Nitrate Effects on Growth of the First Four Main Stem Leaves of a Range of Temperate Cereals and Pasture Grasses

The effects of different applied NO₃^– concentrations onextension growth and final length and area of leaves 1–4of five cereals and six pasture grasses of temperate originwere examined. Increased applied NO₃^– in the range 0.1–50mol m^–3; caused decreased duration of growth but increasedgrowth rate and final length of leaves 2–4 of the cerealsAvena saliva, Hordeum vulgare, Secale cereale x Triticosecaleand Triticum aestivum. For all cereals, increased NO₃^–resulted in increased area of leaves 1-4. Pasture grasses weresupplied either 0.5 or 50 mol m^–3; NO₃^–. Increasedapplied NO₃^– (0.5–50 mol m^–3) resulted indecreased duration of growth and increased growth rate and finalarea of leaves 1–4 of Bromus willdenowii leaves 2–4of Festuca arundinaceae and leaves 3 and 4 of Lolium multiflorum.In addition, length of leaves 3 and 4 of B. willdenowii increasedwith increased NO₃. Increased NO₃ resulted in increased areaof leaves 2–4 of Daciylis glomerata and Lolium perenneand leaves 3 and 4 of Phalaris aquatica but had no effect onextension growth of all three species. Avena saliva L., oat, Hordeum vulgare L., barley, Secale cereaie L., rye, x Triticosecale Wittm, triticale, Triticum aestivum L., wheat, Bromus willdenowii Kunth, prairie grass, Dactylis glomerata L., cocksfoot, Festuca arundinaceae Shreb, tall fescue, Lolium multiflorum Lam, Italian ryegrass, Lolium perenne L, perennial ryegrass, Phalaris aquatica L, nitrate,, leaf extension, leaf expansion     

The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap     

Analysis of the Nitrogen Response of Leaf Extension in Lolium temulentum Seedlings

Lolium temulentum seedlings were grown on a nutrient mediumcontaining NH₄NO₂ at 0, 0·1, 0·5, 1·0 and4·3 mmoll^–1 as the sole N source. Relative andabsolute extension rates, maximal leaf size, duration of extensiongrowth, rate of leaf appearance and plastochron index were determinedfrom the parameters of Richards functions fitted to lengthsof laminae measured at intervals after sowing. The final lengthof leaf I was relatively insensitive to N whereas mean relativeextension rate was increased and duration of growth decreasedwith increasing NH₄NO₂ concentration. Leaves 2 and 3 enlargedprogressively with N at concentrations up to 1·0 mmoll^–1but were unresponsive thereafter. There was no significant correlationbetween final length and mean relative extension rate for leaves1 to 3. Leaves 4 to 6 continued to show increasing length beyond1·0 mmoll^–1 N and final length was significantlycorrelated with mean relative extension rate. Increasing N increasedthe rate of leaf appearance by decreasing the duration of leafextension and plastochron. These results are discussed in relationto the control of leaf and N turnover. Lolium temulentum, rye grass, leaf extension, nitrogen, Richards function, growth analysis     

The Effects of Temperature and Form of Nitrogen Supply on the Relative Contribution of Root Uptake and Remobilization in Supplying Nitrogen for Laminae Regrowth of Lolium perenne L.

Plants of Lolium perenne L. cv. S23 were grown in sand culturesupplied with either ammonium (NH₄⁺) or nitrate (NO₃^–)in an otherwise complete nutrient solution at 12°C or 20°C.Three weeks after germination, plants were clipped weekly tosimulate grazing. After 10 weeks growth all nitrogen (N) wassupplied enriched with ¹⁵N to quantify the effects of form ofN supply and temperature on the relative ability of currentroot uptake and remobilization to supply N for laminae regrowth. The form of N supply had no effect on the dry matter partitioning,while at 20°C more dry weight was allocated to laminae regrowthand less to the remaining plant material. The current root uptakeof N, which subsequently appeared in the laminae regrowth, wassimilar for plants supplied with NH₄⁺ or NO₃^–, and bothwere equally reduced at the lower temperature of growth. Remobilizationof N to laminae regrowth was greater for plants receiving NH₄⁺than NO₃^–; remobilization with either form of N supplywas reduced at the lower temperature of growth. Remobilizationwas reduced to a lesser extent at 12°C than current rootuptake. It was concluded that remobilization became relativelymore important in supplying N for regrowth of laminae at lowertemperatures. Key words: Lolium perenne, ammonium, nitrate, temperature, remobilization     

The Effect of Sulphur Dioxide on the Growth of Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerata L., and Phleum pratense L.

