Changes in soil microbial communities induced by warming and N deposition accelerate the CO 2 emissions of coarse woody debris

Warming and nitrogen(N)deposition are two important drivers of global climate changes.Coarse woody debris(CWD)contains a large proportion of the carbon(C)in the total global C pool.The composition of soil microbial communities and environmental changes(i.e.,N deposition and warming)are the key drivers of CWD decomposition,but the interactive impact between N deposition and warming on the composition of soil microbial communities and CWD decomposition is still unclear.In a laboratory experiment,we study and simulate respiration during decomposition of the CWD(C 98)of Cryptomeria japonica(CR)and Platycarya strobilacea(PL)in response to warming and N deposition over 98 days.Resuts show that either warming or N addition signifi cantly accelerated the C 98 of the two tree species by altering the soil microbial community(bacterial:fungi and G+:G–).The combined treatment(warming+N)resulted in a decomposition eff ect equal to the sum of the individual eff ects.In addition,the species composition of bacteria and fungi was obviously aff ected by warming.However,N deposition had a remarkable infl uence on G+:G–.Our results indicated that N deposition and warming will observably alter the composition and growth of the microbial community and thus work synergistically to accelerate CWD decomposition in forest ecosystems.We also present evidence that N deposition and warming infl uenced the composition and balance of soil microbial communities and biogeochemical cycling of forest ecosystems.

Functional diversity of soil microbial communities in response to supplementing 50% of the mineral N fertilizer with organic fertilizer in an oat field

The effects of supplementing 50%of the mineral N fertilizer with organic fertilizer on the metabolism and diversity of soil microbial communities in an oat field were investigated using Biolog-Eco plates.The experiment consisted of five treatments:no fertilizer(CK),mineral N fertilizer applied at 90 and 45 kg ha^(-1) N in the form of urea(U1 and U2,respectively),and U2 supplemented with organic fertilizer in the form of sheep manure at 90 and 45 kg ha^(-1) N(U2OM1 and U2OM2,respectively).Each treatment had three replications.The experiment was conducted in 2018 and 2019 in Pinglu District,Shanxi Province,China.The carbon source utilization by soil microbial communities,such as amino acids,amines,carbohydrates,carboxylic acids,and polymers,increased when 50%of the mineral N fertilizer was replaced with organic fertilizer in both years.This result was accompanied by increased richness,dominance,and evenness of the microbial communities.The utilization of amino acid,amine,and carboxylic acid carbon sources and community evenness were further improved when the organic fertilizer amount was doubled in both years.Biplot analysis indicated that amines and amino acids were the most representative of the total carbon source utilization by the soil microbial communities in both years.The highest oat yield was achieved at a total N application rate of 135 kg ha^(-1) in the treatment involving 45 kg ha^(-1) N in the form of urea and 90 kg ha^(-1) N in the form of sheep manure in both years.It was concluded that the application of 50%of the conventional rate of mineral N fertilizer supplemented with an appropriate rate of organic fertilizer enhanced both the functional diversity of soil microbial communities and oat yield.Amine and amino acid carbon sources may be used as a substitute for total carbon sources for assessing total carbon source utilization by soil microbial communities in oat fields in future studies.

Analysis of spatiotemporal variations in the characteristics of soil microbial communities in Castanopsis fargesii forests

Castanopsis fargesii is a good afforestation plants and various microorganisms play important roles in mediating the growth and ecological functions of this species.In this study,we evaluated changes in microbial communities in soil samples from C.fargesii forests.The phospholipid fatty acid(PLFA)biomarker method was used to obtain bacteria,fungi,actinomycetes,gram-positive bacteria(G?),gram-negative bacteria(G-),aerobic bacteria,and anaerobic bacteria to investigate spatiotemporal changes in microbial communities during the growing season.The results show that soil microorganisms were mainly concentrated in the upper 20-cm layer,demonstrating an obvious surface aggregation(P<0.05).Large amounts of litter and heavy rainfall during the early growing season resulted in the highest PLFA contents for various microorganisms,whereas relatively low and stable levels were observed during other times.The dominant species during each period were bacteria.G+ or aerobic bacteria were the main bacterial populations,providing insights into the overall trends of soil bacterial PLFA contents.Due to the relative accumulation of refractory substances during the later stages of litter decomposition,the effects of fungi increased significantly.Overall,our findings demonstrate that the main factors influencing microbial communities were litter,rainfall,and soil field capacity.

