Excess Nitrogen Research Articles

Evidence of nitrogen inputs affecting soil nitrogen purification by mediating root exudates of salt marsh plants

Salt marsh has an important ‘purification’ role in coastal ecosystems by removing excess nitrogen that could otherwise harm aquatic life and reduce water quality. Recent studies suggest that salt marsh root exudates might be the ‘control centre’ for nitrogen transformation, but empirical evidence is lacking. Here we sought to estimate the direction and magnitude of nitrogen purification by salt marsh root exudates and gain a mechanistic understanding of the biogeochemical transformation pathway(s). To achieve this, we used a laboratory incubation to quantify both the root exudates and soil nitrogen purification rates, in addition to the enzyme activities and functional genes under Phragmites australis populations with different nitrogen forms addition (NO3−, NH4+ and urea). We found that NO3− and urea addition significantly stimulate P. australis root exudation of total acids, amino acids, total sugars and total organic carbon, while NH4+ addition only significantly increased total acids, amino acids and total phenol exudation. High total sugars, amino acids and total organic carbon concentrations enlarged nitrogen purification potential by stimulating the nitrogen purifying bacterial activities (including enzyme activities and related genes expression). Potential denitrification rates were not significantly elevated under NH4+ addition in comparison to NO3− and urea addition, which should be ascribed to total phenol self-toxicity and selective inhibition. Further, urea addition stimulated urease and protease activities with providing more NH4+ and NO2− substrates for elevated anaerobic ammonium oxidation rates among the nitrogen addition treatments. Overall, this study revealed that exogenous nitrogen could increase the nitrogen purification-associated bacterial activity through accelerating the root exudate release, which could stimulate the activity of nitrogen transformation, and then improve the nitrogen removal capacity in salt marsh.

Research on Enhancing the Yield and Quality of Oat Forage: Optimization of Nitrogen and Organic Fertilizer Management Strategies

In the context of the increasingly serious issues of resource waste, soil degradation, and environmental pollution caused by excessive nitrogen fertilizer application worldwide, this study conducted a two-year field experiment in Qinghai Province to explore suitable nitrogen fertilizer management strategies for the region. Ten fertilization levels were set, incorporating varying ratios of conventional nitrogen fertilizer and organic fertilizer, as well as the proportion of base fertilizer and topdressing. The focus was on monitoring the forage yield, quality, and related physiological indicators of oats during the flowering and milk stages. The use of correlation analysis and the multi-criteria decision-making model TOPSIS was applied for comprehensive data evaluation to determine the optimal fertilization strategy. After systematic data collection and analysis, the results showed that when 75% conventional nitrogen fertilizer was combined with 4500 kg·hm−2 of organic fertilizer (F4), the oat yield during the milking stage reached its peak at 14,722.48 kg·hm−2. Additionally, the yield effect was optimal (13,677.34 kg·hm−2) when using 30% base fertilizer and 70% jointing fertilizer (D2). Regarding nutritional quality, the fertilization strategy combining 75% conventional nitrogen fertilizer with 4500 kg·hm−2 of organic fertilizer, along with 30% base fertilizer and 70% jointing fertilizer (F4D2), significantly reduced the content of acid detergent fiber (ADF), neutral detergent fiber (NDF), and coarse fiber (CF) in oats, while increasing the content of EE (crude fat) and CP (crude protein). This significantly improved the nutritional value of oats. Correlation analysis further revealed the positive effect of fertilization amount and fertilization period on oat yield, as well as a negative correlation with fiber content. Finally, through comprehensive evaluation using the multi-criteria decision-making model TOPSIS, we verified the superiority of the fertilization strategy.

