Propagule size: Its relation to longevity and reproductive capacity

Analysis of published data revealed that there was no correlation between propagule size and longevity among 66 species of microorganisms. The correlation coefficient was —0.204 which was not significantly different from zero at P = 0.05. However, there was an inverse relationship between propagule size and number of propagules produced per unit area of nutrient media among 43 identified species of microorganisms tested. The total volumes (volume x number) of propagules produced per unit area were fairly constant and were not correlated with propagule size. Similar correlations were obtained with propagules produced on diseased fruits by 6 pathogenic fungi. There was a good correlation (r = 0.974) between reproductive capacity and relative abundance in soil among selected microorganisms. It is, therefore, postulated that the higher reproductive capacity of smaller microorganisms, as compared to large microorganisms, is an important factor leading to the inverse size-number relationship among microorganisms in nature.     

Sampling soil microfloras: Optimization of density gradient centrifugation in percoll to separate microorganisms from soil suspensions

Suspensions of non-filamentous microorganisms and clay were prepared by dispersing soil with an ion-exchange resin, sieving, elutriation and ultrafiltration. Cells were separated from clay by density gradient centrifugation in linear gradients of Percoll (limiting densities 1.101 and l.139 gcm⁻³). By fractionating the density gradient, the mixed population could be separated into components of differing density. Percoll could be separated from microorganisms by gel chromatography on columns of Sephacryl S-1000 or centrifugation after dilution.     

Resistance of soil microorganisms to starvation

Most groups of soil microorganisms died when exposed to prolonged starvation in a carbon-free solution, but the relative abundance of Bacillus and actinomycetes increased with time. Certain non-sporeforming bacteria also persisted. The ability of individual soil isolates to endure starvation in solution was not correlated with their glycogen content or rate of endogenous respiration. However, cells of the resistant populations were rich in poly-β-hydroxybutyrate, whereas the starvation-susceptible bacteria generally contained little of this substance. Poly-β-hydroxybutyrate was used rapidly in cells deprived of exogenous sources of carbon.     

Species-specific earthworm population responses in relation to flooding dynamics in a Dutch floodplain soil

Earthworms dominate the animal biomass in moist floodplain soils. They are known to survive long periods in aerated water, but little is known about earthworm population dynamics in floodplain systems with changing inundation frequencies. This study determined earthworm population dynamics in a floodplain system, in relation to frequency and duration of flooding events. From October 2000 to May 2003 earthworms were hand sorted in the ‘Afferdensche en Deestsche Waarden’, a floodplain on the south bank of the river Rhine, near Druten, The Netherlands. Earthworm numbers and biomasses per age class (adult, subadult, juvenile) were recorded. Numbers and biomasses tend to decrease during flooding. Lumbricus terrestris was found in high numbers (>10/m²) only at the end of a flooding period. Allolobophora chlorotica was hardly affected by flooding; their biomass remained stable during the year. Aporrectodea caliginosa showed fluctuating numbers and biomasses during the sampling period that did not correlate with flooding frequency. Numbers and biomasses of Lumbricus rubellus were strongly reduced at the end of each flooding event, but their population densities fully recovered until next flooding event. Earthworm populations in floodplains fluctuate in time, depending on the season and on the time, duration and frequency of flooding. Different earthworm species react differently towards these flooding dynamics.     

Influence of straw size on activity and biomass of soil microorganisms during decomposition

This study relates to the pattern of activity and biomass of soil microorganisms due to varying residue particle sizes during incubation. Wheat straw (8 t ha^–1) of different sizes (powdered, 0.9 cm, 1.8 cm, 2.9 cm and 4.4 cm) was incubated for 90 days at 50% water holding capacity in a loamy sand soil of Typic Camborthid. Dehydrogenase activity, an indicator of the total microbial activity, and microbial biomass were influenced by straw sizes during incubation. The peak dehydrogenase activity was recorded 21 days after incorporation of residue and it was highest in the powdered straw and decreased with increase in the straw length. The maximum biomass C build up was observed between 15 (< 1 cm) and 45 (> 1 cm) days after incorporation. The C:N ratio in the soil after 90 days of residue incorporation varied, with increase in straw size, between 12.1:1 and 20.8:1. The results reveal that for faster decomposition the length of the wheat straw should not exceed 1 cm.     

