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Tobacco, a warm-season crop originating from the Americas, is highly susceptible to cold stress. The utilization of symbiotic fungi as a means to bolster crops' resilience against abiotic stresses has been proven to be a potent strategy. In this study, we investigated the effect of endophytic fungus Piriformospora indica on the cold resistance of tobacco. When exposed to cold stress, the colonization of P.indica in tobacco roots effectively stimulates the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX). This, in turn, reduces the accumulation of reactive oxygen species (ROS), thereby mitigating oxidative damage. Additionally, P. indica elevates the levels of osmolytes, such as soluble sugars, proline, and soluble proteins, thus facilitating the restoration of osmotic balance. Under cold stress conditions, P. indica also induces the expression of cold-responsive genes. Furthermore, this fungus not only enhances photosynthesis in tobacco by stimulating the synthesis of photosynthetic pigments, strengthening Rubisco activity, and elevating PSII efficiency, but also fortifies tobacco's nitrogen assimilation by inducing the expression of nitrate transporter gene and activating enzymes related to nitrogen assimilation. Consequently, this synergistic optimization of nitrogen and carbon assimilation provides a solid material and energetic foundation for tobacco plants to withstand cold stress. Our study demonstrates that a mycorrhizal association between P. indica and tobacco seedlings provides multifaceted protection to tobacco plants against low-temperature stress and offers a valuable insight into how P. indica enhances the cold tolerance of tobacco. [ABSTRACT FROM AUTHOR]

Plant productivity is enhanced by elevated atmospheric CO2 concentration, but N content of leaf is reduced. How atmospheric CO2 affects leaf 15N composition and the related mechanisms remain unclear. δ15N and N content of wheat and sunflower leaves were determined under two CO2 concentration(410 and 820 μmol·mol-1) treatments. The results show that the N content of both species decreases with elevated CO2 concentration, but the response of δ15N to CO2 enrichment is different between wheat and sunflower. Under high CO2 concentration treatment, δ15N of wheat leaves decreases significantly by 6.5‰, while δ15N of sunflower leaves increases slightly by 2.1‰, accompanied by a significant increase in leaf mass and aboveground biomass. Therefore, N nutrition characteristics of wheat are consistent with N assimilation limitation hypothesis, while the response of sunflower is consistent with dilution effect hypothesis. δ15N in wheat leaves decreases significantly with leaf aging and cell aging. Therefore, when using δ15N to infer environmental impacts on plant N metabolism, it is necessary to account for the leaf age effect. The results of meta-analysis show that δ15N of non-legume C3 plants decreases significantly by 0.3‰ under elevated CO2 concentration, in line with our results on wheat plants. The study shows that the inhibited N assimilation is an important mechanism related to the CO2 effect on N metabolism and 15N content of plants [ABSTRACT FROM AUTHOR]

Tobacco, a warm-season crop originating from the Americas, is highly susceptible to cold stress. The utilization of symbiotic fungi as a means to bolster crops’ resilience against abiotic stresses has been proven to be a potent strategy. In this study, we investigated the effect of endophytic fungus Piriformospora indica on the cold resistance of tobacco. When exposed to cold stress, the colonization of P.indica in tobacco roots effectively stimulates the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX). This, in turn, reduces the accumulation of reactive oxygen species (ROS), thereby mitigating oxidative damage. Additionally, P. indica elevates the levels of osmolytes, such as soluble sugars, proline, and soluble proteins, thus facilitating the restoration of osmotic balance. Under cold stress conditions, P. indica also induces the expression of cold-responsive genes. Furthermore, this fungus not only enhances photosynthesis in tobacco by stimulating the synthesis of photosynthetic pigments, strengthening Rubisco activity, and elevating PSII efficiency, but also fortifies tobacco’s nitrogen assimilation by inducing the expression of nitrate transporter gene and activating enzymes related to nitrogen assimilation. Consequently, this synergistic optimization of nitrogen and carbon assimilation provides a solid material and energetic foundation for tobacco plants to withstand cold stress. Our study demonstrates that a mycorrhizal association between P. indica and tobacco seedlings provides multifaceted protection to tobacco plants against low-temperature stress and offers a valuable insight into how P. indica enhances the cold tolerance of tobacco.

Abstract: Nitrogen (N) fertilization in citrus orchards is prone to significant environmental losses. Managing nutrients for sustainable development and optimizing nitrogen use efficiency (NUE) are key tasks in modern agriculture. NUE depends on N uptake and assimilation. In addition to intrinsic fertilizer use efficiency, we evaluated plant growth, nitrate reductase (NRase) activity, and the nutritional status of citrus plants fertilized with different N sources [calcium nitrate (CN), ammonium nitrate (AN), and ammonium sulfate (AS)]. After 240 days, plants supplied with either CN or AN exhibited higher biomass production and N accumulation in the leaves than those fertilized with AS. The supply of ammonium-containing sources (AN and AS) reduced the substrate pH, in which those with AS exhibited lower N partitioning to the leaves, as well as reduced the absorption and accumulation of magnesium and phosphorus. NRase activity was higher in plants supplied with CN or AN compared to AS, and CN fertilization provided the greatest NUE. The data demonstrated that citrus plants fertilized with sources containing nitrate increased the NUE from 10 to 25% and consequently had greater growth compared to those fed with AS.

A mixed nitrate (NO3−) and ammonium (NH4+) supply can promote root growth in maize (Zea mays), however, the changes in root morphology and the related physiological mechanism under different N forms are still unclear. Here, maize seedlings were grown hydroponically with three N supplied in three different forms (NO3− only, 75/25 NO3−/NH4+ and NH4+ only). Compared with sole NO3− or NH4+, the mixed N supply increased the total root length of maize but did not affect the number of axial roots. The main reason was the increased total lateral root length, while the average lateral root (LR) length in each axle was only slightly increased. In addition, the average LR density of 2nd whorl crown root under mixed N was also increased. Compared with sole nitrate, mixed N could improve the N metabolism of roots (such as the N influx rate, nitrate reductase (NR) and glutamine synthase (GS)enzyme activities and total amino content of the roots). Experiments with exogenously added NR and GS inhibitors suggested that the increase in the average LR length under mixed N was related to the process of N assimilation, and whether the NR mediated NO synthesis participates in this process needs further exploration. Meanwhile, an investigation of the changes in root-shoot ratio and carbon (C) concentration showed that C transportation from shoots to roots may not be the key factor in mediating lateral root elongation, and the changes in the sugar concentration in roots further proved this conclusion. Furthermore, the synthesis and transportation of auxin in axial roots may play a key role in lateral root elongation, in which the expression of ZmPIN1B and ZmPIN9 may be involved in this pathway. This study preliminarily clarified the changes in root morphology and explored the possible physiological mechanism under a mixed N supply in maize, which may provide some theoretical basis for the cultivation of crop varieties with high N efficiency.

Compared with sole nitrate (NO3−) or sole ammonium (NH4+) supply, mixed nitrogen (N) supply may promote growth of maize seedlings. Previous study suggested that mixed N supply not only increased photosynthesis rate, but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization. However, whether this process depends on N absorption is unknown. Here, maize seedlings were grown hydroponically with three N forms (NO3− only, 75/25 NO3−/NH4+ and NH4+ only). The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO3− supply at 0–3 d, but was higher than under sole NO3− supply at 6–9 d. 15N influx rate under mixed N supply was greater than under sole NO3− or NH4+ supply at 6–9 d, although NO3− and NH4+ influx under mixed N supply were reduced compared to sole NO3− and NH4+ supply, respectively. qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO3− transporters in roots, such as ZmNRT1.1A, ZmNRT1.1B, ZmNRT1.1C, ZmNRT1.2 and ZmNRT1.3, or NH4+ absorption transporters, such as ZmAMT1.1A, especially the latter. Furthermore, plants had higher nitrate reductase (NR) glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO3− supply. The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth, especially for the reduction of NO3− by NR reductase. This research suggested that the increased processes of NO3− and NH4+ assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.

