Hydrolase activity, microbial biomass and community structure in long-term Cd-contaminated soils

Long-term effects of high Cd concentrations on enzyme activities, microbial biomass and respiration and bacterial community structure of soils were assessed in sandy soils where Cd was added between 1988 and 1990 as Cd(NO₃)₂ to reach concentrations ranging from 0 to 0.36 mmol Cd kg⁻¹ dry weight soil. Soils were mantained under maize and grass cultivation, or ‘set-aside’ regimes, for 1 year. Solubility of Cd and its bioavailability were measured by chemical extractions or by the BIOMET bacterial biosensor system. Cadmium solubility was very low, and Cd bioavailability was barely detectable even in soils polluted with 0.36 mmol Cd kg⁻¹. Soil microbial biomass carbon (B_C) was slightly decreased and respiration was increased significantly even at the lower Cd concentration and as a consequence the metabolic quotient (qCO₂) was increased, indicating a stressful condition for soil microflora. However, Cd-contaminated soils also had a lower total organic C (TOC) content and thus the microbial biomass C-to-TOC ratio was unaffected by Cd. Alkaline phosphomonoesterase, arylsulphatase and protease activities were significantly reduced in all Cd-contaminated soils whereas acid phosphomonoesterase, β-glucosidase and urease activites were unaffected by Cd. Neither changes in physiological groups of bacteria, nor of Cd resistant bacteria could be detected in numbers of the culturable bacterial community. Denaturing gradient gel electrophoresis analysis of the bacterial community showed slight changes in maize cropped soils containing 0.18 and 0.36 mmol Cd kg⁻¹ soil as compared to the control. It was concluded that high Cd concentrations induced mainly physiological adaptations rather than selection for metal-resistant culturable soil microflora, regardless of Cd concentration, and that some biochemical parameters were more sensitive to stress than others.     

Microbial biomass and activity in alkalized magnesic soils under arid conditions

The effects of salinity and Mg²⁺ alkalinity on the size and activity of the soil microbial communities were investigated. The study was conducted along the border area of the alluvial fan of the Taolai River. Thirty soil samples were taken which had an electrical conductivity (EC) gradient of 0.93-29.60 mS cm⁻¹. Soil pH ranged from 8.60 to 9.33 and correlated positively with Mg²⁺/Ca²⁺ ratio, exchangeable Mg²⁺ percentage and HCO₃⁻+CO₃²⁻. Mg²⁺/Ca²⁺ varied considerably from 3.04 to 61.31, with an average of 23.03. Exchangeable Mg²⁺ percentage generally exceeded 60% and had a positive correlation with Mg²⁺/Ca²⁺. HCO₃⁻+CO₃²⁻ averaged 1.63 cmol kg⁻¹ and usually did not exceed 2.0 cmol kg⁻¹.Microbial biomass, indices of microbial activity and the activities of the hydrolases negatively correlated with Mg²⁺/Ca²⁺ or exchangeable Mg²⁺ percentage. Biomass C, biomass N, microbial quotient (the percentage of soil organic C present as biomass C), biomass N as a percentage of total N, potentially mineralizable N, FDA hydrolysis rate and arginine ammonification rate decreased exponentially with increasing EC. The biomass C/N tended to be lower in soils with higher salinity and Mg²⁺ alkalinity, probably reflecting the bacterial dominance in microbial biomass in alkalized magnesic soils. The metabolic quotient (qCO₂) positively correlated with salinity and Mg²⁺ alkalinity, and showed a quadratic relationship with EC, indicating that increasing salinity and Mg²⁺ alkalinity resulted in a progressively smaller, more stressed microbial communities which was less metabolically efficient. Consequently, our data suggest that salinity and Mg²⁺ alkalinity are stressful environments for soil microorganisms.     