A comprehensive framework for assessing the spatiotemporal impact of land use and cover change on lake eutrophication

Excessive nitrogen and phosphorus (N/P) input is the important reason for lake eutrophication, a widespread environmental problem that harms freshwater ecosystems worldwide. Land use land cover changes (LULCCs) strongly affect the migration and transformation process on land of N/P. Aiming to improve the accuracy of N/P estimation and deeply understand the spatiotemporal impact of LULCCs on N/P distribution, this study proposed an optimized framework, InVEST-UM, by integrating an unmixing algorithm with the conventional InVEST model. A comprehensive and intuitive index LPI (LULCCs purification capacity index) is developed for the impact assessment and spatialization. Validation shows a strong correlation (0.94) between the LPI and eutrophication degree of Dianshan Lake. This suggests the LPI effectively captures the spatiotemporal influence of LULCCs on lake eutrophication. Based on the sub-pixel results of N/P estimation, dramatic changes of LPI with an average rate of 46.182% were explored. There is a strong positive correlation (0.91) between vegetation area and LULCCs purification capacity for N/P. Conversely, negative relationships are found between LULCCs purification capacity with bare lands (−0.86), and artificial surfaces (−0.75). Changes in the water bodies have weak influence (−0.33) on LULCCs purification capacity. The increase in vegetation area can not only enhance the lake purification capacity, but also help maintain low ecological sensitivity. By employing this comprehensive framework, this study provides valuable insights into the long-term dynamics of LULCCs changes and their implications for lake ecosystems, and could support the protection and land use planning for the sustainability and ecological balance of the lake.

Role of Nitrogen in Wheat Production System and Nitrogen for Improving Wheat Yield and Quality: A Review

Wheat is the staple food across the different parts of the world. To increase the wheat productivity by utilizing the fertilizers. Nitrogen plays a key role in increasing productivity and the quality of the crops. In this review article, we studied the relationship between nitrogen and wheat parameters, the impact of excessive nitrogen used in wheat, NUE (Nitrogen use efficiency) in wheat production, and examined various nitrogen management strategies aimed at enhancing both yield and quality. Different nitrogen application techniques, such as broadcast and side-dressing, have been evaluated, with the rate of nitrogen showing a significant influence on wheat parameters. Key components influencing NUE in wheat farming, including soil characteristics, nitrogen application timing and rate, environmental factors, and crop genetics, are discussed. Furthermore, innovative nitrogen management practices such as precision farming techniques, cover cropping, and the use of biofertilizers as effective strategies for improving NUE and promoting sustainable wheat production. The abstract underscores the importance of balancing nitrogen application to meet crop demands at different growth stages while minimizing nitrogen losses and environmental risks. By integrating advanced technologies, agronomic practices, and scientific insights, farmers can optimize nitrogen use efficiency in wheat production systems, thereby enhancing both yield and quality outcomes.

Mechanisms behind high N2O emissions from livestock enclosures in Kenya revealed by dual-isotope and functional gene analyses

Livestock manure contributes to global warming due to greenhouse gas (GHG) emissions, especially nitrous oxide (N2O) and methane (CH4). In the arid and semi-arid lands of Sub-Saharan Africa (SSA), extensive pastoral grazing systems are common, with cattle grazing in the savanna during the day and kept in enclosures (called bomas in Kenya) during the night. Manure is usually not removed from bomas but left to accumulate, leading to excessive local nitrogen loads, making these bomas an overlooked N2O emission hotspot in SSA that is currently not accounted for in national and regional GHG budgets. Here, we present the first in-situ isotope measurements of N2O fluxes from 37 cattle bomas along an age gradient ranging from 0 to 5 years after boma abandonment in Kenya along with functional gene analysis of soil and manure samples. The isotopic composition of the emitted N2O from bomas suggests that on average 91 ± 8% N2O was produced via bacterial denitrification and/or nitrifier denitrification, with little variation across boma age class. We also found high levels of N2O reduction to N2 across all sample sites (81 ± 9%), indicating high levels of N2O consumption. The abundances of denitrification-related genes (nirK and narG) were significantly higher than those of nitrification-related genes (amoA: AOA and AOB) in the cattle manure samples taken from the bomas, corroborating N2O emissions largely being attributed to denitrification. Significant abundance of the reduction-related gene (nosZ) also corroborated the high potential for microbial N2O reduction in bomas. Thus, by combining dual-isotope and functional gene analysis, we were able to identify source processes that govern N2O emissions from these systems. More generally, making use of the manure by spreading it in the vicinity of the bomas or on dedicated forage plots could provide a win-win by enhancing savanna productivity while simultaneously mitigating GHG emissions.