Chloroform fumigation technique as a means of determining the size of specialized soil microbial populations: Application to pesticide-degrading microorganisms

A method is proposed for studying the dynamic behaviour of the soil microbial population involved in the degradation of 2,4-D. The method is based on in situ specific-labelling of that population following treatment of the soil with ¹⁴C-labelled herbicide and investigating the kinetics of the incorporation of radioactivity by the soil microflora in treated soil samples subjected to the chloroform-fumigation technique after varying periods of exposure. Non-degraded herbicide still present in the soil after fumigation did not affect the overall flush of CO₂ and was not further broken down at a sufficient rate to appreciably contribute to ¹⁴CO₂ evolution. The validity of the method to assess the soil biomass of the 2,4-D degrading population together with its time variations is discussed in relation to the position of the ¹⁴C on the pesticide molecule.     

泥炭土壤上与胞外酶相关的土壤微生物体与Marsh orchid的交互作用

The nature of the interactions between microbes and roots of plants in a peaty soil were studied in a laboratorybased experiment by measuring activities of β-glucosidase, phosphatase, N-acetylglucosaminidase, and arylsulphatase. The experiment was based on control （autoclaved）, bacteria-inoculated, and plant （transplanted with Dactylorhiza） treatments, and samples were collected over 4 sampling intervals. Higher enzyme activities were associated with the bacteria-inoculated treatment, suggesting that soil enzyme activities are mainly of microbial origin. For example,β-glucosidase activity varied between 25-30μmol g^-1 min^-1 in the bacteria-inoculated samples whilst the activity of the control ranged between 4-12 μmol g^-1 min^-1. A similar pattern was found for all other enzymes. At the end of the incubation, the microcosms were destructively sampled and the enzyme activities determined in bulk soil, rhizospheric soil, and on the root surface. Detailed measurement in different fractions of the peat indicated that higher activities were found in rhizosphere. However, the higher activities of β-glucosidase, N-acetylglucosaminidase, and arylsulphatase appeared to be associated with bacterial proliferation on the root surface, whilst a larger proportion of phosphatase appeared to be released from root surface.     

Microenvironments of soil microorganisms

Summary Ultrastructural studies of soil micro-organisms and the microenvironments surrounding them are reviewed. Soil microfauna, and bacteria, actinomycetes and fungi, fixed and embedded in situ, were examined by electron microscopy (both transmission and scanning). In some cases ultrastructural histochemistry was used to detect and identify the organic matter with which microorganisms were associated and to examine the polymeric microbial materials (enzymes, extracellular polysaccharides) they produced. Although some small organisms (0.3 m diameter) occurred singly in dense fabrics of clay or humified organic matter, larger bacteria occurred in rhizospheres, in small colonies in the larger micropores or associated with substantial deposits of organic matter (faecal pellets, carbohydrate-rich plant cell-wall debris). Whereas rhizospheres had mixed microbial populations, individual microvoids in the bulk soil usually contained only one type of micro-organism. Following chloroform treatment, microorganisms were found only in mucigel deposits or deep in the interiors of micropores, suggesting that these constitute protected sites where microorganisms survive temporarily adverse conditions. Soil microfauna and fungi were mainly confined to the larger voids. Although some live hyphae occurred in the outer regions of aggregates, hyphae deep within soil fabrics were usually devoid of cytoplasmic organelles. Faecal pellets, plant tissues and cell-wall remnants comprised the most frequent, larger organic masses, while the most common micron- and submicron-sized organic matter consisted of fibrous or amorphous humified matter. Unequivocal detection of enzymes was limited to the surface of microorganisms.     

Earthworm density and biomass in relation to plant diversity and soil properties in a Palouse prairie remnant

