Studies On The Characterization And Response Mechanism Of Soil Microbial Communities And Functions To Organic Amendments

In recent years,the excessive application of chemical fertilizers and other unreasonable managements have caused a clear decrease in soil quality of farmland,which is a major concern for the long-term agricultural productivity and stability.Although a large number of studies have shown that organic amendments can increase soil fertility and crop yield,the biological mechanism is still unclear.Soil fertility not only depends on soil physicochemical properties,but also is closely related to soil biological traits.Soil microorganisms play a crucial role in the mediation of multiple ecosystem functions,including driving nutrient biogeochemistry,supplying crop nutrient and enriching soil fertility.Exploring soil microbial community traits and functional potential under long-term fertilization management,therefore,can clarify the microbial mechanism mediating soil fertility.Here we performed a comprehensive meta-analysis where we quantitatively compared the effects of organic amendments versus mineral fertilization on soil properties and crop yields.Meanwhile,two long-term experimental fields were used for the sampling.We using modern molecular techniques,such as quantitative PCR and high-throughput sequencing,to explore the effects of long-term fertilization managements on soil microbial community traits,extracellular enzyme activities and the biological potential of soil nitrogen and phosphorus cycling.Additionally,to demonstrate whether organic amendments can buffer the negative impacts on the functional stability of farmland,soils were collected from an experimental field and then subjected to a microcosm experiment with or without straw addition.The main results were listed as below:1.Under the condition of equal N input,compared with the mineral-only fertilization,organic-only fertilization and combined application of chemical and organic fertilizers significantly increased crop yields by 20%and 31%,respectively.Of all included crop types,wheat showed the highest increments in the yield(27%-36%),followed by maize(19%-20%)and rice(14%-17%).The contents of soil organic C(SOC),total N(TN),microbial biomass C(MBC)and N(MBN)of organically-amended soils showed higher values than mineral-only fertilized soils,and the increments were 31%-33%,17%-19%,38%-44%and 36%-39%,respectively.Compared with mineral-only fertilization,the potential activities of C-,N-,P-cycling and oxidative decomposition(OX)related extracellular enzymes were significantly increased in organically-amended soils.2.The supply of pig manure or composted bean-cake significantly affected the abundance,diversity and community composition of soil fungi and bacteria.The supply of pig manure and composted bean-cake could notably enrich the Proteobacteria within the bacterial communities but decreased the relative abundance of Chloroflexi.The supply of pig manure notably increased the relative abundance of Ascomycota within the fungal communities,while composted bean-cake significantly increased that of Zygomycota.The potential activities of C-,N-,P-and S-cycle related extracellular enzymes enhanced strongly along a gradient of increasing microbial diversity.Soil pH,EC,fine sand,SOC and TN content increased strongly along the diversity gradient,and meanwhile these factors showed a significant relationship with enzyme activities.The supply of pig manure or composted bean-cake corresponded with the increase of ecosystem multifunctionality(EMF),and the EMF was tightly linked to microbial diversity(R2=0.63-0.67;p<0.001).Soil microbial diversity was selected by random forest analysis as the main driver of EMF,followed by C-cycle enzyme activities,pH and the composition of soil particle-size fractions(PSFs).3.Compared with mineral-only fertilization,the supply of pig manure or composted bean-cake notably increased the abundance of diazotrophs,ammonifiers,ammonia-oxidizers,denitrifiers and nitrate-reducers in soil PSFs and non-fractionated bulk soil samples.Soil pH was the major driver for the abundance of nifH,narG,nirK,nirS,norB and gdh genes.The major driver of archeal amoA and bacterial amoA genes was soil EC,and that of napA(30%)and nosZ(32%)was TN content.Fertilization regimes had a highest impact on N-cycling related populations(50%-76%),followed by the composition of soil PSFs(11%-42%).Fertilization regimes could directly affect the composition of soil PSFs,PSFs-associated physiochemical properties and N-cycle gene abundance,which ultimately mediated the N-cycle abundance in non-fractionated bulk soils.4.The supply of pig manure significantly increased the contents of available P,moderately labile organic P,aluminium-associated P and labile organic P over the controls(mineral-only fertilization and no fertilization).The supply of pig manure significantly increased soil potential acid(ACP)and alkaline phosphatase(ALP)activities,phoD gene abundance and phoC gene diversity in comparison with no fertilization.Compared with no fertilization,the supply of pig manure increased the relative abundance of Proteobacteria and Planctomycetes in phoD communities,as well as that of Proteobacteria and Actinobacteria in phoC communities.Compared with the controls,the phoD-harboring species were more closely connected with phoC-harboring species in the organically-amended soils.A greater number of hubs and positive correlations of co-occurrence network were observed in the organically-amended soils than in the controls.Soil C:P ratio,N:P ratio,MBC and MBN content were the main predictor of phoD-harboring populations.Soil C:P ratio and MBC content were identified as the main predictor of potential phosphatase activities.5.Compared with the controls(no straw addition),straw amendments could significantly increase the multifunctionality resistance by 10%-24%over the controls.Compared with the controls,straw additions could significantly increase the abundance and resistance of specific microbial-groups associated with the functions of cellulose and starch degradation,nitrification,N fixation,denitrification,was well as phosphate monoester and phytic-acid degradation.Microbial functional capacity displayed a positive linear relationship with the multifunctionality resistance.In straw amended soils,the abundances of genes related to cellulose(fungcbhIR gene)and xylan degradation(GH51)were selected as the major predictor of multifunctionality resistance by the random forest analysis.The abundances of specific microbial-groups were the most directly related to the multifunctionality resistance,and this result was primarily mediated by NH4+-N:NO3--N ratio,Fungi:Bacteria ratio,AP and dissolved organic C(DOC)content.In conclusion,organic amendments could improve soil biological activity and soil fertility under the premise of ensuring crop yields.Organic amendments could optimize soil aggregate structures and stoichiometric balances and affect soil microbial communities,as well as improve extracellular enzyme activities and soil fertility.Organic amendments could buffer the negative impacts of drying-wetting cycles on ecosystem functioning via enriching functional capacity of microbial communities.