Amino acid composition of azolla as affected by strains and population density

The total nitrogen and amino acid composition of seven Azolla strains were compared at four different growth phases. Total nitrogen content of the individual strains ranged from 2.6% to 5.7% of dry matter and was not significantly influenced by growth phase or population density. The concentration of the sixteen amino acids determined was maximal during the linear growth stage and specific differences occurred among Azolla strains. AnAzolla microphylla strain was the best source of amino acids and anA. filiculoides strain the poorest under the cultural conditions used. The chemical index score demonstrated the potential of some species, such as theA. microphylla strain, as contributor of protein for animals. Strains of other species, such asA. filiculoides, had several limiting amino acids and appear more suited for use solely as a green manure. All Azolla strains contained a similar proportion of essential (55%) and non-essential (45%) amino acids. Leucine, lysine, arginine and phenylanine+tyrosine were the predominant essential amino acids whereas the sulfur containing amino acids (methionine and cystine) were present in smaller amounts.     

Effects of yeast proteolytic activity on Oenococcus oeni and malolactic fermentation

Alcoholic fermentation of synthetic must was performed using either Saccharomyces cerevisiae or a mutant Deltapep4, which is deleted for the proteinase A gene. Fermentation with the mutant Deltapep4 resulted in 61% lower levels of free amino acids, and in 62% lower peptide concentrations at the end of alcoholic fermentation than in the control. Qualitative differences in amino acid composition were observed. Changes observed in amino acids in peptides were mainly quantitative. After alcoholic fermentation, each medium was inoculated with Oenococcus oeni. Malolactic fermentation in the medium with the Deltapep4 strain took 10 days longer than the control. This difference may have been due to a difference in the nitrogen composition of the two media. Free amino acids and amino acids in peptides were poorly consumed by O. oeni. Thus, the qualitative aspects of nitrogen composition, which depend in part on yeast metabolism, may be a determinant for the optimal growth of O. oeni in wine.     

Cytosolic pyruvate,orthophosphate dikinase functions in nitrogen remobilization during leaf senescence and limits individual seed growth and nitrogen content

The protein content of seeds determines their nutritive value, downstream processing properties and market value. Up to 95% of seed protein is derived from amino acids that are exported to the seed after degradation of existing protein in leaves, but the pathways responsible for this nitrogen metabolism are poorly defined. The enzyme pyruvate,orthophosphate dikinase (PPDK) interconverts pyruvate and phosphoenolpyruvate, and is found in both plastids and the cytosol in plants. PPDK plays a cardinal role in C₄ photosynthesis, but its role in the leaves of C₃ species has remained unclear. We demonstrate that both the cytosolic and chloroplastic isoforms of PPDK are up‐regulated in naturally senescing leaves. Cytosolic PPDK accumulates preferentially in the veins, while chloroplastic PPDK also accumulates in mesophyll cells. Analysis of microarrays and labelling patterns after feeding ¹³C‐labelled pyruvate indicated that PPDK functions in a pathway that generates the transport amino acid glutamine, which is then loaded into the phloem. In Arabidopsis thaliana, over‐expression of PPDK during senescence can significantly accelerate nitrogen remobilization from leaves, and thereby increase rosette growth rate and the weight and nitrogen content of seeds. This indicates an important role for cytosolic PPDK in the leaves of C₃ plants, and allows us to propose a metabolic pathway that is responsible for production of transport amino acids during natural leaf senescence. Given that increased seed size and nitrogen content are desirable agronomic traits, and that efficient remobilization of nitrogen within the plant reduces the demand for fertiliser applications, PPDK and the pathway in which it operates are targets for crop improvement.     

Adjustment of growth and central metabolism to a mild but sustained nitrogen-limitation in Arabidopsis

We have established a simple soil-based experimental system that allows a small and sustained restriction of growth of Arabidopsis by low nitrogen (N). Plants were grown in a large volume of a peat–vermiculite mix that contained very low levels of inorganic N. As a control, inorganic N was added in solid form to the peat–vermiculite mix, or plants were grown in conventional nutrient-rich solids. The low N growth regime led to a sustained 20% decrease of the relative growth rate over a period of 2 weeks, resulting in a two- to threefold decrease in biomass in 35- to 40-day-old plants. Plants in the low N regime contained lower levels of nitrate, lower nitrate reductase activity, lower levels of malate, fumarate and other organic acids and slightly higher levels of starch, as expected from published studies of N-limited plants. However, their rosette protein content was unaltered, and total and many individual amino acid levels increased compared with N-replete plants. This metabolic phenotype reveals that Arabidopsis responds adaptively to low N by decreasing the rate of growth, while maintaining the overall protein content, and maintaining or even increasing the levels of many amino acids.     

