Effect of mineral nitrogen on nitrogen nutrition and biomass partitioning between the shoot and roots of pea (Pisum sativum L.).

The effect of mineral N availability on nitrogen nutrition and biomass partitioning between shoot and roots of pea (Pisum sativum L., cv Baccara) was investigated under adequately watered conditions in the field, using five levels of fertiliser N application at sowing (0, 50, 100, 200 and 400 kg N ha^–1). Although the presence of mineral N in the soil stimulated vegetative growth, resulting in a higher biomass accumulation in shoots in the fertilised treatments, neither seed yield nor seed nitrogen concentration was affected by soil mineral N availability. Symbiotic nitrogen fixation was inhibited by mineral N in the soil but it was replaced by root mineral N absorption, which resulted in optimum nitrogen nutrition for all treatments. However, the excessive nitrogen and biomass accumulation in the shoot of the 400 kg N ha^–1 treatment caused crop lodging and slightly depressed seed yield and seed nitrogen content. Thus, the presumed higher carbon costs of symbiotic nitrogen fixation, as compared to root mineral N absorption, affected neither seed yield nor the nitrogen nutrition level. However, biomass partitioning within the nodulated roots was changed. The more symbiotic nitrogen fixation was inhibited, the more root growth was enhanced. Root biomass was greater when soil mineral N availability was increased: root growth was greater and began earlier for plants that received mineral N at sowing. Rooting density was also promoted by increased mineral N availability, leading to more numerous but finer roots for the fertilised treatments. However, the maximum rooting depth and the distribution of roots with depth were unchanged. This suggested an additional direct promoting effect of mineral N on root proliferation.     

Root and nodule growth in Pisum sativum L. in relation to photosynthesis: analysis using 13C-labelling

The effect of the nitrogen source (gaseous nitrogen, N2, or nitrate ions, NO3-) on the use of carbon (C) for root and nodule growth of pea (Pisum sativum L.) was investigated using 13C-labelling of assimilated CO2 at various stages of growth. Nitrate supply and growing conditions (sowing dates, air CO2 concentration) were varied to alter photosynthetic rates. Nodules are the sink with the highest demand for C in both the vegetative and flowering stages, growing at the expense of shoot and root in the vegetative stage, but only at the expense of roots at flowering. Until flowering, the addition of C into root and nodule biomass was linearly related to pre-existing biomass, thus determining net sink strengths which decreased with root and nodule age. Nodule growth patterns did not depend on the N source, whereas root growth was increased by nitrate when nodule biomass was low. At seed filling, the increase in C of biomass of the root system was no longer related to pre-existing biomass and C was preferentially diverted to roots of plants assimilating nitrate, or to nodules for plants fixing N2.     

Genetic variability in nodulation and root growth affects nitrogen fixation and accumulation in pea

BACKGROUND AND AIMS: Legume nitrogen is derived from two different sources, symbiotically fixed atmospheric N(2) and soil N. The effect of genetic variability of root and nodule establishment on N acquisition and seed protein yield was investigated under field conditions in pea (Pisum sativum). In addition, these parameters were related to the variability in preference for rhizobial genotypes. METHODS: Five different spring pea lines (two hypernodulating mutants and three cultivars), previously identified in artificial conditions as contrasted for both root and nodule development, were characterized under field conditions. Root and nodule establishment was examined from the four-leaf stage up to the beginning of seed filling and was related to the patterns of shoot dry matter and nitrogen accumulation. The genetic structure of rhizobial populations associated with the pea lines was obtained by analysis of nodule samples. The fraction of nitrogen derived from symbiotic fixation was estimated at the beginning of seed filling and at physiological maturity, when seed protein content and yield were determined. KEY RESULTS: The hypernodulating mutants established nodules earlier and maintained them longer than was the case for the three cultivars, whereas their root development and nitrogen accumulation were lower. The seed protein yield was higher in 'Athos' and 'Austin', the two cultivars with increased root development, consistent with their higher N absorption during seed filling. CONCLUSION: The hypernodulating mutants did not accumulate more nitrogen, probably due to the C cost for nodulation being higher than for root development. Enhancing exogenous nitrogen supply at the end of the growth cycle, by increasing the potential for root N uptake from soil, seems a good option for improving pea seed filling.     