Cold stress inhibits the early growth of maize, leading to reduced productivity. Nitrogen (N) is an essential nutrient that stimulates maize growth and productivity, but the relationship between N availability and cold tolerance is poorly characterized. Therefore, we studied the acclimation of maize under combined cold stress and N treatments. Exposure to cold stress caused a decline in growth and N assimilation, but increased abscisic acid (ABA) and carbohydrate accumulation. The application of different N concentrations from the priming stage to the recovery period resulted in the following observations: (i) high N supply alleviated cold stress-dependent growth inhibition, as shown by increased biomass, chlorophyll and Rubisco content and PSII efficiency; (ii) cold stress-induced ABA accumulation was repressed under high N, presumably due to enhanced stomatal conductance; (iii) the mitigating effects of high N on cold stress could be due to the increased activities of N assimilation enzymes and improved redox homeostasis. After cold stress, the ability of maize seedlings to recover increased under high N treatment, indicating the potential role of high N in the cold stress tolerance of maize seedlings. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a major limiting factor for plant growth and vegetable production. Understanding the regulatory mechanisms of N uptake, transport, and assimilation is key to improving N use efficiency in plants. Ammonium transporters (AMTs) play an important role in plant N metabolism. In this study, we isolated an important AMT1 subfamily member (BcAMT1;5) with a highly conserved signatural AMT1 subfamily motif from flowering Chinese cabbage. Based on functional complementation in yeast mutant 31019b and overexpression of BcAMT1;5 in Arabidopsis, BcAMT1;5 is a functional AMT. Tissue expression analysis showed that BcAMT1;5 was mainly expressed in roots and showed multiple N regime transcript patterns to respond to varying nutritional conditions. This was up-regulated by N-deficiency and down-regulated by supplying NH4+. The glucuronidase (GUS) activities of BcAMT1;5pro::GUS showed a similar change in response to different N conditions. Overexpression of BcAMT1;5 accelerated the growth of transgenic seedlings, increased NH4+ net influxes, and enhanced the content and accumulation of NH4+ and NO3− at low N concentrations. Additionally, it increased the transcript levels of N assimilation-related genes in shoots. These results indicate that BcAMT1;5 may participate in N uptake and assimilation under various N conditions in flowering Chinese cabbage, but it was differed obviously from other AMT1s. [ABSTRACT FROM AUTHOR]

Aims : High N deposition has been recognized as a major factor influencing plant-plant interactions. We aim to discover whether N deposition could affect competitive relationships between poplars to predict threats posed by the introduction of exotic hybrids to native relative species. Methods: Intra- and interspecific competition was investigated for an introduced hybrid poplar (Populus beijingensis) and the native paternal species P. cathayana under two N deposition regimes. Results: Under control conditions, P. cathayana grown under either intra- or interspecific competition showed consistently greater above-ground biomass, root-to-shoot ratio (R/S), photosynthetic capacity, higher activities of N-assimilation enzymes in leaves, and preference for N-NO3− than corresponding P. beijingensis. Interspecific competition increased leaf area, specific leaf area (SLA), R/S, and photosynthetic nitrogen use efficiency (PNUE) in P. cathayana, but decreased PNUE in P. beijingensis compared to the values under monoculture. Thus, P. cathayana can gain a competitive advantage over P. beijingensis at low N availability. In contrast, under N deposition, P. beijingensis under mixture showed more positive responses in growth, higher plasticity in biomass allocation and root architecture, and the shift for N-NO3− preference when compared with P. cathayana, which resulted in relatively higher values in leaf area, SLA, and biomass accumulation in P. beijingensis. Nitrogen deposition increased the intrinsic water-use efficiency of conspecific P. beijingensis and heterospecific P. cahtayana. Conclusions: Our results suggest that N deposition could reverse competitive relationships between the poplars, and exotic P. beijingensis has the potential to outcompete native P. cathayana under growing N deposition. [ABSTRACT FROM AUTHOR]

Abstract Background Pineapple (Ananas comosus L. Merr.) is the third most important tropical fruit in China. In other crops, farmers can easily judge the nutritional requirements from leaf color. However, concerning pineapple, it is difficult due to the variation in leaf color of the cultivated pineapple varieties. A detailed understanding of the mechanisms of nutrient transport, accumulation, and assimilation was targeted in this study. We explored the D-leaf nitrogen (N), phosphorus (P), and potassium (K) contents, transcriptome, and metabolome of seven pineapple varieties. Results Significantly higher N, P, and K% contents were observed in Bali, Caine, and Golden pineapple. The transcriptome sequencing of 21 libraries resulted in the identification of 14,310 differentially expressed genes in the D-leaves of seven pineapple varieties. Genes associated with N transport and assimilation in D-leaves of pineapple was possibly regulated by nitrate and ammonium transporters, and glutamate dehydrogenases play roles in N assimilation in arginine biosynthesis pathways. Photosynthesis and photosynthesis-antenna proteins pathways were also significantly regulated between the studied genotypes. Phosphate transporters and mitochondrial phosphate transporters were differentially regulated regarding inorganic P transport. WRKY, MYB, and bHLH transcription factors were possibly regulating the phosphate transporters. The observed varying contents of K% in the D-leaves was associated to the regulation of K+ transporters and channels under the influence of Ca2+ signaling. The UPLC-MS/MS analysis detected 873 metabolites which were mainly classified as flavonoids, lipids, and phenolic acids. Conclusions These findings provide a detailed insight into the N, P, K% contents in pineapple D-leaf and their transcriptomic and metabolomic signatures.

Interactions among nutrients have been widely recognized in plants and play important roles in crop growth and yield formation. However, the interplay of Cu and N in rice plants is not yet clear. In this study, rice plants were grown with different combinations of Cu and N supply. The effects of Cu-N interaction on the growth, yield production, Cu and N transport, and gene expression levels were analyzed. The results showed that the effect of N supply on rice growth and yield formation was more pronounced than that of Cu supply. The Cu supply significantly improved the uptake of N (by 9.52–30.64%), while the N supply significantly promoted the root-to-shoot translocation of Cu (by 27.28–38.45%) and distributed more Cu (1.85–19.16%) into the shoots and leaves. The results of qRT-PCR showed that +Cu significantly up-regulated the expression levels of both NO3− and NH4+ transporter genes OsNRTs and OsAMTs, including OsNRT1.1B, OsNRT2.1, OsNRT2.3a, OsNRT2.4, OsAMT1.2, OsAMT1.3, and OsAMT3.1. Meanwhile, +N significantly up-regulated the expression levels of Cu transporter genes OsHMA5 and OsYSL16. In addition, the supply of Cu up-regulated the expression levels of OsGS1;2, OsGS2, and OsNADH-GOGAT to 12.61-, 6.48-, and 6.05-fold, respectively. In conclusion, our study demonstrates a synergistic effect between Cu and N in rice plants. It is expected that our results would be helpful to optimize the application of N and Cu fertilizers in agriculture. [ABSTRACT FROM AUTHOR]

• Aluminum (Al) affected the contents of N-containing compounds in Citrus. • Al affected the activities of N metabolism–related enzymes in Citrus. • Al differentially affected N metabolism between Citrus sinensis and C. grandis. • Increased leaf GOGAT might be an index of Al–tolerance in Citrus plants. Citrus are mostly planted in tropical/subtropical acidic soil areas, and are susceptible to aluminum (Al) toxicity, which affects tree growth and fruit quality. However, the effects of Al stress on the nitrogen (N) metabolism in different Al-tolerant Citrus varieties, and whether N metabolism is related to Al-tolerance in different Citrus varieties, were remained unveiled. In the current study, Al-tolerant "Xuegan" (Citrus sinensis) and Al-sensitive "Sour pummelo" (C. grandis), were irrigated with different nutrient solutions with or without Al. Al decreased the dry weights (DW) of leaves, stems and roots, as well as the N content, the N accumulation, total soluble proteins (TSPs) and total free amino acids (TFAAs) of different tissues of C. grandis , but it increased the ratio of root DW to shoot DW. In contrast, Al did not change the parameters mentioned above, except for decreasing the content and accumulation of N in C. sinensis roots. Al did not change the content of NO 3 – in different position leaves and roots, but decreased the content of NH 4 + in C. grandis. Al decreased the content of NO 3 – in different position leaves and roots, but except for the lower leaf, Al did not change that of NH 4 + in C. sinensis. Although Al affected the activities and gene expression levels of N metabolism–related enzymes in the leaves and roots of these two Citrus species, the effects of Al on these parameters were more pronounced in C. grandis than in C. sinensis. Results from correlation analysis (CoA) and principal components analysis (PCA) indicated that the increased root DW/shoot DW and NO 3 --N content in the roots and middle/upper leaves might be the related indicators of Al toxicity, whereas the enhanced activity of leaf GOGAT might be related to the Al–tolerance in Citrus plants. In conclusion, this study preliminarily revealed that the impact of Al on N metabolism and the response of N metabolism–related indicators to Al stress in Citrus , providing scientific reference for high-yield and high-quality cultivation of Citrus grown in acidic soil areas. [Display omitted] [ABSTRACT FROM AUTHOR]