Afforestation increases microbial diversity in low-carbon soils

Afforestation has an important role in biodiversity conservation and ecosystem function improvement.A meta-analysis was carried out in China,which has the largest plantation area globally,to quantify the effects of plantings on soil microbial diversity.The results showed that the overall effect of afforestation on soil microbial diversity was positive across the country.Random forest algorithm suggested that soil carbon was the most important factor regulating microbial diversity and the positive response was only found with new plantings on low-carbon bare lands but not on high-carbon farmlands and grasslands.In addition,afforestation with broadleaved species increased microbial diversity,whereas planting with conifers had no effect on microbial diversity.This study clarified the effects of plantings on soil microbial diversity,which has an important implication for establishing appropriate policies and practices to improve the multiple functionalities(e.g.,biodiversity conservation and climate change mitigation)during plantation establishment.

Insights into the mechanisms underlying the biodegradation of phenanthrene in biochar-amended soil:from bioavailability to soil microbial communities

The dynamic effect of biochar amendment in contaminated soil on the bioavailability of polycyclic aromatic hydrocarbons(PAHs)and microbial communities and how it comprehensively affects PAH biodegradation remain unclear.This study investigated the effects of wheat straw-derived biochars obtained at 300 and 500℃ at different amendment levels(0.03%and 0.3%)on the mineralization kinetics of phenanthrene with different initial concentrations(2 and 20 mg kg^(−1))in soil by indigenous microorganisms.The results revealed that the addition of biochar inhibited both the rates and extents of mineralization in low-concentration phenanthrene-contaminated soil(PLS)by 38.9-78.3%and 23.9-53.6%,respectively.This was because biochar amendment in the PLS greatly reduced the bioavailable fraction of phenanthrene for degradation owing to its strong sorption and also decreased that to specific degrading bacterial genera,which hindered their growth and reduced their abundances by 1.37-36.6%.However,biochar addition into the soil contaminated with high concentrations of phenanthrene(PHS)resulted in its effective mineralization and enhanced mineralization rates and extents at high amendment levels by 32.4-86.7%and 32.0-44.7%,respectively.This was because biochar amendment in the PHS significantly promoted the abundances of the total bacterial communities(29.9-80.4%)and potential degrading genera(1.89-25.9%)by providing nutrients and stimulated the specific PAH-degradative nidA gene abundance by 1-2 times.These findings will guide the use of biochar to remediate soils with different PAH pollution levels based on the two roles that they play(i.e.,immobilizing PAHs or facilitating PAH degradation).

Effects of land-use patterns on soil microbial diversity and composition in the Loess Plateau,China

In the Loess Plateau of China,land-use pattern is a major factor in controlling underlying biological processes.Additionally,the process of land-use pattern was accompanied by abandoned lands,potentially impacting soil microbe.However,limited researches were conducted to study the impacts of land-use patterns on the diversity and community of soil microorganisms in this area.The study aimed to investigate soil microbial community diversity and composition using high-throughput deoxyribonucleic acid(DNA)sequencing under different land-use patterns(apricot tree land,apple tree land,peach tree land,corn land,and abandoned land).The results showed a substantial difference(P<0.050)in bacterial alpha-diversity and beta-diversity between abandoned land and other land-use patterns,with the exception of Shannon index.While fungal beta-diversity was not considerably impacted by land-use patterns,fungal alpha-diversity indices varied significantly.The relative abundance of Actinobacteriota(34.90%),Proteobacteria(20.65%),and Ascomycota(77.42%)varied in soils with different land-use patterns.Soil pH exerted a dominant impact on the soil bacterial communities'composition,whereas soil available phosphorus was the main factor shaping the soil fungal communities'composition.These findings suggest that variations in land-use pattern had resulted in changes to soil properties,subsequently impacting diversity and structure of microbial community in the Loess Plateau.Given the strong interdependence between soil and its microbiota,it is imperative to reclaim abandoned lands to maintain soil fertility and sustain its function,which will have significant ecological service implications,particularly with regards to soil conservation in ecologically vulnerable areas.

