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Background and Aims: Nitrogen (N) deficiency in soil constrains plant growth, which beneficial soil bacterial communities may potentially alleviate. However, there is limited knowledge of the plant-bacteria interactions of wheat cultivars with different N-use efficiency (NUE) under N deficiency.We investigated the responses of soil and root endosphere bacterial communities as well as root metabolites of two wheat cultivars (cv. Mace and Gladius) with reported high and low NUE, respectively, using a glasshouse experiment and a hydroponic experiment with three N levels.The rhizosphere bacterial community of Mace shifted under N deficiency but not in its root endosphere. Conversely, the rhizosphere bacterial community of Gladius remained unchanged under N deficiency but shifted in its root endosphere. The metagenomic analysis illustrated increased detection of genes related to bacterial growth and motility in the rhizosphere of Mace, but not of Gladius, under N deficiency. A four-fold increase in octadecanoic acid in the root of Mace, but not Gladius, under N deficiency, suggesting the potential role of octadecanoic acid in shaping the rhizobacterial community in Mace with higher reported NUE.Our study highlights the divergent responses of wheat-associated microorganisms and root metabolites to N deficiency in the two cultivars. We found that wheat cultivars with higher NUE increased octadecanoic acid secretion, potentially shaping the rhizobacterial communities and enhancing their growth under N-limited conditions.Methods: Nitrogen (N) deficiency in soil constrains plant growth, which beneficial soil bacterial communities may potentially alleviate. However, there is limited knowledge of the plant-bacteria interactions of wheat cultivars with different N-use efficiency (NUE) under N deficiency.We investigated the responses of soil and root endosphere bacterial communities as well as root metabolites of two wheat cultivars (cv. Mace and Gladius) with reported high and low NUE, respectively, using a glasshouse experiment and a hydroponic experiment with three N levels.The rhizosphere bacterial community of Mace shifted under N deficiency but not in its root endosphere. Conversely, the rhizosphere bacterial community of Gladius remained unchanged under N deficiency but shifted in its root endosphere. The metagenomic analysis illustrated increased detection of genes related to bacterial growth and motility in the rhizosphere of Mace, but not of Gladius, under N deficiency. A four-fold increase in octadecanoic acid in the root of Mace, but not Gladius, under N deficiency, suggesting the potential role of octadecanoic acid in shaping the rhizobacterial community in Mace with higher reported NUE.Our study highlights the divergent responses of wheat-associated microorganisms and root metabolites to N deficiency in the two cultivars. We found that wheat cultivars with higher NUE increased octadecanoic acid secretion, potentially shaping the rhizobacterial communities and enhancing their growth under N-limited conditions.Results: Nitrogen (N) deficiency in soil constrains plant growth, which beneficial soil bacterial communities may potentially alleviate. However, there is limited knowledge of the plant-bacteria interactions of wheat cultivars with different N-use efficiency (NUE) under N deficiency.We investigated the responses of soil and root endosphere bacterial communities as well as root metabolites of two wheat cultivars (cv. Mace and Gladius) with reported high and low NUE, respectively, using a glasshouse experiment and a hydroponic experiment with three N levels.The rhizosphere bacterial community of Mace shifted under N deficiency but not in its root endosphere. Conversely, the rhizosphere bacterial community of Gladius remained unchanged under N deficiency but shifted in its root endosphere. The metagenomic analysis illustrated increased detection of genes related to bacterial growth and motility in the rhizosphere of Mace, but not of Gladius, under N deficiency. A four-fold increase in octadecanoic acid in the root of Mace, but not Gladius, under N deficiency, suggesting the potential role of octadecanoic acid in shaping the rhizobacterial community in Mace with higher reported NUE.Our study highlights the divergent responses of wheat-associated microorganisms and root metabolites to N deficiency in the two cultivars. We found that wheat cultivars with higher NUE increased octadecanoic acid secretion, potentially shaping the rhizobacterial communities and enhancing their growth under N-limited conditions.Conclusion: Nitrogen (N) deficiency in soil constrains plant growth, which beneficial soil bacterial communities may potentially alleviate. However, there is limited knowledge of the plant-bacteria interactions of wheat cultivars with different N-use efficiency (NUE) under N deficiency.We investigated the responses of soil and root endosphere bacterial communities as well as root metabolites of two wheat cultivars (cv. Mace and Gladius) with reported high and low NUE, respectively, using a glasshouse experiment and a hydroponic experiment with three N levels.The rhizosphere bacterial community of Mace shifted under N deficiency but not in its root endosphere. Conversely, the rhizosphere bacterial community of Gladius remained unchanged under N deficiency but shifted in its root endosphere. The metagenomic analysis illustrated increased detection of genes related to bacterial growth and motility in the rhizosphere of Mace, but not of Gladius, under N deficiency. A four-fold increase in octadecanoic acid in the root of Mace, but not Gladius, under N deficiency, suggesting the potential role of octadecanoic acid in shaping the rhizobacterial community in Mace with higher reported NUE.Our study highlights the divergent responses of wheat-associated microorganisms and root metabolites to N deficiency in the two cultivars. We found that wheat cultivars with higher NUE increased octadecanoic acid secretion, potentially shaping the rhizobacterial communities and enhancing their growth under N-limited conditions. [ABSTRACT FROM AUTHOR]

