Temporal changes in soil microbial biomass carbon in an arable soil. Consequences for soil sampling

Sugar beet, winter wheat and winter barley were planted within a crop rotation on an arable soil with conventional soil management. Soil samples were taken monthly from different depths of the whole plough layer (0–10, 10–20 and 20–30 cm) during a 56 month period. The samples were analysed for microbial biomass carbon using the substrate-induced respiration technique. Temporal changes in the amount of microbial biomass carbon were observed. Within a year, microbial biomass-C varied from low values (−15% of total mean) in winter to high values (+15% of total mean) in summer. Relative deviations from the annual means were calculated for each month in the year to demonstrate these fluctuations. Temporal changes in microbial biomass-C depended on the sources of sample variation (5 years, 3 crops, 3 sampling depths). The highest relative deviation from the annual mean microbial biomass-C was attributable to the factor “year”. Less variations were caused by “crops” and “sampling depth”. Soil microbial biomass-C remained constant during frost periods. From the observed temporal changes, recommendations for a suitable date for soil sampling are given, which allows a representative estimation of the mean annual microbial biomass-C content in arable soils.     

生物质炭对水稻土团聚体微生物多样性的影响

生物质炭施用对土壤微生物群落结构的影响已有报道,但土壤团聚体粒组中微生物群落对生物质炭施用的响应的研究还相对不足。以施用玉米秸秆生物质炭两年后的水稻土为对象,采用团聚体湿筛法,通过高通量测序对土壤团聚体的微生物群落结构与多样性进行分析,结果表明:(1)与对照相比,生物质炭施用显著促进了大团聚体(2000—250μm)的形成,并提高了团聚体的稳定性。(2)不同粒径团聚体间微生物相对丰度存在显著差异。在未施生物质炭的处理(C0)中,随着团聚体粒径增大,变形菌门、子囊菌门、β-变形杆菌目、格孢腔菌目的相对丰度逐渐降低,而酸杆菌门、担子菌门、粘球菌目、类球囊霉目的相对丰度逐渐升高。(3)生物质炭施用显著改变了团聚体间的微生物群落结构。与C0处理相比,生物质炭施用处理的大团聚体中变形菌门、鞭毛菌门和β-变形杆菌目的相对丰度分别显著提高了14.37%、33.28%和33.82%;微团聚体(250—53μm)中酸杆菌门、子囊菌门和粘球菌目的相对丰度分别显著降低了20.15%、19.93%和17.66%;粉、黏粒组分(<53μm)中担子菌门的相对丰度升高90.25%,而子囊菌门和鞭毛菌门的相对丰...     

Available soil nitrogen in relation to fractions of soil nitrogen and other soil properties

The available N of 27 soils from England and Wales was assessed from the amounts of N taken up over a 6-month period by perennial ryegrass grown in pots under uniform environmental conditions. Relationships between availability and the distribution of soil N amongst various fractions were then examined using multiple regression. The relationship: available soil N (mg kg^–1 dry soil)=(N_min×0.672)+(N_inc×0.840)+(N_mom×0.227)–5.12 was found to account for 91% of the variance in available soil N, where N_min=mineral N, N_inc=N mineralized on incubation and N_mom=N in macro-organic matter. The N mineralized on incubation appeared to be derived largely from sources other than the macro-organic matter because these two fractions were poorly correlated. When availability was expressed in terms of available organic N as % of soil organic N (N_ao) the closest relationship with other soil characteristics was: N_ao=[N_inc×(1.395–0.0347×CN_mom]+[N_mom×0.1416], where CN_mom=CN ratio of the macro-organic matter. This relationship accounted for 81% of the variance in the availability of the soil organic N.The conclusion that the macro-organic matter may contribute substantially to the available N was confirmed by a subsidiary experiment in which the macro-organic fraction was separated from about 20 kg of a grassland soil. The uptake of N by ryegrass was then assessed on two subsamples of this soil, one without the macro-organic matter and the other with this fraction returned: uptake was appreciably increased by the macro-organic matter.     

