Do plants need nitrate? The mechanisms by which nitrogen form affects plants
TL;DR: It is concluded that the form of N available to plants can affect their time and rate of seed germination, leaf expansion and function, dry matter partitioning between shoot and root, and root architecture.
Abstract: The literature on nitrogen (N) form effects on plants at different stages of their development has been critically reviewed, assessing the possible mechanisms of these effects. In particular, nitrate (NO3−) was compared with the other forms of N utilised by plants. It is concluded that the form of N available to plants can affect their time and rate of seed germination, leaf expansion and function, dry matter partitioning between shoot and root, and root architecture. The magnitude of these effects is dependent on environmental factors outside the supply of N. The mechanism of these effects is variable. Assessment of the importance of root or shoot NO3− assimilation under different environmental conditions is an important area for further study.
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TL;DR: The paper concludes that the rapid advances in sensing technologies and ML techniques will provide cost-effective and comprehensive solutions for better crop and environment state estimation and decision making.
675 citations
TL;DR: Strain-specific legume rhizobia symbioses can develop in particular habitats and are likely to be at least in part related to the relative occurrence of the potential symbionts in soils of the different regions.
Abstract: Most species in the Leguminosae (legume family) can fix atmospheric nitrogen (N₂) via symbiotic bacteria (rhizobia) in root nodules. Here, the literature on legume-rhizobia symbioses in field soils was reviewed and genotypically characterised rhizobia related to the taxonomy of the legumes from which they were isolated. The Leguminosae was divided into three sub-families, the Caesalpinioideae, Mimosoideae and Papilionoideae. Bradyrhizobium spp. were the exclusive rhizobial symbionts of species in the Caesalpinioideae, but data are limited. Generally, a range of rhizobia genera nodulated legume species across the two Mimosoideae tribes Ingeae and Mimoseae, but Mimosa spp. show specificity towards Burkholderia in central and southern Brazil, Rhizobium/Ensifer in central Mexico and Cupriavidus in southern Uruguay. These specific symbioses are likely to be at least in part related to the relative occurrence of the potential symbionts in soils of the different regions. Generally, Papilionoideae species were promiscuous in relation to rhizobial symbionts, but specificity for rhizobial genus appears to hold at the tribe level for the Fabeae (Rhizobium), the genus level for Cytisus (Bradyrhizobium), Lupinus (Bradyrhizobium) and the New Zealand native Sophora spp. (Mesorhizobium) and species level for Cicer arietinum (Mesorhizobium), Listia bainesii (Methylobacterium) and Listia angolensis (Microvirga). Specificity for rhizobial species/symbiovar appears to hold for Galega officinalis (Neorhizobium galegeae sv. officinalis), Galega orientalis (Neorhizobium galegeae sv. orientalis), Hedysarum coronarium (Rhizobium sullae), Medicago laciniata (Ensifer meliloti sv. medicaginis), Medicago rigiduloides (Ensifer meliloti sv. rigiduloides) and Trifolium ambiguum (Rhizobium leguminosarum sv. trifolii). Lateral gene transfer of specific symbiosis genes within rhizobial genera is an important mechanism allowing legumes to form symbioses with rhizobia adapted to particular soils. Strain-specific legume rhizobia symbioses can develop in particular habitats.
223 citations
TL;DR: An updated review of scientific advances regarding nitrate accumulation in plant tissues and a critical examination of the genetic, agroenvironmental and postharvest factors that can modulate nitrate levels in a wide range of horticultural crops are provided.
170 citations
TL;DR: This review presents current knowledge of physiological, metabolic and genetic factors influencing nitrogen uptake and utilization in the context of different nitrogen management systems and the role of root system and its interactions with microorganisms, nitrate assimilation and its relationship with photosynthesis as postanthesis remobilization and nitrogen partitioning.
Abstract: Nitrogen fertilizer is the most used nutrient source in modern agriculture and represents significant environmental and production costs. In the meantime, the demand for grain increases and production per area has to increase as new cultivated areas are scarce. In this context, breeding for an efficient use of nitrogen became a major objective. In wheat, nitrogen is required to maintain a photosynthetically active canopy ensuring grain yield and to produce grain storage proteins that are generally needed to maintain a high end-use quality. This review presents current knowledge of physiological, metabolic and genetic factors influencing nitrogen uptake and utilization in the context of different nitrogen management systems. This includes the role of root system and its interactions with microorganisms, nitrate assimilation and its relationship with photosynthesis as postanthesis remobilization and nitrogen partitioning. Regarding nitrogen-use efficiency complexity, several physiological avenues for increasing it were discussed and their phenotyping methods were reviewed. Phenotypic and molecular breeding strategies were also reviewed and discussed regarding nitrogen regimes and genetic diversity.