A regional examination of the footprint of agriculture and urban cover on stream water quality

Freshwater systems in cold regions, including the Laurentian Great Lakes, are threatened by both eutrophication and salinization, due to excess nitrogen (N), phosphorus (P) and chloride (Cl−) delivered in agricultural and urban runoff. However, identifying the relative contribution of urban vs. agricultural development to water quality impairment is challenging in watersheds with mixed land cover, which typify most developed regions. In this study, a self-organizing map (SOM) analysis was used to evaluate the contributions of various forms of land cover to water quality impairment in southern Ontario, a population-dense, yet highly agricultural region in the Laurentian Great Lakes basin where urban expansion and agricultural intensification have been associated with continued water quality impairment. Watersheds were classified into eight spatial clusters, representing four categories of agriculture, one urban, one natural, and two mixed land use clusters. All four agricultural clusters had high nitrate-N concentrations, but levels were especially high in watersheds with extensive corn and soybean cultivation, where exceedances of the 3 mg L−1 water quality objective dramatically increased above a threshold of ‍∼30 % watershed row crop cover. Maximum P concentrations also occurred in the most heavily tile-drained cash crop watersheds, but associations between P and land use were not as clear as for N. The most urbanized watersheds had the highest Cl− concentrations and expansions in urban area were mostly at the expense of surrounding agricultural land cover, which may drive intensification of remaining agricultural lands. Expansions in tile-drained corn and soybean area, often at the expense of mixed, lower intensity agriculture are not unique to this area and suggest that river nitrate-N levels will continue to increase in the future. The SOM approach provides a powerful means of simplifying heterogeneous land cover characteristics that can be associated with water quality patterns and identify problem areas to target management.

Spatio-temporal evolution mechanism and dynamic simulation of nitrogen and phosphorus pollution of the Yangtze River economic Belt in China

Excess nitrogen and phosphorus inputs are the main causes of aquatic environmental deterioration. Accurately quantifying and dynamically assessing the regional nitrogen and phosphorus pollution emission (NPPE) loads and influencing factors is crucial for local authorities to implement and formulate refined pollution reduction management strategies. In this study, we constructed a methodological framework for evaluating the spatio-temporal evolution mechanism and dynamic simulation of NPPE. We investigated the spatio-temporal evolution mechanism and influencing factors of NPPE in the Yangtze River Economic Belt (YREB) of China through the pollution load accounting model, spatial correlation analysis model, geographical detector model, back propagation neural network model, and trend analysis model. The results show that the NPPE inputs in the YREB exhibit a general trend of first rising and then falling, with uneven development among various cities in each province. Nonpoint sources are the largest source of land-based NPPE. Overall, positive spatial clustering of NPPE is observed in the cities of the YREB, and there is a certain enhancement in clustering. The GDP of the primary industry and cultivated area are important human activity factors affecting the spatial distribution of NPPE, with economic factors exerting the greatest influence on the NPPE. In the future, the change in NPPE in the YREB at the provincial level is slight, while the nitrogen pollution emissions at the municipal level will develop towards a polarization trend. Most cities in the middle and lower reaches of the YREB in 2035 will exhibit medium to high emissions. This study provides a scientific basis for the control of regional NPPE, and it is necessary to strengthen cooperation and coordination among cities in the future, jointly improve the nitrogen and phosphorus pollution tracing and control management system, and achieve regional sustainable development.

