Influence of a volatile inhibitor in natural or limed soil on fungal spore and seed germination

Seed germination on sterilized moist filter or blotting papers resting on natural soils in stacked “Nalgene” plastic specimen dishes was inhibited particularly in alkaline soils in comparison with controls under similar conditions but without soil. The same response was observed when seeds were suspended on filter or blotting papers above the soils, suggesting the influence of an inhibitory volatile factor. Seed germination was not affected in Good's buffers over the pH range of the soil samples tested indicating that inhibition on filter or blotting papers in contact with soils was not due to the direct effect of pH. The observed inhibition of seed germination is similar to that found in the germination of conidia of common soil fungi; a volatile fungistatic factor was also detected in these soils. Liming of moderately acid soils increased conidial inhibition on indirect soil contact or from volatiles: germination of seeds, however, was not affected by liming in five of six soils tested. These results indicate that seeds of higher plants as well as fungal conidia are affected by some natural soils and volatiles are at least partially responsible for inhibition.     

Effects of metals on the germination and growth of fungal isolates from New Caledonian ultramafic soils

Soils of New Caledonian mining areas have relatively high metal contents. Two ultramafic soils rich in extractable Mn, Fe, Ni and Co and two agricultural soils with much lower concentrations of metals were compared through different experiments. Microbial population numbers and their tolerance to Mn²⁺ and Ni²⁺ were estimated. The effect of five metals (Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺ and Mg²⁺) upon spore germination and mycelial growth was investigated for fungi isolated from the two types of soils. Nickel appeared to be the most toxic metal, but the other metals also had inhibitory effects at concentrations similar to those which occur in ultramafic soils. Spore germination was more sensitive to metals than mycelial growth. The toxic effects of the five metals were not cumulative when mixed together into the medium; antagonism between ions, partly neutralizing their effects may account for this. Fungal isolates from ultramafic soils appeared to be more tolerant to metals than those from agricultural soils. Some ultramafic soil isolates appeared to actually require the presence of metals, with their growth being stimulated by relatively high concentrations of these elements. Two fungal isolates of genera which are often common in agricultural soils (i.e. Curvularia and Fusarium), and which are not present in New Caledonian ultramafic soils were also tested. Curvularia was more sensitive to the five metals than all the other isolates and Fusarium was particularly inhibited by Ni²⁺. However, a proportion of the spores of each isolate was able to germinate and to grow moderately well in the presence of relatively high metal concentrations. Their absence from ultramafic soils is thought to result from their elimination by competitors that are more tolerant to metals.     

Effects of hexachlorocyclohexane on rhizosphere fungal propagules and root colonization by arbuscular mycorrhizal fungi in Plantago lanceolata

Lindane ( γ‐hexachlorocyclohexane or γ‐HCH) is an organochlorine insecticide previously used extensively for the control of agricultural pests. We studied the effects of soil HCH contamination on vegetation and its associated arbuscular mycorrhizas (AM). The polluted and unpolluted plots had similar plant cover, with the same species richness and abundance. Plantago lanceolata plants were selected for mycorrhizal analysis because of their presence in both plots and known mycotrophy. The presence of HCH appeared to have no significant effect on the extent of colonization of Plantago roots by AM, suggesting a similar functionality of the fungal symbionts. However, infective AM propagules, the density of AM spores and viable AM hyphae in the rhizosphere were much less in the HCH‐polluted soil than in the unpolluted plot. Pre‐inoculation of four plant species with an isolate of Glomus deserticola obtained from the HCH‐contaminated soil resulted in increased growth and fungal colonization of roots compared with plants pre‐inoculated with the introduced fungus G. macrocarpum or colonized by the consortium of indigenous AM fungal species, when those plants were transplanted to an HCH‐contaminated soil. This suggests that the fungus increases the tolerance of plants to the toxic soil environment. We conclude that herbaceous and woody plants can grow in soil with little P contaminated with <100 mg HCH kg^?1 with the help of tolerant AM, despite the detrimental effect of HCH on AM fungal propagules in soil. The effects of AM fungi on plant growth and soil microbial community structure in HCH‐polluted sites could be important for remediation of the pollutant through the microbial activity in the rhizosphere.     

Compaction by wheels: a numerical model for agricultural soils

A simple, numerical model was developed to predict changes in soil dry bulk density resulting from the passage of wheels. The model uses Söhne's solutions to estimate stress increases, and empirical isotropic stress-strain data to predict soil volume changes. Predicted and measured increases in bulk density, resulting from the passage of various agricultural vehicles, compared favourably at most depths but the model underestimated the compaction of loose soil in close proximity to underlying dense layers. The model may also be used to compare the compaction caused by various types and arrangements of wheels and to assess the contribution made by a particular input variable. Examples of such uses are given.     