144 citations
TL;DR: Results indicate that GS1;2 and NADH-GOGAT1 are important in the primary assimilation of NH4 (+) taken up by rice roots and these two enzymes could be important in remobilization of nitrogen during natural senescence.
Abstract: The functions of the three isoenzymes of cytosolic glutamine synthetase (GS1;1, GS1;2, and GS1;3) and two NADH-glutamate synthases (NADH-GOGAT1 and NADH-GOGAT2) in rice (Oryza sativa L.) were characterized using a reverse genetics approach and spatial expression of the corresponding genes. OsGS1;2 and OsNADH-GOGAT1 were mainly expressed in surface cells of rice roots in an NH4 (+)-dependent manner. Disruption of either gene by the insertion of endogenous retrotransposon Tos17 caused reduction in active tiller number and hence panicle number at harvest. Re-introduction of OsGS1;2 cDNA under the control of its own promoter into the knockout mutants successfully restored panicle number to wild-type levels. These results indicate that GS1;2 and NADH-GOGAT1 are important in the primary assimilation of NH4 (+) taken up by rice roots. OsGS1;1 and OsNADH-GOGAT2 were mainly expressed in vascular tissues of mature leaf blades. OsGS1;1 mutants showed severe reduction in growth rate and grain filling, whereas OsNADH-GOGAT2 mutants had marked reduction in spikelet number per panicle. Complementation of phenotypes seen in the OsGS1;1 mutant was successfully observed when OsGS1;1 was re-introduced. Thus, these two enzymes could be important in remobilization of nitrogen during natural senescence. Metabolite profiling data showed a crucial role of GS1;1 in coordinating metabolic balance in rice. Expression of OsGS1:3 was spikelet-specific, indicating that it is probably important in grain ripening and/or germination. Thus, these isoenzymes seem to possess distinct and non-overlapping functions and none was able to compensate for the individual function of another.
110 citations
Cites background from "Do plants need nitrate? The mechani..."
...Although most plants grown in oxidative upland fields utilize NO3 – as an inorganic nitrogen source (Andrews et al., 2013), rice (Oryza sativa L....
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TL;DR: The efficiency of crop production is defined in thermodynamic terms as the ratio of energy output (carbohydrate) to energy input (solar radiation). Temperature and water supply are the main climatic constraints on efficiency as mentioned in this paper.
Abstract: The efficiency of crop production is defined in thermodynamic terms as the ratio of energy output (carbohydrate) to energy input (solar radiation). Temperature and water supply are the main climatic constraints on efficiency. Over most of Britain, the radiation and thermal climates are uniform and rainfall is the main discriminant of yield between regions. Total production of dry matter by barley, potatoes, sugar beet, and apples is strongly correlated with intercepted radiation and these crops form carbohydrate at about 1.4 g per MJ solar energy, equivalent to 2.4% efficiency. Crop growth in Britain may therefore be analysed in terms of ( a ) the amount of light intercepted during the growing season and ( b ) the efficiency with which intercepted light is used. The amount intercepted depends on the seasonal distribution of leaf area which, in turn, depends on temperature and soil water supply. These variables are discussed in terms of the rate and duration of development phases. A factorial analysis of efficiency shows that the major arable crops in Britain intercept only about 40 % of annual solar radiation and their efficiency for supplying energy through economic yield is only about 0.3%. Some of the factors responsible for this figure are well understood and some are immutable. More work is needed to identify the factors responsible for the large differences between average commercial and record yields.
3,304 citations
TL;DR: The results from this review may provide the most plausible estimates of how plants in their native environments and field-grown crops will respond to rising atmospheric [CO(2)]; but even with FACE there are limitations, which are discussed.
