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  • 1
    ISSN: 1432-0789
    Keywords: Mesic detritivores ; Dry farming ; Mariut desert ; Carabidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The soil fauna of 23 sites in the Mariut region, west of Alexandria, Egypt, was sampled monthly or seasonally for periods of 1,5–2.5 years. These sites range from unutilized littoral sand dunes, to free-grazing pasture, to low- and high-intensity dry farming, to irrigated agriculture. The average population densities of the encountered taxa were compared by corresponding analysis and by ascending hierarchic classification. With intensification of the agricultural practices, true detritivores of the original system, capable of dealing with the available plant and animal litter and adapted to the harsh desert climate, are replaced by other mesic detritivores adapted to the changes in litter quality (less animal and more plant) and also adapted to the new physical and chemical soil conditions. Meanwhile, the increase in plant biomass encourages the appearance and proliferation of cryptic phytophages (agricultural pests), occupying the niche of the removed large (domestic) herbivores. Carnivores (e.g.Carabidae) also change accordingly. Sites can thus be characterized on the basis of their soil faunas, according to the stage of their evolution, and a system of exchange of missing key taxa between sites should be established.
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  • 2
    ISSN: 1432-0789
    Keywords: Rhizosphere bacteria ; Nitrogenase activity ; Triticum aestivum ; Inoculation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Wheat seedlings were inoculated with rhizosphere nitrogen-fixing bacteria and grown gnotobiotically for 15 days. The growth medium consisted of semisolid agar with or without plant nutrients. The bacteria, isolated from roots of field-grown wheat, were three unidentified Gram-negative rods (A1, A2, E1), one Enterobacter agglomerans (C1) and two Bacillus polymyxa (B1, B2). A strain of Azospirillum brasilense (USA 10) was included for comparison. Nitrogenase activity (acetylene reduction activity, ARA) was tested on intact plants after 8 and 15 days of growth. In semisolid agar without plant nutrients, five isolates showed ARA of 0.01–0.9 nmol C2H4 plant−1 h−1, while the two strains of B. polymyxa had higher ARA of 3.3–10.6 nmol C2H4 plant−1 h−1. Plant development was not affected by inoculation with bacteria, except that inoculation with B. polymyxa resulted in shorter shoots and lower root weight. Transmission electronmicroscopy of roots revealed different degrees of infection. A. brasilense, A1 and A2, occurred mainly in the mucilage on the root surface and between outer epidermal cells (low infectivity). B. polymyxa strains and E1 were found in and between epidermal cells (intermediate infectivity) while E. agglomerans invaded the cortex and was occasionally found within the stele (high infectivity).
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  • 3
    ISSN: 1432-0789
    Keywords: Iron ; Phosphorus ; Siderophore ; Hydroxamate ; Chelates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Hydroxamate siderophores (HS) are microbially produced, ferric-specific chelates, known to occur in soil, and to be capable of providing iron to higher plants. This study examined the potential for HS to influence the diffusion of both iron and phosphorus to plant roots in soil. The HS desferrioxamine-B (DFOB) and desferriferrichrome (ferrichrome) were compared with the synthetic chelates ethylenediamine [di(o-hydroxyphenylacetic)acid] (EDDHA) and ethylenediamine-tetraacetic acid (EDTA), and citrate, oxalate, and distilled water in their ability to increase diffusion of iron using a simulated root technique. Chelate solutions were pumped through porous fiber bundles imbedded in soil previously labeled with55Fe. In a sandy loam of pH 7.5,55Fe diffusion caused by 10−4 M DFOB was twice that of water, but similar to that caused by 10−4 M EDDHA. However, 10−3 M EDDHA resulted in greater diffusion than 10-3 M DFOB. The diffusions resulting from equimolar quantities of citrate, oxalate, and EDTA were similar to that with distilled water. In a clay soil of pH 5.2 previously labeled with55Fe and32 P, the response in55Fe diffusion to chelate treatments was: 10−4 M EDDHA 〉 10−4 M ferrichrome 〉 10−3 M DFOB 〉 10−4 M DFOB 〉 water. Both ferrichrome and EDDHA caused2 P diffusion to increase substantially over that of distilled water. These results suggest that hydroxamate siderophores present in the rhizosphere could effectively increase the level of soluble iron for root uptake and possibly increase phosphorus uptake by solubilization of phosphorus from iron phosphates at acid pH.