Effect of Elevated CO_2 and Drought on Soil Microbial Communities Associated with Andropogon gerardii

Our understanding of the effects of elevated atmospheric CO2, singly and in combination with other environmental changes, on plant-soil interactions is incomplete. Elevated CO2 effects on C4 plants, though smaller than on C3 species, are mediated mostly via decreased stomatal conductance and thus water loss. Therefore, we characterized the interactive effect of elevated CO2 and drought on soil microbial communities associated with a dominant C4 prairie grass, Andropogon gerardii Vitman. Elevated CO2 and drought both affected resources available to the soil microbial community. For example, elevated CO2 increased the soil C：N ratio and water content during drought, whereas drought alone decreased both. Drought significantly decreased soil microbial biomass. In contrast, elevated CO2 increased biomass while ameliorating biomass decreases that were induced under drought. Total and active direct bacterial counts and carbon substrate use （overall use and number of used sources） increased significantly under elevated CO2. Denaturing gradient gel electrophoresis analysis revealed that drought and elevated CO2, singly and combined, did not affect the soil bacteria community structure. We conclude that elevated CO2 alone increased bacterial abundance and microbial activity and carbon use, probably in response to increased root exudation. Elevated CO2 also limited drought-related impacts on microbial activity and biomass, which likely resulted from decreased plant water use under elevated CO2. These are among the first results showing that elevated CO2 and drought work in opposition to modulate plant-associated soil-bacteria responses, which should then influence soil resources and plant and ecosystem function.

The invasive potential of a hybrid species: insights from soil chemical properties and soil microbial communities

Aims Natural hybridization between invasive and native species,as a form of adaptive evolution,threatens biodiversity worldwide.However,the potential invasive mechanisms of hybrids remain essentially unexplored,especially insights from soil chemical properties and soil microbial communities.Methods In a field experiment,soil microbial community,potassium-solubilizing bacteria,phosphorus-solubilizing bacteria,enzyme activities,and light-saturated photosynthetic rate were measured in invasive Sphagneticola trilobata and its hybrid with native Sphagneticola calendulacea in 2 years.Important Findings In general,soil dissolved organic carbon and the biomass of phosphorus-solubilizing bacteria were significantly higher under the hybrid treatment than S.trilobata and S.calendulacea.However,there were no significant differences in acid phosphatase,total PLFAs,bacterial PLFAs,fungi PLFAs,cellulase,and urase in these treatments.The hybrids had significantly higher light-saturated photosynthetic rate,photosynthetic nitrogen-,phosphorus-,potassium-use efficiencies than the invasive S.trilobata,but no significant difference with S.calendulacea.The total biomass and root biomass of hybrids were higher than S.calendulacea.Our results indicate that the hybrids species have a higher invasive potential than S.calendulacea,which may aggravate the local extinction of S.calendulacea in the future.

Effects of Different Chinese Hickory Husk Returning Modes on Soil Nutrition and Microbial Community in Acid Forest Soil