NITROGEN LIMITATION EFFECTS OF DIFFERENT NITROGEN SOURCES ON NUTRITIONAL QUALITY OF TWO FRESHWATER ORGANISMS, SCENEDESMUS QUADRICAUDA (CHLOROPHYCEAE) AND SYNECHOCOCCUS SP. (CYANOPHYCEAE)

Food quality for grazers has been related to mineral (nitrogen, phosphorus) and biochemical (amino acids, fatty acids) constituents. The aim of the study was to examine the influence of different nitrogen sources on these constituents in two organisms, the green alga Scenedesmus quadricauda Turp. and the cyanobacterium Synechococcus sp., commonly used in feeding experiments. The two organisms were grown in continuous cultures at different growth rates. Nitrate or ammonium salts were used as nitrogen sources under both replete and limited conditions. Carbon content (mg·g⁻¹ dry weight) was stable in both organisms independent of nitrogen source, nitrogen limitation, and growth rate. Nitrogen content decreased with limitation and growth rate in Scenedesmus and to a lesser degree in Synechococcus , whereas changes in phosphorus content were not statistically significant. The relative proportions of amino acids (% of total amino acids) were relatively stable in both organisms, whereas the proportions of fatty acids varied with growth rate and limitation. Fatty acid content was much lower in Synechococcus than in Scenedesmus . At N limitation, polyunsaturated fatty acids (PUFAs) showed lower levels in both organisms. The change occurred in the ω3 PUFA (linolenic acid) of the green alga and in the ω6 PUFA (linoleic acid) of the cyanobacterium. The difference in the response of N limitation in the two organisms may be traced to the different composition of the chloroplast membranes (the prokaryotic way) and the microsomal membranes (the eukaryotic way) where the desaturation takes place.     

不同氮素形态培养下荞麦叶片中草酸积累的变化

用1/5浓度Hoagland(pH6.0)营养液培养荞麦幼苗3d后,取其中一部分继续用此营养液(硝态氮);另一部分用硫酸氨和氯化钙取代硝态氮(氨态氮)的营养液,均培养至荞麦第一片真叶完全展开。结果表明,以氨态氮为唯一氮源培养荞麦时,植株叶片中草酸含量显著下降。进一步研究表明,氨态氮培养下荞麦根中及根分泌草酸的速率也显著下降,结果排除了叶片中草酸含量的下降是由于叶片中草酸向其根系转运或是因为根分泌草酸速率的差异造成的,而可能与其草酸代谢改变有关。氨态氮培养下叶片中与草酸代谢相关的有机酸含量以及相关酶活性也显著下降,这可能意味着荞麦叶片草酸形成积累可能与相关有机酸代谢有关。     

Free amino acid, ammonium and nitrate concentrations in soil solutions of a grazed coastal marsh in relation to plant growth

Soluble free amino acids, ammonium and nitrate ions as sources of nitrogen for plant growth were measured in soils of a coastal marsh grazed by snow geese in Manitoba, Canada. Amounts of nitrogen, primarily ammonium ions, increased in the latter half of the growing season and over winter, but fell to low values early in the growing season. Free amino acid concentrations relative to ammonium concentrations were highest during the period of rapid plant growth in early summer, especially in soils in the intertidal zone, where the median ratio of amino acid nitrogen to ammonium nitrogen was 0·36 and amino acid concentrations exceeded those of ammonium ions in 24% of samples. Amino acid profiles, which were dominated by alanine, proline and glutamic acid, were similar to goose faecal profiles. In a continuous flow hydroponic experiment conducted in the field, growth of the salt‐marsh grass, Puccinellia phryganodes, on glycine was similar to growth on ammonium ions at an equivalent concentration of nitrogen. When supplies of soil inorganic nitrogen are low, amino acids represent a potentially important source of nitrogen for the re‐growth of plants grazed by geese and amino acid uptake may be as high as 57% that of ammonium ions.     