Earthworms are important soil animals in grassland ecosystems and are considered to be important to soil quality. The overall impact of earthworms on soil properties and plant diversity, however, depends on earthworm species, functional group and the type of ecosystem. The primary purpose of this study was to document the relationship among earthworms, key soil properties and native and exotic plant diversity in the little studied, Palouse prairie grassland (Idaho, USA). A secondary objective was to determine the effectiveness of three methods commonly used to sample earthworms. A hillslope characterized by Palouse prairie vegetation, well-expressed, hummocky (mounded) topography and known to support both exotic and native earthworm species was selected for study. The hillslope was divided into three zones [annual-dominated (AD), mixed (MX) and perennial-dominated (PD)] based on characteristics of the inter-mound plant communities described in previous research. Total earthworm biomass in the MX zone (53.5 g m⁻²) was significantly greater than in the PD zone (14.7 g m⁻²) (P = 0.0384), but did not differ from the AD zone. Earthworm density ranged from 52 to 81.1 individuals m⁻² but was not significantly different across zones. Total C and N at 0 to 10 and 30 to 50 cm depths were significantly greater in the AD and PD zones as compared to the same depths in the MX zone. Soil textural class was silt loam within all zones and the soil silt fraction was positively correlated with total exotic earthworm density (R = 0.783, P = 0.0125) and biomass (R = 0.816, P = 0.0072). Native earthworms were only found in the zone with the greatest total and native plant diversity (PD). Total soil C and N were not correlated to earthworm density, but soil total C and N were significantly negatively correlated with exotic plant density, which indicates that invasive plants may be decreasing soil total C (R = −0.800) and N (R = −0.800). Calculated earthworm densities using data from the electroshocker were generally lower than those based on the hand-sorting method. Electroshocking, however, created lower disturbance and was the only method that resulted in the collection of the deep-burrowing, native species Driloleirus americanus.     

Oxalate-metabolizing microorganisms in sagebrush steppe soil

Oxalate metabolization by soil microorganisms was assessed using a calcium oxalate clearing medium and¹⁴CO₂ release from [¹⁴C]-oxalate. Three saprophytic fungi, two bacteria, and one actinomycete tested produced¹⁴CO₂ when grown in culture with [¹⁴C]-oxalate, yet failed to test positive for oxalate degradation using a calcium-clearing medium. A field plot was then established to determine the effects of oxalate inputs on oxalate metabolism. The amount of [¹⁴C]-oxalate metabolized by soil microorganisms and the number of bacteria metabolizing oxalate increased within 24 h after the addition of oxalic acid at a concentration of 11.1 mol g^-1 soil. Oxalate metabolism and bacterial numbers returned to the baseline within 84 days. Soil phosphate concentrations increased significantly above baseline 7 days after the addition of oxalate and did not return to prespike levels. Fungi, bacteria, and actinomycetes were able to metabolize oxalate. Therefore, while oxalate can influence P cycles by increasing the amount of available phosphates, that increase is mediated by microbes that metabolize the oxalates.     

Transport of microorganisms through soil

Microorganisms migrating into and through soil from sources on the land surface may cause a serious threat to both ground and surface waters. It has been estimated that microorganisms can migrate significant distances in the field. Results from various studies suggested that preferential flow through macropores, worm holes, cracks, and fractures is the main reason for such observations. However, a quantitative representation of this phenomenon has not been provided. Microorganisms migrate through soil by advection and dispersion, while being subjected to effects of filtration, adsorption, desorption, growth, decay, sedimentation and chemotaxis. Both laboratory and field investigations have contributed important information on bacterial movement in soils. Qualitative comparisons are generally transferable from laboratory to field situations. Quantitative agreement is much more difficult to establish. Available mathematical modelling of microbial transport is limited in practical application because of the simplifying assumptions used in its development.     

Selection of soil physical quality indicators in relation to soil erodibility

Soil quality indices based on soil characteristics can be used to assess the sustainability of soil and to assist in soil management decisions. Principal component analysis (PCA) technique was used to identify dominant soil characteristics in relation to soil erodibility in watersheds of submontane Punjab (India). Soil physical and chemical characteristics were evaluated for four locations with four land uses at each location whereas runoff, soil loss and soil erodibility were determined at two locations under natural rainfall conditions and at four locations under simulated rainfall conditions. PCA was performed on 22 physical and chemical soil characteristics, which grouped these soil characteristics into five distinct principal components (PCs). These five PCs namely soil hydraulic factor, density factor, structural factor, sand factor and cation factor, explained 86% variability in data. These PCs also explained 86, 96 and 93% variability under natural rainfall conditions and 75, 76 and 77% variability under simulated rainfall conditions in relation to runoff, soil loss and soil erodibility, respectively. Soil total organic carbon content can be considered as dynamic soil physical quality indicator and can be used to monitor temporal and spatial changes in soil quality.     