Biological crusts as a model system for examining the biodiversity-ecosystem function relationship in soils

Despite that soils may be the greatest repository of biodiversity on Earth, and that most terrestrial ecosystem functions occur in the soil, research on the role of soil biodiversity in ecosystem function has lagged behind corresponding research on aboveground organisms. Soil organisms pose special problems to biodiversity-function research, including the fact that we usually do not know their identity nor what they do in soil ecosystems, cannot easily estimate their biodiversity, and cannot culture the majority of the organisms for use in manipulative experiments. We propose here that biological soil crusts (BSCs) of deserts and many other ecosystems may serve as a useful model system for diversity-function research because the species concept is relatively well-defined within BSC organisms, their functional attributes are relatively well-known, and estimation and manipulation of biodiversity in experiments are feasible, at least within some groups of BSC biota. In spite of these features, there is a pronounced lack of research on biodiversity-function using these organisms. At least two complementary approaches are possible: experiments using artificially-constructed BSCs, and observational studies which statistically control for the effects of other factors which are likely to covary with biodiversity. We applied the latter to four observational datasets collected at multiple spatial scales in Spain and the United States using structural equation models or path analysis using ecosystem function indicators relating to hydrology, trapping and retention of soil resources, and nutrient cycling. We found that, even when total BSC abundance and key environmental gradients are controlled for, direct and approximately linear relationships between species richness and/or evenness and indicators of ecosystem functioning were common. Such relationships appear to vary independently of region or spatial scale, but their strength seems to differ in every dataset. Functional group richness did not seem to adequately capture biodiversity-function relationships, suggesting that bryophyte and lichen components of BSC may exhibit low redundancy. More research employing the multi-trophic, multi-functional, and manipulable BSC system may enable more rapid understanding of the consequences of biodiversity loss in soils, and help enable a biodiversity-function theory that is pertinent to the numerous ecosystem services provided by soil organisms.     

Loss of yield caused by soil erosion on sandy soils in the UK

Abstract. Soil productivity, the intrinsic ability of land to yield useful products, can be affected by soil erosion. While much research has been carried out on the processes, there is as yet little information on the impact of soil erosion on in situ productivity of agricultural land in the British Isles. This paper reports the results of a de-surfacing experiment on deep sandy soils in East Anglia. Grain yields of fertilized barley planted immediately after de-surfacing were at least 15 and 45% less on 15 and 25 cm de-surfaced plots than on non-desurfaced soils. There was strong evidence pointing to an acceleration of soil erosion itself on the de-surfaced plots. Both the amount of water stored in the topsoil and water use by the crop decreased with increasing severity of simulated erosion. We observed a drop in organic matter and readily available nitrogen with erosion. Nitrogen mineralization and leaching losses were also affected by simulated soil erosion. The experiment showed that sudden severe erosion may induce substantial barley production losses on deep sandy soils. The size and effect of de-surfacing depends on a number of factors such as soil depth, subsoil type, precipitation and crop type.     

非饱和土双应力变量广义土水特征曲线模型验证

利用基于轴平移技术的Geo-Expert高级型应力相关土-水特征曲线压力板仪研究不同覆土压力(0、40、100、200 k Pa)对南阳膨胀土土水特征曲线(soil-water characteristic curve,SWCC)的影响;并对提出的考虑土体变形及多孔隙分布形态的双应力变量广义SWCC表征方程进行如下试验验证:1)不同覆土压力下微多孔隙分布形态的南阳膨胀土侧限固结试验及脱湿试验SWCC验证;2)零净法向应力状态双孔隙尺度硅藻土双峰SWCC试验验证;3)不同净围压状态下单孔隙尺度韩国残积土SWCC试验验证;4)多应力路径下法国Bapaume黄土,不同初始干密度下日本Edosaki砂土在脱湿-吸湿过程SWCC试验验证;并比较分析新方程与van Genuchten方程及Fredlund等方程的差异性。结果表明:1)覆土压力会显著改变膨胀土结构及孔隙通道,进而改变SWCC边界效应区、过渡区形态;也改变了双重孔隙尺度土壤的进气值;第1个波峰SWCC进气值均在1 k Pa左右;相比于零覆土压力试样,40、100、200 k Pa覆土压力试样第2个波峰SWCC进气值分别高4.74、17.58、67.23 k Pa;2)未考虑净法向应力影响的单应力状态多峰SWCC、考虑侧限双应力状态多峰SWCC、各向同性净法向应力单峰SWCC、不同脱湿-吸湿路径SWCC及不同初始干密度的SWCC试验拟合曲线均表明,双应力广义SWCC具有包容复杂影响因素的能力;3)新方程能够利用至少3个土-水数据即可拟合出具有较高的精度的整条SWCC。研究为定量描述土壤的持水、渗透及强度特性提供参考。     

