微生物活性指标: 重金属污染下的土壤质量敏感指标

Physicochemical properties, total and DTPA (diethylenetriaminepentaacetic acid)-extractable Cu, Zn, Pb and Cd contents, microbial biomass carbon (C) content and the organic C mineralization rate of the soils in a long-term trace metal-contaminated paddy region of Guangdong, China were determined to assess the sensitivity of microbial indices to moderately metal-contaminated paddy soils. The mean contents of total Cu, Zn, Pb and Cd were 251, 250, 171, and 2.4 mg kg^-1 respectively. DTPA-extractablc metals were correlated positively and significantly with total metals, CEC, and organic C (except for DTPA-extractable Cd), while they were negatively and highly significantly correlated with pH, total Fe and Mn. Metal stress resulted in relatively low ratios of microbial biomass C to organic C and in remarkable inhibition of the microbial metabolic quotient and C minera]ization rate, which eventually led to increases in soil organic C and C/N. Moreover, microbial respiratory activity showed a stronger correlation to DTPA-extractable metals than to total metal content. Likewise, in the acid paddy soils some "linked" microbial activity indices, such as metabolic quotient and ratios of basal respiration to organic C, especially during initial incubation, were found to be more sensitive indicators of soil trace metal contamination than microbial biomass C or basal respiration alone.     

黄土高原中国松人工林演替过程中的土壤微生物和酶活性

Successional and seasonal effects on soil microbial and enzymatic properties were studied in Chinese pine (Pinus tabu- laeformis) plantations in an age sequence of 3-, 7-, 13-, 21- and 28-year-old in northern Ziwuling region in the middle of Loess Plateau, China. The results indicated that plantation age and season affected soil microbial and enzymatic parameters significantly. Soil organic C, total N, microbial biomass C, microbial quotient, basal respiration, dehydrogenase, N-α-benzoyl-L-argininamide (BAA)-protease, urease and β-glucosidase increased quickly and tended to be highest at PF21 (21-year plantation), thereafter they remained nearly at a constant level, whereas the metabolic quotient (qCO 2 ) showed an initial increase and then decreased gradually. Measures of these soil properties showed significant seasonal fluctuations except for organic C and total N, which were found to be relatively stable throughout the study period, and the seasonal distributions were autumn spring summer winter for microbial biomass C, microbial quotient, dehydrogenase, and β-glucosidase; autumn summer spring winter for BAA-protease and urease; and summer autumn spring winter for basal respiration and qCO 2 . Significant season × age interaction was observed for biomass C, basal respiration, dehydrogenase and BAA-protease.     

不同肥力水平和利用历史的红壤磷脂脂肪酸图谱

Analysis of phospholipid fatty acids(PLFAs) was used to estimate the microbial community structures of eight Chinese red soils with different fertility levels and land use histories.The total amounts of PLFAs in the soils were significantly correltaed with soil organic carbon, total nitrogen,microbial biomass C and basal respiration,indicating that total PLFA was closely related to fertility and sustainbility in these highly weathered soils.Soils of the eroded wastelan were rich in Gram-positive species .When the eroded soils were planted with citrus trees,the soil microbial population had changed little in 4 years but took up to 8-12 yearss before it reached a significantly different population,Multivariate analysis of PLFAs demonstrated that land use history and plant cover type had a significant impact on microbial community structure.Howver,the difference of soil microbial community structure in the paddy field compared to other land uses was not larger than expected in this experiment.     

退化喀斯特植被恢复与土壤微生物特征的关系

The mechanism of vegetation restoration on degraded karst regions has been a research focus of soil science and ecology for the last decade.In an attempt to preferably interpret the soil microbiological characteristic variation associated with vegetation restoration and further to explore the role of soil microbiology in vegetation restoration mechanism of degraded karst regions,we measured microbial biomass C and basal respiration in soils during vegetation restoration in Zhenfeng County of southwestern Guizhou Province,China.The community level physiological profiles(CLPP) of the soil microbial community to were estimated determine if vegetation changes were accompanied by changes in functioning of soil microbial communities.The results showed that soil microbial biomass C and microbial quotient(microbial biomass C/organic C) tended to increase with vegetation restoration,being in the order arboreal community stage > shrubby community stage > herbaceous community stage > bare land stage.Similar trend was found in the change of basal respiration(BR).The metabolic quotient(the ratio of basal respiration to microbial biomass,qCO 2) decreased with vegetation restoration,and remained at a constantly low level in the arboreal community stage.Analyses of the CLPP data indicated that vegetation restoration tended to result in higher average well color development,substrate richness,and functional diversity.Average utilization of specific substrate guilds was highest in the arboreal community stage.Principle component analysis of the CLPP data further indicated that the arboreal community stage was distinctly different from the other three stages.In conclusion,vegetation restoration improved soil microbial biomass C,respiration,and utilization of carbon sources,and decreased qCO 2,thus creating better soil conditions,which in turn could promote the restoration of vegetation on degraded karst regions.     

