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Fairfax, VA, United States

Organic fertilizers provide long-term benefits to agronomic soils, but sometimes cause short-term reductions in crop yield due to microbially mediated nitrogen (N) immobilization. A simple, rapid method to assess the integrated use of both, carbon (C) and N by soil microbial communities will be a useful monitoring tool in production agriculture. The present study evaluated a new platform for performing community-level physiological profiles (CLPP) using fluorescent-based detection of O2 consumption by soil slurries within microtiter plates. Response of a spodic Florida soil to 3 organic fertilizer amendment treatments; (1) control with no organic amendment, (2) pelletized class A-A municipal biosolids amendment, and (3) fresh dairy waste solids amendment was measured in soils taken from a corn-rye crop rotation. The CLPP assay was used to assess endogenous and substrate induced (∼75 μg C as acetate, casein, coumaric acid, mannose, or asparagine g-1 soil) respiration, with and without assay N additions (8 μg N-NH4 g-1 soil). Endogenous and substrate-induced respiration were generally greater in the dairy waste-amended soils, as quantified by a reduced lag period and greater response peak. Stimulatory effects from biosolid-amended soils were less extensive and consistent. The degree of N limitation on microbial activity was determined by comparing the response peak with and without N amendment. This difference in response (Ndiff) was greatest for all treatments during the rye exponential growth phase (prior to heading), when extractable soil NH4-N and NO3-N concentrations were lowest (i.e., < 10 mg kg-1). The dairy waste treated soils had greater Ndiff values during the rye crop as compared to the other treatments, particularly for endogenous respiration and mannose-induced respiration. Ndiff was low in all treatments during the corn crop, where extractable soil NH4-N + NO3-N remained at or above 20 mg N kg-1. Plant yield data coincided with our estimates of N-limited microbial activity, with less mid-season rye biomass under dairy waste and no yield response with corn. Overall, these data indicate that this new method allows for a rapid, ecologically relevant evaluation of organic amendment impacts on microbial soil respiration and thereby plant yield response. Further characterization and interpretation of the variation in microbial respiration among specific C substrates and the relative impact of N amendments (i.e., Ndiff), will provide insight to C and N cycling in soils receiving organic N inputs. © 2010 Elsevier B.V. Source

Zabaloy M.C.,National University of the South | Garland J.L.,CSS-Dynamac | Gomez M.A.,National University of the South
Applied Soil Ecology

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) may influence soil microbial communities by altering the balance between resident populations. Our objective was to assess the effect of environmentally relevant levels (ERLs) of 2,4-D on microbial community function and on the population dynamics of 2,4-D degrading bacteria using a microcosm approach. The most probable number approach was used to enumerate 2,4-D-degrading soil bacteria. Carbon substrates utilization was tested with a microtiter-based oxygen sensor system to evaluate short-term functional shifts caused by herbicide treatment. Shifts in the community in response to potential toxicity of 2,4-D were assessed in the agricultural soil and a reference forest soil using the pollution-induced community-tolerance (PICT) approach. Results indicated that the agricultural soil had a stable 2,4-D degrading population able to use the herbicide as C and energy source, which increases immediately after an ERL dose of 2,4-D and remains high for about 1 month after exposure has ceased. An enhanced, dose-dependent response to 2,4-D as substrate was observed in the microtiter assay, while heterotrophic bacterial activity appeared mostly unchanged. The PICT assay showed higher tolerance to 2,4-D in the agricultural soil than in the unexposed forest soil. Our results suggest that agricultural use of 2,4-D at recommended level leads to selection for (1) a copiotrophic degrader population and (2) a persistently herbicide-tolerant, but functionally similar, microbial community. © 2010 Elsevier B.V. Source

Landing W.M.,Florida State University | Caffrey J.M.,University of West Florida | Nolek S.D.,CSS-Dynamac | Gosnell K.J.,University of Connecticut | Parker W.C.,Florida State University
Atmospheric Chemistry and Physics

In an effort to understand and quantify the impact of local, regional, and far-distant atmospheric mercury sources to rainfall mercury deposition in the Pensacola, Florida watershed, a program of event-based rainfall sampling was started in late 2004. Modified Aerochem-Metrics wet/dry rainfall samplers were deployed at three sites in the region around the Crist coal-fired power plant and event-based samples were collected continuously for three years. Samples were analyzed for total Hg and a suite of trace elements including Al, As, Ba, Bi, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, La, Li, Mg, Mn, Na, Nb, Ni, P, Pb, Sb, Se, Si, Sn, Sr, Th, U, V, and Zn. Nutrients (ammonia and nitrate) and major anions (chloride and sulfate) were also measured on each sample. Multivariate statistical methods were used to sort these tracers into factors that represent potential source categories contributing to the rainfall chemistry. As, Hg, Sb, Se, Sn, and non sea-salt sulfate were all significantly correlated (R > 0.6) with one factor which we interpret as an anthropogenic source term reflecting input from coal combustion throughout the southeastern US. Using ratios of total Hg to volatile elements, we estimate that 22-33% of the rainfall Hg results from coal combustion in the southeastern US with the majority coming from the global background. © Author(s) 2010. Source