Estimating respiration of roots in soil: Interactions with soil CO2, soil temperature and soil water content

Little information is available on the variability of the dynamics of the actual and observed root respiration rate in relation to abiotic factors. In this study, we describe I) interactions between soil CO₂ concentration, temperature, soil water content and root respiration, and II) the effect of short-term fluctuations of these three environmental factors on the relation between actual and observed root respiration rates. We designed an automated, open, gas-exchange system that allows continuous measurements on 12 chambers with intact roots in soil. By using three distinct chamber designs with each a different path for the air flow, we were able to measure root respiration over a 50-fold range of soil CO₂ concentrations (400 to 25000 ppm) and to separate the effect of irrigation on observed vs. actual root respiration rate. All respiration measurements were made on one-year-old citrus seedlings in sterilized sandy soil with minimal organic material.Root respiration was strongly affected by diurnal fluctuations in temperature (Q₁₀ = 2), which agrees well with the literature. In contrast to earlier findings for Douglas-fir (Qi et al., 1994), root respiration rates of citrus were not affected by soil CO₂ concentrations (400 to 25000 ppm CO₂; pH around 6). Soil CO₂ was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter method of measuring root respiration reduced soil CO₂ concentration to that of incoming air. Irrigation caused a temporary reduction in CO₂ diffusion, decreasing the observed respiration rates obtained by techniques that depended on diffusion. This apparent drop in respiration rate did not occur if the air flow was directed through the soil. Our dynamic data are used to indicate the optimal method of measuring root respiration in soil, in relation to the objectives and limitations of the experimental conditions.     

The breakdown of malathion in soil and soil components

The disappearance of the organophosphorus insecticide, malathion, from a silt loam soil and from its organic and inorganic components was examined. Half-lives and the time taken for 90% decomposition in nonsterile, sodium azide-treated, and 2.5 Mrad-irradiated soils were similar (3/4–1 1/2 days and 4–6 days, respectively) but breakdown in autoclaved soils was negligible. Decay in nonsterile sand, silt, and clay minus organic matter fractions was 3–6 times slower than that recorded in the original soil. Breakdown of malathion in the clay plus organic matter fraction (organo-mineral complex) was rapid (half-life, 1 day), as was the case in the separated organic matter (half-life, 1 3/4 days). Filter-sterilized organic matter was not as effective in catalyzing the breakdown of malathion (half-life, 4 days), and no loss occurred from any of the autoclaved components. Irradiation doses of 2.5 and 5.0 Mrad had little influence on the ability of soil to degrade malathion. Thereafter, increases up to 20 Mrad had a more drastic, though far from totally inhibitory, effect. Our results suggest that either the colloidal organic matter itself, or a fraction associated with it, is the most important single factor concerned with the rapid breakdown of malathion in the soil studied. Direct microbial metabolism is a slower process and may have a significant role in malathion disappearance in coarsetextured soils low in colloidal organic matter. The catalytic component of the organic matter is suggested to be a stable exoenzyme and is supportive of reports by other workers. The quantitative effect of organo-mineral complex (containing the active degradative ingredient) additions to sand and silt fractions on the rate of subsequent malathion decay is also described.     

耕作方式对潮土土壤团聚体微生物群落结构的影响

为探究不同耕作方式对潮土土壤团聚体微生物群落结构和多样性的影响,采用磷脂脂肪酸(PLFA)法测定了土壤团聚体中微生物群落。试验设置4个耕作处理,分别为旋耕+秸秆还田(RT)、深耕+秸秆还田(DP)、深松+秸秆还田(SS)和免耕+秸秆还田(NT)。结果表明:与RT相比,DP处理显著提高了原状土壤和>5 mm粒级土壤团聚体中真菌PLFAs量和真菌/细菌,为真菌的繁殖提供了有利条件,有助于土壤有机质的贮存,提高了土壤生态系统的缓冲能力;提高了5～2 mm粒级土壤团聚体中细菌PLFAs量,降低了土壤革兰氏阳性菌/革兰氏阴性菌,改善了土壤营养状况;提高了<0.25 mm粒级土壤团聚体中微生物丰富度指数。总的来说,深耕+秸秆还田(DP)对土壤团聚体细菌和真菌生物量有一定的提高作用,并且在一定程度上改善了土壤团聚体微生物群落结构,有利于增加土壤固碳能力和保持土壤微生物多样性。冗余分析结果表明,土壤团聚体总PLFAs量、细菌、革兰氏阴性菌和放线菌PLFAs量与土壤有机碳相关性较强,革兰氏阳性菌PLFAs量与总氮相关性较强。各处理较大粒级土壤团聚体微生物群落主要受碳氮比、含水量、pH值和团聚体质量分数的影响,较小粒级土壤团聚体微生物群落则主要受土壤有机碳和总氮的影响。     

