Nitrogen Transport Research Articles

Tracking anthropogenic nitrogen-compound sources of surface and groundwater in southwestern Nile Delta: hydrochemical, environmental isotopes, and modeling approach

This research aims to assign the specific and potential sources that control migration and transformation mechanisms of ammonium/nitrate contaminants of surface and groundwater systems in the southwestern Nile Delta, Egypt. To achieve that, an integration of hydrogeochemistry, multiple environmental stable isotopes (δ2H-H2O, δ18O-H2O, δ15N-NH4, and δ15N-NO3) coupled with three-dimensional nitrogen transport numerical model (MODFLOW-MT3D) was done. A set of representative water samples (20 canals and drainage water) and 14 groundwater samples were collected and analyzed for physical, chemical, and stable isotope analysis. NH4+ and NO3− concentrations in surface water samples varied from 0.29 to 124 mg/l and 0.52 to 39.67 mg/l, respectively. For groundwater samples, NH4+ and NO3− concentrations varied from 0.21 to 1.75 mg/l and 0.33 to 32.8 mg/l, respectively. Total risk quotient (THQ) level of nitrate (oral and dermal effects) from drinking water exceeds unity for all water samples indicating a potential noncancer risk for the southwestern Nile Delta residents. The potential sources of nitrogen compound pollution are water from sewage treatment plants used for irrigation, sludge and animal manure, septic tanks, soil nitrogen, and artificial fertilizers according to results of δ15N values. Results of ammonium/nitrate modeling in shallow groundwater aquifers are compared with observed concentrations and are found to be in good agreement. Some recommendations are given to decrease nitrogen loads in the study area through suggested a need for adoption of N-fertilizer management practices and treatment of sewage water before to application in agricultural activities.

Effects of Planting Density, Levels, and Forms of Nitrogen Application on the Yield and Nitrogen Utilization of Wheat following Rice in East China

A major challenge is to achieve the goal of synergistically increasing grain yield and nitrogen use efficiency in wheat production. Many studies have focused on one aspect of cultivation such as fertilizer management, suitable planting density, and straw returning. However, there are few studies on the effect of integrated cultivation practices on yield and nitrogen absorption and utilization of wheat. A field experiment to investigate the characteristics was conducted across two years using Yangmai 16 and Yangmai 20 with five cultivation practices including nitrogen blank area (NB), local practices (LP), nitrogen reduction (NR), planting density reduction and nitrogen reduction (DN), and organic fertilizer (OF). As compared with LP, the DN treatment improved the yield (+4.54%), recovery efficiency of N fertilizer (+5.59%), N partial factor productivity (+15.28%), agronomic N use efficiency (+21.43%), physiological N use efficiency (+14.90%), and nitrogen harvest index (+6.45%). All previous indices were increased by 16.84%, 28.18%, 19.59%, 45.81%, 13.96%, and 3.37% under the OF treatment, as compared with LP. The DN and OF significantly improved nitrogen use efficiency, photosynthetic characteristics, dry matter accumulation, root total and active absorbing surface area, root oxidation activity, nitrogen accumulation, nitrogen harvest index, and nitrogen transportation in various organs. The results suggest that integrated cultivation practices are beneficial to achieve high yield and high nitrogen use efficiency through improving the agronomic performance and root physiological characteristics.

The characteristics of nitrogen and phosphorus output in China's highly urbanized Pearl River Delta region