长期重金属胁迫下的土壤微生物特征: 沈阳张士污灌区的案例研究

Soil samples were collected from Zhangshi Wastewater Irrigation Area in the suburb of Shenyang City, China, an area with a 30-year irrigation history with heavy metal-containing wastewater. The chemical properties and microbial characteristics of the soils were examined to evaluate the present situation of heavy metal pollution and to assess the soil microbial characteristics under long-term heavy metal stress. In light of the National Environmental Quality Standards of China, the soil in the test area was heavily polluted by Cd and to a lesser degree by Zn and Cu, even though wastewater irrigation ceased in 1993. Soil metabolic quotient （qCO2） had a significant positive correlation, while soil microbial quotient （qM） had a negative correlation with content of soil heavy metals. Soil microbial biomass carbon （MBC） had significantly negative correlation with Cd, but soil substrate~induced respiration （SIR）, dehydrogenase activity （DHA）, cellulase activity, and culturable microbial populations had no persistent correlations with soil heavy metal content. Soil nutrients, except for phosphorous, showed positive effects on soil microbial characteristics, which to a certain degree obscured the adverse effects of soil heavy metals. Soil Cd contributed more to the soil microbial characteristics, but qM and qCO2 were more sensitive and showed persistent responses to heavy metals stress. It could be concluded that qM and qCO2 can be used as bioindicators of heavy metal pollution in soils.     

城郊土壤不透水表面有土壤机碳转化及其相关性质的研究

Installation of impervious surface in urban area prevents the exchange of material and energy between soil and other environmental counterparts, thereby resulting in negative effects on soil function and urban environment. Soil samples were collected at 0-20 cm depth in Nanjing City, China, in which seven sites were selected for urban open soils, and fourteen sites with similar parent material were selected for the impervious-covered soils, to examine the effect of impervious surface on soil properties and microbial activities, and to determine the most important soil properties associated with soil organic carbon （SOC） transformation in the urban soils covered by impervious surfaces. Soil organic carbon and water-soluble organic carbon （WSOC） concentrations, potential carbon （C） and nitrogen （N） mineralization rates, basal respiration, and physicochemical properties with respect to C transformation were measured. Installation of impervious surface severely affected soil physicochemical properties and microbial activities, e.g., it significantly decreased total N contents, potential C mineralization and basal respiration rate （P 〈 0.01）, while increased pH, clay and Olsen-P concentrations. Soil organic carbon in the sealed soils at 0-20 cm was 2.35 kg m-2, which was significantly lower than the value of 4.52 kg m-2 in the open soils （P 〈 0.05）. Canonical correlation analysis showed WSOC played a major role in determining SOC transformation in the impervious-covered soil, and it was highly correlated with total N content and potential C mineralization rate. These findings demonstrate that installation of impervious surface in urban area, which will result in decreases of SOC and total N concentrations and soil microbial activities, has certain negative consequences for soil fertility and long-term storage of SOC.     