Background: Pineapple (Ananas comosus L. Merr.) is the third most important tropical fruit in China. In other crops, farmers can easily judge the nutritional requirements from leaf color. However, concerning pineapple, it is difficult due to the variation in leaf color of the cultivated pineapple varieties. A detailed understanding of the mechanisms of nutrient transport, accumulation, and assimilation was targeted in this study. We explored the D-leaf nitrogen (N), phosphorus (P), and potassium (K) contents, transcriptome, and metabolome of seven pineapple varieties. Results: Significantly higher N, P, and K% contents were observed in Bali, Caine, and Golden pineapple. The transcriptome sequencing of 21 libraries resulted in the identification of 14,310 differentially expressed genes in the D-leaves of seven pineapple varieties. Genes associated with N transport and assimilation in D-leaves of pineapple was possibly regulated by nitrate and ammonium transporters, and glutamate dehydrogenases play roles in N assimilation in arginine biosynthesis pathways. Photosynthesis and photosynthesis-antenna proteins pathways were also significantly regulated between the studied genotypes. Phosphate transporters and mitochondrial phosphate transporters were differentially regulated regarding inorganic P transport. WRKY, MYB, and bHLH transcription factors were possibly regulating the phosphate transporters. The observed varying contents of K% in the D-leaves was associated to the regulation of K+ transporters and channels under the influence of Ca2+ signaling. The UPLC-MS/MS analysis detected 873 metabolites which were mainly classified as flavonoids, lipids, and phenolic acids. Conclusions: These findings provide a detailed insight into the N, P, K% contents in pineapple D-leaf and their transcriptomic and metabolomic signatures. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a major limiting factor for plant growth and vegetable production. Understanding the regulatory mechanisms of N uptake, transport, and assimilation is key to improving N use efficiency in plants. Ammonium transporters (AMTs) play an important role in plant N metabolism. In this study, we isolated an important AMT1 subfamily member (BcAMT1;5) with a highly conserved signatural AMT1 subfamily motif from flowering Chinese cabbage. Based on functional complementation in yeast mutant 31019b and overexpression of BcAMT1;5 in Arabidopsis, BcAMT1;5 is a functional AMT. Tissue expression analysis showed that BcAMT1;5 was mainly expressed in roots and showed multiple N regime transcript patterns to respond to varying nutritional conditions. This was up-regulated by N-deficiency and down-regulated by supplying NH4+. The glucuronidase (GUS) activities of BcAMT1;5pro::GUS showed a similar change in response to different N conditions. Overexpression of BcAMT1;5 accelerated the growth of transgenic seedlings, increased NH4+ net influxes, and enhanced the content and accumulation of NH4+ and NO3− at low N concentrations. Additionally, it increased the transcript levels of N assimilation-related genes in shoots. These results indicate that BcAMT1;5 may participate in N uptake and assimilation under various N conditions in flowering Chinese cabbage, but it was differed obviously from other AMT1s.

Interactions among nutrients have been widely recognized in plants and play important roles in crop growth and yield formation. However, the interplay of Cu and N in rice plants is not yet clear. In this study, rice plants were grown with different combinations of Cu and N supply. The effects of Cu-N interaction on the growth, yield production, Cu and N transport, and gene expression levels were analyzed. The results showed that the effect of N supply on rice growth and yield formation was more pronounced than that of Cu supply. The Cu supply significantly improved the uptake of N (by 9.52–30.64%), while the N supply significantly promoted the root-to-shoot translocation of Cu (by 27.28–38.45%) and distributed more Cu (1.85–19.16%) into the shoots and leaves. The results of qRT-PCR showed that +Cu significantly up-regulated the expression levels of both NO3− and NH4+ transporter genes OsNRTs and OsAMTs, including OsNRT1.1B, OsNRT2.1, OsNRT2.3a, OsNRT2.4, OsAMT1.2, OsAMT1.3, and OsAMT3.1. Meanwhile, +N significantly up-regulated the expression levels of Cu transporter genes OsHMA5 and OsYSL16. In addition, the supply of Cu up-regulated the expression levels of OsGS1;2, OsGS2, and OsNADH-GOGAT to 12.61-, 6.48-, and 6.05-fold, respectively. In conclusion, our study demonstrates a synergistic effect between Cu and N in rice plants. It is expected that our results would be helpful to optimize the application of N and Cu fertilizers in agriculture.

This study evaluated the transcriptional profile of genes related to nitrogen (N) assimilation in coffee plants susceptible and resistant to rust fungi under N sufficiency and N suppression. For this purpose, we inoculated young coffee leaves with Hemileia vastatrix uredospores and collected them at 0, 12, 24 and 48 hours post-inoculation (HPI) to evaluate the relative expressions of genes encoding cytosolic glutamine synthetase (CaGS1), plastid glutamine synthetase (CaGS2), nitrate reductase (CaNR), and asparagine synthetase (CaAS). The genes exhibited distinct patterns of transcriptional modulation for the different genotypes and N nutritional regimes. The resistant genotype (I59) presented high levels of transcription in response to pathogen inoculation for CaNR and CaGS1 genes, evaluated under N sufficiency in the initial moments of infection (12 HPI). The gene CaGS1 also showed a peak at 48 HPI. The susceptible genotype (CV99) showed increased transcript rates of CaNR at 12 and 24 HPI in response to rust inoculation. The transcriptional patterns observed for CV99, under N suppression, were high levels for CaAS and CaGS2 at all post-inoculation times in response to coffee leaf rust disease. In addition, CaGS1 was up-regulated at 48 HPI for CV99. Cultivar I59 showed high transcript levels at 12 HPI for CaAS and peaks at 24 and 48 HPI for CaGS2 in inoculated samples. Consequently, total chlorophyl concentration was influenced by N suppression and by rust infection. Regarding enzyme activities in vitro for glutamine synthetase and CaNR, there was an increase in infected coffee leaves (I59) and under N sufficiency. Moreover, CV99 was modulated in both N nutritional regimes for GS activity in response to rust. Our results indicate that N transport genes trigger a differential modulation between genotypes through the action of rust disease.

ABSTRACT Prior research on sugarcane showed increment of productivity following molybdenum (Mo) fertilization and some indication of the potential role either on nitrate reductase activity (NRA). However, this increment can depend on sugarcane variety and nitrogen (N) fertilization. This study aimed to evaluate the effect of Mo fertilization on Mo uptake, on NRA, nitrate (NO3--N), and ammonium (NH4+-N) contents in leaves and roots of sugarcane, and the accumulation of N and biomass across two sugarcane varieties (RB 867515 and RB 92579). The varieties were subjected to two rates of N fertilization (without N fertilization and 60 kg ha-1 of N) and two rates of Mo fertilization (without Mo fertilization and 200 g ha-1 of Mo). At 70, 100, 130, 200, and 365 days after planting (DAP), the following parameters were determined: Mo, NO3--N and NH4+-N contents, NRA in the leaves and roots, and the accumulation of N, as well as shoot dry matter (SDM). Molybdenum fertilization increased N accumulation in 36 and 44 % in the varieties RB 867515 and RB 92579, respectively. This increase in N accumulation was associated with NRA stimulation of 13 % in the leaves and 42 % in the roots. The maximum NRA occurred around 100 DAP, and its contents in the leaves and roots of the RB 92579 were 0.83 and 0.46 µmol NO2- g-1 h-1 of fresh matter, respectively, and in RB 867515 these values were 0.61 and 0.43 µmol NO2- g-1 h-1 of fresh matter, respectively. The assimilation of NO3--N was increased with Mo application, both with and without N fertilization, suggesting that Mo fertilization is indicated in nutrition management of sugarcane. This study provides insight into how Mo fertilization interacts with N fertilization and sugarcane varieties, altering N accumulation and dry matter production.