Lockyer, D. R. 1985. The effect of sulphur dioxide on the growthof Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerataL., and Phleum pratense L.?J. exp. Bot. 36: 1851-1859. Fouragriculturally important grasses, Lolium perenne L., Loliummultiflorum Lam., Dactylis glomerata L. and Phleum pratenseL. were exposed to sulphur dioxide (SO₂) in a system of exposurechambers. The plants were exposed for a total of 43 d to meanconcentrations of SO₂ in the air of 0,87 or 448 (µg m^–3and herbage was harvested twice. All four grasses showed chloroticlesions after exposure to the highest concentration of SO₂.The effect of SO₂ on the yield of herbage was statisticallysignificant only at the second harvest and at the highest concentration;the dry weights of shoots of D. glomerata and L. perenne werereduced by 33% and 16% respectively. Significant effects ofSO₂ were also found on the 'transpiration coefficients' measuredfor D. glomerata and P. pratense. The grasses differed in theiruptake of sulphur from the atmosphere but this was not relatedto their sensitivity to SO₂. Total–S concentration inthe shoots of L. perenne, L. multiflorum and D. glomerata increasedalmost linearly in response to increasing SO₂ concentration;with P. pratense only the highest SO₂ concentration raised total-Sabove the level in control plants. These increases were almostentirely due to the accumulation of sulphate–S. Key words: Sulphur diozide, Lolium perenne, Lolium multiflorum, Dactylis glomerata, Phleum pratense     

Plant Growth in Relation to the Supply and Uptake of NO3-: A Comparison Between Relative Addition Rate and External Concentration as Driving Variables

Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO₃^– by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO₃^– at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d^–1, or constant external concentrations ([NO₃^–)of 3, 10, 20, and 100 mmol m^–3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·03–0.12 d^-1, although growth was notlimited by N supply at RAR =0.18 d^-1. Growth rates showed littlechange with [NO₃–] between 10–100 mmol m^–3(RGR=0·15 –0·16 d^-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO₃^–, accumulation of NO₃^– in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO₃^– from 1 mol m^–3 solutions were assessed relativeto the growth-related requirement for NO₃^–, showing thatthe relative uptake capacity increased with RGR between 0·03–0·06d^–1 , but decreased thereafter to a theoretical minimumvalue at RGR     

Nitrate Effects on Pre-emergence Growth and Emergence Percentage of Wheat (Triticum aestivum L.) from Different Sowing Depths

The effects of a range of applied nitrate (NO₃^–) concentrations(0–20 mol m3) on germination and emergence percentageof Triticum aestivum L. cv. Otane were examined at 30, 60, 90and 120 mm sowing depths. Germination percentage was not affectedby either sowing depth or applied NO₃^– concentration whereasemergence percentage decreased with increased sowing depth regardlessof applied NO₃^– concentration. Nitrate did not affectemergence percentage at 30 mm sowing depth, but at 60 to 120mm depth, emergence percentage decreased sharply with an increasedapplied NO₃^– concentration of 0 to 1·0 mol m^–3then decreased only slightly with further increases in appliedNO₃^– of about 5·0 mol m^–3. Root and shoot growth, NO₃^– accumulation and nitrate reductaseactivity (NRA) of plants supplied with 0, 1·0 and 1·0mol m^–3 NO₃^– at a sowing depth of 60 mm were measuredprior to emergence. The coleoptile of all seedlings opened withinthe substrate. Prior to emergence from the substrate, shootextension growth was unaffected by additional NO₃^– butshoot fr. wt. and dry wt. were both greater at 1·0 and1·0 mol m^–3 NO₃^– than with zero NO₃^–.Root dry wt. was unaffected by NO₃^–. Nitrate concentrationand NRA in root and shoot were always low without NO₃^–.At 1·0 and 10 mol m3 NO₃^–, NO₃^– accumulatedin the root and shoot to concentrations substantially greaterthan that applied and caused the induction of NRA. Regardlessof the applied NO₃^– concentration, seedlings which failedto emerge still had substantial seed reserves one month afterplanting. Coleoptile length was substantially less for seedlingswhich did not emerge than for seedlings which emerged, but wasnot affected by NO₃^–. It is proposed that (a) decreasedemergence percentage with increased sowing depth was due tothe emergence of leaf I from the coleoptile within the substrateand (b) decreased emergence percentage with additional NO₃^–was due to the increased expansion of leaf 1 within the substrateresulting in greater folding and damage of the leaf. Key words: Triticum aestivwn L., nitrate, sowing depth, seedling growth, seedling emergence     