The nitrogen (N) and phosphorus (P) transportation due to the anthropogenic activities have strong correlations to the water pollution events. In the highly urbanized Pearl River Delta (PRD) region of China, the main input pathways for N and P have been changed. However, their main output pathways have not yet been understood. Based on the modified export coefficient model (ECM), we have quantified the N and P outputs and identified the main factors affecting the N and P outputs in highly urbanized areas such as PRD. The results showed that the N output intensity of the PRD has increased from 3010 to 3970 kg km−2·a−1 from 2008 to 2016. The P output exhibited a similar trend, from 549 to 769 kg km−2·a−1. In terms of spatial distribution, the output intensity gradually increased from economically underdeveloped regions to economically developed regions. N and P emissions in urban wastewater increased significantly with increasing urbanization rates, with output intensities increasing by 640 kg km−2·a−1 and 141 kg km−2·a−1 from 2008 to 2016, respectively. The correlation analysis showed that population density and urbanization rate were the most relevant factors with N and P outputs intensity in highly urbanized areas. This indicates that improving the effluent standards and utilization rates of wastewater treatment plants in these regions are effective measures to control N and P output. Our findings provide some new theoretical basis for the identification and management of pollution sources in highly urbanized areas for other regions, especially developing countries.

The Influence Research on Nitrogen Transport and Reaction in the Hyporheic Zone with an In-Stream Structure.

The hyporheic zone (HZ) is important for river ecological restoration as the main zone with nitrogen biochemical processes. The engineering of river ecological restoration can significantly change the hydrodynamics, as well as solute transport and reaction processes, but it is still not fully understood. In this study, nitrogen transport and reaction processes were analyzed in the HZ with an in-stream weir structure. An HZ model was built, and three reactions were considered with different design parameters of the weir structure and different permeability characteristics of porous media. The results show that a structure with a greater height on the overlying surface water enables the species to break through deeper porous media. It promotes the mean spatial reaction rates of nitrification and denitrification and results in increased net denitrification in most cases. In addition, increasing the burial depth of the structure leads to the same variation trends in the mean spatial reaction rates as increasing the structure height. Larger permeability coefficients in porous media can enhance flow exchange and increase mean spatial reaction rates. The results can help deepen the understanding of nitrogen transport and transformation in the HZ and optimize the design parameters and location of the in-stream structure.

Sorption and Gas Transport Characteristics of Polyimides Based on a Mixture of Diethyl Toluene Diamine Isomers

The transport of oxygen, nitrogen, and hydrocarbons C1–C4 in polyimides based on 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and biphenyl-3,3',4,4'-tetracarboxylic acid dianhydride (BPDA) and diethyl toluene diamine (DETDA) has been studied. The dependences of the diffusion coefficient on the diffusant effective diameter and the solubility coefficients on the Lennard–Jones potential of pair interaction have been considered. It is shown that the diffusion coefficients of butane are out of the linear dependence of the logarithm of the diffusion coefficient on the square of the effective diameter of the diffusant, which may indicate the plasticization of polymers with butane at a pressure of 1 atm. The permeability of mixtures of gases O2–N2 (29 : 71 v/v) and CO2–CH4 (62 : 38 v/v) has been studied. There are no significant differences in the gas separation parameters in comparison with the experiment for individual gases; however, for a mixture of CO2–CH4, a slight increase in the separation factor has been found as compared to the ideal selectivity. The data on the measurement of sorption isotherms and solubility coefficients O2, N2, and CH4 are also presented in the article. Gas solubility coefficients have been found to be close to the values obtained indirectly as P/D.

EDGE2D-EIRENE and ERO2.0 predictions of nitrogen molecular break-up and transport in the divertor of JET low-confinement mode plasmas

• Nitrogen-seeded partially detached JET l -mode plasmas studied using EDGE2D-EIRENE and ERO2.0. • Nitrogen line intensities (N I to N V) in the outer divertor are reproduced to within 50% with EDGE2D-EIRENE. • Nitrogen line intensity peak locations shown to be highly sensitive to the upstream electron density. • ERO2.0 simulations with nitrogen molecular dissociation reactions included suggest a high-degree of molecular recycling. EDGE2D-EIRENE simulations of nitrogen-seeded partially detached JET l -mode plasmas show that the divertor N I to N V radiation distributions are highly sensitive to the upstream electron density, and less sensitive to changes in the assumed cross-field particle diffusivity for nitrogen ions. The EDGE2D-EIRENE simulations reproduce the peak intensities of N I to N V as measured by vertically viewing divertor filterscopes to within 50 % for a narrow range of the upstream electron density within the experimental uncertainties, while the predicted profiles are narrower than the measured ones. Including nitrogen atoms only in the ERO2.0 simulations implies lower N III and N IV peak intensities by one and two thirds, respectively, compared to EDGE2D-EIRENE. If nitrogen is assumed to recycle exclusively as molecules instead of atoms, ERO2.0 predicts that the N III and N IV intensities in the divertor increase by up to a factor of two and that the time-averaged, volume-integrated number of N 5+ to N 7+ ions in the plasma also increases by approximately a factor of 2.