While nitrogen (N) derived from ammonium would be energetically less expensive than nitrate-derived N, the use of ammonium-based fertilizer is limited by the potential for toxicity symptoms. Nevertheless, previous studies have shown that exposure to elevated CO2 favors ammonium assimilation in plants. However, little is known about the impact of different forms of N fertilizer on stomatal opening and their consequent effects on CO2 and H2O diffusion in wheat plants exposed to ambient and elevated CO2. In this article, we have examined the response of the photosynthetic machinery of durum wheat (Triticum durum, var. Amilcar) grown with different types of N fertilizer (NO3−, NH4+, and NH4NO3) at 400 versus 700 ppm of CO2. Alongside gas exchange and photochemical parameters, the expression of genes involved in CO2 (PIP1.1 and PIP2.3) and H2O (TIP1) diffusion as well as key C and N primary metabolism enzymes and metabolites were studied. Our results show that at 400 ppm CO2, wheat plants fertilized with ammonium as the N source had stress symptoms and a strong reduction in stomatal conductance, which negatively affected photosynthetic rates. The higher levels of PIP1.1 and PIP2.3 expression in ammonium-fertilized plants at 400 ppm CO2 might reflect the need to overcome limitations to the CO2 supply to chloroplasts due to restrictions in stomatal conductance. This stomatal limitation might be associated with a strategy to reduce ammonium transport toward leaves. On the other hand, ammonium-fertilized plants at elevated CO2 did not show stress symptoms, and no differences were detected in stomatal opening or water use efficiency (WUE). Moreover, similar gene expression of the aquaporins TIP1, PIP1.1, and PIP2.3 in ammonium-fertilized plants grown at 700 ppm compared to nitrate and ammonium nitrate plants would suggest that an adjustment in CO2 and H2O diffusion is not required. Therefore, in the absence of a stress context triggered by elevated CO2, ammonium- and ammonium nitrate-fertilized plants were able to increase their photosynthetic rates, which were translated eventually into higher leaf protein content.

This study evaluated the transcriptional profile of genes related to nitrogen (N) assimilation in coffee plants susceptible and resistant to rust fungi under N sufficiency and N suppression. For this purpose, we inoculated young coffee leaves with Hemileia vastatrix uredospores and collected them at 0, 12, 24 and 48 hours post-inoculation (HPI) to evaluate the relative expressions of genes encoding cytosolic glutamine synthetase (CaGS1), plastid glutamine synthetase (CaGS2), nitrate reductase (CaNR), and asparagine synthetase (CaAS). The genes exhibited distinct patterns of transcriptional modulation for the different genotypes and N nutritional regimes. The resistant genotype (I59) presented high levels of transcription in response to pathogen inoculation for CaNR and CaGS1 genes, evaluated under N sufficiency in the initial moments of infection (12 HPI). The gene CaGS1 also showed a peak at 48 HPI. The susceptible genotype (CV99) showed increased transcript rates of CaNR at 12 and 24 HPI in response to rust inoculation. The transcriptional patterns observed for CV99, under N suppression, were high levels for CaAS and CaGS2 at all post-inoculation times in response to coffee leaf rust disease. In addition, CaGS1 was up-regulated at 48 HPI for CV99. Cultivar I59 showed high transcript levels at 12 HPI for CaAS and peaks at 24 and 48 HPI for CaGS2 in inoculated samples. Consequently, total chlorophyl concentration was influenced by N suppression and by rust infection. Regarding enzyme activities in vitro for glutamine synthetase and CaNR, there was an increase in infected coffee leaves (I59) and under N sufficiency. Moreover, CV99 was modulated in both N nutritional regimes for GS activity in response to rust. Our results indicate that N transport genes trigger a differential modulation between genotypes through the action of rust disease. [ABSTRACT FROM AUTHOR]

Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is an important pest of potato crops. Potato foliar amino acids play essential roles in CPB growth. In this study, amino acids were classified into four groups according to their different roles in promoting CPB growth. Then, nitrogen (N) rate effects on the concentrations of amino acid groups were investigated under field conditions. Experiments were carried out with five N rates of 0, 60, 120, 180, and 240 kg N ha−1 in a randomized complete block design. Twenty leaves were collected at 40, 54, 68, and 82 days after planting (DAP) for amino acids analysis. Results showed that N rate had no significant effect on concentrations of each amino acid group at 40 DAP. However, their concentrations linearly increased as N rate increased at 54, 68, and 82 DAP, suggesting that higher N rates could potentially favor CPB growth after potato enters tuber initiation stage. [ABSTRACT FROM AUTHOR]

While nitrogen (N) derived from ammonium would be energetically less expensive than nitrate-derived N, the use of ammonium-based fertilizer is limited by the potential for toxicity symptoms. Nevertheless, previous studies have shown that exposure to elevated CO2 favors ammonium assimilation in plants. However, little is known about the impact of different forms of N fertilizer on stomatal opening and their consequent effects on CO2 and H2O diffusion in wheat plants exposed to ambient and elevated CO2. In this article, we have examined the response of the photosynthetic machinery of durum wheat (Triticum durum , var. Amilcar) grown with different types of N fertilizer (NO3−, NH4+, and NH4NO3) at 400 versus 700 ppm of CO2. Alongside gas exchange and photochemical parameters, the expression of genes involved in CO2 (PIP1.1 and PIP2.3) and H2O (TIP1) diffusion as well as key C and N primary metabolism enzymes and metabolites were studied. Our results show that at 400 ppm CO2, wheat plants fertilized with ammonium as the N source had stress symptoms and a strong reduction in stomatal conductance, which negatively affected photosynthetic rates. The higher levels of PIP1.1 and PIP2.3 expression in ammonium-fertilized plants at 400 ppm CO2 might reflect the need to overcome limitations to the CO2 supply to chloroplasts due to restrictions in stomatal conductance. This stomatal limitation might be associated with a strategy to reduce ammonium transport toward leaves. On the other hand, ammonium-fertilized plants at elevated CO2 did not show stress symptoms, and no differences were detected in stomatal opening or water use efficiency (WUE). Moreover, similar gene expression of the aquaporins TIP1 , PIP1.1, and PIP2.3 in ammonium-fertilized plants grown at 700 ppm compared to nitrate and ammonium nitrate plants would suggest that an adjustment in CO2 and H2O diffusion is not required. Therefore, in the absence of a stress context triggered by elevated CO2, ammonium- and ammonium nitrate-fertilized plants were able to increase their photosynthetic rates, which were translated eventually into higher leaf protein content. [ABSTRACT FROM AUTHOR]

Highlights • NaSH could be a beneficial strategy for improving N assimilation. • Essential amino acids increase with the application of 0.5 mM of NaSH. • High doses of NaSH induced the formation and accumulation of NH 4 +. Abstract Assimilatory pathways of S and N are well coordinated, and addition of S increases the biomass and yield in plantsand improves efficiency in the use of N (NUE). However, no available studies have attempted to explain the effects of NaSH application on crop yield and N metabolism. This study investigates the effects of different doses of hydrogen sulfide as NaSH (0, 0.5, 1,2.5 and 5 mM) in the formation and assimilation of NH 4 + in plants of Brassica oleracea L. 'Bronco'. According to our results, treatments of 0.5 and 1 mMNaSH increased biomass while decreasing the NO 3 − concentration. In the treatment 0.5 mM of NaSH, NH 4 +accumulation diminished with the stimulation of the GS activity, resulting in a greater content in certain amino acids (AAs); this also boosted the soluble-protein content, which could be related to the greater biomass found in this treatment. However, 2.5 and 5 mM of NaSH induced the formation and accumulation of NH 4 + by further reducing this as well as photorespiration. This excessive accumulation of NH 4 + may be responsible for the lower biomass in these treatments (2.5 and 5 mM of NaSH).We conclude that excessive accumulation of NH 4 + may be responsible for the decline in biomass in the treatments 2.5 and 5 mM of NaSH. Therefore, the application of 0.5 mM of NaSH could be a beneficial strategy for improving the processes involved in the N assimilation, accompanied by enhanced crop biomass. [ABSTRACT FROM AUTHOR]

