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Soil Microbial Activity (soil + microbial_activity)
Selected AbstractsEcotoxicological effects of hexahydro-1,3,5-trinitro-1,3,5-triazine on soil microbial activities,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2001Ping Gong Abstract Although hexahydro-1,3,5-trinitro-1,3,5-triazine (also called RDX or hexogen) is a potentially toxic explosive compound that persists in soil, its ecotoxicological effects on soil organisms have rarely been assessed. In this study, two uncontaminated garden soils were spiked with 10 to 12,500 mg RDX/kg dry soil. Soil microbial activities, i.e., potential nitrification, nitrogen fixation, dehydrogenase, basal respiration, and substrate-induced respiration were chosen as bioindicators and were determined after 1-, 4-, and 12-weeks of exposure. Experimental results indicate that RDX showed significant inhibition (up to 36% of control) on indigenous soil microbial communities over the period of this study. All five bioindicators responded similarly to the RDX challenge. The length of exposure also affected the microbial toxicity of RDX, with 12-week exposure exerting more significant effects than the shorter exposure periods, suggesting that soil microorganisms might become more vulnerable to RDX when exposure is extended. The estimated lowest observable adverse effect concentration of RDX was 1,235 mg/kg. No biodegradation products of RDX were detected at all three sampling times. Compared with 2,4,6-trinitrotoluene (TNT), RDX is less toxic to microbes, probably because of its resistance to biodegradation under aerobic conditions, which precludes metabolic activation of nitro groups. [source] Degradation of chlorpyrifos, fenamiphos, and chlorothalonil alone and in combination and their effects on soil microbial activityENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2002Brajesh Kumar Singh Abstract The effects of repeated application and of combinations of pesticides on their degradation rates in soil and on some soil microbial properties were studied. Repeated application of chlorpyrifos did not modify its degradation rate, whereas repeated applications of fenamiphos and chlorothalonil suppressed their own rates of degradation. When applied in combination, the presence of chlorothalonil reduced the degradation rate of both chlorpyrifos and fenamiphos, and the half-life of chlorothalonil was extended in the presence of chlorpyrifos. The dynamics of residues of the major metabolites of the different compounds were also affected by the pesticide combinations and, particularly, by the presence of chlorothalonil. The measured soil microbial parameters (enzyme activities and total microbial biomass) were stable in the pesticide-free control soils throughout the 90-d incubation period, but they were all adversely affected by the presence of chlorothalonil in the soil. The effects from fenamiphos or chlorpyrifos on the soil microbial characteristics were either very small or insignificant. [source] Quantifying the relationship between soil organic carbon and soil physical properties using shrinkage modellingEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2009P. Boivin Summary Changes in soil organic carbon (SOC) may strongly affect soil structure and soil physical properties, which in turn may have feedback effects on the soil microbial activity and SOC dynamics. Such interactions are still not quantitatively described and accounted for in SOC dynamics modelling. The objective of this study was to test the hypothesis that soil shrinkage curve (ShC) analysis allows the establishment of close relationships between soil physical properties and SOC. We sampled a rice-cropped vertisol, a cambisol under conventional tillage and no-tillage and a restored cambisol. Soil samples were analysed for clay and SOC content, bulk volume, hydro-structural stability and plasma and structural pore volumes changes on the full water content range using ShC analysis. Although the soils behaved differently according to their constituents and history, changes in SOC linearly affected most of the soil physical properties, with stronger effects than changes in clay content. The observed effects of increasing SOC, such as increasing hydro-structural stability, specific bulk volume and water retention, agreed well with previously reported results. However, using ShC measurement and modelling allowed the observation of all these different effects simultaneously for small changes in SOC, and in a single measurement. Moreover, the relation between SOC changes and physical properties could be quantified. ShC analysis may, therefore, be used to account for the effect of changes in SOC on soil physical properties. [source] Soil microbial activity along an arctic-alpine altitudinal gradient from a seasonal perspectiveEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008U. C. M. Löffler Summary The knowledge on dynamics of soil microbial activity and its correlation to climate and vegetation is still poor but essential for predicting climatic changes scenarios. Seasonal dynamics of soil microbial activity and cell counts were studied along an arctic-alpine altitudinal gradient. The gradient comprised 12 ridges from 1000 to 1600 m altitude. Soil samples were collected during March, May, July and September 2005. The effect of temperature, snow depth and vegetation, all of which changed with altitude, on soil microbial activity and bacterial cell counts was analysed. The potential activities of phosphatase and chitinase were determined using fluorescent 4-methylumbelliferyl labelled analogues. Total and live bacterial cell counts were determined by live-dead-staining. We detected marked differences in soil microbial variables along the altitudinal gradient, forming three major clusters: a low alpine belt, a middle alpine belt, and an intermediate transition zone. Our results demonstrated that more frequent occurrence of shrubs and bryophytes would also increase microbial activity. Furthermore, we detected a clear relation (R2 = 0.6; P < 0.02) between high soil temperatures and greater soil microbial activity during summer. As higher temperatures are predicted to promote shrubs and higher humidity to promote bryophytes we expect microbial activity in dry heath tundra soils will increase with anticipated warmer, and in the case of Scandinavia, more humid climates. We did not find winter microbial activity to be less at snow-free sites than at sites covered by snow up to depths of 30 cm; hence, possible future decreases in snow depth will not result in reduced winter microbial activity. We demonstrate that shrubs support winter microbial activity not only by trapping snow but also directly by increasing the amount of organic carbon. [source] Patterns of rhizosphere carbon flux in sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) saplingsGLOBAL CHANGE BIOLOGY, Issue 6 2005Richard P. Phillips Abstract Despite its importance in the terrestrial C cycle rhizosphere carbon flux (RCF) has rarely been measured for intact root,soil systems. We measured RCF for 8-year-old saplings of sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) collected from the Hubbard Brook Experimental Forest (HBEF), NH and transplanted into pots with native soil horizons intact. Five saplings of each species were pulse labeled with 13CO2 at ambient CO2 concentrations for 4,6 h, and the 13C label was chased through rhizosphere and bulk soil pools in organic and mineral horizons for 7 days. We hypothesized yellow birch roots would supply more labile C to the rhizosphere than sugar maple roots based on the presumed greater C requirements of ectomycorrhizal roots. We observed appearance of the label in rhizosphere soil of both species within the first 24 h, and a striking difference between species in the timing of 13C release to soil. In sugar maple, peak concentration of the label appeared 1 day after labeling and declined over time whereas in birch the label increased in concentration over the 7-day chase period. The sum of root and rhizomicrobial respiration in the pots was 19% and 26% of total soil respiration in sugar maple and yellow birch, respectively. Our estimate of the total amount of RCF released by roots was 6.9,7.1% of assimilated C in sugar maple and 11.2,13.0% of assimilated C in yellow birch. These fluxes extrapolate to 55,57 and 90,104 g C m,2 yr,1 from sugar maple and yellow birch roots, respectively. These results suggest RCF from both arbuscular mycorrhizal and ectomycorrhizal roots represents a substantial flux of C to soil in northern hardwood forests with important implications for soil microbial activity, nutrient availability and C storage. [source] Long-term carbon exchange in a sparse, seasonally dry tussock grasslandGLOBAL CHANGE BIOLOGY, Issue 10 2004John E. Hunt Abstract Rainfall and its seasonal distribution can alter carbon dioxide (CO2) exchange and the sustainability of grassland ecosystems. Using eddy covariance, CO2 exchange between the atmosphere and a sparse grassland was measured for 2 years at Twizel, New Zealand. The years had contrasting distributions of rain and falls (446 mm followed by 933 mm; long-term mean=646 mm). The vegetation was sparse with total above-ground biomass of only 1410 g m,2. During the dry year, leaf area index peaked in spring (November) at 0.7, but it was <0.2 by early summer. The maximum daily net CO2 uptake rate was only 1.5 g C m,2 day,1, and it occurred before mid-summer in both years. On an annual basis, for the dry year, 9 g C m,2 was lost to the atmosphere. During the wet year, 41 g C m,2 was sequestered from the atmosphere. The net exchange