Characteristics Of Soil Microbial Metabolic Limitation And Their Community Structure And Functional Response In Two Vegetation Succession Sequences

Soil microbial metabolic activities driven by changing vegetation have a key role in the effect of the nutrient cycle on ecosystems.Soil function is supported by microbial community activities,while the soil nutrient supplies fundamentally support microbial composition and functioning,implying that nutrient limitation could crucially regulate the relationships among microbial metabolism,composition,and functions.However,the metabolic characteristics of soil microbial communities and how they affect community diversity,composition,and functions during vegetation succession remain unclear.Herein,we combined the field sampling and lab analysis to test the characteristics of soil microbial metabolism,the dynamic pattern of microbial community structure affected by nutrient limitation,niche differentiation,and soil microbial functional genes changing and the driving factors during forest succession(16yr,23 yr,59yr and natural oak forest)and long-term abandoned cropland(1yr,3yr,5yr,11 yr,65yr,100 yr and 150yr)succession sequences in Qinling Mountains.Eco-enzymatic stoichiometric models were used to quantify microbial metabolic limitation,and the microbial community composition and functional genes were analyzed by high-throughput sequencing and metagenomic.In addition,the soil microbial metabolic limitations were linked to changing community structure and function,aiming to further reveal the response mechanism of microbial communities under metabolic limitation in the above-belowground ecological processes in vegetation succession.The main conclusions are as follows:(1)Soil microbial communities were co-limited by carbon(C)and phosphorus(P)during oak forest succession,but these limitations gradually decreased.The contrast pattern of microbial C and P limitation in rhizosphere soil and bulk soil showed inconsistent,while soil microorganisms in rhizosphere soil were subject to relatively weak C and P limitation compared with those in bulk soil.Microbial C and P limitation in the bulk soils depended mainly on variations in the stoichiometric soil organic carbon(SOC)during oak forest restoration,and the dissolved organic carbon(DOC)were the most important factors driving those in the rhizosphere soils.(2)Microbes maintain stoichiometric homeostasis by nutrient-acquiring extracellular enzymes,whereas plants do not.Microbial communities were limited by C and P and showed a significant negative correlation between C and P limitation.In addition,litter(Litter.P and Litter.N)and soil nutrients(SOC: TP,TP and NO + NH)were the most critical factors in microbial metabolic limitation and microbial C use efficiency(CUE).The microbial CUE showed an increased trend at the late stage of succession further indicating that soil microbial metabolism enhances soil C sequestration during vegetation succession.(3)Microbial C and P limitations were the most important factors affecting bacterial and fungal communities in rhizosphere soil and bulk soil.Bacterial α diversity increased significantly with nutrient limitation during oak forest succession.Bacterial and fungal communities were dominated primarily by stochastic processes,fungal community has a stronger dispersal limitation than Bacterial community,and nutrient limitations also contributed to stochastic processes dominating both bacterial and fungal communities during forest succession.Additionally,microbial community stability increased gradually with oak forest succession,and nutrient limitations enhanced cooperation within communities,but weakened community stability,indicating nutrient limitations drive microbial communities to increase cooperation that in turn increases resource-utilization efficiency.(4)Microbial C and P limitations affected the differentiation process of bacterial and fungal niche breadth,which were inversely related to nutrient limitation.Compared with fungi,bacteria had a larger niche breadth during long-term abandoned cropland succession,and competition within them under common resource conditions.In addition,Soil microbial cooccurrence networks reveal bacterial and fungal into three main functional modules,and B＿Mod#1 and B＿Mod#2 have the most contribution to the bacterial niche breadth,F＿Mod#3contributed the most to the fungal niche breadth,and Acidobacteria in B＿Mod#1 and Basidiomycota in F＿Mod#3 dominated the bacterial and fungal niche breadth,respectively.stoichiometric ratio of soil nutrients(SOC: TP)was the most important factor in bacterial niche breadth,and fungal community composition has an important influence on fungal niche breadth.PLS-PM further showed that there were different pathways of each factor affecting the bacterial and fungal niche breadth.Soil nutrients affect bacterial community niche breadth by influencing community complexity,composition,and metabolic functions,and fungal community niche breadth was affected by soil nutrients affecting the community complexity and composition.In addition,microbial nutrient limitation has negative and positive effects on bacterial and fungal niche breadth,respectively.(5)The composition of genes involved in C and P cycling was significantly affected by microbial metabolism,especially functional genes involved in P cycling.Long-term abandoned cropland succession enhances the α diversity of soil functional genes and significantly affects the functional gene composition,and soil p H was the key environmental driver.The abundance of functional genes encoding C-acquiring enzymes(blg X and cbh A)increased and then gradually decreased with vegetation succession,while the abundance of functional genes encoding N-acquiring enzymes(chitinase and pep A)showed the opposite trend.The abundance of functional genes encoding P-acquiring enzyme(pho N)showed an increasing trend with vegetation succession.blg X and cbh A genes have a significant correlation with most soil nutrients and microbial biomass factors.Moreover,the abundances of the functional gene involved in labile(mal Z、cdh and bgl X)and recalcitrant C(xyl A and pectinase)degradation differed between early and later succession stages,and the lack of organic C in the early succession stage promoted the soil microbes with stronger C fixation ability.Regarding P cycling,microbes in the early succession stage showed a higher potential to mineralize organic P and solubilize inorganic P,whereas higher mineralized phosphate potential in the late succession stage.Collectively,soil microbial community metabolism was limited by C and P in both secondary succession sequences.Oak forest succession process alleviated the microbial C and P limitations,while abandoned cropland succession decreased microbial C limitation and enhanced P limitation.Microbial metabolism limitation increased the microbial community diversity and decreased community stability but promoted cooperation among taxa within communities,further affecting the niche differentiation of bacterial and fungal communities and potential functions of microorganisms involved in soil C and P cycle processes.Our findings provide a theoretical basis and data support for revealing the evolution mechanism of aboveground soil-microbes system during secondary succession.