Supply Of NO3 Research Articles

Signaling function of NH4+ in the activation of Fe-deficiency response in cucumber (Cucumis sativus L.).

NH4+ is necessary for full functionality of reduction-based Fe deficiency response in plants. Nitrogen (N) is present in soil mainly as nitrate (NO3-) or ammonium (NH4+). Although the significance of a balanced supply of NO3- and NH4+ for optimal growth has been generally accepted, its importance for iron (Fe) acquisition has not been sufficiently investigated. In this work, hydroponically grown cucumber (Cucumis sativus L. cv. Maximus) plants were supplied with NO3- as the sole N source under -Fe conditions. Upon the appearance of chlorosis, plants were supplemented with 2mM NH4Cl by roots or leaves. The NH4+ treatment increased leaf SPAD and the HCl-extractable Fe concentration while decreased root apoplastic Fe. A concomitant increase in the root concentration of nitric oxide and activity of FRO and its abolishment by an ethylene action inhibitor, indicated activation of the components of Strategy I in NH4+-treated plants. Ammonium-pretreated plants showed higher utilization capacity of sparingly soluble Fe(OH)3 and higher root release of H+, phenolics, and organic acids. The expression of the master regulator of Fe deficiency response (FIT) and its downstream genes (AHA1, FRO2, and IRT1) along with EIN3 and STOP1 was increased by NH4+ application. Temporal analyses and the employment of a split-root system enabled us to suggest that a permanent presence of NH4+ at concentrations lower than 2mM is adequate to produce an unknown signal and causes a sustained upregulation of Fe deficiency-related genes, thus augmenting the Fe-acquisition machinery. The results indicate that NH4+ appears to be a widespread and previously underappreciated component of plant reduction-based Fe deficiency response.

Precipitation mechanism of Mn ore deposits in the Datangpo Formation, Nanhua Basin, South China

During the interglacial period of the Cryogenian glaciation, the extensive “Datangpo-type” manganese ores were deposited in the Nanhua Basin. However, there has been significant controversy over the precipitation mechanism of manganese for decades. Based on iron and nitrogen isotope data from the manganese ores of the Datangpo Formation in Chongqing (South China), combined with previous research, we propose that the manganese ores of the Datangpo Formation precipitated directly in an anoxic bottom-water environment in the form of rhodochrosite. The δ56Fe values in the Bijiashan manganese ore (δ56Fe = −0.19 ± 0.13 ‰) are close to those of modern marine hydrothermal iron, and there is a strong positive correlation between the δ56Fe value and iron concentration (R2 = 0.81), indicating that the precipitation of manganese ore could be mainly affected by hydrothermal input. After comprehensively comparing the δ56Fe values of the whole rock and pyrite in the manganese ore of the Datangpo Formation, we believe that iron from hydrothermal sources directly and quantitatively combined with sulfides to form pyrite. Additionally, the bottom seawater of the basin was mainly anoxic. The nitrogen isotope composition indicates the presence of a stable nitrate reservoir in the ocean at that time, and manganese ore deposition may have been influenced by the input of high-salinity water from the open ocean. Due to the supply of NO3- from the open ocean to the graben basin, the δ15N in manganese ore is significantly higher than that in black shale. The input from the open ocean led to an increase in alkalinity in the bottom water of the basin, which favored the precipitation of rhodochrosite. Considering that the oxidation potential required for manganese oxidation precipitation is higher than that required for iron oxidation precipitation, it is most reasonable to conclude that under alkaline anoxic conditions in the bottom water layer, Mn2+ directly precipitated in the form of rhodochrosite.