Chinese hickory(Carya cathayensis Sarg.)is an important economic forest in Southeastern China.A large amount of hickory husk waste is generated every year but with a low proportion of returning.Meanwhile,intensive management has resulted in soil degradation of Chinese hickory plantations.This study aims to investigate the effects of three Chinese hickory husk returning modes on soil amendment,including soil acidity,soil nutrition,and microbial community.The field experiment carried out four treatments:control(CK),hickory husk mulching(HM),hickory husk biochar(BC),and hickory husk organic fertilizer(OF).The phospholipid fatty acid(PLFA)biomarker method was employed to determine the soil microbial community.After one year of treatment,the results showed that:(i)HM and BC significantly increased soil pH by 0.33 and 1.71 units,respectively;(ii)HM,BC and OF treatments significantly increased the soil organic carbon,alkaline nitrogen,available phosphorous,and available potassium.The OF treatment demonstrated the most significant improvement in the soil nutrient;(iii)The soil microbial biomass significantly increased in the HM,BC and OF treatments,and all microbial groups showed an increasing trend.HM treatment increased the fungal/bacterial ratio(F/B).The OF treatment significantly decreased the Shannon-Wiener diversity(H’)and evenness index(J)of the microbial community(P<0.05).Considering the treatments effects,costs,and ease of operation,our recommended returning modes of Chinese hickory husk are mulching and organic fertilizer produced by composting with manure.

Effects of Different Agricultural Managements on Characteristics of Soil Microbial Community under Continuous Cropped Strawberry(Fragaria ananassa Duchesne)

[Objective] The objective of this study was to investigate the effects of different agricultural managements on soil microbial population,activity,functional diversity and soil enzyme activity in continuous mono-cropping field of strawberry.[Method]A field plot experiment was carried out to evaluate characteristics of soil microbial community by soil enzyme analysis,microbial cultivation and Biolog analysis.[Result]The results showed that bacteria population proportion,the ration of bacteria to fungi,microorganism amount,AWCD,soil dehydrogenase activity,the Shannon,Simpson,and Mcintosh indices of soil microbial communities were obviously increased under strawberry-rice rotation,soil solarization with rice bran,and calcium cyanamide（CaCN2）treatments,in addition,soil urease activity was significantly increased under strawberry-rice rotation and soil solarization with rice bran treatment,when compared with no fertilization.When compared with conventional fertilization treatment,strawberry-rice rotation and soil solarization with rice bran both significantly increased AWCD and Mcintosh index of soil microbial communities,meanwhile respectively increased soil urease and dehydrogenase activity.PCA analyses suggested that carbon utilization of soil microbial communities under strawberry-rice rotation,soil solarization with rice bran,and calcium cyanamide treatment was obviously different from that of conventional fertilization and no fertilization treatment.[Conclusion] strawberry-rice rotation and soil solarization with rice bran were effective agricultural managements to control soil biological degradation under Continuous Cropped Strawberry.

Screening of Preprocessing Method of Biolog for Soil Microbial Community Functional Diversity

As one of the main methods of microbial community functional diversity measurement, biolog method was favored by many researchers for its simple oper- ation, high sensitivity, strong resolution and rich data. But the preprocessing meth- ods reported in the literatures were not the same. In order to screen the best pre- processing method, this paper took three typical treatments to explore the effect of different preprocessing methods on soil microbial community functional diversity. The results showed that, method B＇s overall trend of AWCD values was better than A and C＇s. Method B＇s microbial utilization of six carbon sources was higher, and the result was relatively stable. The Simpson index, Shannon richness index and Car- bon source utilization richness index of the two treatments were B〉C〉A, while the Mclntosh index and Shannon evenness were not very stable, but the difference of variance analysis was not significant, and the method B was always with a smallest variance. Method B＇s principal component analysis was better than A and C＇s. In a word, the method using 250 r/min shaking for 30 minutes and cultivating at 28 ℃ was the best one, because it was simple, convenient, and with good repeatability.

Responses of Soil Microbial Community Structure and Diversity to Agricultural Deintensification