The effect of nitrogen nutrition on cluster root formation and proton extrusion by Lupinus albus

Nitrogen nutrition can influence cluster root formation in many wild species, but the effect of N form on cluster root formation and root exudation by white lupin is not known. In a solution culture study, we examined the effect of N nutrition (ammonium, nitrate, both or N2 fixation) on cluster root formation and H+ extrusion by white lupin plants under deficient and adequate P supply. The number of cluster roots increased greatly when plants were supplied with I microM P compared with 50 microM P, the increase being 7.8-fold for plants treated with (NH4)2SO4, 3-fold for plants treated with KNO3 and NH4NO3, and 2-4-fold for N2-fixing plants. Under P deficiency. NH4+-N supply resulted in production of a greater number and biomass of cluster roots than other N sources. Dry weight of cluster roots was 30 % higher than that of non-cluster roots in P-deficient plants treated with (NH4)2SO4 and NH4NO3. In plants treated with sufficient P (50 microM), the weight of non-cluster roots was approx. 90 % greater than that of cluster roots. Both total (micromol per plant h(-1)) and specific (micromol g(-1) root d. wt h(-1)) H+ extrusions were greatest from roots of plants supplied with (NH4)2SO4, followed by those supplied with NH4NO3 and N2 fixation, whereas plants receiving KNO3 had negative net H+ extrusion between the third and fifth week of growth (indicating uptake of protons or release of OH- ions). The rate of proton extrusion by NH4+-N-fed plants was similar under P-deficient and P-sufficient conditions. In contrast, proton exudation by N2-fixing plants and KNO3-treated plants was ten-fold greater under P deficiency than under P sufficiency. In comparison with P deficiency, plants treated with 50 microM P had a significantly higher concentration of P in roots, shoots and youngest expanded leaves (YEL). Compared with the N2 fixation and KNO3 treatments, total N concentration was highest in roots, shoots and YEL of plants supplied with (NH4)2SO4 and NH4NO3, regardless of P supply. Under P deficiency, K concentrations in roots decreased at all N supplies, especially in plants treated with (NH4)2SO4 and NH4NO3, which coincided with the greatest H+ extrusion at these P and N supplies. In conclusion, NH4-N nutrition stimulated cluster root formation and H+ extrusion by roots of P-deficient white lupin.     

Plant phenology and genetic variability in root and nodule development strongly influence genetic structuring of Rhizobium leguminosarum biovar viciae populations nodulating pea

The symbiotic relationships between legumes and their nitrogen (N(2))-fixing bacterial partners (rhizobia) vary in effectiveness to promote plant growth according to both bacterial and legume genotype. To assess the selective effect of host plant on its microsymbionts, the influence of the pea (Pisum sativum) genotype on the relative nodulation success of Rhizobium leguminosarum biovar viciae (Rlv) genotypes from the soil populations during plant development has been investigated. Five pea lines were chosen for their genetic variability in root and nodule development. Genetic structure and diversity of Rlv populations sampled from nodules were estimated by molecular typing with a marker of the genomic background (rDNA intergenic spacer) and a nodulation gene marker (nodD region). Differences were found among Rlv populations related to pea genetic background but also to modification of plant development caused by single gene mutation. The growth stage of the host plant also influenced structuring of populations. A particular nodulation genotype formed the majority of nodules during the reproductive stage. Overall, modification in root and nodule development appears to strongly influence the capacity of particular rhizobial genotypes to form nodules.     

Seasonal patterns of 13C partitioning between shoots and nodulated roots of N2- or nitrate-fed Pisum sativum L

The effect of nitrogen source (N(2) or nitrate) on carbon assimilation by photosynthesis and on carbon partitioning between shoots and roots was investigated in pea (Pisum sativum L. 'Baccara') plants at different growth stages using (13)C labelling. Plants were grown in the greenhouse on different occasions in 1999 and 2000. Atmospheric [CO(2)] and growth conditions were varied to alter the rate of photosynthesis. Carbon allocation to nodulated roots was unaffected by N source. At the beginning of the vegetative period, nodulated roots had priority for assimilates over shoots; this priority decreased during later stages and became identical to that of the shoot during seed filling. Carbon allocation to nodulated roots was always limited by competition with shoots, and could be predicted for each phenological stage: during vegetative and flowering stages a single, negative exponential relationship was established between sink intensity (percentage of C allocated to the nodulated root per unit biomass) and net photosynthesis. At seed filling, the amount of carbon allocated to the nodulated root was directly related to net photosynthesis. Respiration of nodulated roots accounted for more than 60 % of carbon allocated to them during growth. Only at flowering was respiration affected by N supply: it was significantly higher for strictly N(2)-fixing plants (83 %) than for plants fed with nitrate (71 %). At the vegetative stage, the increase in carbon in nodulated root biomass was probably limited by respiration losses.     