Effects of seasons and successive upwelling phases on phytoplankton size classes in the Southeast Arabian Sea

The responses of Phytoplankton Size Classes (PSCs) to seasons and the distinct phases of coastal upwelling in the northern Indian Ocean is an understudied aspect. This study introduces observations from a monthly time series conducted at three cross-shore transects in the south, central, and north regions between 6 and 13°N along the southwest coast of India in the Southeastern Arabian Sea (SEAS). The data represent pre-upwelling (late April to early May), early upwelling (early to mid-June), peak upwelling (early to mid-August), late upwelling (mid to late September), and post-upwelling (late October to early November) phases. The pre-upwelling had a stratified and nitrate-depleted upper euphotic column due to the intrusion of low saline Bay of Bengal water and solar heating which resulted in a low phytoplankton biomass (chlorophyll-a) contributed by pico-PSC (av. 56.21 ± 21.23 %) followed by nano-PSC (25.25 ± 5.98 %). During the early upwelling, a dominant micro-PSC was prevalent in the coastal stations in the south transect due to the initiation of upwelling there. The peak upwelling was characterised by significant nutrient enrichment causing the dominance of larger micro- and meso-PSCs in the entire coastal region (av. 79.13 ± 39.68 %). Since the late upwelling had less nutrient enrichment, the contribution of nano- and pico-PSCs increased along the south and central transects. By the post-upwelling phase, the dominance of nano-PSC (av. 57.85 ± 11.02 %) and pico-PSC (av. 21.19 ± 11.72 %) was reestablished in the study area due to the end of the nutrient enrichment of upwelling. The subsurface chlorophyll maxima, which was found below 50 m during the pre-upwelling phase, had altered into a thick layer (30 m) and shifted to the upper water column during the upwelling phases when nutrients were higher and solar radiation was lower in the surface waters. A sequential transition of PSCs from pre-upwelling to post-upwelling was evident and it appears that the very high supply of nutrients NO3 and SiO4 (>5 μM) during different phases of upwelling favoured the dominance of larger PSCs.

Utility of in situ ion‐exchange membranes to assess nutrient availability, productivity, and fertilizer response of coastal Douglas‐fir of the Pacific Northwest

AbstractDouglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] is the predominant forest plantation species in the Pacific Northwest (PNW), with site productivity and fertilizer response influenced by climate and soil variations. This study investigates the utility of in situ 12‐week supply measurements of nitrogen (N), calcium (Ca), and phosphorus (P) to ion‐exchange resins (specifically Plant Root Simulator [PRS] probes) to estimate carbon (C):N ratios, soil nutrient contents (0–1 m), foliar nutrient concentrations, Douglas‐fir productivity (site index and basal area mean annual increment), and fertilizer volume response. PRS nutrient supply rates were correlated with N, Ca, and P soil nutrient contents (0–1 m), C:N ratios, and foliar nutrient concentrations. Low PRS NO3 supply rates (<25 mg N·m−2·burial period−1) were correlated with lower Douglas‐fir productivity and greater fertilizer volume response. PRS NO3 supply rates performed as well as total soil N contents and foliar N concentrations at estimating volume growth response to fertilizer. Twelve weeks after fertilization, PRS NO3, NH4, and Ca supply rates were significantly elevated compared to the unfertilized treatment. This research found that PRS probes were an effective in situ tool and are recommended for understanding N, Ca, and P nutrient availabilities, site productivity, and fertilizer response in Douglas‐fir plantations and for developing fertilizer prescriptions.

Coexistence of Dominant Marine Phytoplankton Sustained by Nutrient Specialization.