Using a scheme of agricultural fields with progressively less intensive management (deintensification), different manage- ment practices in six agroecosystems located near Goldsboro, NC, USA were tested in a large-scale experiment, including two cash-grain cropping systems employing either tillage (CT) or no-tillage (NT), an organic farming system (OR), an integrated cropping system with animals (IN), a successional field (SU), and a plantation woodlot (WO). Microbial phos- pholipid fatty acid (PLFA) profiles and substrate utilization patterns (BIOLOG ECO plates) were measured to examine the effects of deintensification on the structure and diversity of soil microbial communities. Principle component analyses of PLFA and BIOLOG data showed that the microbial community structure diverged among the soils of the six systems. Lower microbial diversity was found in lowly managed ecosystem than that in intensive and moderately managed agro- ecosystems, and both fungal contribution to the total identified PLFAs and the ratio of microbial biomass C/N increased along with agricultural deintensification. Significantly higher ratios of C/N (P < 0.05) were found in the WO and SU systems, and for fungal/bacterial PLFAs in the WO system (P < 0.05). There were also significant decreases (P < 0.05) along with agricultural deintensification for contributions of total bacterial and gram positive (G+) bacterial PLFAs. Agricultural deintensification could facilitate the development of microbial communities that favor soil fungi over bacteria.

Soil Fertility,Microbial Biomass,and Microbial Functional Diversity Responses to Four Years Fertilization in an Apple Orchard in North China

Soil microbial communities play an essential role in maintaining soil fertility and are considered as ecological indicators to evaluate soil health.In the present study,we examined the influence of almost 4 years of fertilization[no fertilizer(CK),nitrogen alone(N),nitrogen,phosphorus and potassium chemical fertilizer(NPK),organicmanure(M),nitrogen plus organic manure(NM),and NPK plus organic manure(NPKM)]on soil fertility and the functional diversity of soil microbial communities in an apple orchard.Compared to CK,fertilization increased soil organic carbon,total nitrogen,and available nutrients,but reduced soil pH in N and NPK treatments.The highest microbial biomass carbon and nitrogen,most probable number of actinomycetes,bacteria,and fungi occurred in the NPKM treatment.The average well color development(AWCD)values followed the order of NPKM>M>NPK and NM>CK and N.The Shannon index in organic manure treatments were significantly higher than in control and in treatments without organic manure.The principal component analysis showed that manure treatment was significantly separated from other treatments.These results indicated that organic manure applied alone or in combination with chemical fertilizers would increase soil fertility and functional diversity of soil microbial communities.Moreover,applying balanced N,P,K fertilizer in combination with organic manure was found to be superior to the use of a single fertilizer in improving soil microbial community quality.

Changes in Transformation of Soil Organic C and Functional Diversity of Soil Microbial Community Under Different Land Uses

Changes in soil biological and biochemical properties under different land uses in the subtropical region of China were investigated in order to develop rational cultivation and fertilization management. A small watershed of subtropical region of China was selected for this study. Land uses covered paddy fields, vegetable farming, fruit trees, upland crops, bamboo stands, and forestry. Soil biological and biochemical properties included soil organic C and nutrient contents, mineralization of soil organic C, and soil microbial biomass and community functional diversity. Soil organic C and total N contents, microbial biomass C and N, and respiration intensity under different land uses were changed in the following order： paddy fields （and vegetable farming） 〉 bamboo stands 〉 fruit trccs （and upland）. The top surface （0-15 cm） paddy fields （and vegetable farming） were 76.4 and 80.8% higher in soil organic C and total N contents than fruit trees （and upland） soils, respectively. Subsurface paddy soils （15-30 cm） were 59.8 and 67.3% higher in organic C and total N than upland soils, respectively. Soil microbial C, N and respiration intensity in paddy soils （0-15 cm） were 6.36, 3.63 and 3.20 times those in fruit tree （and upland） soils respectively. Soil microbial metabolic quotient was in the order： fruit trees （and upland） 〉 forestry 〉 paddy fields. Metabolic quotient in paddy soils was only 47.7% of that in fruit tree （and upland） soils. Rates of soil organic C mineralization during incubation changed in the order： paddy fields 〉 bamboo stands 〉 fruit trees （and upland） and soil bacteria population： paddy fields 〉 fruit trees （and upland） 〉 forestry. No significant difference was found for fungi and actinomycetes populations. BIOLOG analysis indicated a changing order of paddy fields 〉 fruit trees （and upland） 〉 forestry in values of the average well cell development （AWCD） and functional diversity indexes of microbial community. Results also showed that the conversion from paddy fields to vegetable farming for 5 years resulted in a dramatic increase in soil available phosphorus content while insignificant changes in soil organic C and total N content due to a large inputs of phosphate fertilizers. This conversion caused 53, 41.5, and 41.3% decreases in soil microbial biomass C, N, and respiration intensity, respectively, while 23.6% increase in metabolic quotient and a decrease in soil organic C mineralization rate. Moreover, soil bacteria and actinomycetes populations were increased slightly, while fungi population increased dramatically. Functional diversity indexes of soil microbial community decreased significantly. It was concluded that land uses in the subtropical region of China strongly affected soil biological and biochemical properties. Soil organic C and nutrient contents, mineralization of organic C and functional diversity of microbial community in paddy fields were higher than those in upland and forestry. Overuse of chemical fertilizers in paddy fields with high fertility might degrade soil biological properties and biochemical function, resulting in deterioration of soil biological quality.