封闭系统水稻土甲烷氧化的模拟

Methane oxidation by paddy soils in a closed system could be simulated by the equation x=k1xo/(k1 k2x0)exp(k2t)-k2x0 where x0 and x are the CH4 concentrations at time zero and t,respectively;k1 and k2 are constants related to the constant of first-order-kinetics.According to the equation the change of soil ability to oxidize CH4 could be estimated by the equation Ac=k2/k1(x0-x)x0k2/k1-1.The results showed that the soil ability to oxidize CH4 varied,depending on the initial CH4 concentration.High initial CH4 concentration stimulated soil ability to consume CH4,while low concentration depressed the ablility.This characteristic of paddy soil seemed to be of considerable significance to self-adjusting CH4 emission from flooded rice fields if there exist oxic microsites in the soil.     

Low importance for a fungal based food web in arable soils under mineral and organic fertilization indicated by Collembola grazers

We investigated the Collembola community at an arable field where mineral and organic fertilizers have been applied at low and high rates for 27 years. As food resources for Collembola, the soil microbial community was analyzed using phospholipid fatty acids (PLFAs). A special focus was put on AM fungi, which were estimated by the marker 16:1ω5 in PLFA (viable hyphae) and neutral lipid fatty acid (NLFA – storage fat in spores) fractions. Additionally, whole cellular lipids in crop plant tissues and manure were assessed. Greater Collembola species richness occurred in plots where mineral fertilizer was added. In contrast, soil microbial biomass including AM fungal hyphae increased with addition of organic fertilizer, while the amount of AM fungal spores and biomass of saprotrophic fungi were not affected by fertilizer type. The lipid pattern in wheat roots was altered by fertilizer type, application rate and their interaction, indicating different rhizosphere communities. In sum, the availability and composition of food resources for Collembola changed considerably due to farm management practice. The major diet of three dominant Collembola species, Isotoma viridis, Willemia anophthalma and Polyacanthella schäffer was determined by lipid profiling. Multivariate analysis demonstrated species specific lipid patterns, suggesting greater importance of species than management practice on the diet choice. Nevertheless, feeding strategy was affected by fertilizer type and availability of resources, as trophic biomarker fatty acids indicated feeding on wheat roots (and to some extent saprotrophic fungi) with mineral and a shift to soil organic matter (litter, detritus) with organic fertilization. Although AM fungi dominated the soil fungal community, the AMF marker 16:1ω5 was not detected in Collembola lipids, indicating that these were not consumed. The very low amount of saprotrophic fungi in the soil and the fact that Collembola as major fungal grazers did not feed on AM fungi indicates that the fungal energy channel in the investigated arable field is of little importance to the faunal food web.     

A mathematical model for the adsorption of water vapor by soils

A two-parameter mathematical model based on some physical assumptions was developed for the adsorption of water vapor by soils: W = W _mh[(p/p ₀) − (p/p ₀)³ + (p/p ₀)⁶] + W _res. It was shown that one of the model’s parameters is close to a conventional soil-hydrological constant, namely, the maximum hygroscopic moisture, or maximum hygroscopicity W _mh. The second parameter reflects the residual water content W _res as the content of immobilized water, which is bound to the most active part of the adsorbing surface, is adsorbed at the initial stage of adsorption (0 ≤ p/p ₀ ≤ 0.05), and later does not participate in the adsorption processes. Methods were proposed for the differential calculation of singular points and parameters of the model corresponding to the characteristic physical phenomena of water vapor adsorption in soils. The model was tested for the quantitative assessment of the interaction between the soil solid phase and the water vapor in different soils (a soddy-strongly podzolic soil, an ordinary chernozem, a chestnut soil, and a medium-columnar solonetz). A method was proposed for calculating the integral adsorption energy E _max of the soil solid phase-water vapor interaction. It was shown that the E _max values are determined by the physicochemical properties of the soils and characterize the capacity of the separate soil horizons for adsorbing water vapor. The relationship of the integral adsorption energy of the soils with the relative pressure of the water vapor and the water content was studied.     