Valorization of lignin by crosslinking for slow-release urea fertilizer systems: A promising approach for agricultural applications

Slow-release fertilizers hold promise for their extensive use in agriculture. Urea, a commonly employed fertilizer, poses the risk of elevated nitrogen levels in soil due to its water solubility when used improperly. To address this issue, the development of a cost-effective and biodegradable urea slow-release matrix was pursued by crosslinking wheat straw-derived lignin with epichlorohydrin at varying ratios (1:1, 1:2, and 2:1) and subsequently impregnating it with urea. The crosslinked lignin matrices exhibited superior properties compared to unmodified lignin. After 8 days of immersion in water, the percentage release of urea from the crosslinked lignin matrices reached 48%, whereas it was 95% for unmodified lignin. Characterization techniques such as Fourier transform infrared spectroscopy, 13C nuclear magnetic resonance, and thermogravimetry analysis were employed to gain insights into the structural and functional aspects of the crosslinked lignin. The results revealed that the crosslinked lignin possessed a higher surface area and exhibited more suitable functional groups for urea impregnation. The controlled hydrophilic-lipophilic balance of the crosslinked lignin matrices offers significant advantages in fertilizer systems, enabling a controlled and gradual release of urea. This innovative approach not only offers enhanced control over nutrient delivery but also demonstrates the potential of lignin as a sustainable and cost-effective alternative for slow-release fertilizer formulations. This development provides an effective solution to address the issue of excessive nitrogen levels and opens up new avenues in material development, holds promise for sustainable agriculture and paves the way for further advancements in the field.

Effects of nitrogen deposition on the rhizosphere nitrogen-fixing bacterial community structure and assembly mechanisms in Camellia oleifera plantations.

Increased nitrogen deposition is a key feature of global climate change, however, its effects on the structure and assembling mechanisms of the nitrogen-fixing bacteria present at the root surface remain to be elucidated. In this pursuit, we used NH4NO3 to simulate nitrogen deposition in a 10-year-old Camellia oleifera plantation, and set up four deposition treatments, including control N0 (0 kg N hm-2 a-1), low nitrogen N20 (20 kg N hm-2 a-1), medium nitrogen N40 (40 kg N hm-2 a-1) and high nitrogen N160 (160 kg N hm-2 a-1). The results showed that nitrogen deposition affected the soil nitrogen content and the structure of the nitrogen-fixing bacterial community. Low nitrogen deposition was conducive for nitrogen fixation in mature C. oleifera plantation. With increasing nitrogen deposition, the dominant soil nitrogen-fixing bacterial community shifted from Desulfobulbaceae to Bradyrhizobium. When nitrogen deposition was below 160 kg N hm-2 a-1, the soil organic matter content, total nitrogen content, nitrate nitrogen content, ammonium nitrogen content, urease activity, soil pH and nitrate reductase activity influenced the composition of the nitrogen-fixing bacterial community, but the stochastic process remained the dominant factor. The results indicate that the strains of Bradyrhizobium japonicum and Bradyrhizobium sp. ORS 285 can be used as indicator species for excessive nitrogen deposition.

The elite haplotype OsGATA8-H coordinates nitrogen uptake and productive tiller formation in rice

Excessive nitrogen promotes the formation of nonproductive tillers in rice, which decreases nitrogen use efficiency (NUE). Developing high-NUE rice cultivars through balancing nitrogen uptake and the formation of productive tillers remains a long-standing challenge, yet how these two processes are coordinated in rice remains elusive. Here we identify the transcription factor OsGATA8 as a key coordinator of nitrogen uptake and tiller formation in rice. OsGATA8 negatively regulates nitrogen uptake by repressing transcription of the ammonium transporter gene OsAMT3.2. Meanwhile, it promotes tiller formation by repressing the transcription of OsTCP19, a negative modulator of tillering. We identify OsGATA8-H as a high-NUE haplotype with enhanced nitrogen uptake and a higher proportion of productive tillers. The geographical distribution of OsGATA8-H and its frequency change in historical accessions suggest its adaption to the fertile soil. Overall, this study provides molecular and evolutionary insights into the regulation of NUE and facilitates the breeding of rice cultivars with higher NUE.

