Anthropogenic nitrogen (N) addition may substantially alter the terrestrial N cycle. However, a comprehensive understanding of how the ecosystem N cycle responds to external N input remains elusive. ...Here, we evaluated the central tendencies of the responses of 15 variables associated with the ecosystem N cycle to N addition, using data extracted from 206 peer-reviewed papers. Our results showed that the largest changes in the ecosystem N cycle caused by N addition were increases in soil inorganic N leaching (461%), soil NO₃⁻ concentration (429%), nitrification (154%), nitrous oxide emission (134%), and denitrification (84%). N addition also substantially increased soil NH₄⁺ concentration (47%), and the N content in belowground (53%) and aboveground (44%) plant pools, leaves (24%), litter (24%) and dissolved organic N (21%). Total N content in the organic horizon (6.1%) and mineral soil (6.2%) slightly increased in response to N addition. However, N addition induced a decrease in microbial biomass N by 5.8%. The increases in N effluxes caused by N addition were much greater than those in plant and soil pools except soil NO₃⁻, suggesting a leaky terrestrial N system.
Nitrogen-vacancy NV.sup.- centers, which are of considerable interest for quantum electronics, are artificially produced in the diamond structure by irradiation and subsequent annealing. In this ...work, these centers were revealed in natural diamonds of cubic habit (type IaA + Ib according to physical classification) from an industrial placer deposit of the Anabar River (NE Siberian platform) using the method of optically detected magnetic resonance (ODMR). Localization of the NV.sup.- centers in the dislocations slip planes {111}, separated by distances of about 5 mum, was established by means of scanning the ODMR and PL signals with a submicron resolution. In various crystals, one or two intersecting systems of such slip planes have been revealed. The largest amounts of these defects were found in the peripheral zones of crystals containing increased amounts of single isomorphic nitrogen atoms in the structure. The data obtained indicate the formation of the NV.sup.- centers in natural diamonds under post-crystallization plastic deformation, i.e., by a mechanism that differs from the widely used method of their artificial production.
Anthropogenic activities, and in particular the use of synthetic nitrogen (N) fertilizer, have doubled global annual reactive N inputs in the past 50–100 years, causing deleterious effects on the ...environment through increased N leaching and nitrous oxide (N₂O) and ammonia (NH₃) emissions. Leaching and gaseous losses of N are greatly controlled by the net rate of microbial nitrification. Extensive experiments have been conducted to develop ways to inhibit this process through use of nitrification inhibitors (NI) in combination with fertilizers. Yet, no study has comprehensively assessed how inhibiting nitrification affects both hydrologic and gaseous losses of N and plant nitrogen use efficiency. We synthesized the results of 62 NI field studies and evaluated how NI application altered N cycle and ecosystem services in N‐enriched systems. Our results showed that inhibiting nitrification by NI application increased NH₃emission (mean: 20%, 95% confidential interval: 33–67%), but reduced dissolved inorganic N leaching (−48%, −56% to −38%), N₂O emission (−44%, −48% to −39%) and NO emission (−24%, −38% to −8%). This amounted to a net reduction of 16.5% in the total N release to the environment. Inhibiting nitrification also increased plant N recovery (58%, 34–93%) and productivity of grain (9%, 6–13%), straw (15%, 12–18%), vegetable (5%, 0–10%) and pasture hay (14%, 8–20%). The cost and benefit analysis showed that the economic benefit of reducing N's environmental impacts offsets the cost of NI application. Applying NI along with N fertilizer could bring additional revenues of $163 ha⁻¹ yr⁻¹for a maize farm, equivalent to 8.95% increase in revenues. Our findings showed that NIs could create a win‐win scenario that reduces the negative impact of N leaching and greenhouse gas production, while increases the agricultural output. However, NI's potential negative impacts, such as increase in NH₃emission and the risk of NI contamination, should be fully considered before large‐scale application.
