氯嘧磺隆与尿素对土壤微生物生物量碳、氮及无机氮的影响

通过室内培养试验,研究了不同浓度氯嘧磺隆(20、200、2000 μg·kg-1土)单一施用及与尿素(120 mg· kg-1土)配合施用情况下,土壤微生物生物量碳、氮和土壤铵态氮、硝态氮随时间的动态变化规律.结果表明:各浓度氯嘧磺隆单独处理在整个培养期(60 d)中对微生物生物量碳、氮均有抑制作用,且浓度越高,后期抑制作用越强;各浓度氯嘧磺隆处理在培养前期对硝态氮、铵态氮没有明显影响,中期(15 d)能显著提高土壤中铵态氮的含量,后期(30 d后)显著提高了土壤中硝态氮的含量.尿素单独施用及与氯嘧磺隆配施均能在短时间内增加微生物生物量碳、氮,但随后配施处理的促进作用减弱;尿素单独和配施均能持久增加土壤中铵态氮、硝态氮含量.     

Soil microbial carbon uptake characteristics in relation to soil management

Abstract The kinetics of glucose uptake by soil microbial communities in 16 different soild (7 under monocultures and 9 under crop rotations) differing in microbial biomass content, % C_org, pH and clay content were investigated at 22°C. The V _max value of microbial bimasses under monoculture, was o.27 μg C_gluc · μg⁻¹ C_mic · h⁻¹ (range 0.18–0.44), twice as high as the mean value of V _max of microbial biomasses under rotations (0.13 μg C_gluc, range 0.07–0.19). Mean values of K _m were 714 μg C_gluc and 290 μg C_gluc · g⁻¹ soil, respectively.
These differences were highly significant ( P =0.001, based on SE) and could not be relate to particle size distribution of the soils, pH or C_org. A Michaelis-Menten type uptake response was apparent over the total range of glucose concentrations used (45.4–1453.3 μg C_gluc · g⁻¹ soil) for microbial biomasses under rotation while the majority of microbial biomasses under monocultures showed a similar response only at low glucose concentrations. A different uptake mechanism appeared to be involved at higher glucose concentrations (similar to diffusion) in monoculture soils.     

Mound-building termites and soil microbial biomass: An interaction influencing termite abundance

Termites are more abundant in the warmer lower latitudinal regions of the earth. Within these broad geographic regions, however, the precise nature of the factors influencing termite abundance is poorly understood. In this paper I have examined the abundance of detritivorous, mound-building termites and certain aspects of the climate, soils and vegetation at 14 sites in tropical northeastern Australia. No relationship between termite mound density and the particle-size characteristics of surface soil horizons, plant available phosphorous or rainfall was found. Microbial biomass carbon level of the surface soil was found to have a strong negative relationship with termite mound numbers. The negative interaction between the soil microbial population and termites may be due to the limiting effect of the organic matter processing capacity of the soil microbial population on the success of termites in occupying the decomposer niche in any particular area. Microbial biomass may therefore be a major factor influencing termite abundance in tropical Australian landscapes and elsewhere.     

Ambient ultraviolet radiation in the Arctic reduces root biomass and alters microbial community composition but has no effects on microbial biomass

We assessed the effects of ambient solar ultraviolet (UV) radiation on below‐ground parameters in an arctic heath in north‐eastern Greenland. We hypothesized that the current UV fluxes would reduce root biomass and mycorrhizal colonization and that these changes would lead to lower soil microbial biomass and altered microbial community composition. These hypotheses were tested on cored soil samples from a UV reduction experiment with three filter treatments (Mylar, 60% UV‐B reduction; Lexan, up to 90% UV‐B reduction+UV‐A reduction; UV transparent Teflon, filter control) and an open control treatment in two study sites after 3 years' manipulation. Reduction of both UV‐A and UV‐B radiation caused over 30% increase in the root biomass of Vaccinium uliginosum, which was the dominant plant species. UV reduction had contrasting effects on ericoid mycorrhizal colonization of V. uliginosum roots in the two sites, while it had no clear effects on fungal (ergosterol) or microbial biomass (measured both with fumigation–extraction and quantitative lipid biomarker analysis) in soil. However, principal component analysis of lipid biomarkers (phospholipid and glycolipid fatty acid profiles) showed that microbial community composition was altered by UV reduction. Although the UV responses were slight considering the large dose difference between the treatments (from near‐ambient to up to 90% UV‐B reduction), we cannot rule out the possibility that the recovery of ozone layer would change the below‐ground functioning of arctic ecosystems.     