Highlights • Up-regulations of CsGABA-T and CsAlaAT improved low N tolerance of tea plant. • Unilateral fertilization led to nitrogen (N) heterogeneity in soils. • Low N tolerant tea plant had strong ability in transporting N to leaf. • Accumulation of glutamic acid and theanine enhanced low N tolerance of tea tree. Abstract As a leaf crop, tea plants consume a high amount of nitrogen (N), but the physiological and molecular mechanisms of tea in response to N spatial heterogeneity are poorly understood. Based on a common planting pattern of unilaterally fertilized double rows, the phenotype, free amino acid (FAA) contents, N contents of the soil and plants, root growth and gene expression of contrasting tea genotypes (Longjing43 (LJ43) and Liyou002 (LY002)) were compared in this study. Our results showed that, the unilaterally fertilized double row cultivation system led to N spatial heterogeneity in soil. For field growth, the ratio of young to mature leaves, leaf SPAD value, and differences between the two lines (near (-near) and far from (-far) the fertilization side) were smaller for the LJ43 strain than those for LY002. The ratio of secondary to primary roots was much higher in LJ-far than that in LY-far. The N contents of leaves, primary roots and secondary roots were higher in LJ-far than those in LY-far. The leaf distribution of total N and most FAAs were higher in LJ-far than those in LY-far. On lines far from the fertilization sides, γ-aminobutyric acid and alanine tended to accumulate more in LY002 than in LJ43, while glutamic acid and theanine tended to accumulate more in LJ43 than in LY002. Indeed, there were some genes (CsGABA-T, CsGAD1, CsGAD2, CsAlaAT and CsGs(TS)1) involved in the conversion of these amino acids. Moreover, the expression of some genes involved in N transport and assimilation (such as CsNRT2.5 and CsGS2) were up regulated in LJ-far, which may also help improve the low N tolerance in LJ43. In summary, the greater adaptive ability of LJ43 might be related to: (1) preferential development of secondary roots; (2) better N transporting ability; (3) key gene regulation to FAA transformation. Our findings may contribute to the advancement of tea planting patterns and a more complete understanding of the physiological and molecular mechanisms of tea responses to the spatial heterogeneity of N. [ABSTRACT FROM AUTHOR]

The tropical forage grass Brachiaria humidicola (Bh) suppresses the activity of soil nitrifiers through biological nitrification inhibition (BNI). As a result, nitrate (NO3−) formation and leaching are reduced which is also expected to tighten the soil nitrogen (N) cycle. However, the beneficial relationship between reduced NO3− losses and enhanced N uptake due to BNI has not been experimentally demonstrated yet. Nitrification discriminates against the 15N isotope and leads to 15N depleted NO3−, but 15N enriched NH4+ in soils. Leaching of 15N depleted NO3− enriches the residual N pool in the soil with 15N. We hypothesized that altered nitrification and NO3− leaching due to diverging BNI magnitudes in contrasting Bh genotypes influence soil 15N natural abundance (δ15N), which in turn is reflected in distinct δ15N in Bh shoot biomass. Consequently, high BNI was expected to be reflected in low plant δ15N of Bh. It was our objective to investigate under controlled conditions the link between shoot value of δ15N in several Bh genotypes and leached NO3− amounts and shoot N uptake. Additionally, plant 15N and N% was monitored among a wide range of Bh genotypes with contrasting BNI potentials in field plots for 3 years. We measured leaf δ15N of young leaves (regrown after cutback) of Bh and combined it with nitrification rates (NRs) of incubated soil to test whether there is a direct relationship between plant δ15N and BNI. Increased leached NO3− was positively correlated with higher δ15N in Bh, whereas the correlation between shoot N uptake and shoot δ15N was inverse. Field cultivation of a wide range of Bh genotypes over 3 years decreased NRs in incubated soil, while shoot δ15N declined and shoot N% increased over time. Leaf δ15N of Bh genotypes correlated positively with NRs of incubated soil. It was concluded that decreasing plant δ15N of Bh genotypes over time reflects the long-term effect of BNI as linked to lower NO3− formation and reduced NO3− leaching. Accordingly, a low δ15N in Bh shoot tissue verified its potential as indicator of high BNI activity of Bh genotypes.

Balancing of leaf carbohydrates is a key process for maximising crop performance in elevated CO2 environments. With the aim of testing the role of the carbon sink–source relationship under different CO2 conditions, we performed two experiments with two barley genotypes (Harrington and RCSL-89) exposed to changing CO2. In Experiment 1, the genotypes were exposed to 400 and 700 ppm CO2. Elevated CO2 induced photosynthetic acclimation in Harrington that was linked with the depletion of Rubisco protein. In contrast, a higher peduncle carbohydrate-storage capacity in RSCL-89 was associated with a better balance of leaf carbohydrates that could help to maximize the photosynthetic capacity under elevated CO2. In Experiment 2, plants that were grown at 400 ppm or 700 ppm CO2 for 5 weeks were switched to 700 ppm or 400 ppm CO2, respectively. Raising CO2 to 700 ppm increased photosynthetic rates with a reduction in leaf carbohydrate content and an improvement in N assimilation. The increase in nitrate content was associated with up-regulation of genes of protein transcripts of photosynthesis and N assimilation that favoured plant performance under elevated CO2. Finally, decreasing the CO2 from 700 ppm to 400 ppm revealed that both stomatal closure and inhibited expression of light-harvesting proteins negatively affected photosynthetic performance and plant growth. [ABSTRACT FROM AUTHOR]

The tropical forage grass Brachiaria humidicola (Bh) suppresses the activity of soil nitrifiers through biological nitrification inhibition (BNI). As a result, nitrate ( NO 3 − ) formation and leaching are reduced which is also expected to tighten the soil nitrogen (N) cycle. However, the beneficial relationship between reduced NO 3 − losses and enhanced N uptake due to BNI has not been experimentally demonstrated yet. Nitrification discriminates against the 15N isotope and leads to 15N depleted NO 3 − , but 15N enriched NH 4 + in soils. Leaching of 15N depleted NO 3 − enriches the residual N pool in the soil with 15N. We hypothesized that altered nitrification and NO 3 − leaching due to diverging BNI magnitudes in contrasting Bh genotypes influence soil 15N natural abundance (δ15N), which in turn is reflected in distinct δ15N in Bh shoot biomass. Consequently, high BNI was expected to be reflected in low plant δ15N of Bh. It was our objective to investigate under controlled conditions the link between shoot value of δ15N in several Bh genotypes and leached NO 3 − amounts and shoot N uptake. Additionally, plant 15N and N% was monitored among a wide range of Bh genotypes with contrasting BNI potentials in field plots for 3 years. We measured leaf δ15N of young leaves (regrown after cutback) of Bh and combined it with nitrification rates (NRs) of incubated soil to test whether there is a direct relationship between plant δ15N and BNI. Increased leached NO 3 − was positively correlated with higher δ15N in Bh, whereas the correlation between shoot N uptake and shoot δ15N was inverse. Field cultivation of a wide range of Bh genotypes over 3 years decreased NRs in incubated soil, while shoot δ15N declined and shoot N% increased over time. Leaf δ15N of Bh genotypes correlated positively with NRs of incubated soil. It was concluded that decreasing plant δ15N of Bh genotypes over time reflects the long-term effect of BNI as linked to lower NO 3 − formation and reduced NO 3 − leaching. Accordingly, a low δ15N in Bh shoot tissue verified its potential as indicator of high BNI activity of Bh genotypes. [ABSTRACT FROM AUTHOR]