The atmospheric deposition of anthropogenic active nitrogen significantly influences marine primary productivity and contributes to eutrophication. The form of nitrogen deposition has been evolving ...annually, alongside changes in human activities. A disparity arises between observation results and simulation conclusions due to the limited field observation and research in the ocean. To address this gap, our study undertook three field cruises in the South China Sea in 2021, the largest marginal sea of China. The objective was to investigate the latest atmospheric particulate inorganic nitrogen deposition pattern and changes in nitrogen sources, employing nitrogen-stable isotopes of nitrate (δ15N–NO3–) and ammonia (δ15N–NH4+) linked to a mixing model. The findings reveal that the N–NH4+ deposition generally surpasses N–NO3– deposition, attributed to a decline in the level of NOx emission from coal combustion and an upswing in the level of NHx emission from agricultural sources. The disparity in deposition between N–NH4+ and N–NO3– intensifies from the coast to the offshore, establishing N–NH4+ as the primary contributor to oceanic nitrogen deposition, particularly in ocean background regions. Fertilizer (33 ± 21%) and livestock (20 ± 6%) emerge as the primary sources of N–NH4+. While coal combustion continues to be a significant contributor to marine atmospheric N–NO3–, its proportion has diminished to 22 (Northern Coast)–35% (background area) due to effective NOx emission controls by the countries surrounding the South China Sea, especially the Chinese Government. As coal combustion's contribution dwindles, the significance of vessel and marine biogenic emissions grows. The daytime higher atmospheric N–NO3– concentration and lower δ15N–NO3– compared with nighttime further underscore the substantial role of marine biogenic emissions.
The two commonly applied methods to assess dinitrogen (N(2)) fixation rates are the (15)N(2)-tracer addition and the acetylene reduction assay (ARA). Discrepancies between the two methods as well as ...inconsistencies between N(2) fixation rates and biomass/growth rates in culture experiments have been attributed to variable excretion of recently fixed N(2). Here we demonstrate that the (15)N(2)-tracer addition method underestimates N(2) fixation rates significantly when the (15)N(2) tracer is introduced as a gas bubble. The injected (15)N(2) gas bubble does not attain equilibrium with the surrounding water leading to a (15)N(2) concentration lower than assumed by the method used to calculate (15)N(2)-fixation rates. The resulting magnitude of underestimation varies with the incubation time, to a lesser extent on the amount of injected gas and is sensitive to the timing of the bubble injection relative to diel N(2) fixation patterns. Here, we propose and test a modified (15)N(2) tracer method based on the addition of (15)N(2)-enriched seawater that provides an instantaneous, constant enrichment and allows more accurate calculation of N(2) fixation rates for both field and laboratory studies. We hypothesise that application of N(2) fixation measurements using this modified method will significantly reduce the apparent imbalances in the oceanic fixed-nitrogen budget.
It had been suggested that permafrost thaw could promote frozen nitrogen (N) release and modify microbial N transformation rates, which might alter soil N availability and then regulate ecosystem ...functions. However, the current understanding of this issue is confined to limited observations in the Arctic permafrost region, without any systematic measurements in other permafrost regions. Based on a large‐scale field investigation along a 1,000 km transect and a laboratory incubation experiment with a 15N pool dilution approach, this study provides the comprehensive evaluation of the permafrost N status, including the available N content and related N transformation rates, across the Tibetan alpine permafrost region. In contrast to the prevailing view, our results showed that the Tibetan alpine permafrost had lower available N content and net N mineralization rate than the active layer. Moreover, the permafrost had lower gross rates of N mineralization, microbial immobilization and nitrification than the active layer. Our results also revealed that the dominant drivers of the gross N mineralization and microbial immobilization rates differed between the permafrost and the active layer, with these rates being determined by microbial properties in the permafrost while regulated by soil moisture in the active layer. In contrast, soil gross nitrification rate was consistently modulated by the soil
NH4+
content in both the permafrost and the active layer. Overall, patterns and drivers of permafrost N pools and transformation rates observed in this study offer new insights into the potential N release upon permafrost thaw and provide important clues for Earth system models to better predict permafrost biogeochemical cycles under a warming climate.
Based on a large‐scale field investigation along a 1,000‐km transect and a laboratory incubation experiment with a 15N pool dilution approach, this study evaluated the permafrost nitrogen status (i.e., available nitrogen content and nitrogen transformation rates) on the Tibetan Plateau. We found that the Tibetan permafrost had lower soil nitrogen status than the active layer, and rates of nitrogen mineralization and microbial immobilization in the permafrost and active layer were regulated by different factors, while the nitrification rate in both layers was consistently influenced by the substrate. These findings offer new insights into the potential N release upon permafrost thaw.