Pfleeger T.G.,U.S. Environmental Protection Agency | Plocher M.,CSS-Dynamac | Bichel P.,U.S. Environmental Protection Agency
Agriculture, Ecosystems and Environment

Considerable research has documented the effects of ozone on crop plants, but little experimental work has examined the effects of ozone on natural vegetation. Our objective was to determine how a plant community responds over several generations to elevated ozone exposures. Seed bank soil collected from the Oregon State University Farm, containing a population of naturalized plants common to the Willamette Valley, was uniformly dispersed across the surface of nine modified open top chambers. Each chamber was randomly assigned one of three ozone treatments (0, 90 and 120. ppb episodic ozone). Sixty plant species from 22 families emerged in the chambers over the four year study. Seedling emergence was a highly sensitive period. High seedling mortality rates in the ozone treatments allowed more resistant individuals to persist. Communities not exposed to elevated ozone levels also had high rates of mortality probably due to density dependant mortality. No species were eliminated from the communities because of ozone. Plant species did not demonstrate ozone tolerance or susceptibility based on taxonomic relationships. Year-to-year environmental heterogeneity was a stronger influence on community composition than ozone exposures. At the community level, there was a trend of decreasing biomass with increasing ozone exposure. In the ozone treatments, premature senescence of taller species increased light availability to understory species, changing competitive interactions and altering community dynamics in the understory. The effects of ozone on individual species, both direct and indirect, in a community may be detrimental, insignificant, or positive. Predication of a species performance in a community will be difficult due to the many environmental and biological interactions occurring simultaneously or at alternative times during a specific species life cycle. Studies are necessary to decrease the uncertainty in attempting to assess the impact of ozone on both managed and natural ecosystems currently determined from extrapolating the effects on individuals. Currently, plant communities remain protected at an unknown level from ozone exposure. © 2010. Source

Zabaloy M.C.,CONICET | Gomez E.,National University of Rosario | Garland J.L.,CSS-Dynamac | Garland J.L.,U.S. Environmental Protection Agency | Gomez M.A.,CONICET
Applied Soil Ecology

The large scale use of glyphosate to control weeds in transgenic crops and in no-till management systems emphasizes the need to understand its effects on soil microbial communities. The herbicide may change the soil environment due to toxicity to soil microorganisms and through the influx of carbon (C), phosphorus (P) and nitrogen (N) from the cometabolic decay of glyphosate. This study evaluated both the potential effects of glyphosate treatments on microbial community structure and function in laboratory incubation of soils. Soil from two sites in the Pampa region of Argentina (Vertic Argiudoll from Zavalla, ZAV; Petrocalcic Paleustoll from Coronel Dorrego, DOR), with long exposure to glyphosate were used in soil microcosms amended with different doses of herbicide (0, 15 and 150mgkg -1) and incubated for 7 days. Soil from a natural grassland at the ZAV site was used as a reference soil. Community respiration in response to different C and nutrient (N and P) sources, including glyphosate, were assessed using an O 2 consumption-based assay in microtiter plates. Microbial community structure was analyzed using quantitative PCR (qPCR) to estimate the bacterial abundance and terminal restriction fragment length polymorphism (T-RFLP) to investigate the structure of the bacterial community. Glyphosate addition to the microcosms had minimal effects on both structural and functional measures of the microbial community. The addition of a high dose of glyphosate to soil microcosms from one agricultural site significantly reduced N limitation, suggesting that glyphosate breakdown provided N for microbial activity. However, the immediate respiratory response of the reference and chronically exposed soils to glyphosate was distinctive. Glyphosate increased respiration in the reference grassland soil, potentially due to a stress response of glyphosate sensitive species, while it depressed respiration in the chronically exposed soil, probably as a result of selection for organisms acclimated for rapid assimilation of substrates from the cometabolic decay of the molecule. These results suggest that longer term studies involving repeated addition of glyphosate to previously unexposed soils are needed to understand important shifts in community metabolism caused by the typical agricultural use of this herbicide. © 2011 Elsevier B.V. Source

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