Increasing the nitrogen use efficiency of crop plants is a result of the improvement in the mechanisms involved in nitrogen uptake, translocation, assimilation and remobilization. In this study, tobacco plants with high accumulation of proline caused by the insertion of the VaP5CSF129A mutant gene under control of the constitutive promoter CaMV 35S was used as a model to investigate the effect of overexpression of the transgene in the uptake and utilization of N. For this, an experiment was carried out in a completely randomized design, in a 2x5 factorial arrangement, with two genotypes (transgenic event and untransformed control) and five levels of nitrogen fertilization (25, 50, 100, 200 and 400 kg N ha-?), cultivated under greenhouse conditions. Plants were evaluated for height, number of leaves, dry mass, free proline content, nitrogen content, total protein content and use of the applied N (efficiency of absorption - EAbs, efficiency of leaf utilization - EUtil and efficiency of plant use - EUN). The transgenic plants with high proline accumulation were less efficient than the control plants in terms of nitrogen absorption (with lower N levels in root, leaves and whole plant), which resulted in lower EAbs. There was no difference between the transgenic and control genotypes for EUtil. However, the transgenic plants presented lower EUN in comparison to the control plants. Our data showed that transgenic tobacco plants with high proline accumulation do not have potential for direct use in agricultural systems, since the alteration of the biochemical balance between the metabolisms of nitrogen and carbon did not result in plants with higher EUN. [ABSTRACT FROM AUTHOR]

The rhodophyte Gracilaria lemaneiformis plays a significant role in nitrogen (N) utilization as an economic macroalgae. However, very little is known about how G. lemaneiformis adapts to N deprivation. In this study, G. lemaneiformis were pre-cultured in artificial seawater with 50 μM inorganic N for 4 days and two groups were set after the pre-culture, N-deprived treatment with 0 μM N nutrient and N-replete control with 50 μM N nutrient. The response of G. lemaneiformis to N deprivation was analyzed at physiological, transcriptomic and proteomic levels. Physiologically, our data revealed that N depletion resulted in the increase of C/N ratio in a sustained period of N deprivation. Nitrogenous compounds were available in N depletion, including amino acids, phycoerythrin and soluble protein, but not DNA and chlorophyll-a. Furthermore, transcriptomic analysis underscored two major responses of G. lemaneiformis to N deprivation: 1) N assimilation pathway, PSII and PSI initially responded to N deprivation in 4 days, but declined sharply during the N deprivation; 2) Carbon fixation and glycolysis metabolism both rapidly recovered during a sustained period of N deprivation from strong repression of the first 2 days. Proteomics data indicated that electron-transfer proteins in the photosynthesis of G. lemaneiformis increased dramatically, but phycoerythrin protein decreased under N deprivation. However, GS protein and ribulose-bisphosphate carboxylase (RubisCO) protein remained stable. Therefore, this investigation revealed that the C-N metabolism was essential to survival under N deprivation. [ABSTRACT FROM AUTHOR]

Cottonseed is widely used as a source of ruminant feed and for industrial purposes. Therefore, there is a tremendous need to improve the nutritional value of cotton embryos. In this study, a conventional management (CM) and two integrated cotton management strategies (IMS1, IMS2) were performed at two soil fertility levels to study the relationships among soil N, N assimilation, embryonic protein accumulation and protein quality. The levels of proteins, essential amino acids, and semi-essential amino acids, especially those of glutamate, lysine, and methionine, were higher in IMS1 and IMS2 embryos than in CM embryos. These changes were significantly positively correlated with the soil-available N content, glutamine synthetase (GS) activity and peak value of protein accumulation rate and were negatively correlated with the free amino acid level. These results illustrated that integrated management strategies, especially the rates and timing of N application, raise the level of soil available N, which is beneficial for N assimilation in developing cotton embryos. The protein content was limited by the rate of protein accumulation rather than by the free amino acid content. The combination of target yield fertilization, a growth-driven N application schedule, a high plant density and the seedling raising with bio-organic fertilizer can substantially improve protein quality in cotton embryos, especially at a soil with low soil organic matter and total nitrogen.

Efficient control of ion homeostasis and nitrogen (N) metabolism contributes to the salt tolerance in crops. However, limited information is available on the contribution of ion homeostasis and N metabolism regulation towards salt tolerance in sweet potato ( Ipomoea batatas L.) cultivars at adventitious root stage. In this study, NaCl-induced ion homeostasis and N metabolism changes in adventitious roots of two different sweet potato cultivars were investigated. Salt tolerant cultivar (Xushu 22, Xu 22) exhibited better capacity controlling Na + , Cl − , K + and Mg 2+ homeostasis than the salt sensitive cultivar (Xushu Shi 5, Shi 5) under prolonged salinity condition. Net H + efflux and plasma membrane H + -ATPase gene expression were significantly enhanced in NaCl-stressed Xu 22 roots but not in Shi 5 roots. Salt-upregulated PM H + -ATPase contributed to less K + efflux in Xu 22 roots. NaCl stimulated Mg 2+ uptake in Xu 22 roots under prolonged salinity, but promoted Mg 2+ efflux in Shi 5 roots. In addition, NaCl significantly enhanced transcript abundance of genes related to vacuolar Na + and Cl − sequestration in Xu 22 roots. In Xu 22 roots, NaCl triggered an obvious net NH 4 + efflux, which caused a rapid increase of NH 4 + concentration around the rhizosphere. Exogenous supply of NH 4 + markedly inhibited Na + influx and K + efflux under salt shock condition. Moreover, a salt-enhanced NO 3 − net influx was also detected in mature Xu 22 root region and this process may contributes to the normal N assimilation in this cultivar under prolonged saline condition. Taken together, our results suggest that the better capacities of root K + and Mg 2+ retention, vacuolar Na + and Cl − sequestration, transition of NH 4 + /NO 3 − transport and N assimilation maintenance contribute to the salt tolerance of Xu 22 at adventitious root stage. A model showing salt-adaptive mechanisms in salt-tolerant Xu 22 is proposed. [ABSTRACT FROM AUTHOR]

Soybean ( Glycine max (L.) Merrill) new cultivars have high N demands to sustain increasing grain yields. One may ask whether these cultivars would need basal and/or topdressing N application as perhaps symbiotic N 2 fixation would not catch up with the increased N needs. In this study, three field experiments were performed in three different ecoregions of Brazil to compare soybean with determinate (BRS-294-RR and BRS-295-RR) and indeterminate (Vmax-RR, BMX-Potência-RR and BRS 284) growth types. The experiments consisted of four treatments, all inoculated with efficient Bradyrhizobium strains, but with differences in N fertilizer (as urea) application: (T1) control without N fertilizer; (T2) basal application of 30 kg N ha −1 at sowing; (T3) topdressing of 50 kg N ha −1 at full flowering; (T4) 30 kg N ha −1 and 50 kg N ha −1 as basal and topdressing, respectively. None of the basal or topdressing treatments improved biomass production or grain yield. However, N fertilizer negatively affected nodule number and dry weight, pointing out a down-regulation in the symbiotic performance, without improving crop yields. Similar results were observed in cultivars of both growth types, indicating that biological nitrogen fixation can supply N needs of new soybean genotypes of both growth types. [ABSTRACT FROM AUTHOR]

Virgilia divaricata Adamson is a forest margin legume that is known to invade the N- and P-poor soils of the mature fynbos, implying that it tolerates variable soil N and P levels. It is not known how the legume uses inorganic N from soil and atmospheric sources under variable P supply. Little is known about how P deficiency affects the root nodule metabolic functioning of V. divaricata and the associated energy costs of N assimilation. This study aimed to determine whether P deficiency affects the metabolic status of roots and nodules, and the impact on the routes of N assimilation in V. divaricata. V. divaricata had reduced biomass, plant P concentration and biological nitrogen fixation during P deficiency. Based on adenylate data, P-stressed nodules maintained their P status better than P-stressed roots. V. divaricata was able to alterCandNmetabolism differently in roots and nodules under P stress. This was achieved via internal P cycling by possible replacement of membrane phospholipids with sulfolipids and galactolipids, and increased reliance on the pyrophosphate (PPi)-dependent metabolism of sucrose via UDP-glucose (UDPG) and to fructose-6-phosphate (Fru-6-P). P-stressed roots mostly exported ureides as organic N and recycled amino acids via deaminating glutamate dehydrogenase. In contrast, P-stressed nodules largely exported amino acids. Compared with roots, nodules showed more P conservation during low P supply. The roots and nodules of V. divaricata metabolised N differently during P stress, meaning that these organs may contribute differently to the success of this plant in soils from forest to fynbos. [ABSTRACT FROM AUTHOR]