山梨糖发酵产生2—酮基—L—古龙酸氮源代谢规律

对山梨糖发酵产生2-酮基-L-古龙酸氮源代谢规律进行了初步研究。通过对这一混合发酵体系蛋白和尿素代谢的研究表明,氮源代谢与单一菌体发酵相比有其特殊性,主要表现在尿素的加入有两个作用,即作为生理碱性物质调节体系pH和为菌体代谢提供部分氮源,而体系的蛋白含量随发酵时间的延续不断增加,其增加的原因是巨大芽孢杆菌由营养体转变成芽孢所致,这是该发酵体系的特点。本文还对该发酵体系各种氨基酸变化规律进行了讨论,将一共17种氨基酸按其变化规律分成了三类,较好地解释了各种氨基酸的变化情况,为进一步深入研究该体系的动力学特性提供了数据基础。     

Reduced amino acid content in transgenic potato tubers due to antisense inhibition of the leaf H+/amino acid symporter StAAP1

Transport processes across the plasma membrane of leaf vascular tissue are essential for transport and distribution of assimilates. In potato, leaves are the predominant sites for nitrate reduction and amino acid biosynthesis. From there, assimilated amino acids are exported through the phloem to supply tubers with organic nitrogen. To study the role of amino acid transporters in long-distance transport and allocation of organic nitrogen in potato plants, a gene encoding a functional, leaf-expressed amino acid permease StAAP1 was isolated. Similar to the sucrose transporter SUT1, StAAP1 expression was induced during the sink-to-source transition, indicating a role in phloem loading. To test the role of StAAP1, expression was inhibited by an antisense approach. Transgenic plants with reduced StAAP1 expression were phenotypically indistinguishable from wild type, as were photosynthetic capacity and tuber yield. However, tubers from antisense StAAP1 plants showed up to 50% reduction in free amino acid contents. In comparison, starch content was not affected or tended to increase relative to wild type. The reduction in all amino acids except aspartate in the antisense plants is consistent with the properties of amino acid permeases (AAPs) found in heterologous systems. The results demonstrate an important role for StAAP1 in long-distance transport of amino acids and highlight the importance of plasma membrane transport for nutrient distribution in plants.     

不同氮素形态和配比对菘蓝根的生长及含氮成分含量和总量的影响

以来源于安徽亳州、甘肃张掖、安徽阜阳、山西运城和陕西商洛的5个种源菘蓝( Isatis indigotica Fort.)为实验材料,采用田间试验法对不施氮素(对照),仅施用NO3--N(T1)或NH4+-N(T2),混合施用氮素也n(NH4+-N)：n(NO3--N)=75：25(T3)、n(NH4+-N)：n(NO3--N)=50：50(T4)和n(NH4+-N)：n(NO3--N)=25：75(T5)页以及仅施用CO(NH2)2(T6)条件下各种源菘蓝的单株根鲜质量和干质量,根折干率,根中游离总氨基酸、可溶性蛋白质和总氮含量,以及单株根中游离总氨基酸、可溶性蛋白质和总氮总量的差异进行了比较分析。结果表明：在同一施氮条件下不同种源间菘蓝根的各项指标均有一定差异;而与各自的对照相比,不同施氮条件下同一种源菘蓝根的各项指标也有一定差异。总体来看,安徽亳州和山西运城种源菘蓝根的生长指标均在T6组中较高,甘肃张掖种源根的生长指标则在T2组中相对较高,安徽阜阳种源根的生长指标在T5组中最高,陕西商洛种源根的生长指标在T4组中较高。各施氮条件下安徽亳州种源菘蓝的单株根中游离总氨基酸、可溶性蛋白质和总氮总量均低于其对照,并在T6组中相对较高;甘肃张掖和陕西商洛种源根的上述3项指标分别在T2和T3组中最高,而安徽阜阳和山西运城种源根的上述3项指标则分别在T5和T1组中较高。研究结果显示：不同氮素形态和配比对菘蓝根生长和根中含氮成分积累的影响效应存在种源间的差异,并且对同一种源根生长和根中含氮成分积累有益的氮素形态和配比也不同。因此,为了获得高产优质的板蓝根药材,建议在菘蓝的栽培过程中针对不同种源采取适宜的施氮措施,并兼顾生长量和有效成分含量。     

High Nitrogen and Phosphorous Acquisition by Belowground Parts of Caulerpa prolifera (Chlorophyta) Contribute to the Species' Rapid Spread in Ria Formosa Lagoon,Southern Portugal

