Amount Of Reactive Nitrogen Research Articles

Increased microbial sequestration of soil organic carbon under nitrogen deposition over China\u2019s terrestrial ecosystems

BackgroundChina’s terrestrial ecosystems have been receiving increasing amounts of reactive nitrogen (N) over recent decades. External N inputs profoundly change microbially mediated soil carbon (C) dynamics, but how elevated N affects the soil organic C that is derived from microbial residues is not fully understood. Here, we evaluated the changes in soil microbial necromass C under N addition at 11 forest, grassland, and cropland sites over China’s terrestrial ecosystems through a meta-analysis based on available data from published articles.ResultsMicrobial necromass C accounted for an average of 49.5% of the total soil organic C across the studied sites, with higher values observed in croplands (53.0%) and lower values in forests (38.6%). Microbial necromass C was significantly increased by 9.5% after N addition, regardless of N forms, with greater stimulation observed for fungal (+ 11.2%) than bacterial (+ 4.5%) necromass C. This increase in microbial necromass C under elevated N was greater under longer experimental periods but showed little variation among different N application rates. The stimulation of soil microbial necromass C under elevated N was proportional to the change in soil organic C.ConclusionsThe stimulation of microbial residues after biomass turnover is an important pathway for the observed increase in soil organic C under N deposition across China’s terrestrial ecosystems.

Effects of experimental nitrogen enrichment on soil properties and litter decomposition in a Neotropical savanna

AbstractThe amount of reactive nitrogen has more than doubled in terrestrial ecosystems due to human activities such fertiliser application that is predicted to increase dramatically in coming decades. We conducted a 3‐year experiment in a Neotropical savanna in which we determined the effects of increased N deposition on litter decomposition in plots subjected to different levels of N addition (50 kg N ha−1 year−2, 20 kg N ha−1 year−2, or no N addition). For this, we compared the litter decomposition from the bunchgrass Tristachya leiostachya using litter collected from plots with different N addition treatments. Five randomly selected bags of litter from each N addition treatment (origin) were distributed to each plot (destination). We also compared litter nitrogen (N) concentration and indicators of microbial activity (basal respiration, carbon of microbial biomass, metabolic quotient, enzyme activity) in all plots. We found that nitrogen addition influences litter decay, but in idiosyncratic ways that differ between years. In year 1, litter decomposed faster in high‐N addition plots than in low‐N and control plots, regardless of its origin. In contrast, litter from high‐N addition plots decomposing fastest in year 2, regardless of its destination. Finally, there was no effect of either litter origin or destination on the rate of decomposition in year 3. Litter collected in high‐N addition plots had a concentration of N 12–17% higher than litter collected in other plots and higher in 2009 than in other years. Four years after the beginning of the fertilisation experiment, concentration and the microbial activity in the soil did not differ between the treatments. Our findings suggest that the levels of N addition predicted for Neotropical savannas can alter litter N concentrations and the process of litter decomposition, but that the direction and magnitude of these changes may be challenging to predict since that precipitation can influence the mechanisms regulating decomposition in the Cerrado.

Identification of nitrogen flows in agriculture

The flows of reactive nitrogen compounds, which are formed during the production of agricultural products, are determined. Nitrogen flows between the «Agriculture» pool and other pools were considered. The nitrogen emissions from such pools are analyzed: agriculture; energy and fuel; materials and products of industry; people and settlements; waste; atmosphere and hydrosphere. The main sources of chemically active nitrogen emissions from the «Agriculture» were established. The influence of nitrogen on the environment and human health has been established. An algorithm for determining nitrogen balances for agriculture has been developed. The algorithm takes into account both the amount of reactive nitrogen formed in the basin and what was gained as a result of exchange with other basins. The application of the indicator of the efficiency of the use of nutrients as a generalization in the comparative assessment of nitrogen basins and nitrogen fluxes has been analyzed. The utility of the nitrogen use efficiency (NUE) has been established. It is determined that the efficiency of the use of nitrogen in livestock production depends on a set of indicators — the specialization of an agricultural enterprise, types of agricultural crops and categories of animals. Nitrogen balance for a particular farm and NUE are indicators for calculating nitrogen load on the environment and the efficiency of using nitrogen resources, respectively. The dynamics of the change of this indicator in combination with other agroecological indicators can be used to assess the effectiveness of the implementation of measures at the enterprise to improve the technology to reduce the environmental load.