土法炼锌区大气沉降Pb、Zn、Cd及其对土壤质量的影响

Dust emissions from smelters, as a major contributor to heavy metal contamination in soils, could severely influence soil quality. Downwind surface soils within 1.5 km of a zinc smelter, which was active for 10 years but ceased in 2000, in Magu Town, Guizhou Province, China were selected to examine Pb, Zn, and Cd concentrations and their fractionation along a distance gradient from a zinc smelter, and to study the possible effects of Pb, Zn, and Cd accumulation on soil microorganisms by comparing with a reference soil located at a downwind distance of 10 km from the zinc smelter. Soils within 1.5 km of the zinc smelter accumulated high levels of heavy metals Zn (508 mg kg-1), Pb (95.6 mg kg-1), and Cd (5.98 mg kg-1) with low ratios of Zn/Cd (59.1--115) and Pb/Cd (12.4--23.4). Composite pollution indices (CPIs) of surface soils (2.52--15.2) were 3 to 13 times higher than the reference soils. In metal accumulated soils, exchangeable plus carbonate-bound fractions accounted for more than 10% of the total Zn, Pb, and Cd. The saturation degree of metals (SDM) in soils within 1.5 km of the smelter (averaging 1.25) was six times higher than that of the reference soils (0.209). A smaller soil microbial biomass was found more frequently in metal accumulated soils (85.1--438 μg C g-1) than in reference soils (497 μg C g-1), and a negative correlation (P < 0.01) of soil microbial biomass carbon to organic carbon ratio (Cmic/Corg) with SDM was observed. Microbial consumption of carbon sources was more rapid in contaminated soils than in reference soils, and a shift in the substrate utilization pattern was apparent and was negatively correlated with SDM (R = -0.773, P < 0.01). Consequently, dust deposited Pb, Zn, and Cd in soils from zinc smelting were readily mobilized, and weredetrimental to soil quality mainly in respect of microbial biomass.     

不同土地利用方式下上壤微生物群落水平生理图谱(CLP)与土壤碳、氮有效性之间的相互关系（英文）

The goal of this work was to assess soil microbial respiration,determined by the assay of community-level physiological profiling in an oxygen-sensitive microplate(O2-CLPP),in response to endogenous C and several individual C substrates in the soils with different organic C contents(as a function of soil type and management practice).We also used the O2-CLPP to determine the respiratory response of these soils to endogenous C and amended C substrates with N addition.A respiratory quotient(RQ) was calculated based on the ratio of the response to endogenous soil C vs.each C-only substrate,and was related to total organic carbon(TOC).For assessing N availability for microbial activity,the effect of N supplementation on soil respiration,expressed as N_(ratio),was calculated based on the response of several substrates to N addition relative to the response without N.Soils clustered in 4 groups after a principal component analysis(PCA),based on TOC and their respiratory responses to substrates and endogenous C.These groups reflected differences among soils in their geographic origin,land use and C content.Calculated RQ values were significantly lower in natural forest soils than in managed soils for most C-only substrates.TOC was negatively correlated with RQ(r = —0.65),indicating that the soils with higher organic matter content increased respiratory efficiency.The N addition in the assay in the absence of C amendment(i.e.,only endogenous soil C present) had no effect on microbial respiration in any soil,indicating that these soils were not intrinsically N-limited,but substrate-dependent variation in N_(ratio) within soil groups was observed.     

中国亚热带稻田土壤碳氮含量及矿化动态

Dynamics of soil organic matter in a cultivation chronosequence of paddy fields were studied in subtropical China. Mineralization of soil organic matter was determined by measuring CO2 evolution from soil during 20 days of laboratory incubation. In the first 30 years of cultivation, soil organic C and N contents increased rapidly. After 30 years, 0-10 cm soil contained 19.6 g kg^-1 organic C and 1.62 g kg^-1 total N, with the corresponding values of 18.1 g kg^-1 and 1.50 g kg^-1 for 10-20 cm, and then remained stable even after 80 years of rice cultivation. During 20 days incubation the mineralization rates of organic C and N in surface soil （0-10 cm） ranged from 2.2% to 3.3% and from 2.8% to 6.7%, respectively, of organic C and total N contents. Biologically active C size generally increased with increasing soil organic C and N contents. Soil dissolved organic C decreased after cultivation of wasteland to 10 years paddy field and then increased. Soil microbial biomass C increased with number of years under cultivation, while soil microbial biomass N increased during the first 30 years of cultivation and then stabilized. After 30 years of cultivation surface soil （0-10 cm） contained 332.8 mg kg^-1 of microbial biomass C and 23.85 mg kg^-1 of microbial biomass N, which were 111% and 47% higher than those in soil cultivated for 3 years. It was suggested that surface soil with 30 years of rice cultivation in subtropical China would have attained a steady state of organic C content, being about 19 g kg^-1.     