Despite worldwide proliferation of the genus Caulerpa and subsequent effects on benthic communities, little is known about the nutritional physiology of the Caulerpales. Here, we investigated the uptake rates of ammonium, nitrate, amino acids, and phosphate through the fronds and rhizoids + stolon, the internal translocation of nitrogen, and developed a nitrogen budget for the rapidly spreading Caulerpa prolifera in Ria Formosa lagoon, southern Portugal. Caulerpa prolifera acquired nutrients by both aboveground and belowground parts at similar rates, except nitrate, for which fronds showed 2-fold higher uptake rates. Ammonium was the preferential nitrogen source (81% of the total nitrogen acquisition), and amino acids, which accounted for a significant fraction of total N acquisition (19%), were taken up at faster rates than nitrate. Basipetal translocation of ¹⁵N incorporated as ammonium was nearly 3-fold higher than acropetal translocation, whereas ¹⁵N translocation as nitrate and amino acids was smaller but equal in either direction. The estimated total nitrogen acquisition by C. prolifera was 689 μmol · m⁻² · h⁻¹, whereas the total nitrogen requirement for growth was 672 μmol · m⁻² · h⁻¹. The uptake of ammonium and amino acids by belowground parts accounted for the larger fraction of the total nitrogen acquisition of C. prolifera and is sufficient to satisfy the species nitrogen requirements for growth. This may be one reason explaining the fast spreading of the seaweed in the bare sediments of Ria Formosa where it does not have any macrophyte competitors and the concentration of nutrients is high.     

耕作方式及施氮量对砂姜黑土区小麦氮代谢及籽粒产量和蛋白质含量的影响

为明确砂姜黑土区小麦(Triticum aestivum)产量和品质形成的耕作方式及施氮量最优组合, 在大田试验条件下, 以深松、旋耕和常规耕作3种耕作方式为主区, 0、120、225、330 kg·hm^-2 4个施氮量为副区, 研究了不同耕作方式及施氮量组合对小麦拔节后氮代谢、籽粒产量和蛋白质含量的影响。结果表明, 随着生育期的推进, 叶片谷氨酰胺合成酶活性、游离氨基酸含量和可溶性蛋白含量均呈先升后降的趋势, 深松方式配合中高氮处理的峰值在花后10天, 而常规耕作和旋耕的4个施氮处理以及深松的低氮处理峰值多在开花期。与常规耕作和旋耕相比, 深松耕作显著降低了10-40 cm的土壤容重, 提高了土壤总空隙度和根干质量, 有利于中后期根系氮素吸收。耕作方式和施氮量对籽粒产量和蛋白质含量影响显著, 均以深松方式最高。3种耕作方式下小麦产量和蛋白质含量均随施氮量增加而增加, 籽粒产量以深松方式配合330 kg·hm^-2施氮量最高, 而常规耕作和旋耕方式的产量在施氮量为225 kg·hm^-2时达到最大。3种耕作方式下籽粒蛋白质含量均以施氮225 kg·hm^-2最高。因此, 在砂姜黑土区宜采用深松耕作方式配合适宜的施氮量, 以改善土壤条件, 促进根系氮素吸收, 延长叶片功能期, 达到产量与蛋白品质提升之目的。     

Nitrogen nutrition and regulation of cephalosporin production in Streptomyces clavuligerus.

When used as sole nitrogen source, certain amino acids (e.g., proline, asparagine) supported both growth and sporulation by Streptomyces clavuligerus streaked onto solid defined medium. Ammonium supported growth but suppressed sporulation. Amino nitrogen was best for cephalosporin production in liquid defined medium, although urea was almost as useful. A comparison of amino acids showed asparagine and glutamine to be the best nitrogen sources and arginine to be almost as good. Ammonium salts supported a somewhat lower growth rate than asparagine, but antibiotic production was very poor on these inorganic nitrogen sources. Addition of ammonium to asparagine did not affect growth rate but increased mycelial mass; cephalosporin production was reduced by about 75%. Antibiotic production was more closely associated with growth in the absence of ammonium than in its presence, indicating a strong inhibitory and (or) repressive effect of NH4+ on antibiotic production. Ammonium exerted its negative effect when added at 24h or earlier, i.e. before antibiotic formation began.     