Relationship between root length density and soil microorganisms in the rhizospheres of white clover and perennial ryegrass

Abstract

Microbial parameters of rhizosphere soil, such as bacterial numbers or microbial activities, depend on the distance that microbes have to the root surface. In this study we show that the number of bacteria found in rhizosphere soil from white clover is highly correlated with root length density of the rhizosphere soil. In contrast, bacterial numbers, microbial activity (measured as fluorescein diacetate hydrolytic activity), and the amount of extractable carbon (C) in the rhizosphere of perennial ryegrass were independent of the amount of soil recovered from the roots. The missing rhizosphere effect in perennial ryegrass soils can be explained by the high rooting density of ryegrass, whereas the low rooting density of white clover results in gradients of microbial numbers and activities in soils. Results of these studies indicate that it is important to express microbial parameters on root length and soil weight bases, especially for less densely rooted soils.     

红壤腐殖质组成变化特点及其与肥力演变的关系

本文根据面上采样分析和田间定位试验结果,研究红壤腐殖质组成性质变化特点及其与红壤肥力演变的关系。结果表明,旱地红壤腐殖质的H/F比值主要分布在0.1 ~ 0.4,红壤水稻土主要分布在0.3 ~ 0.7,且有从南到北升高,从东到西降低的变化趋势;红壤腐殖质的H/F比值与土壤有机碳含量呈正相关,但在停止外源碳进入8年后,土壤腐殖质的H/F比值和E4值有升高的趋势,侵蚀降低红壤腐殖质的H/F比;土地利用方式的变更由于改变了系统的物质循环状况,对土壤腐殖质的H/F比有明显影响,荒草地和次生林地改为园地,明显提高土壤有机碳含量和腐殖质的H/F比值。     

Ureolytic microorganisms and soil fertility: A review

Abstract

Soil microorganisms play an important role in increasing soil fertility and recycling of nutrients within the soil. Different microorganisms including filamentous fungi, yeasts, mycorrhiza, bacteria, cyanobacteria, and actinomycetes possess the urease enzymes. Urease plays a role in soil enrichment through degradation or hydrolysis of organic nitrogen (N). Urea is an important fertilizer and may enter the soil with the excretions of higher animals and through destruction of the nitrogenous bases contained in the nucleic acids of plant and animal tissues. These products increase soil fertility by an urease. Ureolytic production and activity, and fertility of soil are affected by chemical propertes of soil, environmental factors, sources of urea, and soil microorganism. Problems encountered in use of urea as a fertilizer result from its rapid hydrolysis to ammonium carbonate by soil urease activity and the concomitant rise in pH and accumulation of ammonium. These problems include damage to germinating seedlings and young plants and gaseous loss of urea N as ammonia. The technologies and management practices that can be used to improve urea efficiency and reduce losses include coating of granules, soil incorporation, and use of new slow‐release fertilizers by forming sparingly soluble urea‐aldehyde compounds as ureaforms, crotonylidene diurea, isobutylidene diurea or using natural N‐containing compounds such as composted sludges of municipal and animal wastes. The degradative process of the ureolytic microorganims on animal and plant organic N wastes could help to satisfy condition of eliminating excessive wastes and pollution and simultaneously supply plant with available N.     

Toxicity of arsenic in relation to soil properties: implications to regulatory purposes

Purpose

The present work evaluates the influence of different soil properties and constituents on As solubility in laboratory-contaminated soils, with the aim of assessing the toxicity of this element from the use of bioassays to evaluate the soil leachate toxicity and thereby propose soil guideline values for studies of environmental risk assessment in soil contamination.

Materials and methods

Seven soils with contrasting properties were artificially contaminated in laboratory with increasing concentrations of As. Samples were incubated for 4 weeks, and afterwards, soil solution (1:1) was obtained after shaking for 24 h. The soil leachate toxicity was assessed with two commonly used bioassays (seed germination test with Lactuca sativa and Microtox ® test with Vibrio fischeri).

Results and discussion

The relationship between soluble As and soil properties indicated that iron oxides and organic matter content were the variables most closely related to the reduction of the As solubility, while pH and CaCO₃ increased As solubility in the soil solutions. Toxicity bioassays showed significant differences between soils depending on their properties, with a reduction of the toxicity in the iron-rich soil (no observed effect concentration (NOEC)?=?150 mg kg^?1) and a significant increase in the highly carbonate samples (NOEC between 15 and 25 mg kg^?1).

Conclusions

Soil guideline values for regulatory purposes usually set a single value for large areas (regions or countries) which can produce over- or underestimation of efforts in soil remediation actions. These values should consider different levels according to the main soil properties controlling arsenic mobility and the soil leachate toxicity.     