In the past 50 years, the application of synthetic nitrogen (N) fertilizer to farmland resulted in a dramatic increase in crop yields but with considerable negative impacts on the environment. New solutions are therefore needed to simultaneously increase yields while maintaining, or preferably decreasing, applied N to maximize the nitrogen use efficiency (NUE) of crops. In this review, we outline the definition of NUE, the selection and development of NUE crops, and the factors that interact with NUE. In particular, we emphasize the challenges of developing crop plants with enhanced NUE, using more classical genetic approaches based on utilizing existing allelic variation for NUE traits. The challenges of phenotyping, mapping quantitative trait loci (QTLs), and selecting candidate genes for NUE improvement are described. In addition, we highlight the importance of different factors that lead to changes in the NUE components of nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). [ABSTRACT FROM AUTHOR]

The aim of this work was to address the issue of processed vs. non-processed biowastes for agriculture, by comparing materials widely differing for the amount of process energy consumption. Thus, residual post harvest tomato plants (TP), the TP hydrolysates obtained at pH 13 and 60 °C, and two known biochar products obtained by 650 °C pyrolysis were prepared. All products were characterized and used in a cultivation of radish plants. The chemical composition and molecular nature of the materials was investigated by solid state 13C NMR spectrometry, elemental analysis and potentiometric titration. The plants were analysed for growth and content of chlorophyll, carotenoids and soluble proteins. The results show that the TP and the alkaline hydrolysates contain lignin, hemicellulose, protein, peptide and/or amino acids moieties, and several mineral elements. The biochar samples contain also similar mineral elements, but the organic fraction is characterized mainly by fused aromatic rings. All materials had a positive effect on radish growth, mainly on the diameter of roots. The best performances in terms of plant growth were given by miscanthus originated biochar and TP. The most significant effect was the enhancement of soluble protein content in the plants treated with the lowest energy consumption non processed TP. The significance of these findings for agriculture and the environment is discussed. [ABSTRACT FROM AUTHOR]

Humic-like substances obtained by alkaline hydrolysis of composted organic wastes are known to improve plant productivity. Little is known concerning the effect on plant growth of hydrolysates obtained by alkaline treatment of non-composted vegetal residues. The aim of this study was to prepare, characterize, and apply in horticulture the soluble and the insoluble fractions obtained by alkaline hydrolysis of exhausted tomato plants. The hydrolysates were prepared in a pilot plant from the tomato plants residue in powder form and characterized by solid state 13 C NMR spectrometry, elemental analysis and potentiometric titration. The characterization of the soluble hydrolysate gave evidence of lignin and hemicellulose moieties, together with protein, peptide or amino acids while most of the cellulose was found in the insoluble fraction. Plant beans were grown on a peat and sand substrate fertilized with low application rate of the tomato plant powder and of the corresponding hydrolysates. The effect on bean plants was assessed by determination of plant growth, chlorophyll content, nitrate reductase, glutamine synthetase, glutamate synthase activities and soluble proteins. The tomato plant powder had no effect on all parameters measured on the grown bean plants. On the contrary, the insoluble and soluble substances sourced by alkaline hydrolysis of the tomato plant powder exhibit strong effects, mainly the increase of nitrogen assimilation typical of biostimulants. The results suggest that residual plant biomasses are source of efficient biostimolant and propose the hydrolysis of residual biomass as a viable profitable process to contribute important improvements also for waste management practices. [ABSTRACT FROM AUTHOR]

To compare the effect of arbuscular mycorrhiza (AM) and P-supplement on N uptake and N assimilation under well-watered or drought-stressed conditions, Glomus intraradices-colonised, P-supplemented non-mycorrhizal (P) and non-mycorrhizal (control) plants of Lolium perenne were exposed to 12 days of water treatment. Leaf water potential ( Ψ), photosynthetic ability, and N and P nutritional status were measured at the beginning (day 0) and end (day 12) of water treatment. N absorption, amino acid and protein synthesis were quantified using the isotopic tracer N at day 12. Under well-watered conditions, growth response and physiological parameters were similar in AM and P plants, as compared to controls. Drought (10% water) significantly decreased these parameters in all three treatments. As compared to control plants, the negative impact of water deficit on the Ψ, photosynthesis, biomass, and N and P content was highly alleviated in AM plants, while only slightly improved or remained the same level in P plants. The effect of AM symbiosis on N absorption and N assimilation was greater than that of the P supplement under well-watered and drought-stressed conditions, and this effect was highly enhanced under drought-stressed conditions. At terminal drought stress on day 12, the effect of AM colonisation on de novo synthesis of amino acids and proteins was 4.4- and 4.8-fold higher than that of the P supplement. These results indicate that the AM symbiosis plays an integrative role in N nutrition by alleviating the negative impacts of drought on N or P uptake and N assimilation, whereas the efficiency of a direct P supplement is very limited under drought-stressed conditions. [ABSTRACT FROM AUTHOR]

In the present study, N and S assimilation, antioxidant enzymes activity, and yield were studied in N and S-treated plants of Brassica juncea (L.) Czern. & Coss. (cvs. Chuutki and Radha) under salt stress. The treatments were given as follows: (1) NaCl mM+NS mg kg sand (control), (2) NaCl mM+NS mg kg sand, (3) NaCl mM+NS mg kg sand, (4) NaCl mM+NS mg kg sand, and (5) NaCl mM+NS mg kg sand. The combined application of N (60 mg kg sand) and S (40 mg kg sand) proved beneficial in alleviating the adverse effect of salt stress on growth attributes (shoot length plant, fresh weight plant, dry weight plant, and area leaf), physio-biochemical parameters (carbonic anhydrase activity, total chlorophyll, adenosine triphosphate-sulphurylase activity, leaf N, K and Na content, K/Na ratio, activity of nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, catalase, superoxide dismutase, ascorbate peroxidase and glutathione reductase, and content of glutathione and ascorbate), and yield attributes (pods plant, seeds pod, and seed yield plant). Therefore, it is concluded that combined application of N and S induced the physiological and biochemical mechanisms of Brassica. The stimulation of antioxidant enzymes activity and its synergy with N and S assimilation may be one of the important mechanisms that help the plants to tolerate the salinity stress and resulted in an improved yield. [ABSTRACT FROM AUTHOR]

Abstract: Sewage sludge has been used as N fertilizer because it contains some of inorganic N, principally as nitrate and ammonium ions. However, sewage sludge addition to legumes could result in impaired nodule metabolism due to the presence of inorganic N from sludge. A greenhouse experiment was conducted to examine the effects of sewage sludge on growth, photosynthesis, nitrogen assimilation and nodule metabolism in alfalfa (Medicago sativa L. cv. Aragón). Plants were grown in pots with a mixture of perlite and vermiculite (2:1, v/v). The experiment included three treatments: (1) plants inoculated with rhizobia and amended with sewage sludge at rate of 10% (w/w) (RS); (2) plants inoculated with rhizobia without any amendment (R); and (3) non-inoculated plants fed with ammonium nitrate (N). N2-fixing plants had lower growth and sucrose phosphate synthase activity but higher photosynthesis than nitrate-fed plants because they compensated the carbon cost of the rhizobia. However, sewage sludge-treated plants evidenced a loss of carbon sink strength due to N2 fixation by means of decreased photosynthetic capacity, leaf chlorophylls and N concentration in comparison to untreated plants. Sewage sludge did no affect nodulation but decreased nodule enzyme activities involved in carbon and N metabolisms that may lead to accumulation of toxic N-compounds. [ABSTRACT FROM AUTHOR]