Effect of glycine combined with urea on the absorption, transportation and transformation of nitrogen in wild peach seedlings (Amygdalu spersica (L.) Batsch)

The mechanism of how glycine combined with urea affects the development of peach trees through nitrogen absorption and metabolism is still unclear. In this study, we investigated the transformation of nitrogen in soil, the nitrogen absorption in roots, and the transformation and transportation of nitrogen in the peach tree at different treatment (no nitrogen fertilizer (CK), urea (T1), glycine (T2), glycine:urea (1:1) (T3), glycine:urea (3:7) (T4), and glycine:urea (7:3) (T5)). Compared with CK, the total dry weight of T5 and T2 was significantly increased by 22.95% and 19.09%, while it was lower at T3. The root activity of T5 was significantly higher than CK by 169.27%. The residual NH4+ in the soil was consistent with the application ratio of urea, while the conversion of NO3− was promoted at T5. Under T5, soil amoA and nifH abundance was higher, while the nirK abundance was higher under T1 and T3. In addition, urease activity was higher at T1, while phosphatase, catalase, and dehydrogenase activities were higher at T5. The NO3− content in the root was higher at T5. In roots, the activities of GDH, GOGAT and GS were significantly increased at T5 and T2, while the NR activities of T5 and T1 were significantly increased by 34.60% and 33.64% compared with CK. The aspartic acid and glutamic acid were the main forms of nitrogen transport in wild peaches. PLS-PM analysis showed that nitrogen use efficiency had a very significant direct positive effect on the biomass of peach trees.

The Effect of Plant Growth Promoting Rhizobacteria (PGPRs) on Yield and Some Quality Parameters during Shelf Life in White Button Mushroom (Agaricus bisporus L.).

The use of different bacteria that increase yield and quality in plant production has become common since the 1990s. However, effects of plant growth promoting rhizobacterial (PGPR) treatments during the cultivation period of white button mushroom on quality during marketing duration are not known exactly. This study was carried out to determine the effects of different PGPRs in compost medium on mushroom yield and quality. For this reason, Azospillum lipoferum, Bacillus megaterium, Frateuria aurantia and Thiobacillus thiooxidans, for promoting nitrogen, phosphorus, potassium and sulfur transport, respectively, were applied at a 3 mL per m2 concentration on the 12th day of the spawn run period. Control groups were treated with only water. Azospillum lipoferum increased yield at a rate of 33.3% by enhancing mushroom number per unit area. Shelf life characteristics were observed in mushrooms after storage at 1 °C and at 20 ± 1 °C for 2 days. Bacillus megaterium, Frateuria aurantia and Thiobacillus thiooxidans treatments decreased weight loss and loss in cap firmness, total phenolic compounds and antioxidant capacity during shelf life. However, Azospillum lipoferum for increased yield and Frateuria aurantia and Bacillus megaterium for maintaining postharvest quality were promising treatments during shelf life.