Responses of soil organic matter and microorganisms to freeze-thaw cycles

Soil organic matter (SOM) biomarker methods were utilized in this study to investigate the responses of fungi and bacteria to freeze-thaw cycles (FTCs) and to examine freeze-thaw-induced changes in SOM composition and substrate availability. Unamended, grass-amended, and lignin-amended soil samples were subject to 10 laboratory FTCs. Three SOM fractions (free lipids, bound lipids, and lignin-derived phenols) with distinct composition, stability and source were examined with chemolysis and biomarker Gas Chromatography/Mass Spectrometry methods and the soil microbial community composition was monitored by phospholipid fatty acid (PLFA) analysis. Soil microbial respiration was also measured before and during freezing and thawing, which was not closely related to microbial biomass in the soil but more strongly controlled by substrate availability and quality. Enhanced microbial mineralization (CO₂ flush), considered to be derived from the freeze-thaw-induced release of easily decomposable organic matter from microbial cell lyses, was detected but quickly diminished with successive FTCs. The biomarker distribution demonstrated that free lipids underwent a considerable size of decrease after repeated FTCs, while bound lipids and lignin compounds remained stable. This observation indicates that labile SOM may be most influenced by increased FTCs and that free lipids may contribute indirectly to the freeze-thaw-induced CO₂ flush from the soil. PLFA analysis revealed that fungal biomass was greatly reduced while bacteria were unaffected through the lab-simulated FTCs. Microbial community shifts may be caused by freezing stress and competition for freeze-thaw-induced substrate release. This novel finding may have an impact on carbon and nutrient turnover with predicted increases in FTCs in certain areas, because fungi and bacteria have different degradation patterns of SOM and the fungi-dominated soil community is considered to have a higher carbon storage capacity than a bacteria-dominated community.     

Effects of microbial population and culture phosphate composition on the activity of pyrophosphatases from soil microorganisms

The quantity of intracellular pyrophosphatases produced in mixed cultures was not related to pyrophosphate or orthophosphate concentration in the culture medium, but high pyrophosphate concentration initially depressed microbial growth, delayed the first signs of pyrophosphate hydrolysis and gave rise to a lower initial rate of pyrophosphate hydrolysis in the culture.Not all cultures produced intracellular pyrophosphatases, but when they were present, the same functional kinds of enzymes appeared to be present when compared on the basis of activation by five cations. All cultures inoculated with fresh soil were able to hydrolyse pyrophosphate in the culture medium, but not all cultures inoculated with stored soil displayed culture pyrophosphatase activity. There was evidence that intracellular pyrophosphatases were responsible for culture pyrophosphatase activity.It was found that cultures showing low intracellular and culture pyrophosphatase activity were dominated by Gram +ve rods. When intracellular and culture phosphatase activities were high, Gram ?ve rods and Gram ?ve cocci dominated the culture populations. As cultures dominated by Gram +ve rods were obtained only from stored soil inoculum, it is considered that during soil storage, Gram +ve rods became dominant in the soil because of the ability of some members of this group to form resistant endospores.     

Crystallinity of soil kaolinites in relation to clay particle-size and soil age

The crystallinity of soil kaolinites as a function of clay particle-size and soil age was investigated in soil chronosequences of the Shingle House Creek and Hawkesbury River alluvial terraces in south-eastern Australia. The youngest soils (late Holocene) in each sequence are texturally uniform Entisols containing kaolinite and illite. The oldest soils (Pleistocene to late Tertiary) are Ustalfs with strong textural differentiation and are predominantly kaolinitic. With increasing age, textural B horizons are increasingly enriched in kaolinite and in particles of fine clay (< 0.2 μm) size. In two sub-fractions of the fine clay (0.2-0.06 μm; < 0.03 μm), no corresponding changes were observed in the crystallinity of kaolinites (as measured by the index, C _k) with age. However, values of C _k were significantly higher in the coarse clay (2-0.2 μm) than for both fine clay fractions in all except the Ultic Paleustalf of the oldest, possibly late Tertiary, terrace of the Hawkesbury River sequence. In this soil, C _k values are low in all three clay-size fractions.
In these sequences, the effects of both clay particle-size and soil age were identified in the crystallinity of kaolinites. Disorder as a result of pedogenesis, however, was associated only with the most prolonged weathering and the strongest soil textural differentiation.