红壤退化地森林恢复后土壤有机碳对土壤水库库容的影响

亚热带红壤侵蚀退化地实施生态恢复后生物生产力恢复迅速,但土壤尤其是土壤水库的功能并未获得同步恢复,导致土壤水库对于降水和地表径流的调节能力低下,区域性洪涝灾害和季节性干旱依然突出。采用野外调查和室内分析相结合的方式,研究了南方红壤侵蚀退化地典型植被恢复类型(马尾松与阔叶树复层林、木荷与马尾松混交林、阔叶混交林)0—60cm土层土壤水库各种库容差异,以及土壤总有机碳和活性有机碳密度分布特征,采用典型相关分析方法对土壤水库库容与土壤有机碳密度两组指标进行相关分析。结果表明:随着土层深度的增加,各森林恢复类型死库容呈上升趋势,兴利库容和最大有效库容呈下降趋势,防洪库容变化趋势不明显,木荷与马尾松混交林兴利库容略高。不同森林恢复类型同一土层土壤总有机碳密度均表现为马尾松与阔叶树复层林木荷与马尾松混交林阔叶混交林,而活性有机碳密度则以阔叶混交林最大。典型相关分析表明,土壤有机碳水平对土壤水库库容的增加具有显著的因果影响关系(P=0.01),其中对有机碳水平起到主导性贡献作用的是水溶性有机碳。因此,对于退化红壤地森林恢复初期,可通过适当密植和立体种植,提高林地生物量和土壤碳密度,并在马尾松等先锋树种针叶林分中补植阔叶乔灌木,以增加土壤活性有机碳含量,增大土壤水库容量,从而有利于土壤水库结构和功能以及退化生态系统的快速恢复。     

Uncertainty in soil carbon accounting due to unrecognized soil erosion

The movement of soil organic carbon (SOC) during erosion and deposition events represents a major perturbation to the terrestrial carbon cycle. Despite the recognized impact soil redistribution can have on the carbon cycle, few major carbon accounting models currently allow for soil mass flux. Here, we modified a commonly used SOC model to include a soil redistribution term and then applied it to scenarios which explore the implications of unrecognized erosion and deposition for SOC accounting. We show that models that assume a static landscape may be calibrated incorrectly as erosion of SOC is hidden within the decay constants. This implicit inclusion of erosion then limits the predictive capacity of these models when applied to sites with different soil redistribution histories. Decay constants were found to be 15–50% slower when an erosion rate of 15 t soil ha^?1 yr^?1 was explicitly included in the SOC model calibration. Static models cannot account for SOC change resulting from agricultural management practices focused on reducing erosion rates. Without accounting for soil redistribution, a soil sampling scheme which uses a fixed depth to support model development can create large errors in actual and relative changes in SOC stocks. When modest levels of erosion were ignored, the combined uncertainty in carbon sequestration rates was 0.3–1.0 t CO₂ ha^?1 yr^?1. This range is similar to expected sequestration rates for many management options aimed at increasing SOC levels. It is evident from these analyses that explicit recognition of soil redistribution is critical to the success of a carbon monitoring or trading scheme which seeks to credit agricultural activities.     

Variations of soil enzyme activities in a temperate forest soil

Soil enzyme activities (dehydrogenase, urease, phosphatase, and arylsulfatase) in a temperate forest soil were determined in relation to landscape position and seasons. Overstory of the area is dominated by Quercus mongolica, Kalopanax pictus, Carpicus cordata, and Acer pseudo-sieboldianum. The activities were measured in three patches, namely a north-facing backslope, a ridge, and a south-facing backslope in autumn and spring over 2 years. In addition, spatially more detailed analysis for phosphatase was conducted before and after litterfall production in six patches. Dehydrogenase, urease, phosphatase, and arylsulfatase activities varied 1.8–18.5 μg INT-formazan g⁻¹ h⁻¹, 45.4–347.0 μg NH₄ ⁺ g⁻¹ h⁻¹, 0.9–4.5 mmol pNP g⁻¹ h⁻¹, and 0.7–2.6 mmol pNP g⁻¹ h⁻¹, respectively. In general, higher enzyme activities were found in the northern aspect than in the southern aspect. This variation appears to be related to differences in chemical properties (e.g., Fe, Al, and Mg) of soil as well as distribution of leaf litter. Two patterns were discernible in relation to seasonal variations. Dehydrogenase and urease exhibited a positive correlation with mean air temperature, suggesting that temperature would be a major controlling variable for those enzymes. In contrast, higher activities were detected in autumn for phosphatase and arylsulfatase activities, which appeared to be closely related to litter production and distribution. Overall results of this study indicate that soil enzyme activities in a forest floor are influenced by several variables such as temperature, nutrient availability, and input of leaf litter, which are closely related to landscape position.     