PLFA方法研究连作对加工番茄根际土壤微生物群落结构的影响

通过在石河子大学农学院试验站开展加工番茄连作定点微区试验,采用氯仿熏蒸和磷脂脂肪酸(PLFA)法相结合,研究了不同连作处理(种植1 a、连作3 a、5 a和7 a)对新疆加工番茄花果期和成熟期根际土壤微生物群落结构及土壤微生物量的影响。结果表明,连作导致土壤微生物量碳(SMBC)、微生物量氮(SMBN)和微生物熵(q MB)下降,SMBC/SMBN升高,而微生物量磷(SMBP)随连作年限和生育期的变化而不同。连作显著增加了真菌PLFAs含量,降低了细菌PLFAs含量、土壤PLFAs总量及细菌/真菌PLFAs的比值,而放线菌PLFAs含量变化无规律。连作7 a时,成熟期的细菌PLFAs含量、土壤PLFAs总量较对照分别减少62.9%、50.3%(P0.05),而真菌PLFAs含量较对照升高60.2%(P0.05)。从多样性指数分析看,Shannon-Wiener指数、Simpson指数、Brillouin指数和Pielou指数均随连作年限的延长呈先升后降的变化,其中连作3 a时各项指数最大,连作7 a时最小,表明在本试验年限范围内,连作使得微生物群落多样性与均匀程度皆出现了一定程度的降低。相关性分析表明,土壤微生物各类群PLFAs量、微生物量及土壤肥力之间存在相关性,说明土壤微生物量与土壤肥沃程度相关,可作为评价土壤肥力的生物学指标。可见,加工番茄连作改变了土壤微生物群落结构,降低了土壤微生物量,最终在根际土壤微生态系统和环境因子等因素的综合作用下产生连作障碍。     

长期平衡施肥对潮土微生物活性和玉米养分吸收的影响

利用中国科学院封丘农业生态实验站农田生态系统养分平衡长期定位试验地,研究氮磷钾平衡施肥(NPK)与缺素施肥(NK、PK、NP)对土壤微生物生物量、酶活性、呼吸强度以及玉米养分吸收的影响。结果发现,与不施肥对照(CK)相比,NPK处理玉米根系与茎叶生物量、籽粒产量以及植株氮磷钾吸收量均大幅提高,NP处理次之,PK与NK处理则无显著影响;同一处理玉米茎叶与根系养分含量接近,而籽粒的全氮和全磷含量较高、全钾含量偏低;与NPK处理相比,缺施氮、磷或钾肥均直接导致玉米植株相应养分的明显亏缺或其他养分的过量富集,但在根系、茎叶和籽粒部位的累积情况存在一定差异。与CK相比,所有施加磷肥的处理(NPK、NP、PK)土壤微生物生物量(碳、氮、磷)、脱氢酶、转化酶、脲酶与碱性磷酸酶活性以及土壤微生物代谢活性和土壤基础呼吸强度均显著升高(p<0.05),土壤微生物代谢熵则显著下降(p<0.05),而缺施磷肥的NK处理除显著提高脲酶活性外(p<0.05),对其他指标均无显著影响。结果表明,氮磷钾平衡施肥在促进土壤微生物繁育和保育微生物代谢活性以及促进作物生长和保证养分吸收等方面显得非常重要,而缺素施肥中以缺施磷肥的不利影响最为突出。     

Microbial biomass,activity, and organic matter accumulation in soils contaminated with heavy metals

Chemical characteristics and some parameters related to biological components were determined in 16 soils from a fairly homogeneous area in the north of Italy, contaminated with different levels of heavy metals. Correlation analysis of the parameters studied showed close positive relationships among the metals and with the organic C content in the soils studied. Negative relationships were observed among the heavy metals, soil respiration, and the ratio between evolved CO₂–C and microbial biomass C per unit time (specific respiratory activity). This was ascribed to an adverse heavy metal effect on the soil microflora, which appeared to increase the accumulation of organic matter as the heavy metal content increased, probably because the biomass was less effective in mineralising soil organic matter under these conditions.     

