Microbial role in N2O-NO2 production and CH4 oxidation under active hypogenic settings

<p>The hydrothermal caves linked to active faulting have subterranean atmospheres with a distinctive gaseous composition containing deep endogenous gases, such as carbon dioxide, methane and nitrogen oxides (NOx). Ascending fluids through associated near-surface hydrothermal processes can mobilize endogenous gases into the Critical Zone and, ultimately, to the lower troposphere.<br>Nitrogen oxides are polluting gases and can have adverse effects on human health, especially inhaled NO2. They also catalyse ozone (O3) production in the lower layers of the atmosphere and the greenhouse effect, when they react with volatile organic compounds. The largest source of NOx emissions is anthropogenic. The rest is produced naturally by microbial processes in soil and water, by lightning, volcanic activity, storms, etc. Production of N2O and NO2 is associated with soil and other active-geothermal ecosystems, far less is known about the sources and sinks of these gases within subterranean locations. Here, we report high N2O and NO2 concentrations detected along a hypogenic system associated with an active faulting (Vapour Cave, southern Spain), which enables direct gas exchange with the low-atmosphere. These anomalous concentrations of N2O and, NO2 are about ten and five times higher than the typical atmospheric background, respectively.<br>Gaseous composition analyses of subterranean atmosphere were conducted by high precision field-deployable CRDS and FTIR spectrometers for measuring in situ the target tracer gases (NO2, N2O, CH4, CO2) and δ13C of both carbon-GHGs. DNA extraction, sequencing and phylogenetic analyses were conducted to characterize the microbial community of cave sediments. The results showed that N2O and NO2 emission depends on the activity of nitrification by ammonia oxidizing microorganisms (such as members of the family Nitrosomonadaceae and phylum Thaumarchaeota) and/or as a result of incomplete denitrification by heterotrophic denitrifying bacteria (such as Bacillus, Acinetobacter and Cupriavidus) from this hydrothermal and hypoxic ecosystem.<br>On the other hand, CH4 concentrations and δ13CH4 vary along the cave (with the deep), in deepest cave locations CH4 values are higher with lighter δ13C values in comparison with the more superficial areas, which indicates a deep endogenous origin of methane. However, in areas near the entrance we observe lower concentrations of methane and heavier δ13C values (CH4<1 ppm and δ13C close to −30‰), as a result of methane oxidation by denitrifying methanotrophs of the NC10 phylum during gas migration from the deepest areas to the surface.</p><p>These new findings reveal the sourcing of these nitrogenous gases into the upper vadose zone of a hypogenic/geothermal ecosystem, and its potential release to the lower troposphere. A better understanding of biogeochemical processes controlling the production of nitrogenous gases in subterranean environments will be useful to identify and characterize new possible<br>sources, reservoirs and sinks of greenhouse gases (CO2, CH4, N2O and NOx) in order to calculate more accurately the budgets and for the design of new mitigation strategies of these gases.</p>

Organically fertilized tea plantation stimulates N₂O emissions and lowers NO fluxes in subtropical China

Tea plantations are rapidly expanding in China and other countries in the tropical and subtropical zones, but so far there are very few studies including direct measurements on nitrogenous gases fluxes from tea plantations. On the basis of 2 year field measurements from 2012 to 2014, we provided an insight into the assessment of annual nitrous oxide (N2O) and nitric oxide (NO) fluxes from Chinese subtropical tea plantations under three practices of conventional urea application, alternative oilcake incorporation and no nitrogen fertilization. Clearly, the N2O and NO fluxes exhibited large intra- and inter-annual variations, and furthermore their temporal variability could be well described by a combination of soil environmental factors including soil mineral N, water-filled pore space and temperature, based on a revised "hole-in-the-pipe" model. Averaged over 2 years, annual background N2O and NO emissions were approximately 4.0 and 1.6 kg N ha−1 yr−1, respectively. Compared to no nitrogen fertilization, both urea and oilcake application significantly stimulated annual N2O and NO emissions, amounting to 14.4–32.7 kg N2O-N ha−1 yr−1 and at least 12.3–19.4 kg NO-N ha−1 yr−1. In comparison with conventional urea treatment, on average, the application of organic fertilizer significantly increased N2O emission by 71 % but decreased NO emission by 22 %. Although the magnitude of N2O and NO fluxes was substantially influenced by N source, the annual direct emission factors of fertilizer N were estimated to be 2.8–5.9, 2.7–4.0 and 6.8–9.1 % for N2O, NO and N2O + NO, respectively, which are significantly higher than those defaults for global upland croplands. This indicated that the rarely determined N2O and NO formation appeared to be a significant pathway in the nitrogen cycle of tea plantations, which are a potential source of national nitrogenous gases inventory.

Co-doping Deposition of p-type ZnO Thin Films using KrF Excimer Laser Ablation

ABSTRACTWe report on the attempt to fabricate p-type ZnO thin films using various doping techniques based on the pulsed laser deposition (PLD). As an accepter, we have doped the N atom by using high purity nitric monoxide (NO) ambient gas. NO is dissociated into N and O at an energy of 6.5 eV which is lower than at N2 (9.76 eV). Moreover the dissociation reaction of NO is simpler than other nitrogenous gases such as N2O, NO2, and NH3. One of our doping techniques is co-doping of Ga and N atom by ablating ZnO:Ga target in NO gas, and another is the ablation of the metal Zn target in NO gas. Both of Ga and N co-doped ZnO films and N doped ZnO films have c-axis orientation as well as undoped ZnO films. The surfaces of these doped films are rough while the undoped ZnO thin film is very smooth and have hexagonally shaped grains. We found it possible to fabricate the p-type ZnO film by ablating the metal Zn target in NO gas.

Uptake, cycling and fate of nitrogen in grass-clover swards continuously grazed by sheep

SUMMARYComponents of the N cycle were studied at Hurley, UK, in 1985–87. In grass-clover (Lolium perenne and Trifolium repens) swards, grazed at three intensities, low total inputs of N were associated with low outputs and losses of N. Nevertheless, the flows (intake and excretion) of N through animals were substantial and gave rise, at the higher intensities of grazing, to an acceptably high agricultural output per hectare. This was considered evidence of a fast and efficient recycling of N between plants, animals and soil. The release of N to the environment (as nitrogenous gases and nitrate) was substantially less from the grass–clover swards than from a grass sward fertilized with 420 kg N/ha, and this was at the expense of only 20% loss in production. The mechanisms which might account for the high efficiency of utilization and recycling of N in grass–clover swards are discussed in the context of the balance of the supply of C and N to plant and soil biomasses under grazing. The results confirm that optimizing agricultural output in grass–clover swards has little adverse effect on the environment, but the importance to this end of sustaining a large proportion of N-deficient grass in grass-clover swards is emphasized.