Nitrogen rate is more important than irrigation rate in mitigating nitrogen leaching in flood-irrigated maize: A 6-year lysimeter experiment

Excessive nitrogen (N) fertilization and irrigation prevail in irrigated agriculture worldwide. However, little information is available that systematically evaluates grain yield, plant N uptake, residual soil NO3−-N (RSN), and N leaching under different irrigation–N regimes in an irrigated maize production system. To address such agronomic and environmental issues, a 6-year in situ lysimeter field trial was conducted in the Hetao Irrigation District of China with five treatments: 1) conventional irrigation (3,900 m3/ha) and local farmer fertilizer N rate (490 kg ha−1) (CON); 2) conventional irrigation and the recommended fertilizer N rate (420 kg ha−1) (RN); 3) deficit irrigation (2,730 m3/ha) and the recommended fertilizer N rate (SRN); 4) deficit irrigation and the recommended fertilizer N rate (with ∼ 10 % organic fertilizer N substitution) (SMN); and 5) conventional irrigation and controlled-release N fertilizer (270 kg ha−1) (CRF). Maize yield was not significantly different across treatments in 2015–2020. Averaged across years, SMN, SRN, and CRF significantly increased plant N uptake compared with that in CON by 28.84 %, 19.15 %, and 17.53 %, respectively. Residual soil NO3−-N at 0–90 cm was ranked as SRN > CON ≈ SMN > RN > CRF, whereas cumulative N in leachate from 2015–2020 (Nloss) in CON was 86.2 % to 187.1 % higher than that in other treatments. The Nloss in SRN was equivalent to that in RN and SMN, but Nloss in SMN decreased significantly compared with that in RN, indicating additive benefits of deficit irrigation and organic input on reducing N leaching. Structural equation modelling revealed that irrigation had greater effects on plant N uptake than those of fertilization, whereas N rate had a greater total effect on N leaching than that of irrigation. Overall, rampant excessive irrigation and N fertilization by farmers can be substantially reduced while maintaining grain yield and mitigating N leaching loss, with further benefits gained by applying controlled-release N fertilizer and manure in irrigated maize production.

Assessing landscape N removal in coastal New England catchments using the N-Sink approach with the R Package, nsink

Background Excess nitrogen (N) loading to coastal ecosystems impairs estuarine water quality. Land management decisions made within estuarine watersheds have a direct impact on downstream N delivery. Natural features within watersheds can act as landscape sinks for N, such as wetlands, streams and ponds that transform dissolved N into gaseous N, effectively removing it from the aquatic system. Identifying and evaluating these landscape sinks and their spatial relationship to N sources can help managers understand the effects of alternative decisions on downstream resources. Methods The N-Sink approach uses widely available GIS data to identify landscape sinks within HUC-12 (or larger) catchments, estimate their N removal potential and map the effect of those sinks on N movement through the catchment. Static maps are produced to visualize N removal efficiency, transport and delivery, the latter in the form of an index. The R package nsink was developed to facilitate data acquisition, processing and visualization. Results The R package creates static maps for a specific HUC-12, or users can visit the University of Connecticut website to explore previously mapped areas. Users can also investigate specific flowpaths interactively by clicking on any location within the catchment. A flowpath is generated with a table describing N removal along each segment. We describe the motivation behind developing nsink, discuss implementation in R, and present two use case examples. nsink is available from https://github.com/USEPA/nsink. Conclusions N-Sink is a decision support tool created for local decision-makers to facilitate better understanding of the relationship between land use and downstream N delivery. Local decision-makers that have prioritized N mitigation in their long-term planning can use nsink to better understand the potential impact of proposed development projects and zoning variances. Similarly, land trusts and other NGOs interested in N mitigation can use nsink to identify high priority areas for acquisition or restoration.

The eutrophication-related index of drinking water sources based on the oxidation-reduction potential

Eutrophication caused by excessive nitrogen and phosphorus is an important factor affecting water quality in drinking water sources. Convenient monitoring of eutrophication in water bodies can reduce the use of pesticides and reduce energy consumption, helping to promote ecological and economic development. This study examined the relationship between water eutrophication and the oxidation-reduction potential (ORP). The results showed that various parameters related to eutrophication, such as ammonia nitrogen, total nitrogen, total phosphorus, chlorophyll-a, and cyanobacteria, had correlations with ORP. There is a close relationship between eutrophication and the concentration of cyanobacteria. When cyanobacteria blooms occur in the drinking water source, it may contaminate the drinking water. Because the conventional eutrophication index does not include the concentration of cyanobacteria, principal component analysis (PCA) was utilized to comprehensively analyze these eutrophication-related parameters and obtain the eutrophication-related index, with the cumulative contribution of principal components reaching 81.8%. Different mathematical methods such as neural network model and mathematical fitting were used to study the relationship between ORP and the eutrophication-related index. A three-segment relationship between the ORP and the index was established. This three-stage relationship was confirmed in different reservoirs.