Interactions of NH4+ and L-glutamate with NO3- transport processes of non-mycorrhizal Fagus sylvatica roots

The processes of NO₃^– uptake and transport and the effectsof NH₄⁺ or L-glutamate on these processes were investigatedwith excised non-mycorrhizal beech (Fagus sylvatica L.) roots.NO₃^– net uptake followed uniphasic Michaelis-Menten kineticsin a concentration range of 10µM to 1 mM with an apparentK_m of 9.2 µM and a V_max of 366 nmol g^–1 FW h^–1.NH₄⁺, when present in excess to NO₃^–, or 10 mM L-glutamateinhibited the net uptake of NO₃^– Apparently, part of NO₃^–taken up was loaded into the xylem. Relative xylem loading ofNO₃^– ranged from 3.21.6 to 6.45.1% of NO₃^– netuptake. It was not affected by treatment with NH₄⁺ or L-glutamate.¹⁶N/¹³N double labelling experiments showed that NO₃^–efflux from roots increased with increasing influx of NO₃^–and, therefore, declined if influx was reduced by NH₄⁺ or L-glutamateexposure. From these results it is concluded that NO₃^–net uptake by non-mycorrhizal beech roots is reduced by NH₄⁺or L-glutamate at the level of influx and not at the level ofefflux. Key words: Nitrate transport, net uptake, influx, efflux, ammonium, Fagus, Fagaceae     

Nitrate Stimulation of Mobilization of Seed Reserves in Temperate Cereals: Importance of Water Uptake

Relationships between nitrate (NO^-₃) supply, uptake and assimilation,water uptake and the rate of mobilization of seed reserves wereexamined for the five main temperate cereals prior to emergencefrom the substrate. For all species, 21 d after sowing (DAS),residual seed dry weight (d.wt) decreased while shoot plus rootd.wt increased (15–30%) with increased applied NO^-₃concentrationfrom 0 to 5–20 mM . Nitrogen (N) uptake and assimilationwere as great with addition of 5 mM ammonium (NH⁺₄) or 5 mMNO^-₃but NH⁺₄did not affect the rate of mobilization of seedreserves. Chloride (Cl^-) was similar to NO^-₃in its effect onmobilization of seed reserves of barley (Hordeum vulgare L.).Increased rate of mobilization of seed reserves with additionalNO^-₃or Cl^-was associated with increases in shoot, root and residualseed anion content, total seedling water and residual seed watercontent (% water) 21 DAS. Addition of NH⁺₄did not affect totalseedling water or residual seed water content. For barley suppliedwith different concentrations of NO^-₃or mannitol, the rate ofmobilization of seed reserves was positively correlated (r >0.95)with total seedling water and residual seed water content. Therate of mobilization of seed reserves of barley was greaterfor high N content seed than for low N content seed. Seed watercontent was greater for high N seed than for low N seed, 2 DAS.Additional NO^-₃did not affect total seedling water or residualseed water content until 10–14 DAS. The effects of seedN and NO^-₃on mobilization of seed reserves were detected 10and 14 DAS, respectively. It is proposed that the increasedrate of mobilization of seed reserves of temperate cereals withadditional NO^-₃is due to increased water uptake by the seedlingwhile the seed N effect is due to increased water uptake bythe seed directly. Avena sativa L.; oat; Hordeum vulgare L.; barley; Secale cereale L.; rye; xTriticosecale Wittm.; triticale; Triticum aestivum L.; wheat; nitrate; seed; germination; seed reserve mobilization     

Effects of NO2 and O3 Alone or in Combination on Kidney Bean Plants (Phaseolus vulgaris L.): Growth, Partitioning of Assimilates and Root Activities