Experimental investigation for pulsed laser nitriding of metals

Pulsed laser nitriding of active metals has been regarded as a promising method for performance enhancement of metals. Nevertheless, clarifying the complicated mechanisms of pulsed laser nitriding such as the nitrogen transport and the chemically active state of nitrogen poses challenges due to the rather fast and complex processes. In this work, the in situ momentum measurements, in situ laser-induced breakdown spectroscopy (LIBS) measurements, in situ transient off-axis Digital holography (TODH) measurements and energy dispersive spectroscopy measurements were implemented to investigate the pulsed laser nitriding. It was revealed experimentally that the laser-supported-detonation (LSD) may be the key, and the nitriding process could proceed effectively only when the illumination power density of laser can reach the threshold of generating LSD. The LSD-induced high-speed N+ ions and N atoms flow to the metal surface, which may be the major mechanism for the nitrogen transporting to the metal surface. Moreover, the experimental results of LIBS showed that the chemically active state of nitrogen is N+ ions and their lifetime is at the scale of 102 ns. The lifetime of N+ ions was found to be prolonged as the nitrogen pressure was increased. As indicated by TODH experimental results, the prolonged lifetime of N+ ions may be caused by the smaller shock wave velocity at the higher nitrogen pressure. These experimental findings in this work may clarify the nitrogen transport mechanism and the chemically active state of nitrogen, which may lead to a better understanding of the pulsed laser nitriding and provide the guidance for optimizing the related industrial design in the future.

Effects of low temperature on distribution and metabolism enzyme activity of carbon and nitrogen of Medicago ruthenica (L.)

AbstractLow temperature is one of the abiotic factors that limit the biomass of Medicago ruthenica (L.), and carbon and nitrogen have important roles in the plant's growth and development. However, the information on the distribution of carbon and nitrogen under low temperature conditions is limited. In this study, we investigated the influence of carbon and nitrogen distribution on M. ruthenica (L.) Trautv. cv. ‘Zhilixing’ based on 13C and 15N isotope tracers in two temperature‐controlled chambers (4–10°C and 25°C, respectively) for 30 days. Results showed that under low temperature, plant height significantly decreased by 22.74%, whereas the ratio of underground to aboveground biomass considerably increased by 146.31% compared to the control plants at 30 days. Moreover, low temperature stress significantly increased the activities of sucrose synthase and glutamine synthase in leaves, shoots and roots. The total carbon content and the abundance of 15N increased in leaves, shoots and roots under low temperature, with a greater level of increase in shoots than in leaves and roots. The weight of leaves, shoots and roots was correlated with δ15N. Hence, low temperature inhibited growth and promoted the transport of carbon and nitrogen.

Effects of Nitrogen and Phosphorus Regulation on Plant Type, Population Ecology and Sheath Blight of Hybrid Rice.

(1) Background: Sheath blight is one of the most economically significant rice diseases worldwide. A study was conducted in order to find the relationship and impact of the amount of nitrogen (N) and phosphorus (P) application on the hybrid rice population microclimate and the severity of sheath blight. (2) Methods: Four N and four P application levels were used to determine their impact on plant type, temperature, and humidity variation in different positions of population and the severity of sheath blight in the later stage. (3) Results: We found that N and P application levels could affect the plant type and change the population temperature and humidity by increasing the leaf length and leaf angle. (4) Conclusions: N application had a more significant (p < 0.05) impact on the plant type. High N application caused decreased temperature (hybrid rice population), while increased humidity (especially the population base layer at grain filling stage) resulted in severe sheath blight. High P application had similar impacts; however, P application increased material and nitrogen transport in plants and reduced the severity of sheath blight.

Public health threats of diminished treatment of onsite sewage

Public health threats of diminished treatment of onsite sewage

Nitrogen transport and sources in urban stormwater with different rainfall characteristics.