Soil microbial community composition and its driving factors in alpine grasslands along a mountain elevational gradient

Understanding the vertical distribution patterns of soil microbial community and its driving factors in alpine grasslands in the humid regions of the Tibet Plateau might be of great significance for predicting the soil microbial community of this type of vegetation in response to environmental change. Using phospholipid fatty acids （PLFA）, we investigated soil microbial community composition along an elevational gradient （3094-4131 m above sea level） on Mount Yajiageng, and we explored the impact of plant functional groups and soil chemistry on the soil microbial community. Except for Arbuscular Mycorrhizal fungi （AM fungi） biomarker 18：2ω6,9 increasing significantly, other biomarkers did not show a consistent trend with the elevational gradient. Microbial biomass quantified by total PLFAs did not show the elevational trend and had mean values ranging from 1.64 to 4.09 ktmol per g organic carbon （OC）, which had the maximum value at the highest site. Bacterial PLFAs exhibited a similar trend with total PLFAs, and its mean values ranged from 0.82 to 1.81 μmol （g OC）-1. The bacterial to fungal biomass ratios had the minimum value at the highest site, which might be related to temperature and soil total nitrogen （TN）. The ratios of Gram-negative to Gram-positive bacteria had a significantly negative correlation with soil TN and had the maximum value at the highest site. Leguminous plant coverage and soil TN explained 58% of the total variation in the soil microbial community and could achieve the same interpretation as the whole model. Other factors may influence the soil microbial community through interaction with leguminous plant coverage and soil TN. Soil chemistry and plant functional group composition in substantial amounts explained different parts of the variation within the soil microbial community, and the interaction between them had no impact on the soil microbial community maybe beeause long-term grazing greatly reduces litter. In sum, although there were obvious differences in soil microbial communities along the elevation gradient, there were no clear elevational trends found in general. Plant functional groups and soil chemistry respectively affect the different aspects of soil microbial community. Leguminous plant coverage and soil TN had important effects in shaping soil microbial community.

Microbial community structure and functional metabolic diversity are associated with organic carbon availability in an agricultural soil