Prochlorococcus and Synechococcus are the two dominant picocyanobacteria in the low-nutrient surface waters of the subtropical ocean, but the basis for their coexistence has not been quantitatively demonstrated. Here, we combine in situ microcosm experiments and an ecological model to show that this coexistence can be sustained by specialization in the uptake of distinct nitrogen (N) substrates at low-level concentrations that prevail in subtropical environments. In field incubations, the response of both Prochlorococcus and Synechococcus to nanomolar N amendments demonstrates N limitation of growth in both populations. However, Prochlorococcus showed a higher affinity to ammonium, whereas Synechococcus was more adapted to nitrate uptake. A simple ecological model demonstrates that the differential nutrient preference inferred from field experiments with these genera may sustain their coexistence. It also predicts that as the supply of NO3- decreases, as expected under climate warming, the dominant genera should undergo a nonlinear shift from Synechococcus to Prochlorococcus, a pattern that is supported by subtropical field observations. Our study suggests that the evolution of differential nutrient affinities is an important mechanism for sustaining the coexistence of genera and that climate change is likely to shift the relative abundance of the dominant plankton genera in the largest biomes in the ocean. IMPORTANCE Our manuscript addresses the following fundamental question in microbial ecology: how do different plankton using the same essential nutrients coexist? Prochlorococcus and Synechococcus are the two dominant picocyanobacteria in the low-nutrient surface waters of the subtropical ocean, which support a significant amount of marine primary production. The geographical distributions of these two organisms are largely overlapping, but the basis for their coexistence in these biomes remains unclear. In this study, we combined in situ microcosm experiments and an ecosystem model to show that the coexistence of these two organisms can arise from specialization in the uptake of distinct nitrogen substrates; Prochlorococcus prefers ammonium, whereas Synechococcus prefers nitrate when these nutrients exist at low concentrations. Our framework can be used for simulating and predicting the coexistence in the future ocean and may provide hints toward understanding other similar types of coexistence.

Magnesium deficiency stress in rice can be alleviated by partial nitrate nutrition supply

The problem of nitrogen (N) excess and magnesium (Mg) deficiency in farmland is becoming more common, severe, and widespread in southern China. Magnesium is known to be an essential nutrient for higher plants; however, the physiological responses of field crops to Mg deficiency, particularly to its interaction with N forms, remain largely unknown. In this study, a hydroponic experiment was conducted using three Mg levels (0.01, 1.00, and 5.00 mM) and three nitrate/ammonium ratios (NO3−/NH4+ of 0/100, 25/75, and 50/50) under greenhouse conditions. The results show that Mg deficiency (0.01 mM) could result in yellow leaves, dwarf plants, and fewer tillers during rice growth. Furthermore, Mg deficiency induced a major reduction in root morphology and activity, photosynthetic properties, and nutrient accumulation, while it resulted in a clear increase in malondialdehyde, superoxide dismutase, peroxidase, and catalase activities in rice. However, under Mg-deficiency stress, the supply of partial NO3− led to a significant drop in these antioxidant enzyme activities. Moreover, partial NO3− supply significantly improved the net photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO2 concentrations under Mg-deficiency conditions. In particular, the supply of partial NO3− dramatically promoted the growth of the root system, boosted the occurrence of lateral roots, and enhanced root vitality under Mg-deficiency stress. Additionally, the supply of partial NO3− led to significant increases in dry weight and N and Mg contents under Mg deficiency. The results of this study suggest that the symptoms of Mg-deficiency stress in rice can be alleviated by partial NO3− supply.

Assessments of Nitrate Budgets in the Yellow Sea Based on a 3D Physical-Biogeochemical Coupled Model

Nitrate (NO3–) plays an important role in ecosystems and aquaculture in the Yellow Sea (YS). Sparse observational data suggest that ocean currents and nitrification are crucial to NO3– flux in the YS; however, a quantitative assessment of these fluxes has not yet been performed. This study investigates seasonal and spatial variations in NO3– flux via currents and biological processes in the YS from 2006 to 2019 using a physical-biogeochemical coupled model. The model results show that the current-driven fluxes exceeded biological processes in the eastern and central regions of the YS, unlike in the western and northern regions. Advection of NO3– in the YS is mainly driven by cyclonic circulation in summer and fall, and anticyclonic circulation in spring and winter. The Subei Coastal Current along the coast of China plays a primary role in net advective influx of NO3– to the YS year round. The NO3– influx by the Yellow Sea Warm Current along the lower layer of the southcentral YS is offset by outflux through wind-driven surface currents in winter. The southward movements of the Yellow Sea Bottom Cold Water in summer and the Korean Coastal Current in winter are major NO3– outfluxes to the East China Sea. In terms of biological processes, NO3– is mainly consumed by phytoplankton during the spring bloom and supplied through organic matter decomposition and nitrification. Net supply of NO3– by biological processes was the greatest in the southcentral YS where the Yellow Sea Bottom Cold Water is present.

