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Respiratory ammonification and denitrification are two evolutionarily unrelated dissimilatory nitrogen (N) processes central to the global N cycle, the activity of which is thought to be controlled by carbon (C) to nitrate (NO3 -) ratio. Here we find that Intrasporangium calvum C5, a novel dual-pathway denitrifier/respiratory ammonifier, disproportionately utilizes ammonification rather than denitrification when grown under low C concentrations, even at low C:NO3 - ratios. This finding is in conflict with the paradigm that high C:NO3 - ratios promote ammonification and low C:NO3 - ratios promote denitrification. We find that the protein atomic composition for denitrification modules (NirK) are significantly cost minimized for C and N compared to ammonification modules (NrfA), indicating that limitation for C and N is a major evolutionary selective pressure imprinted in the architecture of these proteins. The evolutionary precedent for these findings suggests ecological importance for microbial activity as evidenced by higher growth rates when I. calvum grows predominantly using its ammonification pathway and by assimilating its end-product (ammonium) for growth under ammonium-free conditions. Genomic analysis of I. calvum further reveals a versatile ecophysiology to cope with nutrient stress and redox conditions. Metabolite and transcriptional profiles during growth indicate that enzyme modules, NrfAH and NirK, are not constitutively expressed but rather induced by nitrite production via NarG. Mechanistically, our results suggest that pathway selection is driven by intracellular redox potential (redox poise), which may be lowered when resource concentrations are low, thereby decreasing catalytic activity of upstream electron transport steps (i.e., the bc1 complex) needed for denitrification enzymes. Our work advances our understanding of the biogeochemical flexibility of N-cycling organisms, pathway evolution, and ecological food-webs.

High performance anion exchange chromatography is used to analyze the changes in extractable anions, following wild fire in a sagebrush-gran community. Concentration of anions in burned soil is compared to that of the unburned soil and significant differences are observed. Anion concentrations are similar in shrub interspaces occupied with cheatgrass. Temperature and exposure time influence the anion concentrations.

Fire is an important component of forests in the western United States. Not only are forests subjected to wildfires, but fire is also an important management tool to reduce fuels loads. Charcoal, a product of fire, can have major impacts on carbon (C) and nitrogen (N) cycling in forest soils, but it is unclear how these effects vary by dominant vegetation. In this study, soils collected from Jeffrey pine (JP) or lodgepole pine (LP) dominated areas and amended with charcoal derived from JP or LP were incubated to assess the importance of charcoal on microbial respiration and potential nitrification. In addition, polyphenol sorption was measured in unamended and charcoal-amended soils. In general, microbial respiration was highest at the 1% and 2.5% charcoal additions, but charcoal amendment had limited effects on potential nitrification rates throughout the incubation. Microbial respiration rates decreased but potential nitrification rates increased over time across most treatments. Increased microbial respiration may have been caused by priming of native organic matter rather than the decomposition of charcoal itself. Charcoal had a larger stimulatory effect on microbial respiration in LP soils than JP soils. Charcoal type had little effect on microbial processes, but polyphenol sorption was higher on LP-derived than JP-derived charcoal at higher amendment levels despite surface area being similar for both charcoal types. The results from our study suggest that the presence of charcoal can increase microbial activity in soils, but the exact mechanisms are still unclear. [ABSTRACT FROM AUTHOR]

In the course of investigating nutrient availability in a montane meadow ecosystem of the Sierra Nevada range, it was determined that resin availability of [Na.sup.+] and [K.sup.+] was significantly affected by season (winter vs. summer and fall). The underlying mechanism(s) controlling this seasonal effect was investigated in the laboratory. Four replicate A horizon samples of a Typic Humaquept (silty clay texture, kaolinitic mineralogy, 3% organic C, pH 5.10) were saturated with [Mg.sup.2+]. Using 5-g subsamples from each replicate, soil was equilibrated for a period of 30 min with 30 mL of a 5.00 mmol solution of [Na.sup.+] and [K.sup.+] at 1, 15, 30, and 45[degrees]C. After centrifugation, the supernatant was analyzed for [K.sup.+], [Na.sup.+], and [Mg.sup.2+]. Exchanger sorption characteristics varied significantly with temperature. Overall, [K.sup.+] was preferentially sorbed over [Na.sup.+], but the proportional sorption of [K.sup.+] decreased significantly at a temperature of 1[degrees]C. The temperature dependence of [K.sup.+] and [Na.sup.+] sorption partially explains seasonal differences in availability. Net sorption ([K.sup.+] + [Na.sup.+] - [Mg.sup.2+]) was statistically similar to 0 at temperatures of 15, 30, and 50[degrees]C, but significantly increased at 1[degrees]C. This increase in cation exchange capacity at low temperature may have special relevance to ecosystems during snowmelt when increased retention of certain cations could occur. doi:10.2136/sssaj2009.0159N