rates were determined mostly by the timing and intensity of spring rainfall. The components of ecosystem respiration were measured using chambers. Combining scaled-up measurements with the eddy CO2 effluxes, it was estimated that 85% of ecosystem respiration emanated from the soil surface. Under well-watered conditions, 26% of the soil surface CO2 efflux came from soil microbial activity. Rates of soil microbial CO2 production and net mineral-N production were low and indicative of substrate limitation. Soil respiration declined by a factor of four as the soil water content declined from field capacity (0.21 m3 m,3) to the driest value obtained (0.04 m3 m,3). Rainfall after periods of drought resulted in large, but short-lived, respiration pulses that were curvilinearly related to the increase in root-zone water content. Coupled with the low leaf area and high root : shoot ratio, this sparse grassland had a limited capacity to sequester and store carbon. Assuming a proportionality between carbon gain and rainfall during the summer, rainfall distribution statistics suggest that the ecosystem is sustainable in the long term. [source] Degradation of phthalate esters (PAEs) in soil and the effects of PAEs on soil microcosm activityJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2010Hui-Jun Xie Abstract BACKGROUND: Phthalate esters (PAEs), a class of refractory and toxic organic compounds, are becoming one of the most widespread contaminants in the environment. Degradation of PAEs in soil has been investigated, but limited to one or a few kinds of PAEs. Microorganisms could be regarded as a sensitive bio-indicator for soil contaminants. Therefore, four commonly used PAEs were chosen to investigate their degradation patterns and potential impacts on soil microbial activity with a series of bioassays. RESULT: PAEs in sterile soils changed slightly, while degradation of PAEs in non-sterile soil followed a single first-order kinetic. Higher concentrations of PAEs led to lower ,-glucosidase activity and higher protease activity, with smooth changes of phosphatase and urease activities. PAEs decreased average well color development (AWCD), while Shannon index (H) showed a tendency to increase after a decrease. Carbon utilization profile was affected significantly by PAEs, especially at 10 mg kg,1 soil. CONCLUSION: Degradation of PAEs was driven mainly by microbial mediated processes. PAEs affected carbon, nitrogen and phosphorus cycles variously, and had temporal effects on metabolic diversity, owing to the adaptation of microbes. Carbon substrates utilization changed from easily degradable sugars and carboxylic acids to recalcitrant compounds during the simulation. Copyright © 2010 Society of Chemical Industry [source] Tebuconazole dissipation and metabolism in Tifton loamy sand during laboratory incubation,PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 7 2004Timothy C Strickland Abstract The fungicide tebuconazole is widely used to control soil-borne and foliar diseases in peanuts and other crops. No published data are currently available on the extent and rate at which this compound degrades in soil. Unpublished data summarized in registration documents suggest that the compound is persistent, with 300,600 days half-life. We conducted a 63-day laboratory incubation to evaluate tebuconazole's dissipation kinetics and impact on soil microbial activity in Tifton loamy sand. Tifton soils support extensive peanut production in the Atlantic Coastal Plain region of Georgia and Alabama. Products containing tebuconazole are applied to an estimated 50% of the peanut acreage in the region. At the end of the incubation, 43 (±42)% of the parent compound was recovered in soil extracts. The first-order kinetic model, which gave a good fit to the dissipation data (r2 = 0.857), yielded a soil half-life (t1/2) of 49 days. This is 6,12 times more rapid than t1/2 values described in unpublished tebuconazole registration documents. Four degradates were identified. Tentative structural assignments indicated that degradates were derived from hydroxylation of the parent compound and/or chlorophenyl ring cleavage. Cleavage products showed a steady increase during the incubation, and on a molar basis were equal to 63% of the time zero tebuconazole concentration. No significant effect on soil microbial biomass was observed, indicating that when the compound is applied at normal agronomic rate it does not impact soil metabolic activity. Use of the soil-half life data derived in this study should improve the accuracy of tebuconazole fate assessments for Coastal Plain peanut production. The study also indicated that environmental assessment of selected degradates may be needed to fully evaluate risks of tebuconazole use. Published in 2004 for SCI by John Wiley & Sons, Ltd. [source] | |||||||||||||