Assessing the Linkages between Tree Species Composition and Stream Water Nitrate in a Reference Watershed in Central Appalachia

Many factors govern the flow of deposited nitrogen (N) through forest ecosystems and into stream water. At the Fernow Experimental Forest in WV, stream water nitrate (NO3−) export from a long-term reference watershed (WS 4) increased in approximately 1980 and has remained elevated despite more recent reductions in chronic N deposition. Long-term changes in species composition may have altered forest N demand and the retention of deposited N. In particular, the abundance and importance value of Acer saccharum have increased since the 1950s, and this species is thought to have a low affinity for NO3−. We measured the relative uptake of NO3− and ammonium (NH4+) by six important temperate broadleaf tree species and estimated stand uptake of total N, NO3−, and NH4+. We then used records of stream water NO3− and stand composition to evaluate the potential impact of changes in species composition on NO3− export. Surprisingly, the tree species we examined all used both mineral N forms approximately equally. Overall, the total N taken up by the stand into aboveground tissues increased from 1959 through 2001 (30.9 to 35.2 kg N ha−1 yr−1). However, changes in species composition may have altered the net supply of NO3− in the soil since A. saccharum is associated with high nitrification rates. Increases in A. saccharum importance value could result in an increase of 3.9 kg NO3−-N ha−1 yr−1 produced via nitrification. Thus, shifting forest species composition resulted in partially offsetting changes in NO3− supply and demand, with a small net increase of 1.2 kg N ha−1 yr−1 in NO3− available for leaching. Given the persistence of high stream water NO3− export and relatively abrupt (~9 year) change in stream water NO3− concentration circa 1980, patterns of NO3− export appear to be driven by long-term deposition with a lag in the recovery of stream water NO3− after more recent declines in atmospheric N input.

Soil Nutrient Supply in Cultivated Bush Bean–Potato Intercropping Grown in Subarctic Soil Managed with Agroforestry

To address food insecurity in northern Canada, some isolated communities started gardening initiatives to reduce dependencies on expensive foods flown in to communities. From 2012–2014, soils in northern Ontario James Bay lowlands were cultivated with bush beans and potatoes, grown in sole and intercropping configurations, in an open field and an agroforestry system enclosed by willow trees. The objective of this study was to compare the supply rates of 15 plant-available nutrients in these soils using in situ ion exchange membranes. After three years of cultivation, the agroforestry site had significantly greater supply of PO4, Ca, and Zn and these nutrients had positive correlations with yield. By contrast, the open site had significantly greater supply of Mg, SO4, and B; these nutrients, and Al, had negative correlations with yield. Whilst there were no differences between sole and intercropping configurations, significantly greater supply of NO3, Ca, Cu, Fe, and Zn occurred early in the growing season, compared to significantly greater supply of K, SO4, B, and Al later in the season. Significantly greater yields have been harvested in the agroforestry site and it is suspected that the presence of a willow shelterbelt improves the microclimate and plant-available PO4, Ca, and Zn.

Soil nutrient availability and microclimate are influenced more by genotype than by planting stock type in hybrid poplar bioenergy buffers on farmland

