| The biological soil crust is widely developed in the loess hilly region abandoned farmland,which is the key factor affecting the soil nutrients and the cycle process in the early stage of vegetation restoration.Soil microorganism is an important part of biological crusts,and their metabolism directly affects soil energy flow and material circulation.However,the metabolic limitation characteristics of soil microorganisms during the development of biological crusts and their effects on microbial communities are still unclear.In this study,the abandoned farmland in the early stage of vegetation restoration on the Loess Plateau was selected as the research object,different types of biological crusts and subsoil(0-2 cm,2-5 cm and 10-20 cm)were collected:light algal crusts(LA),dark algal crusts(DA),algae and moss mixed crust(AM)and moss crusts(M).The main nutrient status,extracellular enzyme activity characteristics related to carbon(C),nitrogen(N),phosphorus(P)circulation and microbial community structure characteristics of different biological crusts were analyzed.To explore the changing process and driving mechanism of microbial nutrient metabolism and microbial community with the development of biological crusts,and to provide a theoretical basis for scientific understanding the ecological function of biological crusts and microbial metabolism.The results of this study were as follows:(1)Soil nutrients and soil microbial biomass were significantly affected by the types of biological crust and soil depth.The soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP)and microbial biomass C,N,P increased gradually with the process of LA,DA,AM,M succession.The contents of SOC,TN and TP in the moss crust were 11.2±0.33,0.88±0.04 and 0.54±0.01g kg-1,respectively.In terms of vertical depth,the effects of biological crusts on soil nutrients were mainly concentrated in the crust layer and 0-2cm soil layer.Soil nutrients and microbial biomass decreased gradually with the increase of depth.The microbial biomass of the crust layer was 3.93?31.8 times that of the underlying soil.(2)The enzyme activities related to C,N,and P cycles increased gradually with the development of the biological crust.Microorganisms met their biomass requirements by accelerating nutrient metabolism.At vertical depth,due to the lack of N and P in the underlying soil,the enzyme activities related to N and P cycles increased at 10-20cm.In addition,soil nutrient status is an important factor affecting extracellular enzyme activity and its stoichiometric ratio.(3)There was an unstable elemental homeostasis in the microbial community of the light-colored algae crust,and the other types showed strong elemental homeostasis with the development of the crust.Soil microorganisms were generally limited by C and P under different types of biological crusts.The relative P limitation of microorganisms decreased with the development of biological crusts.The P limitation of the microbial community was the least in the moss crust(the vector angle was55.6°),suggesting that mosses could provide the best nutrient environment for microorganisms.The results of the partial least squares path model(PLS-PM)showed that nutrient content and nutrient stoichiometric ratio were the key factors affecting the microorganisms'limitation of relative P and C.(4)The development of biological crusts altered the diversity and species composition of prokaryotic and eukaryotic microbe.The alpha-diversity of prokaryotic and eukaryotic microbe increased and decreased significantly,respectively,and the community composition of prokaryotic microbe differed significantly among different types.The development of biological crusts increased the relative abundance of Actinobacteria,Acidobacteria,Proteobacteria,and Streptophyta,while the relative abundance of Cyanobacteria and Ascomycota decreased gradually.In addition,the microbial relative P limitation significantly affects microbial community composition and diversity. |
PDF Full Text Request