Bridging boundaries: Six years of community engagement with biological control implementation and monitoring of water hyacinth on Hartbeespoort Dam, South Africa

Water hyacinth has been present on Hartbeespoort Dam since the 1960s. Historical weed management consisted of herbicide and mechanical/manual removal. However, due to funding constraints, biological control was implemented as a cost-effective and environmentally friendly alternative. The impoundment receives excessive phosphorus and nitrogen due to its location downstream from densely populated cities, which includes one of the capital cities of South Africa, Pretoria. Considering that Hartbeespoort Dam is in a temperate region, with cool winters, we embarked on an augmentative biological control approach. To increase our biological control efforts, we had to bridge the research-implementation gap. We fostered a community of practice, by creating a space for the affected community to actively participate in the programme. This would give us the opportunity to share scientific knowledge to affected stakeholders, gauge the public perception, and align potential goals. Social media, in-person meetings and training sessions were used to engage with the public. To increase the availability of the water hyacinth biological control agent, Megamelus scutellaris, community members (i.e. private stakeholders) were offered the opportunity to manage satellite rearing stations. Between 2018 and 2023, nearly half a million Megamelus scutellaris individuals, sourced from both the Centre for Biological Control’s mass-rearing facility and satellite rearing stations around Hartbeespoort Dam, have been released into the dam. Water hyacinth cover on the dam drastically declined every year following a build-up of Megamelus scutellaris. Over the course of the programme, private stakeholders that were actively involved grew from two (2018) to 16 (2023). Analysing the participation of private stakeholders using a framework that looks at the level of value gained from our interactions, two partners reached a value chain phase that led to an expansion of biological control implementation. Longer-term private stakeholders generated increased interest for biological control implementation in their community, which resulted in recruitment of new private stakeholders. We also evaluated the knowledge of the affected community in 2023 through an online questionnaire. Out of 132 respondents, 51 % had knowledge of what biological control entails, with 56 % acknowledging that biological control has had a positive impact on the management of water hyacinth. Bridging the research-implementation boundary has strengthened biological control efforts, enabling a more sustainable approach to the management of water hyacinth on Hartbeespoort Dam. However, continued community engagement is necessary to increase the public’s knowledge about the practice of biological control.

Balanceando el nitrógeno en la portera del predio

Uruguay's dairy can potentially enhance milk productivity competitively, but intensification risks elevating nitrogen (N) surplus, heightening environmental concerns. This study quantified farm-gate N inputs and outputs, calculating N surplus (input-output) and N use efficiency (NUE=output/input) for 17 commercial modal dairy systems identified in the 2014 and 2019 national surveys and 6 prospective intensified systems based on experimental pastoral farmlets achieving near-maximal rainfed productivity. Current dairy systems maintained N surplus at 71 kg N ha-1 between 2014 and 2019 (range: 44-97 kg N ha-1) while improving NUE from 28.3 to 30.5% (range: 20-35%). Intensification increased N surplus without necessarily reducing NUE. Our analyses highlight three aspects: (i) comparatively low N surplus of current Uruguayan dairy, (ii) nonlinear links between N surplus and stocking rate, feed intake, milk productivity and operating profit, and (iii) inequality between dairy systems in their contribution to national dairy N surplus reflects mainly disparity in farm size. These insights underscore the crucial need for understanding the actual fate of N surpluses: nitrate leaching, ammonia volatilisation, N2 denitrification, or N accumulation in soil organic matter. This is an unavoidable requisite for designing management practices and policies able to effectively optimise the economic and environmental sustainability of Uruguayan dairy.