Microbial activity and hydrolase activities during decomposition of root exudates released by an artificial root surface in Cd-contaminated soils

The aim of this study was to assess the stimulatory effects of different low molecular weight organic compounds commonly present in root exudates on microbial activity and hydrolase activities, and the effects of high Cd concentrations in sandy soils collected from contaminated field plots on the stimulatory effects. Glucose, glutamic acid, citric acid, oxalic acid, or a mixture of all compounds were released by an artificial root surface in a simplified rhizosphere system. The effects were measured at <2 mm (rhizosphere soil layer) and >4 mm (bulk soil layer) distance from the root surface, 7 d after the root exudates release. Results showed that different root exudates were mineralized at different extent and had different stimulatory effects on microbial growth estimated by dsDNA content of soil, and on hydrolase activities, mostly localized in the rhizosphere soil layer. Mineralization of root exudates, microbial growth and stimulation of most of the measured hydrolase activities were drastically reduced by high Cd concentrations in soil.     

免耕和秸秆还田对潮土酶活性及微生物量碳氮的影响

利用中国科学院封丘农业生态实验站玉米-小麦轮作保护性耕作定位试验平台,研究了全翻耕（(T)、免耕（(NT)、全翻耕+秸秆还田（(TS)以及免耕+秸秆还田（(NTS)处理分别对田间0 ~ 10、10 ~ 20和20 ~ 30 cm土层酶活性及土壤微生物量碳、氮的影响。结果表明：①在0 ~ 10和10 ~ 20 cm土层内,土壤碱性磷酸酶、转化酶、脲酶、脱氢酶活性为免耕处理大于全翻耕处理,有秸秆还田处理大于无秸秆还田处理,以NTS处理最高,T处理最低;在20 ~ 30 cm土层中,土壤碱性磷酸酶、转化酶、脱氢酶活性免耕处理大于全翻耕处理,土壤碱性磷酸酶、转化酶、脲酶活性有秸秆还田处理大于无秸秆还田处理。②在0 ~10和10 ~ 20 cm土层内,土壤微生物量碳、氮均为免耕处理大于全翻耕处理,有秸秆还田处理大于无秸秆还田处理;在20 ~ 30 cm土层中,微生物量碳以NTS处理最高,微生物量氮以TS处理最高;③4种处理下的土壤酶活性和微生物量碳、氮均随着土层的加深而减少,且在各土层中差异达显著水平。     

Effects of liming and tillage systems on microbial biomass and glycosidases in soils

This study was undertaken to investigate the long-term influence of lime application and tillage systems (no-till, ridge-till and chisel plow) on soil microbial biomass C (C_mic) and N (N_mic) and the activities of glycosidases (- and -glucosidases, - and -galactosidases and -glucosaminidase) at their optimal pH values in soils at four agroecosystem sites [Southeast Research Center (SERC), Southwest Research Center (SWRC), Northwest Research Center (NWRC), and Northeast Research Center (NERC)] in Iowa, USA. Results showed that, in general, the C_mic and N_mic values were significantly (P <0.001) and positively correlated with soil pH. Each lime application and tillage system significantly (P <0.001) affected activities of the glycosidases. With the exception of -glucosidase activity, there was no lime×tillage interaction effect. Simple correlation coefficients between the enzyme activities and soil pH values ranged from 0.51 (P <0.05) for the activity of -glucosidase at the NWRC site (surface of the no-till) to 0.98 (P <0.001) at the SWRC site. To assess the sensitivity of the enzymes to changes in soil pH, the linear regression lines were expressed in activity/pH values. In general, their order of sensitivity to changes in soil pH was consistent across the study sites as follow: -glucosidase>-glucosaminidase>-galactosidase>-galactosidase>-glucosidase. Lime application did not significantly affect the specific activities (g p -nitrophenol released kg^–1 soil organic C h^–1) of the enzymes. Among the glycosidases studied, -glucosidase and -glucosaminidase were the most sensitive to soil management practices. Therefore, the activities of these enzymes may provide reliable long-term monitoring tools as early indicators of changes in soil properties induced by liming and tillage systems.     