沙漠系统中豆类作物根际附近区域土壤微生物群落研究

The aim of the current study was to gain a better understanding of the changes in soil microbial biomass and basal respiration dynamics in the vicinity of the bean caper （Zygophyllura duraosura） perennial desert shrub and the inter-shrub sites. Microbial biomasses as well as basal respiration were found to be significantly greater in the soil samples taken beneath the Z. duraosura shrubs than from the inter-shrub sampling sites, with no differences between the two sampling layers （0-10 and 10-20 cm） throughout the study period. However, seasonal changes were observed due to autumn dew formation, which significantly affected microbial biomass and basal respiration in the upper-layer inter-shrub locations. The calculated metabolic coefficient （qCO2） revealed significant differences between the two sampling sites as well as between the two soil layers, elucidating the abiotic effect between the sites throughout the study period. The substrate availability index was found to significantly demonstrate the differences between the two sites, elucidating the significant contribution of Z. duraosura in food source availability and in moderating harsh abiotic components. The importance of basal microbial parameters and the derived indices as tools demonstrated the importance and need for basic knowledge in understanding plant-soil interactions determined by an unpredictable and harsh desert environment.     

Size of Microbial Biomass in Soils of China

The microbial biomass C,N and P of soils all over China were determined in this study to study their affecting factors.The results,about 100-417 mg C kg^-1 soil,18-51 mg Nkg^-1 soil and 4.4-27.3mg P kg^-1 soil,showed the biomass C,N and P in linear relationship with the soil total organic C,toal N and soil organic P.The ratios of C:Nand C:P,ranging from 5.6 to 9.6 and from 11.2 to 48.4 respectively,were affected by soil pH.texture,crop rotation,macroclimate etc.The ratio of C:N in soil biomass increases gradually from the north to the south in China.     

利用Illumina高通量测序对复合重金属污染下根际和非根际稻田土壤细菌的研究

There is an increasing concern about rice (Oryza sativa L.) soil microbiomes under the influence of mixed heavy metal contamination.We used the high-throughput Illumina MiSeq sequencing approach to explore the bacterial diversity and community composition of soils in four paddy fields,exhibiting four degrees of mixed heavy metal (Cd,Pb and Zn) pollution,and examined the effects of these metals on the bacterial communities.Our results showed that up to 2 104 to 4 359 bacterial operational taxonomic units (OTUs) were found in the bulk and rhizosphere soils of the paddy fields,with the dominant bacterial phyla (greater than 1％ of the overall community) including Proteobacteria,Actinobacteria,Firmicutes,Acidobacteria,Gemmatimonadetes,Chloroflexi,Bacteroidetes and Nitrospirae.A number of rare and candidate bacterial groups were also detected,and Saprospirales,HOC36,SC-I-84 and Anaerospora were rarely detected in rice paddy soils.Venn diagram analysis showed that 174 bacterial OTUs were shared among the bulk soils with four pollution degrees.Rice rhizosphere soils displayed higher bacterial diversity indices (ACE and Chao 1) and more unique OTUs than bulk soils.Total Cd and Zn in the soils were significantly negatively correlated with ACE and Chao 1,respectively,and the Mantel test suggested that total Pb,total Zn,pH,total nitrogen and total phosphorus significantly affected the community structure.Overall,these results provided baseline data for the bacterial communities in bulk and rhizosphere soils of paddy fields contaminated with mixed heavy metals.     

Clay Addition to Sandy Soil——Influence of Clay Type and Size on Nutrient Availability in Sandy Soils Amended with Residues Differing in C/N ratio

Addition of clay-rich subsoil to sandy soil results in heterogeneous soil with clay peds(2-mm) or finely ground( 2 mm) clay soil(FG), which may affect the nutrient availability. The aim of this study was to assess the effect of clay soil particle size(FG or peds)and properties on nutrient availability and organic C binding in sandy soil after addition of residues with low(young kikuyu grass,KG) or high(faba bean, FB) C/N ratio. Two clay soils with high and low smectite percentage, clay and exchangeable Fe and Al were added to a sandy soil at a rate of 20%(weight/weight) either as FG or peds. Over 45 d, available N and P as well as microbial biomass N and P concentrations and cumulative respiration were greater in soils with residues of KG than FB. For soils with KG residues,clay addition increased available N and initial microbial biomass C and N concentrations, but decreased cumulative respiration and P availability compared to sandy soil without clay. Differences in measured parameters between clay type and size were inconsistent and varied with time except the increase in total organic C in the 53 μm fraction during the experiment, which was greater for soils with FG than with peds. We concluded that the high exchangeable Fe and Al concentrations in the low-smectite clay soil can compensate a lower clay concentration and proportion of smectite with respect to binding of organic matter and nutrients.     