Ten-day old kidney bean plants (Phaseolus vulgaris L. cv. Shin-edogawa)were exposed to 2.0 and 4–0 parts 10^–6 NO2, and0.1, 0.2, and 0.4 parts 10^–6 O3 alone or in combinationfor 2, 4, and 7 d. The effects of these air pollutants wereexamined with respect to the growth, partitioning of assimilates,nitrogen uptake, soluble sugar content, and root respiration. Decreased dry matter production was significant with all treatmentsexcept 2.0 parts 10^–6 NO₂ and 0.1 parts 10^–6 O₃.Exposure to mixtures of the gases produced more severe suppressionof growth than exposure to the single gases. Root/shoot ratiowas significantly lowered at 7 d by the gas treatments otherthan 2.0 parts 10^–6 NO₂ and 0.1 parts 10^–6 O₃. Thetotal nitrogen content of plants was increased by all treatments;the higher percent of nitrogen found with O₃ exposure will resultfrom the growth retardation which increases the concentrationof nitrogen in the plants because the absorption of nitrogenby roots was unaffected. The combination of O₃ with NO₂ significantlydecreased the assimilation of NO₂ by the plants. The concentration of soluble sugars in roots was decreased bythe gas treatments. There was a strong positive correlationbetween soluble sugar content and dry weight of the roots harvestedat 7 d. Root respiration was relatively unchanged until 5 dand then decreased significantly at 7 d by 2.0 parts 10^–6NO₂ and 0–2 parts 10^–6 O₃. Retarded growth of theroots and the decreased root respiration may be due to diminishedtranslocation of sugars from leaves to roots caused by exposureto air pollutants. The uptake of soil nitrogen was not closelyrelated with root respiration in the case of O₃ exposure. Key words: NO₂, O₃, Phaseolus vulgaris, Growth, Sugars, Root respiration     

Influx and Efflux of Nitrate and Ammonium in Italian Ryegrass and White Clover Roots: Comparisons Between Effects of Darkness and Defoliation

Seedlings of Italian ryegrass (Lolium multiflorum Lam. cv. RVP)and clonal stolon cuttings of white clover (Trifolium repensL. cv. Blanca) were grown for 19 d in flowing solution culture,with N supplied as either 250 mmol m^–3 NO₃^– or NH₃⁺.Rates of net uptake, influx and translocation of NO₃^–and NH₄⁺ were then determined using ¹⁵N and ¹³N labelling techniques:between 3–5 h into the photoperiod following 8 h darknessfor white clover (CL), and for ryegrass plants that were eitherentire (IL) or with shoots excised 90 min prior to ¹³N influx(IC); and 75 min into the photoperiod following 37–39h darkness for ryegrass (ID). Rates of net uptake, influx andefflux of NH₄⁺ exceeded those of NO₃^– in IL and IC ryegrassplants: the opposite occurred in white clover (CL). The decreasein net uptake following defoliation of ryegrass was greaterfor NH₄⁺ (62%) than NO₃^– (40%). For NH₄⁺ this was associatedwith a large decrease in influx from 110 to 6.0µmol h^–1g^–1 root fr. wt; but for NO₃^–, influx only decreasedfrom 42 to 37 µmol h^–1 g^–1. Prolonged exposureto darkness (ID plants) also lowered net uptake of NO₃^–and NH₄⁺ by, respectively, 86% and 95% of IL levels. For NH₄⁺this was characterized by a large decrease in influx and a smalldecrease in efflux; whilst for NO₃^– the effect of a largedecrease in influx was reinforced by a smaller increase in efflux. The data were used to estimate the translocatory fluxes of NO₃^–(03–20µmol h^–1 g^–1) and NH₄⁺ (003–0.4µmolh^–1 g^–1), assimilation in the roots of NO₃^–(02–26µmol h^–1 g^–1) and NH⁺⁴ (05–89 µmolh^–1 g^–1), and the concentrations of NO₃^– (9–15mol m^–3) in the cytoplasmic compartment of the roots.The relevance of variable influx and efflux to models for theregulation of N uptake is discussed. Key words: Lolium multiflorum, Trifolium repens, influx, efflux, nitrate, ammonium, ¹³N     

Orthophosphate Relations of Root: NO-3 Effects on Orthophosphate Influx, Accumulation and Secretion into the Xylem