Abstract: Responses of soluble amino acids and organic acids to either ambient (36Pa) or elevated (100Pa) CO2 treatments were determined using barley primary leaves (Hordeum vulgare L. cv. Brant). Total soluble amino acids were increased 33% by CO2 enrichment 9 days after sowing (DAS), but a decrease relative to the ambient CO2 treatment was observed with increasing leaf age. Marked declines of glutamine and asparagine were observed under CO2 enrichment, both diurnally and with advancing leaf age. Consequently, total soluble amino acids were 59% lower in the elevated compared to the ambient CO2 treatment 17 DAS. It was likely that chlorosis in response to CO2 enrichment negatively impacted soluble amino acid levels in older barley primary leaves. In contrast to the ambient CO2 treatment, glutamine and most other soluble amino acids decreased as much as 60% during the latter half of a 12h photoperiod in primary leaves of 13-day-old seedlings grown under enhanced CO2. Malate was decreased about 9 percent by CO2 enrichment and citrate and succinate were increased by similar amounts when measured 9 and 13 DAS. Malate accumulation was also decreased about 20% by CO2 enrichment on a diurnal basis. The onset of CO2-dependent leaf yellowing had much less of an effect on organic acids than on soluble amino acids. This above results emphasized the sensitivity of N metabolism to CO2 enrichment in barley. Increased levels of citrate and succinate in response to CO2 enrichment suggested that the tricarboxylic acid cycle was upregulated in barley by CO2 enrichment. In summary, organic and amino acid levels in barley primary leaves were dynamic and were altered by age, diurnally and in response to CO2 enrichment. [Copyright &y& Elsevier]

Isotope pool dilution studies are increasingly reported in the soils and ecology literature as a means of measuring gross rates of nitrogen (N) mineralization, nitrification, and inorganic N assimilation in soils. We assembled data on soil characteristics and gross rates from 100 studies conducted in forest, shrubland, grassland, and agricultural systems to answer the following questions: What factors appear to be the major drivers for production and consumption of inorganic N as measured by isotope dilution studies? Do rates or the relationships between drivers and rates differ among ecosystem types? Across a wide range of ecosystems, gross N mineralization is positively correlated with microbial biomass and soil C and N concentrations, while soil C:N ratio exerts a negative effect on N mineralization only after adjusting for differences in soil C. Nitrification is a log-linear function of N mineralization, increasing rapidly at low mineralization rates but changing only slightly at high mineralization rates. In contrast, NH4+ assimilation by soil microbes increases nearly linearly over the full range of mineralization rates. As a result, nitrification is proportionately more important as a fate for NH4+ at low mineralization rates than at high mineralization rates. Gross nitrification rates show no relationship to soil pH, with some of the fastest nitrification rates occurring below pH 5 in soils with high N mineralization rates. Differences in soil organic matter (SOM) composition and concentration among ecosystem types influence the production and fate of mineralized N. Soil organic matter from grasslands appears to be inherently more productive of ammonium than SOM from wooded sites, and SOM from deciduous forests is more so than SOM in coniferous forests, but differences appear to result primarily from differing C:N ratios of organic matter. Because of the central importance of SOM characteristics and concentrations in regulating rates, soil organic matter depletion in agricultural systems appears to be an important determinant of gross process rates and the proportion of NH4+ that is nitrified. Addition of 15N appears to stimulate NH4+ consumption more than NO3- consumption processes; however, the magnitude of the stimulation may provide useful information regarding the factors limiting microbial N transformations. [ABSTRACT FROM AUTHOR]

The article presents a study on the brown macroalgae, also known as Fucus vesiculosus, using the nitrogen stable-isotope ratio. Also noted is the impact of nutrient discharges from sewage treatment plants on the eutrophication of coastal and estuarine areas. Discussed is the result of nutrient budget calculations during the study.

Phenotypic plasticity and competitive strength are major mechanisms determining the success of invasive species and are influenced by abiotic factors. A rise in the ratio of ammonium (NH 4 +) to nitrate (NO 3 −) in soils is frequently associated with the invasion of bamboo into broad-leaved evergreen forests. However, the influence of soil nitrogen (N) chemistry on plant growth and interspecific competition in the context of invasion remains insufficiently studied. In the present work, differences in plasticity and interspecific competition between native tree species in broad-leaved evergreen forests and invasive bamboo in response to different N forms were investigated using seedlings grown in a controlled environment. We show that moso bamboo responded positively and strongly to increased soil NH 4 +/NO 3 − ratios, while the native tree species Sapium sebiferum , Camellia oleifera , and Machilus pauhoi responded negatively and exhibited limited plasticity. Native tree species growth was significantly inhibited in the presence of moso bamboo under high-NH 4 + conditions, whereas native tree species were less affected by interspecific competition when NO 3 − was supplied as the sole N source. By contrast, moso bamboo growth was significantly inhibited, followed by seedling death, in both monoculture and in mixed culture with prolonged NO 3 − treatment. All species tested exhibited significantly higher rates of 15NH 4 + than 15NO 3 − uptake, but the Michaelis constant (K m) for 15NH 4 + uptake was lower in moso bamboo, indicating higher substrate affinity. Nitrate reductase (NR) and nitrite reductase (NiR) activities showed no inducible effects in moso bamboo compared to the induction response seen in the native tree species in response to NO 3 −. Activities of glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) significantly increased with NH 4 + provision in roots of moso bamboo, contrasted by a less plastic response in the native tree species. Enhanced ammonification and reduced nitrification in soils is typically observed during bamboo invasion and appears to create a positive soil-plant feedback loop that, due to highly flexible and opportunistic NH 4 +-acquisition pathways, favours bamboo fitness and invasion into native forests when NH 4 + is the dominant N form. [ABSTRACT FROM AUTHOR]

The arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith was grown in symbiosis with Cucumis sativus L. cv. Aminex (F1 hybrid) in mesh bags surrounded by a sand-filled hyphal compartment (HC), allowing only the fungal hyphae to protrude into the HC. The hyphac in the HC were supplied with 15N-labe1led NH4+ or NO3- after 60 d (expt 1). Following a 48 h labelling period, the sand was removed from the HC and the hyphae extracted. In another experiment (expt 2), the hyphae were extracted from the sand before being incubated in vitro in a nutrient solution containing 15N-labelled NH4+ for 15 h. The hyphal material was incubated in a 0 or 2.5 mM solution of the GOGAT-inhibitor albizzine prior to labelling. In both experiments the hyphal content of free amino acids and fatty acids were measured as well as the amino acid 15N enrichment. Asparagine was the hyphal amino acid measured in highest concentration followed by glutamine, glutamate, aspartate and alanine. Ornithine, serine and glycine were detected in lower concentrations, but γ-aminobutyric acid and citrulline were not detectable. This pattern was the same in both experiments and was unaffected by the type of N applied to the hyphae or by preincubation with albizzine, although the amino-acid concentration decreased considerably in expt 2 compared with expt 1. Both NH4--N and NO3--N were assimilated into amino acids but the levels of 15N enrichment following application of NO3- were much lower than those following application of NH4+ indicating that the latter was more readily assimilated. Albizzine decreased the hyphal amino acid concentration by c 30% (without affecting the 15N enrichment of the individual amino acids) indicating that the AM-fungal hyphae might possess a GS-GOGAT enzyme system for assimilation of inorganic N. The fatty-acid profiles (especially phospholipid fatty acids 16: 1ω5 and 20 : 5) obtained from the hyphae of G. intraradices showed that contamination of the samples by fungi other than G. intraradices and bacteria was insignificant, and confirmed the usefulness of specific fatty-acid measurement to estimate soil AM-fungal content. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance spectroscopy was used to monitor 15NH4+ assimilation and amino acid biosynthesis in the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton. (strain S238). In mycelium growing rapidly on 15NH4+, [amido-15N]glutamine was the major 15N-labelled species. When 15N-labelled mycelium was transferred into medium containing 14NH4+, the resonance for [amido-15N]glutamine decreased with a half-life of about 3.0 h, whereas the resonance for [amino-15N]glutamine remained unchanged. Such behaviour is consistent with glutamine synthetase (GS) being the major route of 15NH4+ assimilation. However, the higher accumulation of 15N]alanine observed in the presence of the GS inhibitor, methionine sulfoximine, indicated that a part of the glutamate pool was formed by the glutamate dehydrogenase (GDH) pathway. When the mycelium was in stationary phase (i. e. low extracellular NH4+), the intramolecular 15N labelling of glutamine suggested that the GDH and GS pathways were simultaneously assimilating NH4+. The N supply and the growth stage, therefore, influence the expression of the activities of GDH and GS. The current isotopic data identify other fates of absorbed 15N : glutamate decarboxylation gives rise to γ-aminobutyrate; transamination between glutamate and pyruvate yields alanine; and arginine accumulates. It is concluded that GS is the main pathway of primary assimilation of NH4+ in L. bicolor, but GDH may also contribute significantly to this process. [ABSTRACT FROM AUTHOR]