Background: Excessive application of N fertilizer can inhibit plant growth, reduce N-use efficiency (NUE) and lead to production reduction. Watermelon is an important crop that often restricted by inappropriate N supply. The study aims to test whether grafting with bottle gourd rootstock can improve the NUE and growth performance of watermelon under reduced nitrate application and to clarify the underlying mechanism. Methods: Grafted (self-grafted and rootstock-grafted watermelon) and ungrafted (watermelon and bottle gourd) seedlings were treated separately with 9 mM (control) and 4 mM (reduced-nitrate) N concentrations for 18 days under hydroponic conditions. Results: The growth and NUE of bottle gourd rootstock-grafted watermelon seedlings increased under reduced-nitrate, while decreased slightly in self-grafted seedlings compared with the control. Rootstock-grafted plants had higher root morphological traits, NO3− accumulation, NR and GS activities, photosynthesis, and NUE traits than self-grafted plants under reduced-nitrate. Reduced-nitrate treatment significantly up-regulated the expression of nitrate transporter genes NRT1.5 and NRT2.1 and N metabolizing enzyme genes NR2, NR3, NiR, GS1 and GS2 in rootstock-grafted plants. Conclusion: Under reduced-nitrate treatment, grafted watermelon can make better use of the developed rootstock roots to increase the NO3− absorption and transportation to the shoot, so as to enhance the N metabolism potential and photosynthetic capacity of scions, and finally improve plant growth and NUE. The enhanced NO3− uptake and utilization of rootstock-grafted plants were regulated at the transcriptional level. Grafting with the bottle gourd rootstock may be beneficial to the efficient production of watermelon and economic application of N fertilizer. [ABSTRACT FROM AUTHOR]

Background and aims: The modern wheat cultivars have been selected for non-limiting nitrogen (N) input situations and therefore require large amounts of fertiliser N. The relatively high price of fossil fuels increases the cost of N fertilisers, putting pressure on wheat farmers. Doubled-haploid mapping populations can lead to identification of specific loci that might be useful in marker-assisted breeding for increased N-use efficiency. Methods: Forty-one mostly Australian genotypes of wheat ( Triticum aestivum L.) (parents of existing doubled-haploid mapping populations) were grown to maturity in soil in a glasshouse. Two N treatments were tested: optimal (685 mg N pot) and low (171 mg N pot). Results: Plant growth was significantly lower in most genotypes (with the exception of Mendos and Gamenya) at low compared with optimal N supply. Leaf-6 extension rate in the low-N treatment was on average 76 % of that in the optimal N treatment. Grain yield was significantly affected by the treatment x genotype interaction, ranging from 2.5 (genotype WAWHT2046) to 7.0 g per plant (genotype Mendos) under low N supply, and from 3.8 (genotype Wilgoyne) to 10.1 g per plant (genotype Lang) under optimal N supply. Based on responses to differential N supply, Mendos and Wilgoyne ranked as N-use efficient. In contrast, ten genotypes (Cadoux, Frame, Gamenya, Halberd, Janz, Lang, Neepawa, Spear, Sunco and Tasman) were ranked as N-use inefficient. The old genotype Gamenya was relatively N-use efficient, but had a poor response to N fertilisation. Amery and Janz responded similarly to Gamenya. Conclusions: Even though genotypes used in the current study were bred mostly for yield, a range of differential responses to the low- and optimal-N treatments implies that efficient use of N at low supply and efficient response to N fertilisation might have been inadvertently selected for in some breeding programmes, suggesting a potential for breeding wheat cultivars with improved N-use efficiency. [ABSTRACT FROM AUTHOR]