Lamaze, T., Sentenac, H. and Grignon, C. 1987. Orthophosphaterelations of root: NO^–₃effects on orthophosphate influx,accumulation and secretion into the xylem.—J. exp. Bot.38: 923–934. Orthophosphate (Pi) accumulation by barley (Hordeum vulgareL.) roots was specifically inhibited by NO^–₃ as comparedto Cl^– and SO₄^{2 –}, and Pi secretion into the xylemwas stimulated. The inhibition of Pi accumulation by NO^–₃was also observed in roots of intact photosynthesizing horsebean(Vicia faba L.), rice (Oryza sativa L.) and soybean (Glycinemax L.) plants. NO^–₃ effects on Pi transport by rootswere more thoroughly investigated with corn (Zea mays L.). Theywere due to intracellular NO^–₃. Pi secretion was stillstimulated by NO^–₃ after Pi withdrawal from the absorptionsolution. ³²Pi influx decreased during Pi accumulation, supportingthe hypothesis that this ion allosterically regulated its owntransport system by feedback control. This control was modulatedby other anions: the decrease was more pronounced in the presenceof nitrate. Chronologically, the depressive effect of NO^–₃on ³²Pi influx appeared after the inhibition of Pi accumulation.Furthermore, under conditions where Pi accumulation was notaffected by NO^–₃, ³²Pi influx and Pi secretion into thexylem became insensitive to the presence of nitrate. Our hypothesisis that the stimulative effect of NO^–₃ on Pi secretionand the depressive one on ³²Pi influx are the repercussionsof an increase in the Pi cytosolic concentration due to an NO^–₃-induced decrease in Pi uptake by the vacuoles. Key words: Root, orthophosphate fluxes, orthophosphate accumulation, nitrate, ionic interaction     

Nitrogen utilization by plant species from acid heathland soils: II. Growth and shoot/root partitioning of NO3- assimilation at constant low pH and varying NO3-/NH4+ ratio

The growth of four heathland species, two grasses (D. flexuosa,M. caerulea) and two dwarf shrubs (C. vulgaris, E. tetralix),was tested in solution culture at pH 4.0 with 2 mol m^–3N, varying the N0₃^–/NH₄⁺ ratio up to 40% nitrate. In addition,measurements of NRA, plant chemical composition, and biomassallocation were carried out on a complete N0₃^–/NH₄⁺ replacementseries up to 100% nitrate. With the exception of M. caerulea, the partial replacement ofNH₄⁺ by NO₃^– tended to enhance the plant's growth ratewhen compared to NH₄⁺ only. In contrast to the other species,D. flexuosa showed a very flexible response in biomass allocation:a gradual increase in the root weight ratio (RWR) with NO₃^–increasing from 0 to 100%. In the presence of NH₄⁺, grassesreduced nitrate in the shoot only; roots did not become involvedin the reduction of nitrate until zero ambient NH₄⁺. The dwarfshrubs, being species that assimilate N exclusively in theirroots, displayed an enhanced root NRA in the presence of nitrate;in contrast to the steady increase with increasing NO₃^–in Calluna roots, enzyme activity in Erica roots followed arather irregular pattern. Free nitrate accumulated in the tissuesof grasses only, and particularly in D. flexuosa. The relative uptake ratio for NO₃^– [(proportion of nitratein N uptake)/(proportion of nitrate in N supply)] was lowestin M. caerulea and highest in D. flexuosa. Whereas M. caeruleaand the dwarf shrubs always absorbed ammonium highly preferentially(relative uptake ratio for NO₃^– <0.20), D. flexuosashowed a strong preference for NO₃^– at low external nitrate(the relative uptake ratio for N0₃^– reaching a value of2.0 at 10% NO₃^–). The ecological significance of thisprominent high preference for NO₃^– at low NO₃^–/NH₄⁺ratio by D. flexuosa and its consequences for soil acidificationare briefly discussed. Key words: Ammonium, heathland lants, N0₃^–/NH₄⁺ ratio, nitrate, nitrate reductase activity, soil acidification, specific absorption rate     

Diurnal regulation of NO3- uptake in soybean plants III. Implication of the Dijkshoorn-Ben Zioni model in relation with the diurnal changes in NO3- assimilation