Exploration of soil environmental characteristics governing soil microbial community structure and activity may improve our understanding of biogeochemical processes and soil quality. The impact of soil environmental characteristics especially organic carbon availability after 15-yr different organic and inorganic fertilizer inputs on soil bacterial community structure and functional metabolic diversity of soil microbial communities were evaluated in a 15-yr fertilizer experiment in Changping County, Beijing, China. The experiment was a wheat-maize rotation system which was established in 1991 including four different fertilizer treatments. These treatments included： a non-amended control（CK）, a commonly used application rate of inorganic fertilizer treatment（NPK）; a commonly used application rate of inorganic fertilizer with swine manure incorporated treatment（NPKM）, and a commonly used application rate of inorganic fertilizer with maize straw incorporated treatment（NPKS）. Denaturing gradient gel electrophoresis（DGGE） of the 16 S r RNA gene was used to determine the bacterial community structure and single carbon source utilization profiles were determined to characterize the microbial community functional metabolic diversity of different fertilizer treatments using Biolog Eco plates. The results indicated that long-term fertilized treatments significantly increased soil bacterial community structure compared to CK. The use of inorganic fertilizer with organic amendments incorporated for long term（NPKM, NPKS） significantly promoted soil bacterial structure than the application of inorganic fertilizer only（NPK）, and NPKM treatment was the most important driver for increases in the soil microbial community richness（S） and structural diversity（H）. Overall utilization of carbon sources by soil microbial communities（average well color development, AWCD） and microbial substrate utilization diversity and evenness indices（H＇ and E） indicated that long-term inorganic fertilizer with organic amendments incorporated（NPKM, NPKS） could significantly stimulate soil microbial metabolic activity and functional diversity relative to CK, while no differences of them were found between NPKS and NPK treatments. Principal component analysis（PCA） based on carbon source utilization profiles also showed significant separation of soil microbial community under long-term fertilization regimes and NPKM treatment was significantly separated from the other three treatments primarily according to the higher microbial utilization of carbohydrates, carboxylic acids, polymers, phenolic compounds, and amino acid, while higher utilization of amines/amides differed soil microbial community in NPKS treatment from those in the other three treatments. Redundancy analysis（RDA） indicated that soil organic carbon（SOC） availability, especially soil microbial biomass carbon（Cmic） and Cmic/SOC ratio are the key factors of soil environmental characteristics contributing to the increase of both soil microbial community structure and functional metabolic diversity in the long-term fertilization trial. Our results showed that long-term inorganic fertilizer and swine manure application could significantly improve soil bacterial community structure and soil microbial metabolic activity through the increases in SOC availability, which could provide insights into the sustainable management of China＇s soil resource.

Metagenomic insights into seasonal variations in the soil microbial community and function in a Larix gmelinii forest of Mohe,China

The eff ect of seasons on the soil microbiome in a Larix gmelinii forest of Mohe,China,where winter temperatures are generally below−40°C,was evaluated with metagenomics analysis.Taxonomic profi ling using sequencing information revealed that Proteobacteria,Actinobacteria,Acidobacteria and Verrucomicrobia were the dominant phyla in spring,summer,and fall,as were Bradyrhizobium,Chthoniobacter,Streptomyces,Acid Candidatus Koribacter at the genus level.Some species that were abundant in spring and fall greatly diminished in abundance in summer.Clusters of orthologous groups(COG)of proteins,carbohydrate-active enzymes(CAZy),Kyoto Encyclopedia of Genes and Genomes(KEGG)and NCBI databases were used to elucidate the function of diverse proteins and metabolites of the microbial community of L.gmelinii forest.COG analysis showed that fewer genes were detected in spring than in fall and summer,indicating that many soil microbes in the L.gmelinii forest were not tolerant to cold.Based on KEGG analysis,some pathways in the soil microbes were activated in spring and autumn and deactivated in summer.CAZy analysis revealed that most CAZy were more active in summer than in spring or autumn and were severely inhibited in the spring.Many functional pathways,proteins,and CAZy involved in the community changes were concerned with cold or heat resistance.Therefore,the soil in the L.gmelinii forest can be a valuable resource for further research on heat and cold tolerance of soil microbes.

Effects of coal-fired power plants on soil microbial diversity and community structures

Long-term deposition of atmospheric pollutants emitted from coal combustion and their effects on the eco-environment have been extensively studied around coal-fired power plants.However,the effects of coal-fired power plants on soil microbial communities have received little attention through atmospheric pollutant deposition and coal-stacking.Here,we collected the samples of power plant soils(PS),coal-stacking soils(CSS)and agricultural soils(AS)around three coal-fired power plants and background control soils(BG)in Huainan,a typical mineral resource-based city in East China,and investigated the microbial diversity and community structures through a high-throughput sequencing technique.Coal-stacking significantly increased(p<0.05)the contents of total carbon,total nitrogen,total sulfur and Mo in the soils,whereas the deposition of atmospheric pollutants enhanced the levels of V,Cu,Zn and Pb.Proteobacteria,Actinobacteria,Thaumarchaeota,Thermoplasmata,Ascomycota and Basidiomycota were the dominant taxa in all soils.The bacterial community showed significant differences(p<0.05)among PS,CSS,AS and BG,whereas archaeal and fungal communities showed significant differences(p<0.01)according to soil samples around three coal-fired power plants.The predominant environmental variables affecting soil bacterial,archaeal and fungal communities were Mo-TN-TS,Cu-V-Mo,and organic matter(OM)-Mo,respectively.Certain soil microbial genera were closely related to multiple key factors associated with stacking coal and heavy metal deposition from power plants.This study provided useful insight into better understanding of the relationships between soil microbial communities and long-term disturbances from coal-fired power plants.