Nitrogen pollution in urban stormwater has led to serious quality issues in urban water. Nitrogen pollution mitigation requires fully understanding the transport process and major nitrogen sources in urban stormwater. In this study, the concentrations and flux of various nitrogen forms during urban stormwater transport were analyzed. It was found that the concentration and flux of NO3--N and NH3-N decreased in the order of roof runoff, road runoff, and drainage runoff, while the concentration and flux of dissolved organic nitrogen (DON) and particulate nitrogen (PN) were found to be the highest in road runoff. Source quantification found that roof runoff (34%) and rainwater (34%) were the main contributors to nitrate pollution during light and moderate rains (<25 mm), while road runoff was identified as the major source (49%) of nitrate pollution during heavy rains (>25 mm) due to the large road runoff volume. Regarding particulate organic nitrogen (PON), the road runoff in commercial areas contributed most (23%) to PON pollution during light and moderate rains, while the runoff generated from pervious surfaces and drainage sediments were the primary two sources (22%) of PON during heavy rains. Moreover, the influence of rainfall characteristics on nitrate and PON source contributions was identified. The results show that antecedent dry periods were an important factor influencing nitrogen source contributions during light and moderate rains, while rainfall amount and intensity were critical factors impacting the nitrogen source contributions during heavy rains. Taking various transport processes, source contributions, and rainfall characteristics into consideration, several recommendations were given for the mitigation of nitrogen pollution in urban stormwater. This study can provide a useful perspective to understand the transport and sources of nitrogen, thus developing constructive strategies to control urban nonpoint source pollution management.

Modeling water and nitrogen dynamics from processing tomatoes under different management scenarios in the San Joaquin Valley of California

Study regionThe Southern San Joaquin Valley (SSJV), California. Four representative soil types were evaluated. Study focusEvaluation of regional scale hydrology and nitrogen (N) fate and transport requires a robust modeling framework that considers critical local scale environmental conditions and crop root zone physical processes. Two widely used yet conceptually and mechanistically different models, HYDRUS(2D/3D) and SWAT (Soil and Water Assessment Tool), were used to investigate water and N dynamics in processing tomato fields across a range of soil types and management scenarios over a 30-year period in the SSJV. New hydrological insights for the regionThis study implements a framework to evaluate a regional scale model against a field scale model and provides a framework for assessing percolation and N transport results from regional scale simulations in the absence of extensive field observations. Field scale models developed in HYDRUS (2D/3D) produced similar results to a regional-scale SWAT model in four specific soils in terms of responses to percolation and N losses as a function of varying N fertilizer and irrigation management practices. This model-to-model agreement at the local scale provides confidence in region-scale hydrological and N fate and transport findings, particularly in the absence of extensive field observations. Both models suggest that promoting conservation practices targeting the optimization of irrigation and fertilizer-N management would have a large impact in protecting regional groundwater quality.

LjAMT2;2 Promotes Ammonium Nitrogen Transport during Arbuscular Mycorrhizal Fungi Symbiosis in Lotus japonicus.

Arbuscular mycorrhizal fungi (AMF) are important symbiotic microorganisms in soil that engage in symbiotic relationships with legumes, resulting in mycorrhizal symbiosis. Establishment of strong symbiotic relationships between AMF and legumes promotes the absorption of nitrogen by plants. Ammonium nitrogen can be directly utilised by plants following ammonium transport, but there are few reports on ammonium transporters (AMTs) promoting ammonium nitrogen transport during AM symbiosis. Lotus japonicus is a typical legume model plant that hosts AMF. In this study, we analysed the characteristics of the Lotus japonicus ammonium transporter LjAMT2;2, and found that it is a typical ammonium transporter with mycorrhizal-induced and ammonium nitrogen transport-related cis-acting elements in its promoter region. LjAMT2;2 facilitated ammonium transfer in yeast mutant supplement experiments. In the presence of different nitrogen concentrations, the LjAMT2;2 gene was significantly upregulated following inoculation with AMF, and induced by low nitrogen. Overexpression of LjAMT2;2 increased the absorption of ammonium nitrogen, resulting in doubling of nitrogen content in leaves and roots, thus alleviating nitrogen stress and promoting plant growth.

Simulation of water and nitrogen movement mechanism in cold regions during freeze-thaw period based on a distributed nonpoint source pollution model closely coupled water, heat, and nitrogen processes at the watershed scale.