Microbial biomass and growth kinetics of microorganisms in chernozem soils under different land use modes

The carbon content of microbial biomass and the kinetic characteristics of microbial respiration response to substrate addition have been estimated for chernozem soils under different land use: arable lands used for 10, 46, and 76 years, mowed meadow, natural forest, and forest shelter belt. Microbial biomass and the content of microbial carbon in humus (C_mic /C_org) decreased in the following order: soils under forest cenoses—mowed meadow—10-year arable land—46- and 75-year arable land. The amount of microbial carbon in the long-plowed horizon was 40% of its content in the upper horizon of natural forest. Arable soils were characterized by a lower metabolic diversity of microbial community and by the highest portion of microorganisms able to grow directly on glucose introduced into soil. The effects of different scenarios of carbon sequestration in soil on the amounts and activity of microbial biomass are discussed.     

油松-辽东栎混交林地表凋落物与氮添加对土壤微生物生物量碳、氮及其活性的影响

2010年9月-2011年10月,在山西省灵空山油松和辽东栎混交林样地采取随机区组设计,研究了地表凋落物和氮添加处理对土壤微生物生物量碳、氮和微生物活性的影响.凋落物处理包括:剔除凋落物(N)、叶凋落物加倍(L)、枝果凋落物加倍(B)和混合凋落物加倍(LB);氮添加量分别为0(N0)、5 g· m-2·a-1(N1)和10 g·m-2·a-1(N2).结果表明:剔除地表凋落物且无氮添加时,油松和辽东栎混交林地的土壤有机碳(SOC)含量显著降低,其他试验处理间对SOC的影响无显著差异.土壤微生物生物量碳(MBC)、氮(MBN)及其活性(MR)的变化范围依次为:262.42 ～ 873.16 mg·kg-1、73.55 ～ 173.85 mg·kg-1和2.38～3.68mg·kg-1·d-1.MBC、MBN和MR两两间呈极显著正相关.氮添加对MBC、MBN和MR均无显著影响;凋落物处理对MR影响显著,表现为混合凋落物加倍处理的MR最高,叶凋落物加倍处理次之,剔除凋落物处理最低,而对MBC和MBN无显著影响.凋落物和氮添加处理在整个试验过程中未表现出交互作用.短期的氮添加处理和森林地表凋落物变化对土壤微生物过程的影响有限.     

Effect of starvation length upon microbial activity in a biomass recycle reactor

The kinetics of substrate degradation and bacterial growth was determined in a microbial community from a biomass recycle reactor that had been deprived of substrate feed for 0–32 days. Starvation caused changes in bacterial numbers, community composition, and physiological state. Substrate starvation for less than 1 day resulted in modest (less than threefold) changes in endogenous respiration rate, ATP content, and biomass level. During a starvation period of 32 days, there were substantial changes in microbial community composition, as assessed by denaturing gradient gel electrophoresis (DGGE) fingerprinting of PCR amplicons of a portion of the 16S rDNA or by phospholipid fatty acid (PLFA) analysis. When the starved communities were stimulated with organic nutrients, the growth kinetics was a function of the length of the starvation period. For starvation periods of 2–8 days prior to nutrient addition, there was a phase of suboptimal exponential growth (S-phase) in which the exponential growth rate was about 30% of the ultimate unrestricted growth rate. S-phase lasted for 2–8 h and then unrestricted growth occurred at rates of 0.3–0.4 h⁻¹. At starvation times of 12 and 20 days, a lag phase preceded S-phase and the unrestricted growth phase. Received 04 January 2002/ Accepted in revised form 08 August 2002     

Comparative assessment of soil microbial biomass determined by the methods of direct microscopy and substrate-induced respiration

The content of microbial biomass (MB) was determined in samples of gray forest, chestnut, and tundra soils with different physicochemical properties (0.4–22.7% C_org; 8.4–26.8% silt particles; pH 4.3–8.4) by the methods of substrate-induced respiration (MB_SIR) and direct microscopy (MB_M). The samples of two upper soil layers, 0–5 and 5–10 cm (without plant litter), from different ecosystems (forest, forest shelter belt, meadow, fallow, and arable) and elements of relief of interfluvial tundra (block/upper land plateau, depression between blocks) have been analyzed. The content of microbial biomass in the 0–5-cm soil layer was 216–8134 and 348–7513 μg C/g soil as measured by the methods of substrate-induced respiration and direct microscopy, respectively. The MB_SIR and MB_M values closely correlated with each other: r = 0.90 and 0.74 for 0–5 and 5–10 cm, respectively. The average MB_SIR/MB_M ratio was 90 and 60% for 0–5 and 5–10 cm, respectively. The portion of microbial carbon in total organic soil carbon was, on average, 4 and 3% (SIR) and 5 and 7% (direct microscopy) for 0–5 and 5–10 cm, respectively. Possible reasons for the differences between MB_SIR and MB_M values in the soils under study are discussed.     