Soil microbial activity and crop sustainability in a long-term experiment with three soil-tillage and two crop-rotation systems

Reduction in soil disturbance can stimulate soil microbial biomass and improve its metabolic efficiency, resulting in better soil quality, which in turn, can increase crop productivity. In this study we evaluated microbial biomass of C (MB-C) by the fumigation-extraction (FE) or fumigation-incubation (FI) method; microbial biomass of N (MB-N); basal respiration (BR) induced or not with sucrose; metabolic quotient (obtained by the ratio BR/MB-C) induced (qCO₂(S)), or not with sucrose (qCO₂); and crop productivity in a 14-year experiment in the state of Paraná, southern Brazil. The experiment consisted of three soil-tillage systems [no-tillage (NT), conventional tillage (CT) and no-tillage using a field cultivator every 3 years (FC)] and two cropping systems [a soybean–wheat-crop sequence (CS), and a soybean–wheat–white lupin–maize–black oat–radish crop rotation (CR)]. There were six samplings in the 14th year, starting at the end of the winter crop (wheat in the CS and lupin in the CR plots) and finishing at full flowering of the summer crop (soybean in the CS and maize in the CR). Differences in microbiological parameters were greater than those detected in the total C (TCS) and total N (TNS) contents of the soil organic matter (SOM). Major differences were attributed to tillage, and on average NT was higher than the CT in the following parameters: TCS (19%), TNS (21%), MB-C evaluated by FE (74%) and FI (107%), and MB-N (142%). The sensibility of the microbial community and processes to soil disturbance in the tropics was highlighted, as even a moderate soil disturbance every 3 years (FC) affected microbial parameters but not SOM. The BR was the parameter that most promptly responded to soil disturbance, and strong differences were perceived by the ratio of qCO₂ evaluated with samples induced and non-induced with sucrose. At plowing, the qCO₂(S):qCO₂ was five times higher under CT, indicating a C-starving low-effective microbial population in the C-usage. In general, crop rotation had no effect on microbial parameters or SOM. Grain yield was affected by tillage and N was identified as a limiting nutrient. Linear regressions between grain yields and microbial parameters showed that soybean was benefited from improvements in the microbial biomass and metabolic efficiency, but with no significant effects observed for the maize crop. The results also indicate that the turnover of C and N in microbial communities in tropical soils is rapid, reinforcing the need to minimize soil disturbance and to balance inputs of N and C.     

有机栽培和常规栽培水稻体系土壤酶及微生物量的比较研究

本研究探讨了有机栽培与常规栽培体系下水稻土微生物量及脲酶、酸性磷酸酶和过氧化氢酶的动态变化过程,以及有机栽培体系不同肥料调控措施对上述指标的影响.结果表明:与常规栽培水稻体系相比,有机栽培水稻有利于土壤微生物的生长和繁衍;水稻生长不同时期有机栽培方式的土壤微生物生物量碳、脲酶、酸性磷酸酶和过氧化氢酶活性均高于常规栽培体系.就水稻全生育期而言,土壤微生物生物量碳高于常规栽培7.3%～9.1%;脲酶、酸性磷酸酶和过氧化氢酶活性分别高于常规栽培7.3%～14.5%、5.2%～6.5%和12.5%～29.2%;有机水稻栽培体系下配施生态肥,在有机肥施用量减半时,土壤微生物生物量碳含量及土壤脲酶、酸性磷酸酶和过氧化氢酶活性较单施有机肥平均分别提高1.6%、6.8%、1.3%和14.8%,在水稻生长前期和中期该增加作用尤为显著.     