非饱和土双应力变量广义土水特征曲线理论模型构建

土水特征曲线(soil-water characteristic curve,SWCC)方程是非饱和土力学中最重要的土性表征手段之一。该文评价当前经典的SWCC方程,指出其未具有包容复杂因素的能力,具有灵活性的优点但却同时具有对试验数据量依赖性高的缺点,不能处理多孔隙尺度集群土体固-液-气共同运动及作用的水力-力学耦合效应问题。建立双应力变量广义SWCC概念图示并定义相对体积含水比,基于Fredlund双应力变量理论及van Genuchten土-水表征方程,构建考虑土体变形及多孔隙分布形态的双应力状态变量的广义SWCC方程。相较于2个参数的Brooks等的方程、3个参数的van Genuchten方程以及4个参数的Fredlund等的方程,广义SWCC方程仅3个参数,其中2个参数在双对数坐标系的"相对体积含水比-吸力"平面中进行最小二乘法线性拟合得到,仅1个参数需非线性最小二乘法拟合得到。该模型可利用不同应力状态下的至少3个土水试验数据点,绘制出1条具有适宜精度的单峰SWCC;方程考虑了多峰孔隙概率密度函数分布及土体变形因素,实现了从应力历史推广到应力状态的广义情况,为定量描述不同孔隙结构土体双应力状态下的持水特性、渗透特性和强度特性提供了一条途径。     

Impact of heavy metal amended sewage sludge on forest soils as assessed by bacterial and fungal biosensors

Bacterial and fungal bioluminescence-based biosensors were used as indicators of potential heavy metal toxicity to microorganisms in the needle litter of a mature Pinus radiata forest under heavy metal contaminated sewage sludge. Sewage sludge was amended with increasing concentrations of Cu, Ni and Zn and applied to the surface of a mature P. radiata forest. The response of the bacterial and fungal biosensors to soluble Cu, Ni and Zn in needle litter extracts was investigated. The bioluminescence response of the bacterial biosensor Escherichia coli HB101 pUCD607 declined as water-soluble Zn concentrations increased. The effective concentrations that gave a 50% reduction in bioluminescence (EC₅₀ values) for water-soluble Zn and total litter Zn were 1.3 mg l⁻¹ and 3700 mg kg⁻¹, respectively. The bioluminescence response of the fungal biosensor Armillaria mellea declined as soluble Cu concentrations increased. The EC₅₀ values for water-soluble Cu and total litter Cu were 0.12 mg l⁻¹ and 540 mg kg⁻¹, respectively. No decline in bioluminescence was noted for either the bacterial or fungal biosensor on exposure to increasing concentrations of water-soluble Ni. The use of a combination of bacterial and fungal biosensors offers a rapid and sensitive tool for assessing toxicity of heavy metals to microorganisms and, thus, elucidating the environmental impact of contaminants in sewage sludge on litter dwelling microorganisms.     

Suitability of a hydraulic‐conductivity model for predicting salt effects on swelling soils

Many empirical approaches have been developed to analyze changes in hydraulic conductivity due to concentration and composition of equilibrium solution. However, in swelling soils these approaches fail to perform satisfactorily, mainly due to the complex nature of clay minerals and soil–water interactions. The present study describes the changes in hydraulic conductivity of clay (Typic Haplustert) and clay‐loam (Vertic Haplustept) soils with change in electrolyte concentration (TEC) and sodium‐adsorption ratio (SAR) of equilibrium solution and assesses the suitability of a model developed by Russo and Bresler (1977) to describe the effects of mixed Na‐Ca‐Mg solutions on hydraulic conductivity. Four solutions encompassing two TEC levels viz., 5 and 50 mmol_c L^–1 and two SAR levels viz., 2.5 and 30 mmol^1/2 L^–1/2 were synthesized to equilibrate the soil samples using pure chloride salts of Ca, Mg, and Na at Ca : Mg = 2:1. Diluting 50 mmol_c L^–1 solution to 5 mmol_c L^–1 reduced saturated hydraulic conductivity of both soils by 66%, and increasing SAR from 2.5 to 30 mmol^1/2 L^–1/2 decreased saturated hydraulic conductivity by 82% and 79% in clay and clay‐loam soils, respectively. Near saturation, the magnitude of the change in unsaturated hydraulic conductivity due to the change in TEC and SAR was of 10³‐ and 10²‐fold, and at volumetric water content of 0.20 cm³ cm^–3, it was of 10¹⁴‐ and 10⁶‐fold in clay and clay‐loam soils, respectively. Differences between experimental and predicted values of saturated hydraulic conductivity ranged between 0.6% and 11% in clay and between 0.06% and 2.1% in clay‐loam soils. Difference between experimental and predicted values of unsaturated hydraulic conductivity widened with drying in both soils. Predicted values were in good agreement with the experimental values of hydraulic conductivity in clay and clay‐loam soils with R² values of 0.98 and 0.94, respectively. The model can be satisfactorily used to describe salt effects on hydraulic conductivity of swelling soils in arid and semiarid areas, where groundwater quality is poor.     