Analysis of the life cycle of the soil saprophyte Bacillus cereus in liquid soil extract and in soil

Bacillus is commonly isolated from soils, with organisms of Bacillus cereus sensu lato being prevalent. Knowledge of the ecology of B. cereus and other Bacillus species in soil is far from complete. While the older literature favors a model of growth on soil-associated organic matter, the current paradigm is that B. cereus sensu lato germinates and grows in association with animals or plants, resulting in either symbiotic or pathogenic interactions. An in terra approach to study soil-associated bacteria is described, using filter-sterilized soil-extracted soluble organic matter (SESOM) and artificial soil microcosms (ASM) saturated with SESOM. B. cereus ATCC 14579 displayed a life cycle, with the ability to germinate, grow, and subsequently sporulate in both the liquid SESOM extract and in ASM inserted into wells in agar medium. Cells grew in liquid SESOM without separating, forming multicellular structures that coalesced to form clumps and encasing the ensuing spores in an extracellular matrix. Bacillus was able to translocate from the point of inoculation through soil microcosms as shown by the emergence of outgrowths on the surrounding agar surface. Microscopic inspection revealed bundles of parallel chains inside the soil. The motility inhibitor L-ethionine failed to suppress outgrowth, ruling out translocation by a flagellar-mediated mechanism such as swimming or swarming. Bacillus subtilis subsp. subtilis Marburg and four Bacillus isolates taken at random from soils also displayed a life cycle in SESOM and ASM and were all able to translocate through ASM, even in presence of L-ethionine. These data indicate that B. cereus is a saprophytic bacterium that is able to grow in soil and furthermore that it is adapted to translocate by employing a multicellular mode of growth.     

Phage-host interactions in soil

Abstract Phages are abundant and ubiquitous in nature, and are therefore important components of microbial communities. They can impact on host populations in several ways, including predation and alteration of host phenotype by genetic interactions. The dynamic survival of phage populations in soil requires infective interactions with host populations which must be undergoing growth. Hence survival is limited by the activity of soil bacteria, and phage populations must adopt strategies to overcome periods of inactivity. One of the most effective strategies is the lysogenic cycle of temperate phages. It is argued here that lysogeny in soil has a distinct advantage over virulence for phage and host survival, as opposed to aquatic ecosystems where virulence seems a more successful strategy for phage populations.     

Hydrogen consumption in soil

Summary Gas chromatographic analysis of hydrogen in non-sterile soil incubated aerobically and anaerobically revealed that consumption of the gaseous hydrogen correlated very highly with the initial hydrogen substrate concentration. Hydrogen consumption was not observed in sterile soil. In anaerobically incubated soil, methane evolution was not related to H₂ consumption. The optimum temperature range for H₂ consumption in both aerobic and anaerobically incubated soil was between 20 and 30°C. Activity rapidly decreased at soil temperatures above and below this optimum temperature range.     

盐碱土壤微生物

<正>盐碱地是世界性的低产土壤,有些甚至是不毛之地。但作为一种重要的土地资源,盐渍地的改良利用成为世界性的课题,更被世人关注[1]。甘肃河西走廊地区具有丰富的光热资源,是我国著名的以商品粮生产和优质农作物育种为主的多种农产品生产基地,该区有6.67万hm2盐渍化土地。对该地区盐碱土壤中微生物种群结构、优势菌群及在土壤盐碱化过程中微生物和土壤理化因子之间的交互影响,至今没有系统研     

黄土丘陵区植被恢复的土壤碳水效应

黄土高原大规模植被恢复显著影响了这一区域土壤水分和有机碳(SOC),从而影响其承载的土壤水源涵养和固碳服务。明确深层土壤水分和有机碳对植被恢复的响应特征是当前黄土高原地区生态水文与生态系统服务研究的一个重要科学问题,其中植被类型以及生长年限是这一过程的重要影响因素。然而,目前关于深层土壤有机碳和土壤水分对植被恢复的响应及二者关系的研究较少。通过对陕北典型黄土丘陵区不同植被类型和生长年限下0—5 m土壤水分与有机碳的监测,分析了深层土壤水分和有机碳对植被恢复的响应及其特征。研究发现:(1)植被恢复后0—5 m土层均出现水分亏缺,土壤水分亏缺在表层1 m最低,2—3 m最高;对于不同恢复方式,林地土壤水分亏缺在恢复至21—30a时显著高于前一阶段(11—20a),而在恢复31a后水分开始恢复,而灌木、草地土壤水分亏缺程度则随恢复年限延长不断增加。(2)林地、灌木、草地0—5 m平均土壤有机碳含量为1.97、1.77、1.72 g/kg;林地土壤固碳量随恢复年限的增加而增加,并且在恢复20a时固碳量与对照农田相比出现净增;灌木土壤固碳量随恢复年限先增加后降低;草地土壤固碳量则随退耕年限增加呈下降趋势并且低于对照农田。(3)表层0—1 m土壤水分随恢复年限增加变化不显著,深层土壤水分则随恢复年限增加显著降低;相比而言,随恢复年限增加,土壤有机碳随年限的变化在各层土壤中均不显著。深层土壤水分与土壤有机碳呈现显著的正相关,且土壤有机碳的增加速率低于土壤水分,研究认为,深层土壤固碳与土壤水分关系密切,且深层土壤固碳需要充足水分参与。深层土壤水分亏缺可能限制植被细根的发展,使深层土壤有机碳输入减少。     