皇甫川流域退化草地和恢复草地土壤微生物生物量的研究

土壤微生物生物量常被作为植物所需营养元素的转化因子和资源库,是表明土壤发育状况和生化强度的一项主要指标。在内蒙古伊盟准格尔旗皇甫川流域,对退化草地和恢复草地土壤微生物生物量进行了研究。结果表明,土壤微生物生物量的垂直分布依次为0～10>10～20>20～30>30～40>40～50cm,随土层加深而递减;0～10cm土层细菌和丝状微生物生物量超过其他土层;恢复草地各土层中的土壤微生物生物量均高于退化草地;恢复草地的土壤微生物生物量与土壤肥力密切相关。     

天台山七子花群落下土壤微生物生物量的季节动态

研究天台山七子花群落下土壤微生物生物量的季节变化规律及生态特性。根据实测数据分别对根际、根围微生物生物量碳、氮与土壤环境因子之间进行相关性分析,并建立了土壤微生物指标与环境因素之间的回归方程,以此为基础对天台山七子花群落下土壤微生物生物量的季节变化进行预测。回归分析表明：土壤温度、水分对微生物生物量的影响大于土壤pH值对微生物生物量的影响,而且土壤温度、水分对微生物生物量氮的影响大于对微生物生物量碳的影响。土壤温度对微生物生物量碳、氮的影响最大。     

淹水培养条件下土壤微生物生物量碳、氮和可溶性有机碳、氦的动态

以洞庭湖区2个典型水稻土（红黄泥和紫潮泥）为对象,研究了25℃、淹水培养条件下稻草-硫铵配施和单施硫铵处理土壤微生物生物量碳、氮（SMBC、SMBN）和可溶性有机碳、氦（SDOC、SDON）的动态变化．结果表明,SMBC、SMBN和SDOC、SDON在培养前期达到峰值,之后降低,并趋于稳定．添加底物后,2种土壤不同处理土壤微生物生物量碳与有机碳（SMBC／TC）和土壤微生物生物量氮与全氮（SMBN／TN）的平均值都在2％-3％之间变化;可溶性碳与全碳（SDOC／TC）的平均值为1％左右,可溶性氮与全氮（SDON／TN）平均值为5％-6％．2种土壤中SMBC峰值单施硫铵处理最大,但与稻草-硫铵配施处理差异均不显著;SMBN、SDOC和SDON峰值稻草-硫铵配施最大．稻草．硫铵配施与单施硫铵处理中,低肥力红黄泥的SMBN、SDOC和SDON峰值差异显著;而高肥力紫潮泥SMBN和SDOC峰值差异不显著．前7d,SMBC／SMBN〈10;14d后,同一时刻单施硫铵处理SMBC／SMBN〉稻草．硫铵配施．不同处理的SDOC!SDON3d时最大．28d时最小．     

Influence of synthetic sheep urine on the microbial biomass,activity and community structure in two pastures in the Scottish uplands

The impact of urine on the microbial biomass, activity and community structure was compared in the soil beneath two pastures in the Scottish uplands; Fasset, a natural Agrostis capillaris–Festuca ovina–Galium saxatile grassland and Strathfinella, a semi-natural grassland, improved with fertiliser addition. Community level physiological profiles (CLPP) were used to characterise the microbial communities. The utilisation of sugars, oligosaccharides, alcohols, carboxylic acids, long chain aliphatic acids, acidic, basic and neutral amino acids, amide N, phenolic acids and long chain aliphatic acids was used to compare the soils and the impact of synthetic urine addition. In the untreated soils, the utilisation of all the substrates decreased from the first week in May through to October. Averaged over all times and urine treatment, the potential utilisation of all substrates except for phenolic acids, long chain aliphatic acids and carboxylic acids was greater in the improved and more intensively grazed Strathfinella site. When averaged over all sample times, urine increased the utilisation of sugars, oligosaccharides, basic amino acids and amide N and the increases were greater in the unimproved, less intensively grazed, Fasset soil than that at Strathfinella. The effect of urine tended to be greatest during the period between 2 and 5 weeks after urine addition when utilisation of alcohols, acidic and neutral amino acids was also increased. Microbial biomass C in the control soils was 155.9 and 112.7 g C m⁻² at Fasset and Strathfinella, respectively. Values did not change significantly with time and were unchanged by the addition of urine. However, urine addition significantly increased basal respiration rates at Fasset and decreased them at Strathfinella. Urine also increased bacterial numbers in both soils, but had no consistent effect on fungi or yeasts. The significance of these findings for studies of soil microbial community structure and activity in grazed upland grasslands is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Positive effects of plant diversity on soil microbial biomass and activity are associated with more root biomass production