Peroxynitrite-Triggered Carbon Monoxide Donor Improves Ischemic Stroke Outcome by Inhibiting Neuronal Apoptosis and Ferroptosis.

Cerebral ischemia-reperfusion injury produces excessive reactive oxygen and nitrogen species, including superoxide, nitric oxide, and peroxynitrite (ONOO-). We recently developed a new ONOO--triggered metal-free carbon monoxide donor (PCOD585), exhibiting a notable neuroprotective outcome on the rat middle cerebral artery occlusion model and rendering an exciting intervention opportunity toward ischemia-induced brain injuries. However, its therapeutic mechanism still needs to be addressed. In the pharmacological study, we found PCOD585 inhibited neuronal Bcl2/Bax/caspase-3 apoptosis pathway in the peri-infarcted area of stroke by scavenging ONOO-. ONOO- scavenging further led to decreased Acyl-CoA synthetase long-chain family member 4 and increased glutathione peroxidase 4, to minimize lipoperoxidation. Additionally, the carbon monoxide release upon the ONOO- reaction with PCOD585 further inhibited the neuronal Iron-dependent ferroptosis associated with ischemia-reperfusion. Such a synergistic neuroprotective mechanism of PCOD585 yields as potent a neuroprotective effect as Edaravone. Additionally, PCOD585 penetrates the blood-brain barrier and reduces the degradation of zonula occludens-1 by inhibiting matrix metalloproteinase-9, thereby protecting the integrity of the blood-brain barrier. Our study provides a new perspective for developing multi-functional compounds to treat ischemic stroke.

Soil gross N2O emission and uptake under two contrasting agroforestry systems: riparian tree buffer versus alley-cropping tree row

In addition to the removal of excess mineral nitrogen (N) via root uptake, trees in agroforestry systems may mitigate negative effects of high N fertilization of adjacent crops by enhancing complete denitrification of excess mineral N aside from root uptake. Presently, little is known about the potential for NO3− reduction through denitrification (conversion to greenhouse gas N2O and subsequently to non-reactive N2) in contrasting agroforestry systems: riparian tree buffer versus tree row of an upland alley-cropping system. Our study aimed to (1) quantify gross N2O emissions (both N2O + N2 emissions) and gross N2O uptake (N2O reduction to N2), and (2) determine their controlling factors. We employed the 15N2O pool dilution technique to quantify gross N2O fluxes from 0 to 5 cm (topsoil) and 40 to 60 cm (subsoil) depths with seasonal field measurements in 2019. The riparian tree buffer exhibited higher topsoil gross N2O emissions and uptake than the alley-cropping tree row (P < 0.03). Gross N2O emissions were regulated by N and carbon (C) availabilities and aeration status rather than denitrification gene abundance. Gross N2O uptake was directly linked to available C and nirK gene abundance. In the subsoil, gross N2O emission and uptake were low in both agroforestry systems, resulting from low mineral N contents possibly due to N uptake by deep tree roots. Nonetheless, the larger available C and soil moisture in the subsoil of riparian tree buffer than in alley-cropping tree row (P < 0.05) suggest its large potential for N2O uptake whenever NO3− is transported to the subsoil.

How much nutrient reaches a stream: Insights from a hybrid model and implications for watershed nitrogen export and removal

Excess nitrogen (N) discharged into streams and rivers degrades freshwater quality and threatens ecosystems worldwide. Land use patterns may influence riverine N export, yet the effect of location on N export and removal is not fully understood. We proposed a hybrid model to analyze N export and removal within the watersheds. The proposed model is satisfied for the riverine N modelling. The KGE and R2 are 0.75 and 0.72 in the calibration period which are 0.76 and 0.61 in the validation period. Human-impacted land use may modify the N yield in the watershed, and the net N export from built-up to the in-stream system was highest in the urbanized sub-watersheds (0.81), followed by the agricultural sub-watersheds (0.88), and forested sub-watersheds (0.96). Agricultural activities make a large contribution to the N exports in the watersheds, and the mean N input from the agricultural land use to in-stream were 2069–4353 kg km−2 yr−1. Besides, the excess inputs of N by overapplication of fertilizer and manure during the agricultural activities may increase legacy N in soil and groundwater. Biological processes for the riverine N removal may be controlled by the available substrate in the freshwater system, and temperature sensitivity of denitrification is highest in the flood seasons, especially for the human-impacted sub-watersheds. The riverine biological processes may be limited by other competitions. Our model results provide evidence that quantity and location of specific land use may control biogeochemistry within watersheds. We demonstrate the need to understand nutrient export and removal within watersheds by improving the representation of spatial patterns in existing watershed models, and we consider this study to be a new effort for the spatially explicit modeling to support land-use based N management in watersheds.

