Revisiting the involvement of ammonia oxidizers and denitrifiers in nitrous oxide emission from cropland soils.

Nitrous oxide (NO), an ozone-depleting greenhouse gas, is generally produced by soil microbes, particularly NH oxidizers and denitrifiers, and emitted in large quantities after N fertilizer application in croplands. NO can be produced via multiple processes, and reduced, with the involvement of more diverse microbes with different physiological constraints than previously thought; therefore, there is a lack of consensus on the production processes and microbes involved under different agricultural practices. In this study, multiple approaches were applied, including NO isotopocule analyses, microbial gene transcript measurements, and selective inhibition assays, to revisit the involvement of NH oxidizers and denitrifiers, including the previously-overlooked taxa, in NO emission from a cropland, and address the biological and environmental factors controlling the NO production processes.

Nitrogen and Oxygen Isotope Signatures of Nitrogen Compounds during Anammox in the Laboratory and a Wastewater Treatment Plant.

Isotopic fractionation factors against N and O during anammox (anaerobic ammonia oxidization by nitrite) are critical for evaluating the importance of this process in natural environments. We performed batch incubation experiments with an anammox-dominated biomass to investigate nitrogen (N) and oxygen (O) isotopic fractionation factors during anammox and also examined apparent isotope fractionation factors during anammox in an actual wastewater treatment plant. We conducted one incubation experiment with high δO of water to investigate the effects of water δO.

Dual nitrogen and oxygen isotope fractionation during anaerobic ammonium oxidation by anammox bacteria.

Natural abundance of stable nitrogen (N) and oxygen (O) isotopes are invaluable biogeochemical tracers for assessing the N transformations in the environment. To fully exploit these tracers, the N and O isotope effects (ε and ε) associated with the respective nitrogen transformation processes must be known. However, the N and O isotope effects of anaerobic ammonium oxidation (anammox), one of the major fixed N sinks and NO producers, are not well known.

Control of the Nitrogen Isotope Composition of the Fungal Biomass: Evidence of Microbial Nitrogen Use Efficiency.

Changes in N/N in the soil microbial biomass during nitrogen (N) mineralization have been hypothesized to influence N/N in soil organic matter among ecosystem sites. However, a direct experimental test of this mechanism has not yet been performed. To evaluate the potential control of microbial N mineralization on the natural N isotope composition, we cultured fungi (Aspergillus oryzae) in five types of media of varying C:N ratios of 5, 10, 30, 50, and 100 for 4 d, and tracked changes in δN in the microbial biomass, NH, and dissolved organic N (DON: glycine) over the course of the experiment.

Nitrate is an important nitrogen source for Arctic tundra plants.

Plant nitrogen (N) use is a key component of the N cycle in terrestrial ecosystems. The supply of N to plants affects community species composition and ecosystem processes such as photosynthesis and carbon (C) accumulation. However, the availabilities and relative importance of different N forms to plants are not well understood.

Angiopoietin-2 may contribute to multiple organ dysfunction and death in sepsis*.

Objective: : In sepsis, quiescent blood vessels become leaky and inflamed by mechanisms that are incompletely understood. We hypothesized that angiopoietin-2, a partial antagonist of the endothelium-stabilizing receptor Tie-2 secreted by endothelium, contributes to adverse outcomes in this disease.

Design: : Laboratory and animal research.

Adiponectin diminishes organ-specific microvascular endothelial cell activation associated with sepsis.

Experimental sepsis was induced in male C57BL/6j, adiponectin-deficient mice (ADPNKO), and wild-type littermates by i.p. injection of 16 mg/kg lipopolysaccharide or cecal ligation and puncture.

Leptin exacerbates sepsis-mediated morbidity and mortality.

The adipose-derived hormone leptin is well known for its contribution to energy metabolism and satiety signaling in the hypothalamus. Previous studies suggested that obesity is an independent risk factor for sepsis morbidity and mortality, and it is associated with elevated baseline levels of circulating leptin in normal, nonseptic patients. In mouse endotoxemia and cecal ligation puncture models of sepsis, we observed elevated levels of leptin and soluble leptin receptor (sLR).