The nitrogen cycle in cold regions during the freeze-thaw period is complex. Although previous studies have investigated the phenomenon of nitrogen transport and transformation, the underlying mechanisms are vague. Existing models have limitations in terms of loose coupling or weak physical mechanisms. Therefore, a new distributed nonpoint source pollution model, the water and energy transfer processes and nitrogen cycle processes model in cold regions, was developed in this study, with closely coupled water, heat, and nitrogen processes at the watershed scale. The model considered the driving effects of pressure, gravity, solute, and temperature potentials on water and nitrogen movement in soil and the transformation relationship among nitrogen forms. Physical evaluation and simulations were conducted for the Heidingzi River Watershed during two freeze-thaw periods: 2017-2018 and 2018-2019. The soil temperature absolute error was < 0.82℃. The relative errors in stratified liquid water, soil nitrogen content, river flow rate, and river nitrogen concentration were mostly < 10%. Nitrogen transport with water had an obvious "upward agglomeration effect" during the freezing period and a "concentrated release effect" during the thawing period, which was attributed to changes in soil water potential as the freezing front moved down. Disregarding the effects of solute potential and temperature potential will result in an underestimate of the outflow of pollutants during the thawing period. The model can be applied to reveal water quality deterioration in cold regions during thawing.

Identification of nitrogen sources and cycling along freshwater river to estuarine water continuum using multiple stable isotopes

Nitrogen (N) transport from terrene to river water is a major source of N in estuarine water, contributing to eutrophication, harmful algal blooms and hypoxia. However, there is a lack of holistic and systematic research on N sources and transformation in the freshwater river-estuarine water continuum. In this study, multiple stable isotope signatures of nitrate (δ15N-NO3−, δ18O-NO3−), ammonium (δ15N-NH4+), and suspended particulate nitrogen (δ15N-PN) were employed to differentiate the sources and transformations of N and calculate the proportional contribution of NO3− sources by Bayesian model in Qiantang River (QTR)-Hangzhou Bay (HZB) during the dry season. The results showed that: (1) Evidences from isotopic signatures suggested the occurrence of N transformation instead of conservation mixing. (2) Negative correlations between the δ15N-NO3− and δ15N-NH4+, the relationships between δ15N-NO3− and NO3−-N concentrations, and smaller δ18O-NO3− values were found in almost all surface water, indicating that nitrification was the dominant N transformation. (3) In addition to the nitrification evidence, significant correlations between δ15N-PN and δ15N-NH4+ revealed that assimilation and nitrification jointly affected the N transformation in the QTR's upstream, midstream and lower tributaries, which are unaffected or less affected by tides. (4) The lack of a relationship between δ15N-NO3− and δ18O-NO3− or ln(NO3−) indicated that denitrification was weakened in all surface waters. (5) Qualitative identification of N pollution sources and quantitative calculation of NO3−-N potential sources revealed that sewage was the dominant source of N in the QTR and the HZB, while the internal nitrification was also important factor in determining N levels. This study provided evidence to further understand the sources, transport, and transformation of N in the river-estuary continuum, which deepens the understanding of the land-ocean integrated management of N contaminant.

Redox controls on H and N speciation and intermolecular isotopic fractionations in aqueous fluids at high pressure and high temperature: Insights from in-situ experiments