清水灌溉在消除土壤多环芳烃中的作用及对土壤微生物特征的影响: 以沈抚灌区为例

To evaluate the effect of groundwater irrigation on the polycyclic aromatic hydrocarbons(PAHs) pollution abatement and soil microbial characteristics,a case study was performed in the Shenfu irrigation area of Shenyang,Northeast China,where the irrigation with petroleum wastewater had lasted for more than fifty years,and then groundwater irrigation instead of wastewater irrigation was applied due to the gradually serious PAHs pollution in soil.Soil chemical properties,including PAHs and nutrients contents,and soil microbial characteristics,including microbial biomass carbon,substrateinduced respiration,microbial quotient(qM),metabolic quotient(qCO2),dehydrogenase(DH),polyphenol oxidase(PO),urease(UR) and cellulase(CE) in surface and subsurface were determined.Total organic C,total N,total P,and available K were significantly different between the sites studied.The PAHs concentrations ranged from 610.9 to 6362.8 μg kg-1 in the surface layers(0-20 cm) and from 404.6 to 4318.5 μg kg-1 in the subsurface layers(20-40 cm).From the principal component analysis,the first principal component was primarily weighed by total PAHs,total organic C,total N,total P and available K,and it was the main factor that influencing the soil microbial characteristics.Among the tested microbial characteristics,DH,PO,UR,CE,qM and qCO2 were more sensitive to the PAHs stress than the others,thus they could serve as useful ecological assessment indicators for soil PAHs pollution.     

黄土高原半干旱地区撂荒地次生植被演替过程中土壤微生物活性研究

To show the vegetation succession interaction with soil properties, microbial biomass, basal respiration, and enzyme activities in different soil layers (0--60 cm) were determined in six lands, i.e., 2-, 7-, 11-, 20-, 43-year-old abandoned lands and one native grassland, in a semiarid hilly area of the Loess Plateau. The results indicated that the successional time and soil depths affected soil microbiological parameters significantly. In 20-cm soil layer, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), MBC/MBN, MBC to soil organic carbon ratio (MBC/SOC), and soil basal respiration tended to increase with successional stages but decrease with soil depths. In contrast, metabolic quotient (qCO2) tended to decrease with successional stages but increase with soil depths. In addition, the activities of urease, catalase, neutral phosphatase, β-fructofuranosidase, and carboxymethyl cellulose (CMC) enzyme increased with successional stages and soil depths. They were significantly positively correlated with microbial biomass and SOC (P < 0.05), whereas no obvious trend was observed for the polyphenoloxidase activity. The results indicated that natural vegetation succession could improve soil quality and promote ecosystem restoration, but it needed a long time under local climate conditions.     

黄土高原某些耕作土壤中土壤微生物生物量C、N与矿化N的关系

The chloroform fumigation-incubation method was used to measure the soil microbial biomass C (SMBC) and N (SMBN) in 16 loessial soils sampled from Ansai, Yongshou and Yangling in Shaanxi Province. The SMBC contents in the soils ranged from 75.9 to 301.0 μg C g^-1 with an average of 206.1 μg C g^-1, accounting for 1.36%~6.24% of the total soil organic C with an average of 3.07%, and the SMBN contents from 0.51 to 68.40 μg N g^-1 with an average of 29.4 μg N g^-1, accounting for 0.20%~5.65% of the total N in the soils with an average of 3.36%. A close relationship was found between SMBC and SMBN, and they both were positively correlated with total organic C, total N, NaOH hydrolizable N and mineralizable N. These results confirmed that soil microbial biomass had a comparative role in nutrient cycles of soils.     

广东大宝山矿区土壤重金属污染

Soil contamination in the vicinity of the Dabaoshan Mine, Guangdong Province, China, was studied through determi- nation of total concentrations and chemical speciation of the toxic metals, Cu, Zn, Cd, and Pb, using inductively coupled plasma mass spectrometry. The results showed that over the past decades, the environmental pollution was caused by a combination of Cu, Zn, Cd, and Pb, with tailings and acid mine drainage being the main pollution sources affecting soils. Significantly higher levels （P ≤ 0.05） of Cu, Zn, Cd, and Pb were found in the tailings as compared with paddy, garden, and control soils, with averages of 1486, 2516, 6.42, and 429 mg kg^-1, respectively. These metals were continuously dispersed downstream from the tallings and waste waters, and therefore their concentrations in the paddy soils were as high as 567, 1 140, 2.48, and 191 mg kg^-1, respectively, being significantly higher （P ≤ 0.05） as compared with those in the garden soils. The results of sequential extraction of the above metals from all the soil types showed that the residual fraction was the dominant form. However, the amounts of metals that were bound to Fe-Mn oxides and organic matter were relatively higher than those bound to carbonates or those that existed in exchangeable forms. As metals could be transformed from an inert state to an active state, the potential environmental risk due to these metals would increase with time.     