Nitrogen immobilization usually leads to nitrogen retention in soil and, thus, influences soil nitrogen supply for plant growth. Understanding soil nitrogen immobilization is important for predicting ...soil nitrogen cycling under anthropogenic activities and climate changes. However, the global patterns and drivers of soil nitrogen immobilization remain unclear. We synthesized 1350 observations of gross soil nitrogen immobilization rate (NIR) from 97 articles to identify patterns and drivers of NIR. The global mean NIR was 8.77 ± 1.01 mg N kg−1 soil day−1. It was 5.55 ± 0.41 mg N kg−1 soil day−1 in croplands, 15.74 ± 3.02 mg N kg−1 soil day−1 in wetlands, and 15.26 ± 2.98 mg N kg−1 soil day−1 in forests. The NIR increased with mean annual temperature, precipitation, soil moisture, soil organic carbon, total nitrogen, dissolved organic nitrogen, ammonium, nitrate, phosphorus, and microbial biomass carbon. But it decreased with soil pH. The results of structural equation models showed that soil microbial biomass carbon was a pivotal driver of NIR, because temperature, total soil nitrogen, and soil pH mostly indirectly influenced NIR via changing soil microbial biomass. Moreover, microbial biomass carbon accounted for most of the variations in NIR among all direct relationships. Furthermore, the efficiency of transforming the immobilized nitrogen to microbial biomass nitrogen was lower in croplands than in natural ecosystems (i.e., forests, grasslands, and wetlands). These findings suggested that soil nitrogen retention may decrease under the land use change from forests or wetlands to croplands, but NIR was expected to increase due to increased microbial biomass under global warming. The identified patterns and drivers of soil nitrogen immobilization in this study are crucial to project the changes in soil nitrogen retention.
This study is among the first attempts to explore the global patterns and drivers of gross soil nitrogen immobilization rate (NIR) by compiling 1350 observations from terrestrial ecosystems. Soil microbial biomass carbon was identified as the pivotal driver in terrestrial NIR at the global scale. Soil NIR was likely to increase due to increased soil microbial biomass carbon under global warming, but decrease under the land cover change from forests or wetlands to croplands. The identified drivers of soil nitrogen immobilization offer empirical evidence for improving soil nitrogen models to predict changes in soil nitrogen retention under global changes.
•The impacts of N application over two growing seasons for seed and forage production were checked in perennial grassland.•Fall nitrogen application in previous year matches the N requirement of a ...crucial stage in inflorescence and tiller formation.•A high rate of fall N application in the previous year is an optimum choice to achieve greater seed yield (or forage yield) and N use efficiency.
Efforts to maximize seed or forage yield with nitrogen (N) fertilizer are common in cropping systems. However, only limited attention has been paid to investigate N fertilizer application in different seasons, especially for perennial grasses, whose seed production requires two or more growing seasons. We conducted a two-year field experiment to evaluate the impacts of N application timing (fall in previous year and spring in current year) and N application rate (0, 28 and 56kgNha−1yr−1) on seed yield, forage production and N use efficiency for a semi-arid, perennial grass (Leymus chinensis). As compared to the spring N application, we found that fall N application at the inflorescence stage in the previous year significantly increased seed yield, forage yield, seed agronomic N use efficiency (s-aNUE), forage agronomic N use efficiency (f-aNUE), seed physiological N use efficiency (s-PE) and forage physiological N use efficiency (f-PE). Seed yield and forage yield were both higher with high N-rate treatment as compared to low N-rate in both years. Nitrogen rate effects on N use efficiency indices varied with year and N-timing. We conclude that N application in the fall of the previous year matches N demand for increases in seed yield and forage yield and this is an optimum choice to achieve greater seed yield and forage yield with high N use efficiency. Our research implies that N application in the fall increases inflorescence number and fall tillers by stimulating inflorescence and/or fall tillers numbers. Future research should focus on determining for each physiological stage that control the seed and/or forage yield components, the limiting resource. Then targeting the limiting resource at each physiological stage can increase yield, and, for perennial crops, the key stages regulating seed and/or forage yield components can be in different years, as we found for Leymus chinensis.
Rapid development of agriculture and fossil fuel combustion greatly increased US reactive nitrogen emissions to the atmosphere in the second half of the 20th century, resulting in excess nitrogen ...deposition to natural ecosystems. Recent efforts to lower nitrogen oxides emissions have substantially decreased nitrate wet deposition. Levels of wet ammonium deposition, by contrast, have increased in many regions. Together these changes have altered the balance between oxidized and reduced nitrogen deposition. Across most of the United States, wet deposition has transitioned from being nitrate-dominated in the 1980s to ammonium-dominated in recent years. Ammonia has historically not been routinely measured because there are no specific regulatory requirements for its measurement. Recent expansion in ammonia observations, however, along with ongoing measurements of nitric acid and fine particle ammonium and nitrate, permit new insight into the balance of oxidized and reduced nitrogen in the total (wet + dry) US nitrogen deposition budget. Observations from 37 sites reveal that reduced nitrogen contributes, on average, ∼65% of the total inorganic nitrogen deposition budget. Dry deposition of ammonia plays an especially key role in nitrogen deposition, contributing from 19% to 65% in different regions. Future progress toward reducing US nitrogen deposition will be increasingly difficult without a reduction in ammonia emissions.
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