Aqueous magmatic fluids are essential to the transport of hydrogen (H), carbon (C), and nitrogen (N) from the mantle to the surface, during which changes in pressure, temperature, and redox conditions affect the chemical speciation and intermolecular isotopic fractionations of H, C, and N. Here, we performed a series of hydrothermal diamond-anvil cell experiments to evaluate the role of pressure, temperature, and redox conditions on the speciation and intermolecular fractionations of H and N during the decompression and cooling of aqueous fluids from 780 MPa to 800°C to 150 MPa and 200°C. We used Raman spectroscopy to investigate the distribution and exchange reactions of H and N isotopologues between water, methane, ammonia, and di-nitrogen molecules under changing physicochemical conditions. Our experiments show that upon decompression, a C- and N-bearing fluid will preferentially degas D-rich methane and 15N-rich N2, depleting the residual aqueous fluid in those isotopes. If this fluid precipitates N-rich (i.e., NH4+-bearing) minerals, the observed N isotopic fractionation is opposite to that during N2 degassing, enriching the aqueous fluid in 15N. Because these fractionations result from changes in H, C, and N speciation in the aqueous fluid, their magnitudes depend on redox conditions as well as pressure and temperature. Our new in-situ experimental results are consistent with the large H and N isotopic fractionations observed between water, methane, and ammonia species in aqueous fluids at high pressures and temperatures, although the magnitude of the fractionations in our experiments cannot be quantified. Nonetheless, our results suggest that statistical thermodynamic models likely underestimate isotopic fractionation effects for isotopic molecules under these conditions, and should account for solubility and isotopic effects of the solvent associated with the solvation of water, methane, and ammonia isotopologues in aqueous fluids.This work has significant implications for interpreting isotopic measurements of natural samples from hydrothermal systems because it offers insights into isotopic fractionations in multicomponent and multiphase systems under hydrothermal temperatures and pressures.

Controls for multi-temporal patterns of riverine nitrogen and phosphorus export to lake: Implications for catchment management by high-frequency observations

Intensifying human activity coupled with climate change increase the transport of excess riverine nitrogen (N) and phosphorus (P) loading from catchment to lake, leading to eutrophication and harmful algal blooms worldwide. To improve understanding of multi-temporal patterns of riverine N and P export and their hydro-biogeochemical controls over both episodic events and long-term trend, we analyzed and interpreted high-frequency data of total nitrogen (TN), ammonia-nitrogen (NH4–N), and total phosphorus (TP) provided by an automatic water quality monitoring station in a typical agricultural catchment draining to Lake Chaohu, China. Mann-Kendall test revealed a significant decreasing trend of riverine N and P concentration most of the time during 2018–2020. At the sub-daily scale, intraday TN concentrations varied by more than 1 mg/L in 31.8% of the period. Monthly TN and TP concentrations were particularly high in December 2019, indicating combined effect of hydrologic (long dry antecedent period and subsequent intensive rainfall events) and anthropogenic controls (fertilization and agricultural drainage). Significantly higher TN concentrations in winter and TP concentrations in summer reflected coupled dominances of precipitation and temperature on hydrologic and biogeochemical processes. Rainfall events with very heavy intensity drove disproportionate N and P loads (more than 20% of the total export) in only 3.2% of the period. Moderate and very heavy events registered the highest TN and TP concentrations, respectively. Our results highlighted the importance of automatic water quality monitoring station to reveal dynamics of riverine N and P export, which may imply future nutrient loading abatement plans for lake-connected catchment.

Enhanced proteostasis, lipid remodeling, and nitrogen remobilization define barley flag leaf senescence.

Leaf senescence is a developmental process allowing nutrient remobilization to sink organs. We characterized flag leaf senescence at 7, 14, and 21 d past anthesis in two near-isogenic barley lines varying in the allelic state of the HvNAM1 transcription factor gene, which influences senescence timing. Metabolomics and microscopy indicated that, as senescence progressed, thylakoid lipids were transiently converted to neutral lipids accumulating in lipid droplets. Senescing leaves also exhibited an accumulation of sugars including glucose, while nitrogen compounds (nucleobases, nucleotides, and amino acids) decreased. RNA-Seq analysis suggested lipid catabolism via β-oxidation and the glyoxylate cycle, producing carbon skeletons and feeding respiration as a replacement of the diminished carbon supply from photosynthesis. Comparison of the two barley lines highlighted a more prominent up-regulation of heat stress transcription factor- and chaperone-encoding genes in the late-senescing line, suggesting a role for these genes in the control of leaf longevity. While numerous genes with putative roles in nitrogen remobilization were up-regulated in both lines, several peptidases, nucleases, and nitrogen transporters were more highly induced in the early-senescing line; this finding identifies processes and specific candidates which may affect nitrogen remobilization from senescing barley leaves, downstream of the HvNAM1 transcription factor.