According to the Dijkshoorn-Ben Zioni model, NO₃^– uptakein the roots is stimulated by NO₃^– assimilation in theshoots, through downward phloem transport of malate synthesizedin response to reduction of NO₂^– to NH³. In this paper,one hypothesis resulting from this model was tested, i.e. thatthe diurnal changes in NO₃^– uptake are due to the lightdependence of NO₃^– reduction in the leaves. This dependencewas studied in detached leaves transferred to deionized wateror supplied via the transpiration stream with similar amountsof ¹⁵NO₃^– in light or darkness. In the dark, the reductionof previously stored NO₃^– or xylem-borne ¹⁵NO₃^–was generally about 40–50% of that measured in the light.Glucose supply to the detached leaves stimulated NO₃^–reduction in the dark, but not enough to increase it up to thesame rate as in the light. Nitrite reduction in detached leaveswas much less affected by darkness, and could be maintainedat a high level by exogenous supply of substrate. Advantagewas taken from this last observation to sustain NO₂^–reductionin attached darkened shoots at the same rate as in the light,by ensuring an appropriate delivery of NO₂^– from the xylem.Although this was assumed to restore the light level of theassociated synthesis of malate, it led to a marked inhibitionof NO₃^– uptake. In addition, the direct supply of malateto the shoots or to the roots failed to prevent the decreaseof NO₃^– uptake in darkness. Thus, our conclusion is thatthe mechanisms evoked in the Dijkshoorn-Ben Zioni model do notplay an important role in the diurnal variations of NO₃^–uptake in soybean plants. Key words: Glycine max, light/dark cycle, malate synthesis, NO₃^– reduction, NO₃^– uptake     

Concurrent Rates of N2 Fixation, Nitrate and Ammonium Uptake by White Clover in Response to Growth at Different Root Temperatures

Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown for 71 d in flowing nutrient solutions containingN as 10 mmol m_–3 NH₄NO₃, under artificial illumination,with shoots at 20/15°C day/night temperatures and root temperaturereduced decrementally from 20 to 5°C. Root temperatureswere then changed to 3, 7, 9, 11, 13, 17 or 25°C, and theacquisition of N by N₂ fixation, NH₄+ and NO₃^– uptakewas measured over 14 d. Shoot specific growth rates (d. wt)doubled with increasing temperature between 7 and 17°C,whilst root specific growth rates showed little response; shoot:root ratios increased with root temperature, and over time at11°C. Net uptake of total N per plant (N₂ fixation + NH₄++ NO₃^–) over 14 d increased three-fold between 3 and 17°C.The proportion contributed by N₂ fixation decreased with increasingtemperature from 51% at 5°C to 18% at 25°C. Uptake ofNH₄+ as a proportion of NH₄+ + NO₃^– uptake over 14 d variedlittle (55–62%) with root temperature between 3 and 25°C,although it increased with time at most temperatures. Mean ratesof total N uptake per unit shoot f. wt over 14 d changed littlebetween 9 and 25°C, but decreased progressively with temperaturebelow 9°C, due to the decline in the rates of NH₄+ and NO₃^–uptake, even though N₂ fixation increased. The results suggestthat N₂ fixation in the presence of sustained low concentrationsof NH₄+ and NO₄^– is less sensitive to low root temperaturethan are either NH₄+ or NO₃^– uptake systems. White clover, Trifolium repens L. cv. Huia, root temperature, nitrogen fixation, ammonium, nitrate     

Changes in the growth rates of saline-lake diatoms in response to variation in salinity, brine type and nitrogen form

The growth rates of four saline-lake diatom taxa were measuredunder varying conditions of salinity (5, 8 and 11), brine type(sulfate- versus bicarbonate-dominated) and nitrogen form (NH₄⁺versus NO₃^–), using a full factorial design. With NO₃^–as the nitrogen source, Cyclotella quillensis, Cymbella pusillaand Anomoeoneis costata exhibited lower growth rates in thesulfate versus bicarbonate media. The strain of Chaetoceroselmorei used in these experiments, isolated from a sulfate-dominatedlake, was unable to grow on NO₃^– alone. In the NH₄⁺ treatments,neither salinity nor brine type affected the growth rates ofC.quillensis or C.elmorei. When supplied with NH₄⁺, C.pusillaand A.costata had higher growth rates in the bicarbonate versussulfate media, although for C.pusilla the difference on NH₄⁺was not as great as on NO₃^–. The impact of brine typeon NO₃^– use is consistent with the theory that sulfateinhibits molybdate uptake, as molybdenum is required for NO₃^–use but not NH₄⁺. Cymbella pusilla was the only taxon affectedby changes in salinity. The four taxa used in these experimentsare frequently found in saline lakes and saline-lake sediments,hence they are used in paleoclimate reconstructions; the resultspresented here provide additional information that may enhancethese diatom-based reconstructions.     