Microbial biomass activities in urban soils in two consecutive years

Ecological soil functions are protected in Germany. Thus, for the sustainable use of urban soil resources data on the function of soils to serve as a habitat are required. Soil microbial biomass and activities were studied in two surface horizons in two consecutive years at nine sites in Stuttgart, Germany, differing in land use. Microbial biomass (chloroform‐fumigation extraction, substrate‐induced respiration) and microbial activities (potential N mineralization, potential ammonium oxidation, and enzyme activities of dehydrogenase, urease, arylsulfatase, and phosphatase) were determined in 2001 and 2002. DIN/ISO standard methods were applied as far as they were available. Furthermore, soil chemical properties were determined in the 2001‐samples. Large differences in chemical and microbiological properties among surface horizons were found. Concentrations of microbial biomass and microbial activities were, however, often comparable to agricultural or forest surface soils. The lowest microbial biomass and activities were observed at a highly disturbed railway area where vegetation was missing and total organic C (TOC) had been altered by anthropogenic organic particles. In contrast, microorganisms were promoted at vegetated sites and where organic impurities were negligible. As TOC was altered by obscure organic matter, total N (TN) and not TOC closely correlated with soil microbiological properties. Biomass and activity generally decreased with depth, but mixing of organic matter resulted in more uniform depth distribution of microbial properties in one garden soil. In 2002, microbial biomass and activity were often lower compared to 2001, but interpretation of this difference hampered as the number of samples taken was probably not sufficient to address the spatial variability in soil properties. Additional studies are needed to develop simple and cost‐effective procedures for the evaluation of ecological quality of urban soils by combined efforts of city planners and soil scientists.     

Microbial biomass and activity in urban soils contaminated with Zn and Pb

Summary The effects of heavy metals on microbial biomass and activity were investigated in 30 urban soils, contaminated mainly with Zn and Pb to different extents, in terms of the physicochemical and biological characteristics of the soils. Evaluated by simple and multiple regression analyses, the microbial biomass was not affected significantly by easily soluble Zn + Pb (extractable with 0.1 NHCI). The biomass was accounted for as a function of cation exchange capacity (CEC), total organic C and the numbers of fungal colonies present (R ² = 0.692). Carbon dioxide evolution from soils, which reflected microbial activity, was studied on soils incubated with microbial-promoting substrates (glucose and ammonium sulfate) or without. Carbon dioxide evolution was negatively related to Zn+Pb, and this inhibitory effect of the metals was greater in the soils incubated with substrates. Carbon dioxide evolution in soils with substrates was closely related to Zn+Pb, bacterial numbers and the numbers of fungal colonies (R ² = 0.718). Carbon dioxide evolution in soils without substrates was accounted for as a function of Zn + Pb, biomass and the C/N ratio (R ² = 0.511). Using these relationships, the effects of heavy metals on soil microorganisms are discussed in terms of metabolically activated and dormant populations.     

Microbial biomass dynamics in recently air-dried and rewetted soils compared to others stored air-dry for up to 103 years

Our aim was to compare the soil microbial biomass concentration and its activity (measured as CO₂-C evolved) following the rewetting and aerobic incubation of soils which have previously been stored air-dry for different periods. Some of the soils have been stored in the Rothamsted sample archive for 103 years, others were comparable freshly sampled soils following air-drying and rewetting and other soils were stored air-dry for 2 years then rewetted for the work described here. Following air-drying, soil ATP concentrations were variable in recently air-dried soil, comprising about 10-35% of the initial ATP concentrations in fresh soil. Following rewetting, the percentage recovery of ATP increased in all soils by 7 days, then declined to between 73% and 87% of the original ATP concentration in the air-dried soils by day 12. Storage of air-dried soils decreased the ability of the microbial biomass to restore its ATP concentrations. For example, the ATP concentration in a soil sampled from stubbed (i.e. tree seedling, saplings and bushes cut frequently to ground level) grassland of the Broadbalk continuous wheat experiment at Rothamsted then air-dried for 2 years was only about 14% of that in the fresh soil at 2 days after rewetting. In other soils from the Hoosfield Barley Experiment, also at Rothamsted, previously given NPK or FYM since 1852, and sampled then stored air-dry for between 13 and 83 years, from 52% to 57% of the ATP in the comparable fresh soils was measured at two days after rewetting. The soil ATP concentration then changed little more up to 12 days. One of the most interesting findings was that while the microbial biomass ATP concentration in the above NPK soils only ranged from about 2 to 4 μmol ATP g⁻¹ biomass C, in the FYM soil the microbial biomass ATP concentrations (range 11.5-13.6 μmol ATP g⁻¹ biomass C) were the same as we repeatedly measure in fresh moist aerobic soil. We do not yet know the reasons for this. More than twice as much CO₂-C was evolved from the long-term stored soils than from freshly sampled ones. However, the specific respiration of the microbial biomass did not change much after the first 12 years of storage, indicating that loss of viability mainly occurred in the earlier years.     