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  • 4
    ISSN: 1432-0789
    Keywords: Cyanophyceae ; Ostracoda ; Ricefields ; Grazing ; N2-fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A dry season field experiment conducted for two consecutive years highlighted problems of achieving increased populations of N2-fixing blue-green algae (BGA) in wetland rice fields. Inoculation of non-indigenous BGA strains, either dried or as fresh viable inocula even at high levels of application, was unsuccessful. A limiting effect of grazing invertebrate populations on BGA establishment was evident, but other factors were involved. Reducing grazer pressure did not permit establishment of inoculated BGA; interspecific competition and environmental factors may explain the inoculation failure. Grazer regulation permitted the establishment of a fast-growing indigenous N2-fixing Anabaena and the doubling of N2-fixing activity over a control. Neither inoculation nor grazer control affected grain yields significantly.
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  • 5
    ISSN: 1432-0789
    Keywords: Dormant populations ; Maintenance carbon requirements ; Microbial biomass ; Biomass carbon loss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary An experimental approach was attempted for determining the maintenance carbon requirements of the dormant microbial biomass of two agricultural soils (I, II) and one, forest soil (III). The amount of carbon needed for preventing microbial-C loss during incubation expressed as coefficient m (mg glucose-C·mg-1 biomass-C·h-1) was 0.00031, 0.00017 and 0.00017 h-1 at 28°C and 0.000043, 0.000034 and 0.000016 h-1 at 15°C for soils I, II and III, respectively. Depending on the temperature, the determined m values of the dormant population were two to three orders of magnitude below known values from pure cultures or m values of metabolically activated biomasses under in situ conditions. Corresponding microbial-C loss quotients were comparable to the observed maintenance coefficients but were always above m. The metabolic quotient q for CO2 (mg CO2-C·mg-1 biomass-C·h-1) of the dormant populations in the three soils tested was at q = 0.0018 h-1 (22°C) one order of magnitude below metabolically activated cells but did not correspond to the low maintenance values determined, which implies that in addition to possible utilization of native soil organic matter dormant biomasses must largely have an endogenously derived respiratory activity.
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  • 6
    ISSN: 1432-0789
    Keywords: Hexachlorocyclohexane isomers ; Persistence ; Flooded soil ; Rice rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The relative persistence of α-, β and γ-isomers of hexachlorocyclohexane (HCH) was studied in a flooded soil with and without rice seedlings under greenhouse conditions. β-HCH was more stable than α- and γ-HCH in both planted and unplanted systems. α- and γ-HCH decreased to negligible levels (5.5% for the α-isomer and 2.4% for the γ-isomer) after 30 days in planted and unplanted soils. During the same period, 30.9% of the added β-HCH was recovered from planted soil and 50.6% from unplanted soil. Likewise, in anaerobically (H2 + CO2 atmosphere) incubated mineral salts solution inoculated with suspensions from rice rhizosphere and non-rhizosphere soils, γ-HCH decreased to low levels (〈 15%) within 5 days. Most of the added β-HCH was recovered from mineral solution inoculated with nonrhizosphere soil suspension even after 30 days while β-HCH decreased to 53.6% of the original level in mineral solution inoculated with rice rhizosphere soil suspension. The data reveal that the degradation of anaerobically unstable HCH isomers is not retarded by the possible aeration of a flooded soil by rice roots.