The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. cv. Bien venu in Flowing Solution Culture: II. UPTAKE FROM SOLUTIONS CONTAINING NH4NO3

Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. CV. Bien venu in flowing solution culture.II. Uptake from solutions containing NH₄NO₃.—J. exp. Bot.38: 53–66 The effects of root temperature on uptake and assimilation ofNH₄⁺ and NO₃^– by oilseed rape (Brassica napus L. CV. Bienvenu) were examined. Plants were grown for 49 d in flowing nutrientsolution at pH 6?0 with root temperature decrementally reducedfrom 20?C to 5?C; and then exposed to different root temperatures(3, 5, 7, 9, 11, 13, 17 or 25?C) held constant for 14 d. Theair temperature was 20/15?C day/night and nitrogen was suppliedautomatically to maintain 10 mmol m^–3 NH₄NO₃ in solution.Total uptake of nitrogen over 14 d increased threefold between3–13?C but was constant above 13?C. Net uptake of NH₄⁺exceeded that of NO₃^– at all temperatures except 17?C,and represented 47–65% of the total uptake of nitrogen.Unit absorption rates of NH₄⁺ and of 1?5–2?7 for NO₃^–suggested that NO₃^– absorption was more sensitive thanNH₄⁺ absorption to temperature. Rates of absorption were relativelystable at 3?C and 5?C compared with those at 17?C and 25?C whichincreased sharply after 10 d. Tissue concentration of N in theshoot, expressed on a fresh weight basis, was independent ofroot temperature throughout, but doubled between 3–25?Cwhen expressed on a dry weight basis. The apparent proportionof net uptake of NO₃^– that was assimilated was inverselyrelated to root temperature. The results are used to examinethe relation between unit absorption rate adn shoot:root ratioin the context of short and long term responses to change ofroot temperature Key words: Brassica napus, oilseed rape, root temperature, nitrogen uptake     

Assimilation of 15N2 and 15NO3- by Partially Nitrate-Tolerant Nodulation Mutants of Soybean

Growth-chamber studies were conducted to evaluate nitrogen assimilationby three hypernodulated soybean [Glycine max (L.) Merr.] mutants(NOD1–3, NOD2–4, NOD3–7) and the Williamsparent. Seeds were inoculated at planting and transplanted atday 7 to nutrient solution with 1 mol m^–3 urea (optimizesnodule formation) or 5 mol m^–3 NO₃^– (inhibits noduleformation). At 25 d after planting, separate plants were exposedto ¹⁵NO₂ or ¹⁵NO₃^– for 3 to 48 h to evaluate N₂ fixationand NO₃^– assimilation. Plant growth was less for hypernodulatedmutants than for Williams with both NO₃^– and urea nutrition.The major portion of symbiotically fixed ¹⁵N was rapidly assimilated(30 min) into an ethanol-soluble fraction, but by 24 h aftertreatment the ethanolinsoluble fraction in each plant part wasmost strongly labelled. Distribution patterns of ¹⁵N among organswere very similar among lines for both N growth treatments aftera 24 h ¹⁵N₂ fixation period; approximate distributions were40% in nodules, 12% in roots, 14% in stems, and 34% in leaves.With urea-grown plants the totalmg ¹⁵N fixed plant^–1 24h^–1 was 1·18 (Williams), 1·40 (N0D1-3),107 (NOD2-4), and 0·80 (NOD3-7). The 5 mol m^-3 NO₃^- treatmentresulted in a 95 to 97% decrease in nodule mass and ¹⁵N₂ fixationby Williams, while the three mutants retained 30 to 40% of thenodule mass and 17 to 19% of the ¹⁵N₂ fixation of respectiveurea-grown controls. The hypernodulated mutants, which had restrictedroot growth, absorbed less ¹⁵NO₃^- than Williams, irrespectiveof prior N growthcondition. The ¹⁵N from ¹⁵NO₃^- was primarilyretained in the soluble fraction of all plant parts through24 h. The ¹⁵N incorporation studies confirmed that nodule developmentis less sensitive to external NO₃^- in mutant lines than in theWilliams parent, and provide evidence that subsequent metabolismand distribution within the plant was not different among lines.These results further confirm that the hypernodulated mutantsof Williams are similar in many respects to the hyper- or supernodulatedmutants in the Bragg background, and suggest that a common mutationalevent affectingautoregulatory control of nodulation has beentargeted. Key words: Glycine max (L.) Merr., soybean, N₂fixation, nitrate assimilation, nodulation mutants, ¹⁵N isotope     

Apoplastic Solute Concentrations of Organic Acids and Mineral Nutrients in the Leaves of Several Fagaceae