Quantitative effects of soil nitrate,growth potential and phenology on symbiotic nitrogen fixation of pea (Pisum sativum L.)

The influence of soil nitrate availability, crop growth rate and phenology on the activity of symbiotic nitrogen fixation (SNF) during the growth cycle of pea (Pisum sativum cv. Baccara) was investigated in the field under adequate water availability, applying various levels of fertiliser N at the time of sowing. Nitrate availability in the ploughed layer of the soil was shown to inhibit both SNF initiation and activity. Contribution of SNF to total nitrogen uptake (%Ndfa) over the growth cycle could be predicted as a linear function of mineral N content of the ploughed layer at sowing. Nitrate inhibition of SNF was absolute when mineral N at sowing was over 380 kg N ha^–1. Symbiotic nitrogen fixation was not initiated unless nitrate availability in the soil dropped below 56 kg N ha^–1. However, SNF could no longer be initiated after the beginning of seed filling (BSF). Other linear relationships were established between instantaneous %Ndfa and instantaneous nitrate availability in the ploughed layer of the soil until BSF. Instantaneous %Ndfa decreased linearly with soil nitrate availability and was nil above 48 and 34 kg N ha^–1 for the vegetative and reproductive stages, respectively, levels after which no SNF occurred. Moreover, SNF rate was shown to be closely related to the crop growth rate until BSF. The ratio of SNF rate over crop growth rate decreased linearly with thermal time. Maximum SNF rate was about 40 mg N m^–2 degree-day^–1, equivalent to 7 kg N ha^–1, regardless of the N treatment. From BSF to the end of the growth cycle, the high N requirements of the crop were supported by both SNF and nitrate root absorption but, of the two sources, nitrate root absorption seemed to be less affected by the presence of reproductive organs. However, since soil nitrate availability was low at the end of the growth cycle, SNF was the main source of nitrogen acquisition. The onset of SNF decrease at the end of the growth cycle seemed to be first due to nodule age and then associated to the slowing of the crop growth rate.     

Biological nitrogen fixation: Investments,expectations and actual contributions to agriculture

Inputs of biologically fixed N into agricultural systems may be derived from symbiotic relationships involving legumes and Rhizobium spp., partnerships between plants and Frankia spp. or cyanobacteria, or from non-symbiotic associations between free-living diazotrophs and plant roots. It is assumed that these N₂-fixing systems will satisfy a large portion of their own N requirements from atmospheric N₂, and that additional fixed N will be contributed to soil reserves for the benefit of other crops or forage species. This paper reviews the actual levels of N₂ fixation attained by legume and non-legume associations and assesses their role as a source of N in tropical and sub-tropical agriculture. We discuss factors influencing N₂ fixation and identify possible strategies for improving the amount of N₂ fixed.     

Role of oxygen limitation and nitrate metabolism in the nitrate inhibition of nitrogen fixation by pea

The impact of nitrate (5–15 m M , 2 to 7 days) on nitrogenase activity and nodule-oxygen limitation was investigated in nodulated, 21-day-old plants of a near-isogenic nitrate reductase-deficient pea mutant (A3171) and its wild-type parent ( Pisum sativum L. cv. Juneau). Within 2 days, 10 or 15 m M nitrate, but not 5 m M nitrate, inhibited the apparent nitrogenase activity (measured as in situ hydrogen evolution from nodules of intact plants) of wild-type plants; none of these nitrate levels inhibited the apparent nitrogenase activity of A3171 plants. Nodule-oxygen limitation, measured as the ratio of total nitrogenase activity to potential nitrogenase activity, was increased in both wild-type and A3171 plants by all nitrate treatments. By 3 to 4 days the apparent nitrogenase activity of A3171 and wild-type plants supplied with 5 m M nitrate declined to 53 to 69% of control plants not receiving nitrate. By 6 to 7 days the apparent nitrogenase activity of A3171 plants was similar to the control value whereas that of the wild-type plants continued to decline. From 3 to 7 days, no significant differences in nodule-oxygen limitation were observed between the nitrate (5 m M ) and control treatments. The results are interpreted as evidence for separate mechanisms in the initial (O₂ limitation) and longer-term (nitrate metabolism) effects of nitrate on nitrogen fixation by effectively nodulated pea.     