Bioenergy buffers planted with fast-growing woody crops such as hybrid poplars (Populus spp.) are increasingly integrated into agricultural land to enhance the provision of ecosystem services. Genotype and planting stock type selection may influence buffer establishment success and soil properties, which may affect buffer functions such as soil nutrient removal, hydrological regulation (i.e. soil dewatering) or local climate regulation (i.e. temperature reduction). This farm-scale study tested the effects of two unrelated hybrid poplar genotypes (P. deltoides × P. nigra, genotype D × N-3570 and P. maximowiczii × P. balsamifera, genotype M × B-915311) and two planting stock types (unrooted whips and bare-root stocks) on biomass growth, soil nutrient availability and soil microclimate in 15 m wide bioenergy buffers located downslope of hayfields in the cold temperate region of southern Québec, Canada. Poplar genotype had an important effect on biomass growth, soil microclimate and the supply rates of several macronutrients and micronutrients, while planting stock type had little effect on these variables. The P. maximowiczii × P. balsamifera genotype produced the highest biomass and had generally lower nutrient availability in the soil, but not for soil NO3, which was less available under the P. deltoides × P. nigra genotype. Compared to the hayfield soils, only the P. maximowiczii × P. balsamifera genotype maintained a lower supply rate of available P in the buffer soil. Compared to the hayfield soils, NH4 supply rates were lower in the buffers for both genotypes, while NO3 supply rates were similar or higher. Both genotypes had the capacity to maintain cooler soil temperatures and lower moisture content in the soil of the buffer compared to the adjacent hayfields, but this capacity was greater for the P. maximowiczii × P. balsamifera genotype. Because plant-soil interactions are strongly affected by hybrid poplar genetics, genotype selection is an important consideration in the design of multifunctional agricultural buffers. In temperate agroecosystems, future studies should try to identify productive poplar genotypes that would decrease topsoil NO3 and P availability and reduce soil water content in order to minimize potential N and P losses from buffer soils during runoff events.

Nitrogen supply in combination of nitrate and ammonium enhances harnessing of elevated atmospheric CO2 through improved nitrogen and carbon metabolism in wheat (Triticum aestivum)

Elevated carbon dioxide (e-CO2) levels from ambient (a-CO2) enhance plant biomass production and yield. However, this response is highly dependent on the availability and possibly the form of nitrogen (N) supply to plants. This study aimed to investigate changes in C and N metabolism of wheat (Triticum aestivum L.) in response to e-CO2 and N source. e-CO2 enhanced net CO2 assimilation but at highly variable rates depending on the form of N supply. Under e-CO2, net CO2 assimilation rate was in the order NO3– > NH4NO3 > NH4+ > urea. Plants supplied with ammonium and nitrate (i.e. NH4NO3) performed better in terms of biomass production and expressed a higher biomass enhancement ratio by e-CO2 than plants receiving sole applications of NO3–, NH4+ or urea. Supply of NH4NO3 also resulted in lower intercellular CO2, higher photoassimilate translocation to roots and lower accumulation of free amino acids than other N forms, indicating a better exploitation of the e-CO2 environment. Our results conclude that major physiological pathways of photosynthesis and protein and carbohydrate metabolism are differentially influenced by e-CO2 depending on the source of N supply. A balanced supply of NO3– and NH4+ to plant roots is the key to harnessing e-CO2 while minimising its adverse effects on quality of the produce.

Partial replacement of nitrate by ammonium increases photosynthesis and reduces oxidative stress in tanzania guinea grass exposed to cadmium

In order to grow and effectively uptake and accumulate cadmium (Cd), plants used for phytoextraction have to cope with toxicity, which may be influenced by the supply of nitrate (NO3−) and ammonium (NH4+). Thus, we evaluated the effect of these nitrogen forms on the photosynthetic and antioxidant enzyme activities of Panicum maximum cv. Tanzania (tanzania guinea grass) under Cd stress. Plants were grown in nutrient solution under greenhouse conditions and subjected to a 3 × 3 factorial experiment. They were supplied with three NO3−/NH4+ ratios (100/0, 70/30 and 50/50) and exposed to three Cd rates (0.0, 0.5 and 1.0 mmol L−1), being arranged in a randomized complete block design with three replications. Gas exchange parameters, oxidative stress indicators, proline concentration and antioxidant enzyme activities were studied. Exposure to Cd reduced photosynthesis by causing stomatal closure and impairing electron transport. However, the simultaneous supply of NO3− and NH4+, particularly at a 50/50 ratio, restored gas exchange and improved the function of photosystem II, increasing the photosynthetic capacity of the grass. Plants grown with 50/50 showed reduced lipid peroxidation along with increased proline synthesis. Moreover, this NO3−/NH4+ ratio increased the tolerance of tanzania guinea grass to Cd by inducing high superoxide dismutase and glutathione reductase activities in shoots and roots, respectively, maintaining cellular homeostasis and reducing oxidative stress. The negative effects of Cd on photosynthesis and on the balance between oxidants and antioxidants are attenuated by the partial replacement of NO3− by NH4+ in the nutrient solution.