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  • 7
    ISSN: 1432-0789
    Keywords: Soil respiration ; 14C-glucose metabolites ; Zn effects ; bacterial and fungal populations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The effects of zinc added to a diluvial sandy clay loam soil on its microflora and the metabolic products of amended glucose in the soil were investigated, and its influences on both biological and chemical turnover are discussed. Changes in the soil microflora were followed by counting the microbes and measuring their contributions to soil respiration. The transformations of 14C-glucose products were traced in five divided fractions. Amended glucose was readily assimilated into microbial tissues and transformed to metabolites in the control soil. Within the initial 24 h of the incubation, most of the glucose was decomposed and about 40% of the substrate evolved as carbon dioxide. This primary metabolism was attributed to the bacterial population, and the subsequent secondary metabolism was associated with fungal growth rather than bacteria. On the other hand, zinc (1000 μg/g) added as chloride prolonged the primary metabolism of glucose and a large part of the incubation period for 96 h was occupied by this metabolism, which was mostly dependent on the fungal population. Viable bacterial number noticeably within the first 24 h of the incubation. During the course of the subsequent incubation, however, this number increased and the selection for zinc tolerance was suggested.
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  • 8
    ISSN: 1432-0789
    Keywords: Nitrification ; MPN of ammonium oxidizers ; Chlorate inhibition ; Arable soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The number of ammonium-oxidizing bacteria was measured with the most probable number (MPN) method while potential ammonium oxidation rates were determined with a chlorate inhibition technique in two arable soils. A new method for measuring actual in situ ammonium oxidation in soil cores is presented. One soil was cropped for 4 years with one of four crop-fertilizer combinations: Unfertilized lucerne ley, unfertilized barley, nitrate-fertilized grass ley, or nitrate-fertilized barley. The highest ammonium oxidizer numbers and potential rates were found in the grass ley. The unfertilized barley had one-third the number and activity of the grass ley. Actual rates were in general 5–25 times lower than potential rates. The other soil was that undergoing a 27-year-old field trial with a fallow and four different cropping treatments: No addition, nitrate, nitrate + straw, or manure. Ammonium oxidizer numbers were highest in the manure and straw treatments. MPN numbers and potential rates were lowest in the fallow treatment. Typical specific potential rates were 30 ng N oxidized cell−1 h−1. Actual rates were in general 40 times lower than potential rates. Actual ammonium oxidation measurements seem to correspond to actual in situ activity at the moment of sampling, whereas the MPN technique and the potential measurements reflect events that occurred weeks to months before the sampling.
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  • 9
    ISSN: 1432-0789
    Keywords: Microorganisms ; Polysaccharide ; SoilStabilization ; Straw
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Studies using cocultures of a cellulolytic fungus with a capsular organism show that microbial polysaccharides can be synthesized during the degradation of wheat straw. Polysaccharide accounted for up to 1.6% (w/w) of the initial straw weight but the sugar composition and viscosity indicated that a large fraction was low molecular weight material of plant origin. Nevertheless several cocultures produced sufficient microbial polysaccharide effectively to stabilize aggregates of Hamble silt loam. This correlated significantly with increased viscosity and also stabilization of Mount St. Helens volcanic ash. Four cocultures, Sordaria alcina with two strains of Enterobacter cloacae and a Pseudomonas sp. and Trichoderma harzianum with E. cloacae, were significantly more effective than a natural inoculum from straw. Inoculation of straw to produce a “compost” which can increase the stability of poorly structured soils is suggested.
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  • 10
    ISSN: 1432-0789
    Keywords: Earthworm bioassay ; Soil toxicity assessment ; Complex mixtures ; Hazardous materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Three different laboratory earthworm protocols for assessing the potential toxicity of environmental samples were evaluated using Eisenia fetida. The 48-h Contact Test (CT) is a short test and may indicate the presence of water-soluble chemicals. The 14-day Soil Test (ST) is best suited to assess chemical impacts of either known or unknown chemicals in soils. The Giant Axon Conduction Velocity protocol (GACVT) used with either the CT or the ST can detect sublethal neurotoxic effects in shorter periods of time and at lower chemical concentrations than mortality tests. The use of these tests is suggested as an estimate of potential toxicity of environmental soil samples.
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