This study aims to explore relationships between plant diversity and soil microbial function and the factors that mediate the relationships. Artificial plant communities (1, 2, 4 and 8 species) were established filled with natural and mine tailing soils, respectively. After 12 months, the plant species richness positively affected the soil microbial functional diversity in both soil environments but negatively affected microbial biomass and soil basal respiration in the natural soil. The root biomass positively correlated with the microbial biomass, cultural bacterial activity and soil basal respiration in both soil environments. Moreover, the D_i (deviations between observed performances and expected performances from the monoculture performance of each species of mixture) of microbial biomass, cultural bacterial activity and soil basal respiration positively correlated with the D_i of root biomass in both soil environments. Consistent with stress-gradient hypothesis, the D_mix (over-function index) of aboveground biomass positively correlated plant species richness in the mine tailing soil. Results suggest that the root biomass production is an important mechanism that affects the effects of plant diversity on soil microbial functions. Different responses of soil microbial function to increasing plant diversity may be due to root biomass production mediated by other factors.     

Soil microbial biomass influence on strontium availability in mine soil

Abstract

The main aim of our work was to assess whether strontium (Sr) affects soil microbial biomass size and activity, and the involvement of said biomass in the availability process of the metal. In addition, information concerning the distribution and mobility of the stable element within ecosystems may allow the prediction of the behaviour of its radioisotope counterpart, ⁹⁰Sr. Samples were collected in the surroundings of a strontium mine and characterised for total and diethylene triamine pentaacetic acid (DTPA)-extractable Sr, total organic C (TOC), microbial biomass C (MBC), MBC/TOC ratio and metabolic quotient (qCO₂). Moreover, MBC and DTPA-extractable Sr were measured during a 45-day incubation experiment of samples soils amended with maize. Overall, increased levels of total Sr had a negative effect on both TOC and MBC. DTPA-extractable Sr was significantly correlated to MBC/TOC suggesting a possible role of soil microbial biomass in the mobilisation of the element. The synthesis of new microbial biomass after soil amendment was negatively affected by the initial content of DTPA-extractable Sr. Conversely, there was a linear positive relationship between newly formed MBC and DTPA-extractable Sr during the incubation, indicating that soil microbial biomass may promote the mobilisation of Sr. These findings indicate that soil amendment with easily degradable organic substrate significantly increases Sr mobility and availability.     

Liming and nitrogen fertilization affects phosphatase activities, microbial biomass and mycorrhizal colonisation in upland grassland

We have studied the effects of factorial combinations of lime and N additions on soil microbial biomass, respiration rates and phosphatase activity of an upland grassland. We also used an Agrostis capillaris seedling bioassay to assess the effect of the treatments on the activity of arbuscular-mycorrhizal (AM) fungi and root surface phosphatase enzymes and the concentrations of N and P in the bioassay plant shoots. In the F and H horizons, soil microbial biomass carbon (C^mic) decreased in response to the liming, while addition of lime and N together reduced basal respiration rates. In the Ah horizon, C^mic was unaffected by the treatments but basal respiration rates decreased in the plots receiving nitrogen. Soil phosphatase activity decreased only in the Ah horizon in plots receiving lime, either in combination with N or alone. The mass of root fwt. colonized by AM fungi increased in response to the treatments in the order nitrogenR²=28.7%, P=0.004). The results demonstrate the sensitivity of both free-living heterotrophic microorganisms and symbiotic mycorrhizal fungi to short-term (2 years) applications of lime and N to long-term upland grassland, particularly in relation to the key P cycling activities undertaken by these organisms.     