Investigating drivers of microbial activity and respiration in a forested bog

Northern peatlands store nearly one-third of terrestrial carbon(C)stocks while covering only 3%of the global landmass;nevertheless,the drivers of C cycling in these often-waterlogged ecosystems are different from those that control C dynamics in upland forested soils.To explore how multiple abiotic and biotic characteristics of bogs interact to shape microbial activity in a northern,forested bog,we added a labile C tracer(13C-labeled starch)to in situ peat mesocosms and correlated heterotrophic respiration with natural variation in several microbial predictor variables,such as enzyme activity and microbial biomass,as well as with a suite of abiotic variables and proximity to vascular plants aboveground.We found that peat moisture content was positively correlated with respiration and microbial activity,even when moisture levels exceeded total saturation,suggesting that access to organic matter substrates in drier environments may be limiting for microbial activity.Proximity to black spruce trees decreased total and labile heterotrophic respiration.This negative relationship may reflect the influence of tree evapotranspiration and peat shading effects;i.e.,microbial activity may decline as peat dries and cools near trees.Here,we isolated the response of heterotrophic respiration to explore the variation in,and interactions among,multiple abiotic and biotic drivers that influence microbial activity.This approach allowed us to reveal the relative influence of individual drivers on C respiration in these globally important C sinks.     

Effects of Epigeic Earthworms on Decomposition of Wheat Straw and Nutrient Cycling in Agricultural Soils in a Reclaimed Salinity Area:A Microcosm Study

Earthworms,one of the most important macroinvertebrates in terrestrial ecosystems of temperate zones,exert important influences on soil functions.A laboratory microcosm study was conducted to evaluate the influence of the earthworm Eisenia fetida on wheat straw decomposition and nutrient cycling in an agricultural soil in a reclaimed salinity area of the North China Plain.Each microcosm was simulated by thoroughly mixing wheat straw into the soil and incubated for 120 d with earthworms added at 3 different densities as treatments:control with no earthworms,regular density(RD)with two earthworms,and increased density(ID)with six earthworms.The results showed that there was no depletion of carbon and nitrogen pools in the presence of the earthworms.Basal soil respiration rates and metabolic quotient increased with the increase in earthworm density during the initial and middle part of the incubation period.In contrast,concentrations of microbial biomass carbon and microbial biomass quotient decreased in the presence of earthworms.Earthworm activity stimulated the transfer of microbial biomass carbon to dissolved organic carbon and could lead to a smaller,but more metabolically active microbial biomass.Concentrations of inorganic nitrogen and NO₃^--N increased significantly with the increase in earthworm density at the end of the incubation(P<0.05),resulting in a large pool of inorganic nitrogen available for plant uptake.Cumulative net nitrogen mineralization rates were three times higher in the ID treatment than the RD treatment.     

中国北方温带草原土壤微生物对气温变暖与添加氮素的响应特征

The responses of soil microbes to global warming and nitrogen enrichment can profoundly affect terrestrial ecosystem functions and the ecosystem feedbacks to climate change. However, the interactive effect of warming and nitrogen enrichment on soil microbial community is unclear. In this study, individual and interactive effects of experimental warming and nitrogen addition on the soil microbial community were investigated in a long-term field experiment in a temperate steppe of northern China. The field experiment started in 2006 and soils were sampled in 2010 and analyzed for phospholipid fatty acids to characterize the soil microbial communities. Some soil chemical properties were also determined. Five-year experimental warming significantly increased soil total microbial biomass and the proportion of Gram-negative bacteria in the soils. Long-term nitrogen addition decreased soil microbial biomass at the 0-10 cm soil depth and the relative abundance of arbuscular mycorrhizal fungi in the soils. Little interactive effect on soil microbes was detected when experimental warming and nitrogen addition were combined. Soil microbial biomass positively correlated with soil total C and N, but basically did not relate to the soil C/N ratio and pH. Our results suggest that future global warming or nitrogen enrichment may significantly change the soil microbial communities in the temperate steppes in northern China.