Doubling the thermoelectric power factor of earth abundant tin nitride thin films through tuned (311) orientation by magnetron sputtering

Thermoelectricity has been considered a promising green energy source for mankind. This method of energy generation poses challenges due to scarcity of the constituent elements of the efficient thermoelectric materials. The development of high performance materials for thermoelectric generation is limited with the co-responsive nature of transport parameters. In this work, earth abundant tin nitride (Sn3N4) thin films were deposited by reactive radio frequency magnetron sputtering and investigated its thermoelectric response. The electron bands of the prepared thin films were actively aligned to optimize the trade-off between the Seebeck coefficient and electrical conductivity for the enhancement of power factor (S2σ). The reduction in nitrogen gas pressure of reactive sputtering reduced both working pressure and the amount of reactive nitrogen. This experimental approach of combined effect introduced preferred orientation (PO) and stoichiometric variations simultaneously in the fabricated thin films. The increased scattering associated with preferred orientation and increased carrier concentration associated with stoichiometric variations converged the conduction band along with shifting of Fermi energy toward the conduction band minimum. The engineered band structure of tin nitride thin film realized over 2-fold hike in power factor up to 390 μW/m-K2 at 250 °C with a Seebeck coefficient of −144 μV/K and resistivity of 53.11 μΩ-m. This study reveals the potential nature of the earth abundant nitrides in the field of renewable energy generation. The experimental strategy adopted in this study provides an alternative approach to engineer the band structure of a thin film for optimized transport parameters.

Chinese coastal seas are facing heavy atmospheric nitrogen deposition

As the amount of reactive nitrogen (N) generated and emitted increases the amount of N deposition and its contribution to eutrophication or harmful algal blooms in the coastal zones are becoming issues of environmental concern. To quantify N deposition in coastal seas of China we selected six typical coastal sites from North to South in 2011. Concentrations of NH3, HNO3, NO2, particulate NH4+ (pNH4+) and pNO3− ranged from 1.97– 4.88, 0.46 –1.22, 3.03 –7.09, 2.24 – 4.90 and 1.13–2.63 μg N m−3 at Dalian (DL), Changdao (CD), Linshandao (LS), Fenghua (FH), Fuzhou (FZ), and Zhanjiang (ZJ) sites, respectively. Volume-weighted NO3−–N and NH4+–N concentrations in precipitation varied from 0.46 to 1.67 and 0.47 to 1.31 mg N L−1 at the six sites. Dry, wet and total deposition rates of N were 7.8–23.1, 14.2–25.2 and 22.0 – 44.6 kg N ha−1 yr−1 across the six coastal sites. Average N dry deposition accounted for 45.4% of the total deposition and NH3 and pNH4+ contributed to 76.6% of the dry deposition. If we extrapolate our total N deposition of 33.9 kg N ha−1 yr−1 to the whole Chinese coastal sea area (0.40 million km2), total N deposition amounts to 1.36 Tg N yr−1, a large external N input to surrounding marine ecosystems.

An assessment of nitrogen saturation in Pinus banksiana plots in the Athabasca Oil Sands Region, Alberta

During the past 15 years, there has been a dramatic increase in the amount of reactive nitrogen (N) in the atmosphere, leading to concerns that chronic elevated N deposition may result in negative effects on natural ecosystems. This study examines the response of jack pine (Pinus banksiana) plots to N air concentrations within the Athabasca Oil Sands Region (AOSR) in northern Alberta, which has experienced elevated N emissions since the 1990s. Air concentrations of nitrogen dioxide (NO2), ammonia, and nitric acid at the study plots are generally low although NO2 is strongly correlated with sulphur dioxide indicating an exposure gradient associated with industrial emissions. Nitrogen concentrations in P. banksiana foliage and two lichen indicator species (Hypogymnia physodes and Evernia mesomorpha) were significantly correlated with annual NO2 exposure. Relationships between NO2 (or N exposure) and other aspects of N cycling were less evident. Nitrogen content and carbon to nitrogen ratio in the forest floor and soil or potential net N mineralization rates were not correlated with N exposure. Nitrification was negligible suggesting efficient ecosystem immobilization of current N deposition. Based on the response of foliage to N exposure, sites closest to industrial activity appear to be in the early stages of N saturation.