Chlorophyll-type compounds in soil

Summary The degradation of chlorophyll-type compounds (chlorophyll and its derivatives) in soil were followed by spectrophotometric and chromatographic techniques to find how closely they represent the bulk of plant material in soil. Tissue enzymes rapidly decomposed chlorophyll in chopped plant material mixed with soil, and decomposition was much slower in material in which the enzymes had been inactivated. This slow decomposition is by micro-organisms which seem to be the important cause of chlorophyll degradation in soil.Micro-organisms decomposed both chlorophyllsa andb in two to four months in field soils; chlorophylla was attacked most. Of the chlorophyll-type compounds, pheophytin, the most closely related derivative of chlorophyll, resisted decomposition largest; chlorophyllide and pehophorbide were found rarely in soil and never in large amounts.Microbiological decomposition increased with increasing moisture content of soil, was fastest at 50 to 60 per cent of the water-holding capacity. Decomposition slowed with increasing soil acidity and was very slow at pH below 4.0. Raising the temperature from 5° to 25°C increased the rate of degradation Neither the species nor quantity of plant material had much effect on the rate of decomposition.     

Effects of soil frost on soil respiration and its radiocarbon signature in a Norway spruce forest soil

Apart from a general increase of mean annual air temperature, climate models predict a regional increase of the frequency and intensity of soil frost with possibly strong effects on C cycling of soils. In this study, we induced mild soil frost (up to −5 °C in a depth of 5 cm below surface) in a Norway spruce forest soil by removing the natural snow cover in the winter of 2005/2006. Soil frost lasted from January to April 2006 and was detected down to 15 cm depth. Soil frost effectively reduced soil respiration in the snow removal plots in comparison to undisturbed control plots. On an annual basis 6.2 t C ha⁻¹ a⁻¹ were emitted in the control plots compared with 5.1 t C ha⁻¹ a⁻¹ in the snow removal plots. Only 14% of this difference was attributed to reduced soil respiration during the soil frost period itself, whereas 63% of this difference originated from differences during the summer of 2006. Radiocarbon (Δ¹⁴C) signature of CO₂ revealed a considerable reduction of heterotrophic respiration on the snow removal plots, only partly compensated for by a slight increase of rhizosphere respiration. Similar CO₂ concentrations in the uppermost mineral horizons of both treatments indicate that differences between the treatments originated from the organic horizons. Extremely low water contents between June and October of 2006 may have inhibited the recovery of the heterotrophic organisms from the frost period, thereby enhancing the differences between the control and snow removal plots. We conclude that soil frost triggered a change in the composition of the microbial community, leading to an increased sensitivity of heterotrophic respiration to summer drought. A CO₂ pulse during thawing, such as described for arable soils several times throughout the literature, with the potential to partly compensate for reduced soil respiration during soil frost, appears to be lacking for this soil. Our results from this experiment indicate that soil frost reduces C emission from forest soils, whereas mild winters may enhance C losses from forest soils.     

Chlorophyll-type compounds in soil

Summary The quantities of chlorophyll-type compounds in a group of 24 arable soils were significantly correlated with nitrogen uptake (r=0.79 and yield (r=0.84) of ryegrass grown in pots in the glasshouse. Partial correlation coefficients showed the amounts of mineral N released on incubating the rewetted air-dry soils were related both to chlorophyll units (measure of chlorophyll-type compounds) and organic C. The chlorophyll units (CU) apparently represented some fraction of organic matter that liberated inorganic nitrogen, because the quantities of chlorophyll-type compounds in the soil were too small (only 0.5–3.0 pounds per acre) to supply this nitrogen. It is likely that the compounds were a residue that resisted decomposition. The CU in soil that had been ploughed from ley decreased very slowly during 3 years of arable cropping.