Community-level physiological profiling performed with an oxygen-sensitive fluorophore in a microtiter plate.
ABSTRACT Community-level physiological profiling based upon fluorometric detection of oxygen consumption was performed on hydroponic rhizosphere and salt marsh litter samples by using substrate levels as low as 50 ppm with incubation times between 5 and 24 h. The rate and extent of response were increased in samples acclimated to specific substrates and were reduced by limiting nitrogen availability in the wells.
Full-textDOI: · Available from: Jay L Garland, Mar 17, 2014
- SourceAvailable from: Annette Bérard[Show abstract] [Hide abstract]
ABSTRACT: The MicroResp™ method allows soil respiration and microbial community physiological profiles to be determined colorimetrically in microplates. This method, however, neglects CO2 storage in the agar gel carrying the colorimetric indicator, and calcite dissolution associated with CO2-induced change in soil solution pH. Our objective was to improve the method by taking into account CO2 in the gel in the calculation of microbial respiration, describing the effect of microbial CO2 on the pH of the soil solution and calcite dissolution, and checking whether CO2 distribution among calcite, soil solution, air and gel is near equilibrium after incubation. We propose a thermodynamic equilibrium model describing (a) distribution of CO2 among calcite, soil solution, gel and air, (b) dissociations of water, carbonic acid, cresol red, and substrates in the gel and soil solution, (c) exchange of adsorbed cations with H3O+ in the gel, and (d) calcite dissolution in soil. In-gel experiments were designed to calibrate the model, quantify the rate of CO2 exchange with air, and compare conservation procedures. On-soil experiments were designed to check whether calcite dissolution is near equilibrium and whether the model predicts the effect of CO2 on the pH of the solution. In-microplate experiments were designed to assess the effects of incubation period and soil quantity on estimated microbial respiration. The model can describe the distribution and speciation of CO2 in the gel, the soil solution and the air space of each microplate well. Initial properties of the gel vary with storage: soda lime partly extracts CO2 supplied as NaHCO3, and dries out the gel, which can skew the calibration. When incubation is over, the proportion of microbial CO2 in the gel is higher at lower microbial respiration. Incubations shorter than 4 h underestimate microbial respiration due to the slow diffusion of CO2 in the gel. CO2 in the soil solution cannot be overlooked; it decreases the soil pH and may promote calcite dissolution in calcareous soil. It is important to precisely estimate initial CO2 air fraction and to control temperature, which affects both thermodynamic constants and microorganisms.Geoderma 10/2013; s 207–208:82–91. DOI:10.1016/j.geoderma.2013.05.010 · 2.51 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Rising atmospheric carbon dioxide (CO2 ) could alter the carbon (C) and nitrogen (N) content of ecosystems, yet the magnitude of these effects are not well known. We examined C and N budgets of a subtropical woodland after 11 yr of exposure to elevated CO2 . We used open-top chambers to manipulate CO2 during regrowth after fire, and measured C, N and tracer (15) N in ecosystem components throughout the experiment. Elevated CO2 increased plant C and tended to increase plant N but did not significantly increase whole-system C or N. Elevated CO2 increased soil microbial activity and labile soil C, but more slowly cycling soil C pools tended to decline. Recovery of a long-term (15) N tracer indicated that CO2 exposure increased N losses and altered N distribution, with no effect on N inputs. Increased plant C accrual was accompanied by higher soil microbial activity and increased C losses from soil, yielding no statistically detectable effect of elevated CO2 on net ecosystem C uptake. These findings challenge the treatment of terrestrial ecosystems responses to elevated CO2 in current biogeochemical models, where the effect of elevated CO2 on ecosystem C balance is described as enhanced photosynthesis and plant growth with decomposition as a first-order response.New Phytologist 05/2013; DOI:10.1111/nph.12333 · 6.55 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: a b s t r a c t Land use effects on microbial communities may have profound impacts on agricultural productivity and ecosystem sustainability as they are critical in soil quality and health. The main aim of this study was to characterize the microbial communities of pristine and agricultural soils in the central Yungas region in Northwest Argentina. As a first step in the development of biological indicators of soil quality in this region, a comprehensive approach involving a structural and functional evaluation of microbial commu-nities was used to detect changes in soil as consequence of land use. The sites selected included two pristine montane forest sites (MF1 and MF2), two plots under sugarcane monoculture for 40 and 100 years (SC40 and SC100), one plot under 20 years of soybean monoculture (SB20), a recently deforested and soybean cropped site (RC), and two reference sites of native forest adjacent to the sugarcane and soybean plots (PF1 and PF2). We used three microbial community profiling methods: denaturing gradi-ent gel electrophoresis (DGGE) analysis of PCR amplified 16S rRNA genes, community-level physiological profiling (CLPP) using a BD oxygen biosensor system (BDOBS-CLPP) and phospholipid fatty acid (PLFA) analysis. Deforestation and agriculture caused expected increases in pH and decreases in organic car-bon and microbial biomass. Additionally, shifts in the microbial community structure and physiology were detected with disturbance, including reduced diversity based on PLFA data. The higher respiratory response to several carbon substrates observed in agricultural soils suggested the presence of microbial communities with lower growth yield efficiency that could further reduce carbon storage in these soils. Using an integrated multivariate analysis of all data measured in this study we propose a minimum data set of variables (organic carbon, pH, sucrose and valeric acid utilizations, a17:0 and a15:0 PLFA biomarkers and the value of impact on microbial diversity) to be used for future studies of soil quality in Northwest Argentina.Applied Soil Ecology 03/2011; 47(3):176-183. DOI:10.1016/j.apsoil.2010.12.008 · 2.21 Impact Factor