Heterotrophic cultivation of T. obliquus under non-axenic conditions by uncoupled supply of nitrogen and glucose

A fed-batch strategy is proposed to produce microalgae biomass under non-axenic heterotrophic conditions. The strategy induces the alternation of N-deplete (Glucose-replete) and N-replete (Glucose-deplete) cultivation phases by the periodic and uncoupled supply of glucose and NO3− to the culture. Cultivation of the microalga T. obliquus with this strategy reduced the ratio of the bacteria to microalgae cell concentration from 1.6, attained by conventional photoautotrophic cultivation, to 0.03. During the N-deplete phase, microalgae duplication stopped and biomass concentration increased 1.9 times, while during the N-replete phase, microalgae duplicated halving their average size and losing about 25% of their weight. The process proved to be effective under several consecutive cycles. Biomass productivity until 6.1 g/Ld and biomass concentration until 26 g/L were achieved. The results demonstrate that the proposed strategy can effectively prevent bacterial contamination, paving the way to the large scale production of microalgae biomass under non-axenic heterotrophic conditions.

Nitrate N influences the accumulations and subcellular distributions of Cd and Zn to mediate the Cd/Zn interactions in dwarf Polish Wheat (Triticum polonicum L.) seedlings

ABSTRACT Nitrate (NO3 –) assimilation and transport play important roles in Cd transport. Transcript profiling indicated that several NO3 − metabolism-related genes were involved in Cd/Zn interactions in roots of dwarf Polish Wheat (DPW). In this study, the effects of NO3 − on Cd and Zn accumulations and subcellular distributions in DPW under Cd, Zn, and Cd + Zn applications with lack or supply of NO3 − were investigated. Compared with lack of NO3 –, supply of NO3 − enhanced the Cd accumulation and the NO3 − uptake in roots under Cd application; it reduced the Zn accumulation and the NO3 − uptake in roots under Zn application; it did not affect the Cd accumulation and the NO3 − uptake, but reduced the Zn accumulation in roots under Cd + Zn application. Supply of NO3 − increased the Cd concentration in soluble fraction (including vacuole) to enhance the Cd capacity in roots under Cd application; it reduced the Zn concentration in soluble fraction under Zn application, and in all fractions under Cd + Zn application. Under lack or supply of NO3 –, application of Zn inhibited the Cd accumulation in roots with reducing the Cd concentration of soluble fraction, but promoted in shoots with increasing the Cd concentration of organelle fraction; application of Cd promoted the Zn accumulation in roots, but inhibited in shoots (except of supply of NO3 –). These results indicated that NO3 − influenced the subcellular distributions of Cd and Zn to affect their accumulations, although the affections were different.

Managing the power grid: how myoglobin can regulate PO2 and energy distribution in skeletal muscle.

Managing the power grid: how myoglobin can regulate PO2 and energy distribution in skeletal muscle.

Riparian buffer growth and soil nitrate supply are affected by tree species selection and black plastic mulching

