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Soil microbial organisms are central to carbon (C) and nitrogen (N) transformations in soils, yet not much is known about the stable isotope composition of these essential regulators of element cycles. We investigated the relationship between C and N availability and stable C and N isotope composition of soil microbial biomass across a three million year old semiarid substrate age gradient in northern Arizona. The δ15N of soil microbial biomass was on average 7.2‰ higher than that of soil total N for all substrate ages and 1.6‰ higher than that of extractable N, but not significantly different for the youngest and oldest sites. Microbial 15N enrichment relative to soil extractable and total N was low at the...
Models project that land ecosystems may be able take up a considerable proportion of the carbon dioxide released by human activities, thereby counteracting the anthropogenic emissions. In their Perspective, Hungate et al. argue that these carbon uptake estimates are too high because the models do not take other nutrients such as nitrogen into account appropriately. The authors estimate that there will not be enough nitrogen available to sustain the high carbon uptake scenarios. Nutrients other than nitrogen may also affect carbon uptake in ways not captured by most models. Published in Science, volume 302, issue 5650, on pages 1512 - 3, in 2003.
Categories: Publication; Types: Citation, Journal Citation; Tags: Science
Rising atmospheric carbon dioxide (Ca), a product of fossil fuel burning, land-use change, and cement manufacture, is expected to cause a large carbon sink in land ecosystems, partly mitigating human-driven climate change (1). Increasing biological nitrogen fixation with rising Ca has been invoked as a means to provide the N necessary to support C accumulation (2). As in many short-term experiments (3), we found that Ca enrichment increased N fixation during the first year of treatment in an oak woodland. However, the effect declined and disappeared by the third year. Ca enrichment consistently depressed N fixation during the 5th, 6th, and 7th years of treatment. Reduced availability of the micronutrient molybdenum,...
Categories: Publication; Types: Citation, Journal Citation; Tags: Science
The amount of carbon plants allocate to mycorrhizal symbionts exceeds that emitted by human activity annually. Senescent ectomycorrhizal roots represent a large input of carbon into soils, but their fate remains unknown. Here, we present the surprising result that, despite much higher nitrogen concentrations, roots colonized by ectomycorrhizal (EM) fungi lost only one-third as much carbon as non-mycorrhizal roots after 2 years of decomposition in a piñon pine (Pinus edulis) woodland. Experimentally excluding live mycorrhizal hyphae from litter, we found that live mycorrhizal hyphae may alter nitrogen dynamics, but the afterlife (litter-mediated) effects of EM fungi outweigh the influences of live fungi on root...
We report the first simultaneous measurements of δ15N and δ13C of DNA extracted from surface soils. The isotopic composition of DNA differed significantly among nine different soils. The δ13C and δ15N of DNA was correlated with δ13C and δ15N of soil, respectively, suggesting that the isotopic composition of DNA is strongly influenced by the isotopic composition of soil organic matter. However, in all samples DNA was enriched in 13C relative to soil, indicating microorganisms fractionated C during assimilation or preferentially used 13C enriched substrates. Enrichment of DNA in 15N relative to soil was not consistently observed, but there were significant differences between δ15N of DNA and δ15N of soil for...
Forest management, climatic change, and atmospheric N deposition can affect soil biogeochemistry, but their combined effects are not well understood. We examined the effects of water and N amendments and forest thinning and burning on soil N pools and fluxes in ponderosa pine forests near Flagstaff, Arizona (USA). Using a 15N-depleted fertilizer, we also documented the distribution of added N into soil N pools. Because thinning and burning can increase soil water content and N availability, we hypothesized that these changes would alleviate water and N limitation of soil processes, causing smaller responses to added N and water in the restored stand. We found little support for this hypothesis. Responses of fine...