Corn cob biochar increases soil culturable bacterial abundance without enhancing their capacities in utilizing carbon sources in Biolog Eco-plates

Biochar has been shown to influence soil microbial communities in terms of their abundance and diversity.However,the relationship among microbial abundance,structure and C metabolic traits is not well studied under biochar application.Here it was hypothesized that the addition of biochar with intrinsic properties（i.e.,porous structure）could affect the proliferation of culturable microbes and the genetic structure of soil bacterial communities.In the meantime,the presence of available organic carbon in biochar may influence the C utilization capacities of microbial community in Biolog Eco-plates.A pot experiment was conducted with differenct biochar application（BC）rates：control（0 t ha^-1）,BC1（20 t ha^-1）and BC2（40 t ha^-1）.Culturable microorganisms were enumerated via the plate counting method.Bacterial diversity was examined using denaturing gradient gel electrophoresis（DGGE）.Microbial capacity in using C sources was assessed using Biolog Eco-plates.The addition of biochar stimulated the growth of actinomyces and bacteria,especially the ammonifying bacteria and azotobacteria,but had no significant effect on fungi proliferation.The phylogenetic distribution of the operational taxonomic units could be divided into the following groups with the biochar addition：Firmicutes,Acidobacteria,Gemmatimonadetes,Actinobacteria,Cyanobacteria andα-,β-,γ-andδ-Proteobacteria（average similarity〉95%）.Biochar application had a higher capacity utilization for L-asparagine,Tween 80,D-mannitol,L-serine,γ-hydroxybutyric acid,N-acetyl-D-glucosamine,glycogen,itaconic acid,glycyl-L-glutamic acid,α-ketobutyricacid and putrescine,whereas it had received decreased capacities in using the other 20 carbon sources in Biolog Eco-plates.Redundancy analysis（RDA）revealed that the physico-chemical properties,indices of bacterial diversity,and C metabolic traits were positively correlated with the appearance of novel sequences under BC2 treatment.Our study indicates that the addition of biochar can increase culturable microbial abundance and shift bacterial genetic structure without enhancing their capacities in utilizing C sources in Biolog Eco-plates,which could be associated with the porous structure and nutrients from biochar.

Silicon impacts on soil microflora under Ralstonia Solanacearum inoculation

Silicon(Si) can increase plant resistance against bacterial wilt caused by Ralstonia solanacearum and enhance plant immune response. However, whether Si alleviates soil-borne disease stress through altering soil microbial community component and diversity is not clear. In this study, effects of Si application under R. solanacearum inoculation with or without plant on soil bacterial and fungal communities were investigated through high-throughput pyrosequencing technique. The results showed that Si addition significantly reduced bacterial wilt incidence. However, Si did not reduce the amount of R. solanacearum in rhizosphere soil. Principal components analysis showed that soil microbial community composition was strongly influenced by Si addition. Total 63.7% bacterial operational taxonomic units(OTUs) and 43.8% fungal OTUs were regulated by Si addition regardless of the presence of tomato plants, indicating the independent effects of Si on soil microbial community. Si-added soil harbored a lower abundance of Fusarium, Pseudomonas, and Faecalibacterium. Our finding further demonstrated that exogenous Si could significantly influence soil microbial community component, and this may provide additional insight into the mechanism of Si-enhanced plant resistance against soil-borne pathogens.