Tree species selection in the design of agricultural riparian buffers is important to optimize particular ecosystem services, while vegetation management (weed treatment) is often critical in obtaining first-rate tree growth and survival. This farm-scale study took place along a 1km section of a headwater stream in southern Québec (southeastern Canada). Five tree species with contrasted ecological characteristics were planted (Populus×canadensis, Fraxinus pennsylvanica, Quercus macrocarpa, Quercus rubra and Pinus strobus), with black plastic (polyethylene) mulches as the vegetation management method, as well as a control with no vegetation management, all within a fenced herbaceous riparian buffer. Tree growth and survival were measured along with soil nutrient supply. Significant Species×Vegetation treatment interactions where observed for all growth variables (p<0.001), but also for soil nitrate (NO3) supply (p<0.01). All species benefited from the plastic mulch treatment, but varied greatly in their responses. After 5 years, mulched hybrid poplar produced 774 times more stem volume than red oak without mulch. Across all species/vegetation treatment combinations, a 13-fold variation in soil NO3 supply rate was observed during the 4th growing season. Compared to the other species, NO3 supply rate in hybrid poplar plots was 39–87% lower in the plastic mulch treatment and 48–62% lower in the control treatment. Significantly higher soil NO3 supply rates were observed beneath the mulches of non nitrophilous species (white pine and red oak). Red oak growth was negatively correlated with NO3 supply (R2=0.57, p<0.05) in the mulch treatment. Early-successional nitrophilous species (hybrid poplar and red ash) planted with the plastic mulch led to the lowest increase in soil NO3 and the greatest gains in buffer structural attributes (stem volume, diameter and height). Hybrid poplar growth was positively correlated with soil NO3 supply (R2=0.86, p<0.001) in the control treatment. Natural abandoned field/grassland invaders (white pine and bur oak) grew well without black plastic mulch, while the growth of non-mulched red oaks was marginal. In the control treatment, stem volume was a strong negative predictor (across all species) of soil NO3 supply (R2=0.91, p<0.05), indicating that under herbaceous vegetation competition larger trees have a greater ability to reduce soil NO3. This study provides evidence that particular tree species/vegetation management treatment combinations strongly influence early riparian buffer structural development and soil NO3 dynamics in agricultural riparian zones.

Nitrate Increased Cucumber Tolerance to Fusarium Wilt by Regulating Fungal Toxin Production and Distribution.

Cucumber Fusarium wilt, induced by Fusarium oxysporum f. sp. cucumerinum (FOC), causes severe losses in cucumber yield and quality. Nitrogen (N), as the most important mineral nutrient for plants, plays a critical role in plant–pathogen interactions. Hydroponic assays were conducted to investigate the effects of different N forms (NH4+ vs. NO3‒) and supply levels (low, 1 mM; high, 5 mM) on cucumber Fusarium wilt. The NO3‒-fed cucumber plants were more tolerant to Fusarium wilt compared with NH4+-fed plants, and accompanied by lower leaf temperature after FOC infection. The disease index decreased as the NO3‒ supply increased but increased with the NH4+ level supplied. Although the FOC grew better under high NO3− in vitro, FOC colonization and fusaric acid (FA) production decreased in cucumber plants under high NO3− supply, associated with lower leaf membrane injury. There was a positive correlation between the FA content and the FOC number or relative membrane injury. After the exogenous application of FA, less FA accumulated in the leaves under NO3− feeding, accompanied with a lower leaf membrane injury. In conclusion, higher NO3− supply protected cucumber plants against Fusarium wilt by suppressing FOC colonization and FA production in plants, and increasing the plant tolerance to FA.

Forward osmosis process for supply of fertilizer solutions from seawater using a mixture of draw solutions

Novel desalination approaches are required to provide both drinking and agricultural water as there is ever increasing stress upon precious freshwater resources. It was our hypothesis that a modified Forward Osmosis (FO) process had the potential for production of irrigation water comprising of appropriate concentrations of fertilizers from a seawater feed. Four agents, KNO3, Na2SO4, CaNO3, and MgCl2, plus 35 g/L seawater were used as the draw and feed solutions of the FO process. Net Driving Pressure (NDP) in the FO process was manipulated either by increasing the concentration of draw solution (FO process) or by increasing feed pressure (Pressure Assisted FO (PAFO) process). A series of nanofiltration (NF) and reverse osmosis (RO) membranes were used for the regeneration of draw solution. The results suggested that a PAFO process was more energy efficient than simple forward osmosis, provided the energy relating to the brine flow from the NF/RO membrane for pressurizing the feed solution of PAFO process was used. Furthermore, this study suggested using a mixture of a primary draw solution, MgCl2, and a secondary draw solution, KNO3, for NO3 supply into the irrigation water was preferable. As such, MgCl2 provided the driving force for fresh water extraction while KNO3 was the source of fertilizer in the irrigation water. Results showed that water quality provided by application of a MgCl2+KNO3 draw solution was better than that from KNO3 or Ca(NO3)2. The concentrations of NO3 and SO4 in irrigation water were within recommended levels when the diluted draw solution was regenerated by a dual stage low pressure RO process.