Seasonal patterns of growth and nitrogen fixation in field-grown pea

The seasonal patterns of growth and symbiotic N₂ fixation under field conditions were studied by growth analysis and use of¹⁵N-labelled fertilizer in a determinate pea cultivar (Pisum sativum L.) grown for harvest at the dry seed stage. The patterns of fertilizer N-uptake were almost identical in pea and barley (the non-fixing reference crop), but more fertilizer-N was recovered in barley than in pea. The estimated rate of N₂ fixation in pea gradually increased during the pre-flowering and flowering growth stages and reached a maximum of 10 kg N fixed per ha per day nine to ten weeks after seedling emergence. This was the time of early pod-development (flat pod growth stage) and also the time for maximum crop growth rate and maximum green leaf area index. A steep drop in N₂ fixation rate occurred during the following week. This drop was simultaneous with lodging of the crop, pod-filling (round pod growth stage) and the initiation of mobilization of nitrogen from vegetative organs. The application of fertilizer-N inhibited the rate of N₂ fixation only during that period of growth, when the main part of fertilizer-N was taken up and shortly after. Total accumulation of fixed nitrogen was estimated to be 244, 238 and 213 kg N ha⁻¹ in pea supplied with nil, 25 or 50 kg NO ₃ ⁻ −N ha⁻¹, respectively. About one-fourth of total N₂ fixation was carried out during preflowering, one fourth during the two weeks of flowering and the remainder during post-flowering. About 55% of the amount of N present in pods at maturity was estimated to be derived from mobilization of N from vegetative organs. “Starter” N (25 or 50 kg NO ₃ ⁻ −N ha⁻¹) did not significantly influence either dry matter and nitrogen accumulation or the development of leaf area. Neither root length and root biomass determined 8 weeks after seedling emergence nor the yield of seed dry matter and nitrogen at maturity were influenced by fertilizer application.     

Gene centres,a source for genetic variants in symbiotic nitrogen fixation: The symbiotic response of the cultivated pea toRhizobium leguminosarum strains from Europe and the Middle East

Summary Soil samples from several European countries; Sweden, the Netherlands, Spain, Italy and Greece, contained rhizobial populations capable of forming an effective symbiosis with the cultivated pea cv. Rondo from the Netherlands. The range of variation among the European Rhizobium strains, as expressed on pea cv. Rondo, was not so large and almost the same variation could be found within the rhizobial population within each country. Superior Rhizobium strains for the Dutch pea were not restricted to soils from the Netherlands but were also found in those from Sweden and Italy.Soils from Turkey and Israel also contained Rhizobium strains capable of nodulating pea cv. Rondo. However, the genetic variation among these Middle East Rhizobium strains was much larger than that of the European strains. When tested on pea cv. Rondo the majority of the Middle East strains belonged to the medium or low effective classes and only a few strains were comparable with European Rhizobium strains.Dutch Rhizobium strains induced effective nodules on both the Dutch pea cv. Rondo and the Swedish cv. L 110. However, in association with a Turkish Rhizobium strain effective nodules were formed on pea cv. Rondo and ineffective nodules on cv. L 110.We suggest that the genetic uniformity of EuropeanR. leguminosarum strains is the result of selection and domestication of Rhizobium strains originally derived from the gene centres of the pea plant.     

外源氮对沼泽湿地CH4和N2O通量的影响

三江平原沼泽湿地受到大气沉降、地表径流、农业排水等外源氮素的输入,对湿地生态系统CH₄和N₂O通量有重要影响。采用野外原位施肥试验模拟外源氮输入,设0,60,120,240kgN•hm^-2 4种试验处理,探讨外源氮对沼泽湿地CH₄和N₂O通量的影响。结果表明,外源氮促进了CH₄和N₂O排放。与对照处理比较,各施氮水平CH₄平均排放通量分别增加了181％,254％和155％,N2O排放通量分别增加了21％,100％和533％。外源氮输入对CH₄排放的季节变化形式影响不大,而N²O的季节变化形式随着氮输入表现出波动变化的趋势。不同施氮水平对CH₄排放的促进作用与植物生长阶段和产CH₄的微生物过程密切相关,N₂O排放通量随氮输入量呈指数增加（R²＝0.97,p<0.01）。外源氮通过影响湿地微生物过程来进一步影响CH₄和N₂O的排放。     

Crop residue application increases nitrogen fixation and dry matter production in groundnut (Arachis hypogaea L.) grown on an acid sandy soil in Niger,West Africa