Microbial and enzyme properties of apple orchard soil as affected by long-term application of copper fungicide

Copper-based fungicides have been applied in apple orchards for a long time, which has resulted in increasing soil Cu concentration. However, the microbial and enzyme properties of the orchard soils remain poorly understood. This study aimed to evaluate the effect of long-term application of Cu-based fungicides on soil microbial (microbial biomass carbon (C_mic), C mineralization, and specific respiration rate) and enzyme (urease, acid phosphatase, and invertase activities) properties in apple orchards. Soil samples studied were collected from apple orchards 5, 15, 20, 30, and 45 years old, and one adjacent forest soil as for reference. The mean Cu concentrations of orchard soils significantly increased with increasing orchard ages ranging from 21.8 to 141 mg kg⁻¹, and the CaCl₂-extractable soil Cu concentrations varied from 0.00 to 4.26 mg kg⁻¹. The soil mean C_mic values varied from 43.6 to 116 mg kg⁻¹ in the orchard soils, and were lower than the value of the reference soil (144 mg kg⁻¹). The ratio of soil C_mic to total organic C (C_org) increased from 8.10 to 18.3 mg C_mic g⁻¹ C_org with decreasing orchard ages, and was 26.1 mg C_mic g⁻¹ C_org for the reference soil. A significant correlation was observed between total- or CaCl₂-extractable soil Cu and soil C_mic or C_mic/C_org, suggesting that the soil Cu was responsible for the significant reductions in C_mic and C_mic/C_org. The three enzyme activity assays also showed the similar phenomena, and declined with the increasing orchard ages. The mean soil C mineralization rates were elevated from 110 to 150 mg CO₂-C kg⁻¹ soil d⁻¹ compared with the reference soil (80 mg CO₂-C kg⁻¹ soil d⁻¹), and the mean specific respiration rate of the reference soil (0.63 mg CO₂-C mg⁻¹ biomass C d⁻¹) was significantly smaller than the orchard soils from 1.19 to 3.55 mg CO₂-C mg⁻¹ biomass C d⁻¹. The soil C mineralization rate and the specific respiration rate can be well explained by the CaCl₂-extractable soil Cu. Thus, the long-term application of copper-based fungicides has shown adverse effects on soil microbial and enzyme properties.     

Substrate inputs and pH as factors controlling microbial biomass, activity and community structure in an arable soil