Testing a mechanistic model. IV. Describing the effects of pH on zinc retention by soils

Samples of two soils were incubated at 60°C for 24 h with several levels of either calcium carbonate or hydrochloric acid. Zinc retention was then measured on subsamples of the treated soil over 24 h at 25°C. The results were compared with published experiments (Bar-Yosef, 1979; Harter, 1983) in which zinc retention was also measured over a range of concentrations and pH values, but using different experimental conditions. Zinc retention increased as pH increased. In all cases, this effect could be described by assuming that the ZnOH⁺ ion was retained and the effect of pH was due to the increased proportion of this ion in solution. Over most of the pH range it was not necessary to assume any contribution from a decrease in the electrostatic potential of the reacting surfaces with increasing pH. This contrasts with the effects of pH on phosphate and fluoride retention and suggests that the materials that react with zinc differ from those that react with anions. The shape of plots of zinc retention against ZnOH⁺ concentration was reproduced using a model in which it was assumed that there was a range of values of electrostatic potential. A similar model had previously been used for anions. Zinc would tend to react with the most negative end of this range and phosphate with the least negative end. This further suggests that zinc and anions may react with different materials.     

Integrated phytoremediation system for uranium-contaminated soils by adding a plant growth promoting bacterial mixture and mowing grass

Journal of Soils and Sediments - Plant-microorganism combined bioremediation is an efficient tool to decontaminate contaminated soils, and seeking the best matching partners between plants and...     

Identification of degraded forest soils by means of a fuzzy‐logic based model

The term ”︁forest soil degradation” is frequently used in forest ecology. It is a highly integrated site property summarizing negative effects over a wide, yet undefined range of variables and a complex range of processes. In forest ecology, different, undefined, and idiosyncratic meanings of the term ’︁soil degradation’ are used. The evaluation for a particular soil is therefore not clear and may be inconsistent among experts. We integrated indicators of forest soil degradation into a fuzzy‐logic based model and predicted forest soil degradation for a set of sites by means of standard soil chemical data and easily accessible site characteristics. For validation we used expert judgements on selected sites. We also compared if the predicted soil degradation agrees with the results of a recent assessment of the ”︁naturalness” (hemeroby) of Austrian forests. The predicted results were consistent with our expectations: sites with a long history of nutrient exploitation were found to be degraded by the model. The fuzzy‐logic based model is open. Rules can be changed, additional rules can be included and others can be removed, if desired. We want to promote fuzzy‐logic based modeling as a means to support experts decisions in complex situations, where clarification can be added by crisply defining the pathway of the decision making process.     

Development and testing of a model for predicting tillage effects on nitrate leaching from cracked clay soils

Both water movement and nitrate leaching in structured soils are strongly influenced by the nature of the macro-porosity. That macro-porosity can however also be manipulated by choice of tillage operations. In order to investigate the potential impacts of tillage on rates of nitrate leaching from structured soils, a model specific to these soils, CRACK-NP was developed. The model, its application and validation for an experimental site on a heavy clay soil (Verti-Eutric Gleysoil) at Brimstone Farm, Oxfordshire, UK, is described. The model considers the soil as a series of aggregates whose size is also the spacing of the macro-porosity. Water and solutes move in the macro-pores, but within the peds they move only by diffusion, internal infiltration and root uptake (evaporation). The model reflects the influence of diffusion limitation in the release of solutes to by-passing water. The model was then used to investigate the influence of variable ped spacings which were created by variations in tillage practices. The results both from the model and from the field data demonstrated that finer soil structures, which have larger surface contact areas and shorter diffusion path lengths, present greater opportunities for interaction between peds and the water moving around them, and so release more nitrates through the drainage waters.