Effect of growth conditions on accumulation of internal nitrate,ammonium, amino acids,and protein in three marine diatoms

The capacity of marine phytoplankton to change their cellular content of nitrate, ammonium, amino acids, and protein in response to different growth conditions was systematically investigated. Cellular concentrations of these compounds were measured in N-starved, N-deficient, and N-sufficient Skeletonema costatum (Grev.) Cleve and in N-deficient Chaetoceros debilis Cleve and Thalassiosira gravida Cleve, both before and after the addition of a pulse of nitrogen.N-sufficient Skeletonema costatum contains high concentrations of protein, large persistent pools of amino acids, and, if it is growing on nitrate, sizeable amounts of nitrate. As it becomes N-starved, the total cellular nitrogen decreases, the internal nitrate and amino acids become entirely depleted, and the protein content is drastically reduced. After nitrogen additions to N-deficient and N-starved cultures, transient pools of unassimilated nitrogen form which can account for a large fraction of newly taken up nitrogen. The size and kind of pool which accumulates is determined by the preconditioning of the cells, the nitrogen compound which is added, and the species identity. The pools which form in S. costatum indicate that nitrate reduction is the slowest step in nitrogen assimilation, the synthesis of protein from amino acids is the next slowest, and the incorporation of ammonium into amino acid is the fastest. However, the rate limiting steps may vary between diatom species.For the first time, measurements of the variation in cellular nitrogen compounds over a wide range of environmental conditions reveal the ability of some phytoplankton to buffer the effects of a changing, and sometimes growth-limiting, nitrogen supply. They accomplish this by utilizing stored internal nitrogen for growth when the external supply is low and by quickly storing unassimilated nitrogen when the external supply is suddenly increased beyond their ability to immediately assimilate it. The accumulation of large pools of unassimilated nitrogen compounds can explain the often observed difference between nitrogen uptake rates and growth rates.     

Amino acid uptake systems in Bacteroides ruminicola

Uptake of amino acids by Bacteroides ruminicola was observed in cells grown in a complete defined medium, containing ammonia as the nitrogen source. A high rate of uptake occurred only in fresh medium, as an inhibitory substance, possibly acetate, apparently accumulated during growth. All amino acids except proline were taken up and incorporated into cold trichloroacetic acid precipitable material. Different patterns of incorporation and different responses to 2,4-dinitrophenol and potassium ferricyanide indicated multiple uptake systems were involved. Kinetic inhibition patterns suggested six distinct systems were present for amino acid uptake, with specificities related to the chemical structures of the amino acids. Thus, the failure of free amino acids to act as sole nitrogen sources for growth of B. ruminicola is not due to the absence of transport systems for these compounds.     

Variation in rates of nitrogen fixation in termites: response to dietary nitrogen in the field and laboratory

Abstract. Termites contribute nitrogen to their habitat through the nitrogenase activity of their bacterial symbionts. Previous studies indicate that high levels of dietary nitrogen suppress nitrogen fixation in termites. We examined the effects of dietary nitrogen on fixation rates in termites in both field and laboratory experiments. Ten field cplonies of Reticulitermes were collected and assayed for nitrogenase activity in July 1993, October 1993, January 1994, and April 1994. The nitrogen content of the wood collected with each colony was determined. There was no correlation between termite nitrogen fixation rates and the amount of nitrogen in their food for any of the four collection periods. In laboratory experiments, nitrogen fixation rates decreased when termites were fed filter paper treated with 2% and 5% ammonium nitrate or a 5% mixture of the amino acids proline, tryptophan and leucine, compared to water-treated controls. By contrast, the nitrogenase activity of termites fed filter paper treated with 2% and 5% ammonium phosphate, a mixture of the amino acids histidine, serine and aspartic acid, or 2% and 5% urea did not differ from the controls. However, nitrogenase activity increased when termites were fed with 2% uric acid. No clear association exists between termite nitrogen fixation and the nitrogen content of their food.     

Nitrogen partitioning and blood meal utilization by Aedes aegypti (Diptera Culicidae)

The utilization of the blood meal by mosquitoes was investigated by first feeding females quantities of blood ranging from 1 to 5 mg, and then analyzing the faeces for the various by-products of protein catabolism that were subsequently eliminated. The nitrogeneous waste products in order of importance were uric acid, histidine, ammonia and arginine. Only traces of the other amino acids were excreted.The total amount of each faecal substance varied linearly with the quantity of blood ingested, however their relative proportions did not change. Regardless of blood meal size the quantily of uric acid and ammonia produced indicates that about 80% of the non-histidine and arginine amino acids are deaminated and utilized for metabolic purposes other than egg protein synthesis.Most of the histidine and about one half of the arginine content of the blood were excreted as free amino acids, but the other amino acids were lost in trace amounts.Nineteen per cent of the total ingested amino acids was incorporated into soluble yolk proteins and this proportion was constant even for small blood meals that result in a reduction in the numbers of eggs produced.The comparative aspects of nitrogen partitioning and blood meal utilization by haematophagous insects, as well as the factors that affect blood meal utilization and fecundity in A. aegypti are discussed.     