Our aim was to determine whether the smaller biomasses generally found in low pH compared to high pH arable soils under similar management are due principally to the decreased inputs of substrate or whether some factor(s) associated with pH are also important. This was tested in a soil incubation experiment using wheat straw as substrate and soils of different pHs (8.09, 6.61, 4.65 and 4.17). Microbial biomass ninhydrin-N, and microbial community structure evaluated by phospholipid fatty acids (PLFAs), were measured at 0 (control soil only), 5, 25 and 50 days and CO₂ evolution up to 100 days. Straw addition increased biomass ninhydrin-N, CO₂ evolution and total PLFA concentrations at all soil pH values. The positive effect of straw addition on biomass ninhydrin-N was less in soils of pH 4.17 and 4.65. Similarly total PLFA concentrations were smallest at the lowest pH. This indicated that there is a direct pH effect as well as effects related to different substrate availabilities on microbial biomass and community structure. In the control soils, the fatty acids 16:1ω5, 16:1ω7c, 18:1ω7c&9t and i17:0 had significant and positive linear relationships with soil pH. In contrast, the fatty acids i15:0, a15:0, i16:0 and br17:0, 16:02OH, 18:2ω6,9, 17:0, 19:0, 17:0c9,10 and 19:0c9,10 were greatest in control soils at the lowest pHs. In soils given straw, the fatty acids 16:1ω5, 16:1ω7c, 15:0 and 18:0 had significant and positive linear relationships with pH, but the concentration of the monounsaturated 18:1ω9 PLFA decreased at the highest pHs. The PLFA profiles indicative of Gram-positive bacteria were more abundant than Gram-negative ones at the lowest pH in control soils, but in soils given straw these trends were reversed. In contrast, straw addition changed the microbial community structures least at pH 6.61. The ratio: [fungal PLFA 18:2w6,9]/[total PLFAs indicative of bacteria] indicated that fungal PLFAs were more dominant in the microbial communities of the lowest pH soil. In summary, this work shows that soil pH has marked effects on microbial biomass, community structure, and response to substrate addition.     

Microbial activity and community structure in degraded soils on the Loess Plateau of China

Soil erosion is the main process leading to soil degradation on the Loess Plateau of China. The effects of soil‐erosion intensity (sheet, rill, and gully erosion) and different land use (140 y–old secondary forest site, 16 y–old bare site, 6 y–old succession site, and 43 y–old arable site) on gross and net N mineralization, soil organic‐carbon (SOC) turnover, the size and structure of the soil microbial community (phospholipid fatty acid analysis) were assessed. Erosion intensity in the bare plot increased from top slope (sheet erosion) to down slope (gully erosion). The more severe the soil erosion the stronger was the decline of SOC, total N, and microbial biomass (MB). The MBC/SOC ratio decreased whereas the metabolic quotient (qCO₂) increased. Differences in nutrient turnover in the different erosion zones of the bare plot were not significant. The microbial community changed towards less Gram negative bacteria and relative more fungi in the gully‐erosion zone. In forest soils, qCO₂ and the MBC/SOC ratio demonstrate a higher substrate‐use efficiency of the microbial biomass than in bare soils. Gross N mineralization and gross NH consumption clearly indicated a higher microbial activity in forest than in bare soils. Arable land use shifted the soil microbial community towards a higher relative abundance of fungi and a lower one of actinomycetes. During 6 y of natural succession on former bare plots, soil nutrient content and turnover as well as microbial biomass and structure developed towards forest conditions.     

土壤微生物量作为土壤肥力指标的探讨

对不同利用方式19个黑土样品的微生物量和养分进行了分析,结果表明林地的微生物量明显高于玉米地和大豆地,但玉米地和大豆地之间未表现出显著差异,土壤微生物量和土壤养分含量大体上都呈现出林地>大豆地>玉米地的一致的趋势;同时土壤微生物量与土壤有机质、全氮、全磷、速效钾和碱解氮呈现出显著或极显著正相关关系,分析结果还表明土壤微生物量碳作为评价土壤肥力指标比土壤微生物量氮更为灵敏。因此,土壤微生物量可以作为评价不同利用方式的黑土肥力水平的一个生物指标。     

Microbial biomass and activity at various soil depths in a Brazilian oxisol after two decades of no-tillage and conventional tillage