Tracing the contribution and fate of synthetic nitrogen fertilizer in young apple orchard agrosystems

Excessive synthetic nitrogen (N) inputs in intensive orchard agrosystems of developing countries are a growing concern regarding their adverse impacts on fruit production and the environment. Quantifying the distribution and contribution of fertilizer N is essential for increasing N use efficiency and minimizing N loss in orchards. A 15N tracer experiment was performed in a young dwarf apple orchard over two growing seasons to determine the fertilizer N transformation and fate. Fertilizer N primarily contributed to 25 % to 75 % of soil nitrate in the top 60 cm, but the contribution to soil microbial biomass N and fixed ammonium was <8 %, with the contribution to plant N ranging from 9 % to 19 %. In most growth periods, soil nitrate and fixed ammonium contents derived from native soil with N fertilization were higher than those not receiving N fertilizer. The N use efficiency of plants was only 2.6 % and 4.9 % in the first and second seasons, respectively, in contrast to 56.6 % and 54.0 % of N recovered in soil. Meanwhile, N assimilated into microbial biomass accounted for 0.8 %, and the proportion fixed by clay minerals was 3.5 %–5.2 %. One season after N fertilization, the nitrate below the 1 m soil layers accounted for 4.6 % of the applied N fertilizer, and the proportion increased to 22.5 % after two seasons. The N loss rate via N2O emission was 0.4 % over two years. The application of N fertilizer facilitated indigenous soil N mineralization, and abiotic ammonium fixation more efficiently retained synthetic N than microbial immobilization. These findings provide new insight into orchard N cycling, and attention should be given to the improvement of soil N retention and turnover capacity regulated by soil microbial and abiotic processes, as well as the potential environmental impacts of additional soil N mineralization resulting from prolonged chemical N fertilization.

Environmental transport of excess nitrogen fertilizer in peach orchard: Evidence arising from 15N tracing trial

In pursuit of high fruit yield, overwhelming amount of nitrogen (N) fertilizer was unreasonably applied in orchard, resulting in lower fertilizer N uptake and higher environmental loss. It is crucial to propose appropriate fertilization timing and optimal N management by clarifying fruit tree N uptake pattern in orchard systems. Here, a 15N isotope enrichment trial was conducted in peach orchard to assess the transport of applied synthesized fertilizer-N to the plant and environment in the Taihu Lake region. Ammonium sulfate ((NH4)2SO4, 10.12 atom % 15N), as the N source, was applied with four split applications at 382.5 kg N ha−1 during one plant growth cycle. Results showed N deriving from fertilizer (NDFF) accounted for 24.5% in leaves and 38.4% in fruits, respectively. During the annual growth cycle, the applied fertilizer-N uptake and utilization was higher in reproductive growth stage than vegetative growth stage. After harvest, 28.8% of applied fertilizer-N was absorbed by peach tree, 9.5% was lost to the environment through surface runoff, ammonia (NH3) volatilization and nitrous oxide (N2O) emission, 29.6% was retained in the 0–160 cm soil profile, the remaining 32.1% was unaccounted N including N leaching and N loss from the N removal progress. Generally, more applied fertilizer-N moved to the environment in high N input peach orchard. In order to promote optimal N management, the applied fertilizer-N rate should be reduced by 30% and emphasized on fertilization at the reproductive growth period according to tree N uptake pattern.