elements for vegetation restoration in terrestrial ecosystems.3.The contents of C,N and P of soil and microbial biomass increased with shrub restoration,and the difference of community structure led to the difference of stoichiometric ratios of soil and microbial biomass elements.The ratio of soil N:P,microbial C:N ratio,C:P ratio and N:P ratio showed an increasing trend with the recovery of shrub community.Soil C:N ratio decreased with shrub restoration.4.With the restoration of shrub community,the activities of C,N and P extracellular enzymes in soil increased.The ratio of natural logarithms of C,N and P obtained enzymes ranged from 1:1.16:1.69 to 1:0.96:1.13,with an average value of1:1.01:1.30,which deviated from the global average ratio of 1:1:1,indicating that soil microorganisms were limited by both N and P.With the restoration of shrub,the ratio of extracellular enzyme N:P decreased and the vector Angle increased,indicating that soil microorganisms were gradually enhanced by the restriction of P.In addition,the close relationship between soil C,N,and P acquisition enzymes and the C:N:P ratio of soil and microbial biomass suggests that soil extracellular enzyme stoichiometric homeostasis depends on the availability of microbial resources.5.There were significant differences in the total PLFAs biomass and diversity level(alpha and beta diversity)of soil microorganisms at different restoration stages of S.moorcroftiana shrub,that is,the microbial alpha diversity increased significantly from the moving sandy land to the fixed sandy land stage,and the microbial beta diversity varied significantly between different restoration stages.These results indicated that soil microorganisms were obviously affected by vegetation community structure in alpine desert fragile ecosystem.At the same time,the relative abundance of bacterial PLFAs decreased significantly with shrub restoration,especially gram-negative bacteria.Actinobacteriota,Proteobacteria and Bacteroidetes were the main bacterial communities in soil.Among them,Actinobacteriota is the most abundant and decreased significantly with shrub restoration.The dominant phyla Ascomycota and Basidiomycota showed significant differences in different recovery stages,but their changing trends were inconsistent.6.There was a complex dynamic equilibrium network among C,N,P stoichiometric ratios of plants,soil,microorganisms and extracellular enzymes in the S.moorcroftiana shrub in different restoration stages,and this equilibrium relationship might be driven by different levels of stromal nutrition.The contents of C,N and P in plant-soil system and the ecological stoichiometric ratio interact with the composition and diversity of soil microbial community.Especially,the extracellular enzyme C:N ratio is the most sensitive and has a great influence on soil microbial community.In addition,microbial communities regulate the balance of C,N and P elements in vegetation-soil system by adjusting their own community composition and diversity in the changing environment(changes in plant community structure and soil characteristics). |
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