Field experiments were conducted during the rainy reasons of 1989, 1990 and 1991 on an acid sandy soil in Niger, West Africa, to assess the effect of millet straw application (+CR) on growth and N₂ fixation of groundnut (Arachis hypogaea L.).Three years of +CR (4 t ha^–1 yr^–1) increased symbiotic N₂ fixation, total dry matter production (haulm plus pods) by 83% and total nitrogen (N) accumulation by 100%. Concentration of N in the shoot dry matter and total N in the soil were only slightly affected by the +CR treatment.Crop residue application increased the concentration of potassium (K) and molybdenum (Mo) and decreased the concentrations of aluminium (Al) and manganese (Mn) distinctly, both in the plant (shoot and nodule dry matter) and in the soil.The increase in dry matter production and N uptake was mainly due to improved N₂ fixation reflected by enhanced formation and growth of nodules as well as nitrogenase activity. This was attributed to improved chemical soil conditions, particularly to the higher availability of Mo and the lowered content of available Al and Mn.Although with the application of 4 t CR ha^–1, 60 kg K were supplied, increased growth could not be attributed to the additional supply of K.ICRISAT Journal Article No. 1229.ICRISAT Journal Article No. 1229.     

Nitrogen fixation in several grain legume species with contrasting sensitivities to copper nutrition

The nitrogen fixation response to copper nutrition in faba bean, yellow lupin and soybean was studied. Copper nutrition significantly increased the pod yields of all tested grain legumes but faba bean gave the greatest Cu-use efficiency for pod and grain production. The accumulation of dry matter in vegetative parts, nodules, N and leghemoglobin concentration in nodules and nitrogen accumulation in the whole plants were increased by copper supply in faba bean and yellow lupin in contrast with soybean. Cu nutrition significantly increased the Cu concentrations in nodules of all cultivated plants. The differential sensitivity of N₂ fixation in tested grain legume species to copper nutrition could be connected with the level of phenols in nodules and depended on both the host plants and strains of rhizobia, which differ in their ability to produce catechol-like siderophores. Copper requirements by symbiotic N₂ fixation could also depend on the nature of phenols in nodules (presence of o-dihydroxyphenols or number of hydroxyls in molecule).     

Host-genetic control of nitrogen fixation in the legume-Rhizobium symbiosis: complication in the genetic analysis due to maternal effects

Summary In pea cv. Afghanistan a recessive gene sym 6 prevents the full expression of nitrogenase activity in root nodules, induced byRhizobium leguminosarum strain F 13. In contrast, nitrogenase activity is fully expressed in pea cv. Iran. A comparison of the reciprocal hybrids of these two plants showed that the size of the plant was determined by the mother plant (maternal effect). Therefore the shoot weight and the total amount of nitrogen fixed are not suitable as parameters for a genetic analysis. The % nitrogen of the shoot and the specific activity of the nodules per gram of nodules are more reliable, but for practical purposes the specific activity of the nodules expressed per gram of shoot tissue can be used.     

Gene centres,a source for genetic variants in symbiotic nitrogen fixation: Host-induced ineffectivity inPisum sativum ecotype fulvum

Summary Pisum sativum ecotype fulvum forms ineffective nodules with Rhizobium strains, isolated from effective nodules of the cultivated pea in Europe. Rhizobium strains isolated from nodules of fulvum peas in Israel are fully effective on this host plant, but in association with the cultivated pea they induce nodules of poor N₂-fixing activity. The distribution of these fulvum-specific Rhizobium strains is restricted to regions where the fulvum pea occurs naturally. Rhizobium strains from other geographical regions induce mainly ineffective, or partially effective nodules on fulvum plants.A wide genetic variation, with regard to symbiotic response to a standard set of Rhizobium strains, was demonstrated in the fulvum plants collected in Israel. Based on variation in N₂-fixation three groups of plants can be distinguished. These plants offer the possibility for the study of host-genetic control on symbiotic nitrogen fixation.     

The15N methodology in estimating N2 fixation by vetch and pea grown in pure stand or in mixtures with oat

Cereal-legume mixtures are frequently the best management decision for forage production instead of growing crops in pure stands. Nitrogen fertilization of cereal-legume mixtures is questionable since combined nitrogen could depress N₂ fixation by legumes. The objectives of this study were (1) to examine the effect of N fertilization on N₂ fixation by vetch and field peas in pure and in mixed stands with oats, and (2) to examine if there is any transfer of N from legumes to associated cereals. The field experiment was conducted for two growing seasons. The treatments were pure stands of vetch, pea and oats, and the mixtures of the two legumes with oats at the seeding ratios 90:10 and 75:25, fertilized with labelled¹⁵N at the rates of 15 and 90 kg N ha⁻¹. Nitrogen fertilization of 90 kg N ha⁻¹ suppressed N₂ fixation in both legumes grown in pure and in mixed stands. Crops grown in mixtures in many instances had lower atom %¹⁵N excess. Whether this was due to high N₂ fixation in the case of legume and transfer in the case of oat or the differences were due to practical problems of the¹⁵N technique is not clearly shown by the results, so based on the literature the aspect is discussed as well as the precautions which should be considered in using the¹⁵N technique in such studies.     