Effects of night warming on the uptake of inorganic nitrogen by two dominant species in subalpine coniferous forests

Aims Plant roots play a critical role in the uptake of nutrients, and nitrogen (N) absorption is considered as the first step and a pivotal process in N metabolism of plants. Our objective was to better understand the absorption of two major inorganic N forms (NH4 and NO3) in subalpine coniferous forests under global warming. Methods Experimental warming using infrared heater was applied to two dominant species in subalpine coniferous forests of Sichuan, China, Picea asperata and Abies fargesii var. faxoniana. The non-invasive micromeasurement technology was used to investigate the effects of warming on the uptake rates of NH4 and NO3 and the potential interactions between these two ions. Important findings Results showed that the maximal net root uptake of NH4 and NO3 occurred at a distance of 17–18 mm and 17 mm from root tips, respectively for P. asperata. and at a distance of 11 mm and 11.5 mm from root tips respectively for A. fargesii var. faxoniana. Experimental warming elevated the uptake rates of NH4 and NO3 in both species, but the interactions between NH4 and NO3 differed between the two species. While NO3 uptake was inhibited in the presence of NH4 for both P. asperata and A. fargesii var. faxoniana, net NH4 uptake was promoted by NO3 supply only in P. asperata roots under experimental warming.

Nitrate-Dependent Control of Shoot K Homeostasis by the Nitrate Transporter1/Peptide Transporter Family Member NPF7.3/NRT1.5 and the Stelar K+ Outward Rectifier SKOR in Arabidopsis.

Root-to-shoot translocation and shoot homeostasis of potassium (K) determine nutrient balance, growth, and stress tolerance of vascular plants. To maintain the cation-anion balance, xylem loading of K(+) in the roots relies on the concomitant loading of counteranions, like nitrate (NO3 (-)). However, the coregulation of these loading steps is unclear. Here, we show that the bidirectional, low-affinity Nitrate Transporter1 (NRT1)/Peptide Transporter (PTR) family member NPF7.3/NRT1.5 is important for the NO3 (-)-dependent K(+) translocation in Arabidopsis (Arabidopsis thaliana). Lack of NPF7.3/NRT1.5 resulted in K deficiency in shoots under low NO3 (-) nutrition, whereas the root elemental composition was unchanged. Gene expression data corroborated K deficiency in the nrt1.5-5 shoot, whereas the root responded with a differential expression of genes involved in cation-anion balance. A grafting experiment confirmed that the presence of NPF7.3/NRT1.5 in the root is a prerequisite for proper root-to-shoot translocation of K(+) under low NO3 (-) supply. Because the depolarization-activated Stelar K(+) Outward Rectifier (SKOR) has previously been described as a major contributor for root-to-shoot translocation of K(+) in Arabidopsis, we addressed the hypothesis that NPF7.3/NRT1.5-mediated NO3 (-) translocation might affect xylem loading and root-to-shoot K(+) translocation through SKOR. Indeed, growth of nrt1.5-5 and skor-2 single and double mutants under different K/NO3 (-) regimes revealed that both proteins contribute to K(+) translocation from root to shoot. SKOR activity dominates under high NO3 (-) and low K(+) supply, whereas NPF7.3/NRT1.5 is required under low NO3 (-) availability. This study unravels nutritional conditions as a critical factor for the joint activity of SKOR and NPF7.3/NRT1.5 for shoot K homeostasis.