Nutrition and growth of coniferous seedlings at varied relative nitrogen addition rate

The growth of two provenances of Pinus sylvestris L. were compared with two provenances of Picea abies (L.) Karst. and with Pinus contorta Dougl. when grown in solution cultures with low nutrient concentrations. Nitrogen was added at different exponentially increasing rates, and the other nutrients were added at a rate high enough to ensure free access of them to the seedlings. During an initial period of the culture (a lag phase), when the internal nutrient status was changing from optimum to the level of the treatment, deficiency symptoms appeared. The needles yellowed and the root/shoot ratio increased. The initial phase was followed by a period of exponential growth and steady-state nutrition. The needles turned green again, and the root/shoot ratio stabilized at a level characteristic of the treatment. These patterns were the same as previously reported for other tree species. The relative growth rate during exponential growth was numerically closely equal to the relative nitrogen addition rate. The maximum relative growth rates were about 6 to 7.5% dry weight increase day^-1. This is a much lower maximum than for broad-leaved species (about 20 to 30% day^-1) under similar growth conditions. The internal nitrogen concentrations of the seedlings and the relative growth rates were stable during the exponential period. Close linear relationships were found between these parameters and the relative addition rate up to maximum growth. During steady state the relative growth rates of the different plant parts were equal. However, there were large differences between genotypes in absolute root growth rate at the same seedling size because of differences in root/shoot ratio. Lodgepole pine had the highest root growth rate, whereas that of Norway spruce, especially the southern provenance, was remarkably low. Yet, Norway spruce had a high ability to utilize available nutrients. In treatments with free nutrient access, growth allocation to the shoot had a high priority in all genotypes, but there was still a marked tendency for luxury uptake of nutrients. Nitrogen productivity (growth rate per unit of nitrogen) was lower than in broadleaved species and highest in lodgepole pine. The relevance of the dynamic factors, i.e. maximum relative growth rate, nutrient uptake rate, nitrogen productivity, growth allocation and root growth rate, are discussed with regard to conifer characteristics and selection value.     

Regrowth dynamics of <Emphasis Type="Italic">Calamagrostis epigejos</Emphasis> after defoliation as affected by nitrogen availability

Young plants of a rhizomatous grass Calamagrostis epigejos (L.) Roth were grown from seed in nutrient solutions containing nitrogen in concentrations 0.1, 1.0, and 10 mM. After six weeks of cultivation the plants were defoliated and changes in growth parameters and in content of storage compounds were measured in the course of regrowth under highly reduced nitrogen availability. Plants grown at higher nitrogen supply before defoliation had higher amount of all types of nitrogen storage compounds (nitrates, free amino acids, soluble proteins), which was beneficial for their regrowth rate, in spite of lower content of storage saccharides. Amino acids and soluble proteins from roots and stubble bases were the most important sources of storage compounds for regrowth of the shoot. Faster growth of plants with higher N content was mediated by greater leaf area expansion and greater number of leaves. In plants with lower contents of N compounds number of green leaves decreased after defoliation significantly and senescing leaves presumably served as N source for other growing organs. Results suggest that internal N reserves can support regrowth of plants after defoliation even under fluctuating external N availability. Faster regrowth of C. epigejos with more reserves was mediated mainly by changes in plant morphogenesis.     

The carbon bonus of organic nitrogen enhances nitrogen use efficiency of plants

The importance of organic nitrogen (N) for plant nutrition and productivity is increasingly being recognized. Here we show that it is not only the availability in the soil that matters, but also the effects on plant growth. The chemical form of N taken up, whether inorganic (such as nitrate) or organic (such as amino acids), may significantly influence plant shoot and root growth, and nitrogen use efficiency (NUE). We analysed these effects by synthesizing results from multiple laboratory experiments on small seedlings (Arabidopsis, poplar, pine and spruce) based on a tractable plant growth model. A key point is that the carbon cost of assimilating organic N into proteins is lower than that of inorganic N, mainly because of its carbon content. This carbon bonus makes it more beneficial for plants to take up organic than inorganic N, even when its availability to the roots is much lower – up to 70% lower for Arabidopsis seedlings. At equal growth rate, root:shoot ratio was up to three times higher and nitrogen productivity up to 20% higher for organic than inorganic N, which both are factors that may contribute to higher NUE in crop production.