Assessment of genetic variability for N2 fixation between and within provenances of Leucaena leucocephala and Acacia albida estimated by 15N labelling techniques

Nitrogen fixed in 13 provenances of Acacia albida and 11 isolines of Leucaena leucocephala inoculated with effective Rhizobium strains was measured by ¹⁵N techniques and the total N difference method. In the test soil, on the average, L. leucocephala derived about 65% of its total N from atmospheric N₂ fixation compared to about 20% by A. albida. Significant differences in the percentage of N derived from atmospheric N₂ (% Ndfa) occurred, between provenances or isolines within species. The % Ndfa ranged from 37 to 74% within L. leucocephala and from 6 to 37 within A. albida; (equivalent to 20–50 mg N plant^–1 and 4–37 mg N plant^–1 for the two species over three months, respectively) and was correlated with the nodule mass (r=0.91). The time course of N₂ fixation of three selected provenances (low, intermediate and good fixers) was followed at 12 weekly intervals over a 36 week period. The % Ndfa of all provenances and isolines increased with time; and except for one of the L. leucocephala provenances, % Ndfa was similar within species at the 36 weeks harvest. There was a significant correlation between % Ndfa and the amount of N₂ fixed (r=0.96). Significant interactions occurred between provenances and N treatments and often growth of uninoculated but N fertilized plants was less variable than for inoculated unfertilized plants.     

Contribution of N2 fixing cyanobacteria to rice production: availability of nitrogen from 15N-labelled cyanobacteria and ammonium sulphate to rice

This study investigate the potential contribution of nitrogen fixation by indigenous cyanobacteria to rice production in the rice fields of Valencia (Spain). N₂-fixing cyanobacteria abundance and N₂ fixation decreased with increasing amounts of fertilizers. Grain yield increased with increasing amounts of fertilizers up to 70 kg N ha^-1. No further increase was observed with 140 kg N ha^-1. Soil N was the main source of N for rice, only 8–14% of the total N incorporated by plants derived from ¹⁵N fertilizer. Recovery of applied ¹⁵N-ammonium sulphate by the soil–plant system was lower than 50%. Losses were attributed to ammonia volatilization, since only 0.3–1% of applied N was lost by denitrification. Recovery of ¹⁵N from labeled cyanobacteria by the soil–plant system was higher than that from chemical fertilizers. Cyanobacterial N was available to rice plant even at the tillering stage, 20 days after N application. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrate uptake,nitrate reductase distribution and their relation to proton release in five nodulated grain legumes

Nitrate uptake, nitrate reductase activity (NRA) and net proton release were compared in five grain legumes grown at 0.2 and 2 mM nitrate in nutrient solution. Nitrate treatments, imposed on 22-d-old, fully nodulated plants, lasted for 21 d. Increasing nitrate supply did not significantly influence the growth of any of the species during the treatment, but yellow lupin (Lupinus luteus) had a higher growth rate than the other species examined. At 0.2 mM nitrate supply, nitrate uptake rates ranged from 0.6 to 1.5 mg N g(-1) d(-1) in the order: yellow lupin > field pea (Pisum sativum) > chickpea (Cicer arietinum) > narrow-leafed lupin (L angustifolius) > white lupin (L albus). At 2 mM nitrate supply, nitrate uptake ranged from 1.7 to 8.2 mg N g(-1) d(-1) in the order: field pea > chickpea > white lupin > yellow lupin > narrow-leafed lupin. Nitrate reductase activity increased with increased nitrate supply, with the majority of NRA being present in shoots. Field pea and chickpea had much higher shoot NRA than the three lupin species. When 0.2 mM nitrate was supplied, narrow-leafed lupinreleased the most H+ per unit root biomass per day, followed by yellow lupin, white lupin, field pea and chickpea. At 2 mM nitrate, narrow-leafed lupin and yellow lupin showed net proton release, whereas the other species, especially field pea, showed net OH- release. Irrespective of legume species and nitrate supply, proton release was negatively correlated with nitrate uptake and NRA in shoots, but not with NRA in roots.