Aims: Rice is known as an ammonium (NH)-tolerant species. Nevertheless, rice can suffer NH toxicity, and excessive use of nitrogen (N) fertilizer has raised NH in many paddy soils to levels that reduce vegetative biomass and yield. Examining whether thresholds of NH toxicity in rice are related to nitrogen-use efficiency (NUE) is the aim of this study. Methods: A high-NUE (Wuyunjing 23, W23) and a low-NUE (Guidan 4, GD) rice cultivar were cultivated hydroponically, and growth, root morphology, total N and NH concentration, root oxygen consumption, and transmembrane NH fluxes in the root meristem and elongation zones were determined. Results: We show that W23 possesses greater capacity to resist NH toxicity, while GD is more susceptible. We furthermore show that tissue NH accumulation and futile NH cycling across the root-cell plasma membrane, previously linked to inhibited plant development under elevated NH, are more pronounced in GD. NH efflux in the root elongation zone, measured by SIET, was nearly sevenfold greater in GD than in W23, and this was coupled to strongly stimulated root respiration. In both cultivars, root growth was affected more severely by high NH than shoot growth. High NH mainly inhibited the development of total root length and root area, while the formation of lateral roots was unaffected. Conclusions: It is concluded that the larger degree of seedling growth inhibition in low- vs. high-NUE rice genotypes is associated with significantly enhanced NH cycling and tissue accumulation in the elongation zone of the root. [ABSTRACT FROM AUTHOR]

Aims: The improvement of nitrogen-deficiency tolerance (NDT) and nitrogen-use efficiency (NUE) traits is an important objective of many rice breeding programs. A better understanding of their relationship is required for more efficient breeding. The objectives of this study were to map quantitative trait loci (QTLs) for NDT and NUE traits, and to gain a better understanding about the genetic basis of the relationships between NUE and NDT traits. Methods: 127 recombinant inbred lines (RILs) deriving from the cross of Zhenshan97/Minghui63 were tested in field conditions with low nitrogen (LN, 0 kg/ha) and normal nitrogen conditions (NN, 135 kg/ha in 2006 and 130 kg/ha in 2007). NDT traits were the ratio of a trait value under LN to NN, including grain yield, biomass yield, grain nitrogen and biomass nitrogen. NUE traits were nitrogen response, grain yield response and physiological nitrogen-use efficiency (PE). Results: For NDT traits, seven and eight QTLs were identified in 2006 and 2007, respectively. These QTLs were on chromosomes 1, 2, 3, 4, 7, 9, 10 and 11. For NUE traits, five and six QTLs were detected on chromosomes 1, 2, 3, 4, 6, 7, 9, 10 and 11 in 2006 and 2007, respectively. Four genomic regions, including G393-C922 on chromosome 1, RM232-C63 on chromosome 3, G235-G102 on chromosome 4 and RG678-R1440 on chromosome 7, were found to contain QTLs for NDT and NUE traits. NUE traits significantly negatively correlated with NDT traits in the two testing years, except for the correlations between physiological nitrogen-use efficiency and relative biomass nitrogen. Conclusion: The four QTL clusters harboring QTLs for both NDT and NUE traits, provides partial explanation and genetic mechanism for the observed correlations between NDT and NUE traits, and could be used as targets for improving NDT and NUE traits in future breeding. [ABSTRACT FROM AUTHOR]

The effects on growth, quality and N uptake by turfgrass ( Cynodon dactylon L.) during sod production of four fertiliser types applied at three application rates (100, 200 or 300 kg N ha−1 per ‘crop’) under two irrigation treatments (70% and 140% daily replacement of pan evaporation) were investigated. The fertiliser types were: water-soluble (predominately NH4NO3), control-release, pelletised poultry manure, and pelletised biosolids; and the experiment was conducted on a sandy soil in a Mediterranean-type climate. Plots were established from rhizomes, with the turfgrass harvested as sod every 16–28 weeks depending upon the time of the year. Four crops were produced during the study. Applying water-soluble and control-release fertilisers doubled shoot growth and improved turfgrass greenness by up to 10% in comparison with plots receiving pelletised poultry manure and pelletised biosolids. Nitrogen uptake into the shoots after four crops (averaged across irrigation treatments and N rates) was 497 kg N ha−1 for the water-soluble fertiliser, 402 kg N ha−1 for the control-release, 188 kg N ha−1 for the pelletised poultry manure and 237 kg N ha−1 for the pelletised biosolids. Consequently, the agronomic nitrogen-use efficiency (NAE, kg DM kg−1 N applied) of the inorganic fertilisers was approximately twice that of the organic fertilisers. Increasing irrigation from 70% to 140% replacement of pan evaporation was detrimental to turfgrass growth and N uptake for the first crop when supplied with the water-soluble fertiliser. Under the low irrigation treatment, inorganic N fertilisers applied at 200–300 kg N ha−1 were adequate for production of turfgrass sod. [ABSTRACT FROM AUTHOR]