Impact of elevated atmospheric CO2 concentration on soil microbial biomass and activity in a complex, weedy field model ecosystem

Although soil organisms play an essential role in the cycling of elements in terrestrial ecosystems, little is known of the impact of increasing atmospheric CO₂ concentrations on soil microbial processes. We determined microbial biomass and activity in the soil of multitrophic model ecosystems housed in the Ecotron (NERC Centre for Population Biology, Ascot, UK) under two atmospheric CO₂ concentrations (ambient vs. ambient + 200 ppm). The model communities consist of four annual plant species which naturally co-occur in weedy fields and disturbed ground throughout southern England, together with their herbivores, parasitoids and soil biota. At the end of two experimental runs lasting 9 and 4.5 months, respectively, root dry weight and quality showed contradictory responses to elevated CO₂ concentrations, probably as a consequence of the different time-periods (and hence number of plant generations) in the two experiments. Despite significant root responses no differences in microbial biomass could be detected. Effects of CO₂ concentration on microbial activity were also negligible. Specific enzymes (protease and xylanase) showed a significant decrease in activity in one of the experimental runs. This could be related to the higher C:N ratio of root tissue. We compare the results with data from the literature and conclude that the response of complex communities cannot be predicted on the basis of oversimplified experimental set-ups.     

Carbon and nitrogen cycling during old-field succession: Constraints on plant and microbial biomass

Soil C and N dynamics were studied in a sequence of old fields of increasing age to determine how these biogeochemical cycles change during secondary succession. In addition, three different late-successional forests were studied to represent possible "steady state" conditions. Surface soil samples collected from the fields and forests were analyzed for total C, H₂O-soluble C, total N, potential net N mineralization, potential net nitrification, and microbial biomass. Above-and belowground plant biomass was estimated within each of the old field sites.Temporal changes in soil organic C, total N and total plant biomass were best described by a gamma function [y =at ^b e ^ctd +f] whereas a simple exponential model [y =a(l – e^–bt ) + c] provided the best fit to changes in H₂O-soluble C, C:N ratio, microbial C, and microbial N. Potential N mineralization and nitrification linearly increased with field age; however, rates were variable among the fields. Microbial biomass was highly correlated to soil C and N pools and well correlated to the standing crop of plant biomass. In turn, plant biomass was highly correlated to pools and rates of N cycling.Patterns of C and N cycling within the old field sites were different from those in a northern hardwood forest and a xeric oak forest; however, nutrient dynamics within an oak savanna were similar to those found in a 60-yr old field. Results suggest that patterns in C and N cycling within the old-field chronosequence were predictable and highly correlated to the accrual of plant and microbial biomass.     

Modelling the impact of microbial grazers on soluble rhizodeposit turnover

Rhizodeposition represents a relatively large carbon flow from a plant’s root into the surrounding soil. This carbon flow may have important implications for nitrogen mineralisation and carbon sequestration, but is still poorly understood. In this paper we use a simple compartment model of carbon flow in the rhizosphere to investigate the proposed benefits of rhizodeposition and the effect of microbial grazers. Model parameters were fitted to published, experimental data. Analysis of the model showed that dead organic matter (necromass) had a much longer time-scale than the other carbon pools (soluble, microbial and grazer carbon), which allowed an approximate, mathematical solution of the model to be derived. This solution shows that the level of necromass in the soil is an important factor in many processes of interest. The short-term carbon and nitrogen turnover increases with the level of necromass. Microbial grazers decrease carbon turnover at high levels of necromass, whilst at lower, and possibly more realistic, levels of necromass grazers increase turnover. However, the largest effect of grazers was to increase carbon turnover by 10%, suggesting that grazers are relatively unimportant in larger scale models of soil organic matter turnover. The marginal benefits of rhizodeposition increase with the level of necromass. The model suggests that the short-term benefits of rhizodeposition to a plant are marginal, but long-term benefits may still occur.     

Application of the chloroform fumigation-incubation method to the estimation of soil microbial biomass in burned and unburned Japanese red pine forests

Abstract Estimation of soil microbial biomass in burned and unburned Japanese red pine forests was attempted using the chloroform fumigation-incubation method. As the amount of CO₂-C evolved from the fumigated soil for 10–20 days after fumigation (designated as F') was always lower than that from the unfumigated soil during the same period (UF'), the formula, microbial biomass-C(M) = the amount of CO₂-C evolved from the fumigated soil for 0–10 days after fumigation, F) − F'/ k _c, was proposed instead of Jenkinson's conventional formula, M = (F − UF')/ k _c. The k _c value was also determined as 0.30 using 3 fungal and 3 bacterial cultured species as internal standards. Microbial biomass-C calculated by (F − F')/0.30 decreased with soil depth at both the burned (Nenoura, 3.5 years after fire) and unburned (Ato) sites, showing the significant correlation with the decrease of soil respiration and organic C content along soil depth. Microbial biomass-C in the 0–2 cm soil layer at the burned site at Nenoura was 130 mg/100 g dry soil and those in the HF horizon and 0–2 cm soil layer at the unburned site at Ato were 686 and 146 mg/100 g dry soil, respectively.