The advantages of no-tillage (NT) over conventional tillage (CT) systems in improving soil quality are generally accepted, resulting from benefits in soil physical, chemical and biological properties. However, most evaluations have only considered surface soil layers (maximum 0-30 cm depth), and values have not been corrected to account for changes in soil bulk density. The objective of this study was to estimate a more realistic contribution of the NT to soil fertility, by evaluating C- and N-related soil parameters at the 0-60 cm depth in a 20-year experiment established on an oxisol in southern Brazil, with a soybean (summer)/wheat (winter) crop succession under NT and CT. At full flowering of the soybean crop, soil samples were collected at depths of 0-5, 5-10, 10-20, 20-30, 30-40, 40-50 and 50-60 cm. For the overall 0-60 cm layer, correcting the values for soil bulk density, NT significantly increased the stocks of C (18%) and N (16%) and microbial biomass C (35%) and N (23%) (MB-C and -N) in comparison to CT. Microbial basal respiration and microbial quotient (qMic) were also significantly increased under NT. When compared with CT, NT resulted in gains of 0.8 Mg C ha⁻¹ yr⁻¹ (67% of which was in the 0-30 cm layer) and 70 kg N ha⁻¹ yr⁻¹ (73% in the 0-30 cm layer). In the 0-5-cm layer, MB-C was 82% higher with NT than with CT; in addition, the 0-30 cm layer accumulated 70% of the MB-C with NT, and 58% with CT. In comparison to CT, the NT system resulted in total inputs of microbial C and N estimated at 38 kg C ha⁻¹ yr⁻¹ and 1.5 kg N ha⁻¹ yr⁻¹, respectively. Apparently, N was the key nutrient limiting C and N stocks, and since adoption of NT resulted in a significant increase of N in soils which were deficient in N, efforts should be focused on increasing N inputs on NT systems.     

Microbial biomass and activity in composts of different composition and age

The aim of this study was to perform a comparison of microbial activity and biomass in biowaste (BWC), yard waste (YWC), and cattle‐manure composts (CMC) of different age. Two different methods for either biomass (microbial C following fumigation‐extraction and microbial lipid phosphate) or activity measurements (CO₂‐production rate and fluorescein diacetate hydrolysis) provided comparable information, as judged from their strong correlation. Microbial biomass and activity declined with time in all composts. Microbial biomass C was strongly correlated with microbial activity but was even stronger correlated with pH. CMC proved to be very distinct from the two other compost types by having the highest biomass and the lowest specific activity (i.e., activity per unit biomass). The microbiological properties analyzed allow us to discriminate among different compost types, helping to assign their potential applications.     

醋糟菌糠对3种作物土壤微生物及酶活性的影响

为研究醋糟菌糠作为一种生物肥料对土壤肥力的影响,为解决食用菌菌糠对环境污染及其有效利用提供科学依据,本文通过田间试验,对玉米、高粱、糯玉米3种作物基施醋糟菌糠后不同生育期的土壤脲酶、蔗糖酶和过氧化氢酶活性,细菌、放线菌和真菌数量,及微生物量碳、氮含量进行测试。研究结果表明:1)醋糟菌糠显著提高了作物根际土壤细菌、放线菌和真菌的数量。在作物整个生育期,加入醋糟菌糠的土壤细菌数量比对照提高32%~54%;放线菌数量在成熟期提高明显,玉米田土壤放线菌数量增幅最大,为101%;真菌数量变化总体趋势呈现先升高后下降的趋势。2)醋糟菌糠的施入增加了作物根际土壤脲酶、过氧化氢酶、蔗糖酶的活性。种植高粱、玉米和糯玉米土壤的脲酶活性增长率分别为239%、189%和185%;3种作物的土壤过氧化氢酶活性在抽穗期最高,最大增长率为40%;3种作物的土壤蔗糖酶活性在不同生育期变化趋势不同,玉米各生育期土壤蔗糖酶活性变化较为稳定,其增长率分别为38%、28%、48%。3)醋糟菌糠的施入增加了作物根际土壤微生物碳氮的含量,不同生育期3种作物的土壤微生物碳含量增幅为58.10~407.67 mg·kg-1,微生物氮含量增幅为11.98~27.55 mg·kg-1。由此可见,醋糟菌糠的施用可以增强土壤生产力的可持续性,从而达到保护和改善土壤环境的效果。同时该研究也为醋糟菌糠的有效利用提供了一定的科学依据。