Abstract: Contents
Summary 1
I. What is FACE? 2
II. Materials and methods 2
III. Photosynthetic carbon uptake 3
IV. Acclimation of photosynthesis 6
V. Growth, above-ground production and yield 8
VI. So, what have we learned? 10
Acknowledgements 11
References 11
Appendix 1. References included in the database for meta-analyses 14
Appendix 2. Results of the meta-analysis of FACE effects 18
Summary
Free-air CO2 enrichment (FACE) experiments allow study of the effects of elevated [CO2] on plants and ecosystems grown under natural conditions without enclosure. Data from 120 primary, peer-reviewed articles describing physiology and production in the 12 large-scale FACE experiments (475–600 ppm) were collected and summarized using meta-analytic techniques. The results confirm some results from previous chamber experiments: light-saturated carbon uptake, diurnal C assimilation, growth and above-ground production increased, while specific leaf area and stomatal conductance decreased in elevated [CO2]. There were differences in FACE. Trees were more responsive than herbaceous species to elevated [CO2]. Grain crop yields increased far less than anticipated from prior enclosure studies. The broad direction of change in photosynthesis and production in elevated [CO2] may be similar in FACE and enclosure studies, but there are major quantitative differences: trees were more responsive than other functional types; C4 species showed little response; and the reduction in plant nitrogen was small and largely accounted for by decreased Rubisco. The results from this review may provide the most plausible estimates of how plants in their native environments and field-grown crops will respond to rising atmospheric [CO2]; but even with FACE there are limitations, which are also discussed.
3,140 citations
TL;DR: In this article, the authors quantified the biomass allocation patterns to leaves, stems and roots in vegetative plants, and how this is influenced by the growth environment, plant size, evolutionary history and competition.
Abstract: Contents
Summary 30
I. Allocation in perspective 31
II. Topics of this review 32
III. Methodology 32
IV. Environmental effects 33
V. Ontogeny 36
VI. Differences between species 40
VII. Physiology and molecular regulation 41
VIII. Ecological aspects 42
IX. Perspectives 45
Acknowledgements 45
References 45
Appendices A1–A4 49
Summary
We quantified the biomass allocation patterns to leaves, stems and roots in vegetative plants, and how this is influenced by the growth environment, plant size, evolutionary history and competition. Dose–response curves of allocation were constructed by means of a meta-analysis from a wide array of experimental data. They show that the fraction of whole-plant mass represented by leaves (LMF) increases most strongly with nutrients and decreases most strongly with light. Correction for size-induced allocation patterns diminishes the LMF-response to light, but makes the effect of temperature on LMF more apparent. There is a clear phylogenetic effect on allocation, as eudicots invest relatively more than monocots in leaves, as do gymnosperms compared with woody angiosperms. Plants grown at high densities show a clear increase in the stem fraction. However, in most comparisons across species groups or environmental factors, the variation in LMF is smaller than the variation in one of the other components of the growth analysis equation: the leaf area : leaf mass ratio (SLA). In competitive situations, the stem mass fraction increases to a smaller extent than the specific stem length (stem length : stem mass). Thus, we conclude that plants generally are less able to adjust allocation than to alter organ morphology.
1,959 citations
TL;DR: This review discusses the major themes of NH 4 + toxicity, including the occurrence ofNH 4 + in the biosphere, response differences to NH 4+ nutrition among wild and domesticated species, symptoms and proposed mechanisms underlying toxicity, and means by which it can be alleviated.
1,488 citations
TL;DR: The limiting factors in plant metabolism for maximizing NUE are different at high and low N supplies, indicating great potential for improving the NUE of current cultivars, which were bred in well-fertilized soil.
Abstract: Crop productivity relies heavily on nitrogen (N) fertilization. Production and application of N fertilizers consume huge amounts of energy, and excess is detrimental to the environment; therefore, increasing plant N use efficiency (NUE) is essential for the development of sustainable agriculture. Plant NUE is inherently complex, as each step—including N uptake, translocation, assimilation, and remobilization—is governed by multiple interacting genetic and environmental factors. The limiting factors in plant metabolism for maximizing NUE are different at high and low N supplies, indicating great potential for improving the NUE of current cultivars, which were bred in well-fertilized soil. Decreasing environmental losses and increasing the productivity of crop-acquired N requires the coordination of carbohydrate and N metabolism to give high yields. Increasing both the grain and N harvest index to drive N acquisition and utilization are important approaches for breeding future high-NUE cultivars.
1,382 citations
Additional excerpts
...Also, both root NH4+ and NO3− uptake are carried out by high-affinity transport systems (HATS) and low-affinity transport systems (LATS) (Ludewig et al., 2007; Miller et al., 2007; Kraiser et al., 2011; Xu et al., 2012)....
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...Two forms of NO3− HATS have been described, a constitutive system and an inducible system that is stimulated by NO3− (Miller et al., 2007; Kraiser et al., 2011; Xu et al., 2012)....
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...At the plant level, N use efficiency (NUE) is dependent on N uptake efficiency (N uptake/N available from the soil) and N utilisation efficiency (dry matter or protein yield/N uptake) (Andrews et al., 2004; Hirel et al., 2011; Kant et al., 2011; Lea & Miflin, 2011; Chardon et al., 2012; McAllister et al., 2012; Xu et al., 2012)....
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