Ion chromatographic methods determined organic acids and mainnutrient minerals in the apoplastic solution from leaves ofseveral Fagaceae (Quercus ilex L., Quercus cerris L., Quercusvirgiliana (Ten.) Ten, and Fagus sylvatica L.). The anions oforganic acids found in high amounts (250 to 650 µM) werequinate, malate, and oxalate. Lactate, pyruvate, formate andacetate were detected in relatively low amounts with concentrationsbetween 20 and 200 µM. The total concentration of organicacids in the apoplastic sap ranged between 1.5 and 2 mM. Thetotal concentration of inorganic cations (K⁺, Mg²⁺, NH₄⁺, Ca²⁺,Na⁺) and anions (C1^–, NO₃^–, SO^2–₄ and PO^3–₄)in the apoplastic sap varied between 5 and 10 mM, and 0.35 and1.8 mM, respectively. We conclude that the concentration oforganic acid ions in the leaf apoplast depends mainly on theexchange with the leaf cells and is influenced by the electrochemicalgradient between the symplast and the apoplast in relation tothe water potential of the leaf. The determination of formateand acetate in the apoplastic compartment of leaves lend weightto the argument that the production of these acids by treesis a important emission source to the atmosphere. (Received June 9, 1998; Accepted April 8, 1999)     

Acclimation of NO-3 fluxes to low root temperature by Brassica napus in relation to NO-3 supply

Acclimation of NO^–₃ transport fluxes (influx, efflux)in roots of oilseed rape (Brassica napus L. cv. Bien venu) andtheir sensitivity to growth at low root temperature was studiedin relation to external NO^–₃ supply, defined by constantconcentrations ranging from sub- to supra-optimal with respectto plant growth rate. Plants were grown from seed in flowingnutrient solutions containing 250 mmol m^–3 NO^–₃at 17°C for 20d, and solution temperature in half the cultureunits was then lowered decrementally over 3 d to 7°C. Threedays later plants were supplied with NO^–₃ at 1, 10, 100or 1000 mmol m^–3 maintained for 18 d. Dry matter productionwas decreased more by low root zone temperature than low [NO^–₃]_e. Root specific growth rates were inversely related to [NO^–₃]_eand shoot:root ratios increased with time at [NO^–₃]_e between10–1000 mmol m^–3. Net uptake of NO^–₃ at 17°Cwas twice that at 7°C, and at both temperatures it doubledwith increasing [NO^–₃]_e between 1–10 mmol m^–3with further small increases at higher [NO^–₃]_e. Mean unitabsorption rates of NO^–₃ between 0–6 d and 6–14d were linearly related (r² of 0.79–0.99) to log₁₀[NO].Steady-state Q₁₀ (7–17°C) for uptake between 0–6d were 0.91, 1.62, 1.27, and 1.10, respectively, at [NO^–₃]_eof 1, 10, 100, and 1000 mmol m^–3, compared with correspondingvalues of 0.98, 1.38, 1.68, and 1.89 between 6–14 d. Thedata indicated that net uptake rates at 7 and 17°C divergedover time at high [NO^–₃]_e. Short-term uptake rates from1 mol m^–3 NO^–₃ measured at 17°C were higherin plants grown with roots at 7°C than at 17°C; for7°C plants there was a strong inverse linear relationship(r²=0.94) between uptake rate and treatment log₁₀ [NO^–₃]_ewhilst rates in 17°C plants were independent of prior [NO^–₃]_e. Rates of NO^–₃ influx and efflux under different steady-stateconditions of NO^–₃ supply and root temperature were calculatedfrom dilution of ¹⁵N added to culture solutions. Efflux wassubstantial relative to net uptake in all treatments, and wasinversely related to [NO^–₃]_e at 17°C but not at 7°C.Ratios of influx: efflux ranged from 1.6–2.9 at 17°Cand 1.3–1.8 at 7°C, indicating the proportionatelygreater impact of efflux at low root temperature. Ratios ofefflux: net uptake were 0.53–1.56 at 17°C and 1.21–3.58at 7°C. The apparent sensitivities of influx and effluxto steady-state root temperature varied with [NO^–₃]_e.Both fluxes were higher at 17°C than 7°C in the presenceof 100–1000 mmol m^–3 NO^–₃ but the trend wasreversed at 1–10 mmol m^–3 NO. Concentrations oftotal N measured in xylem exudate were at least 2-fold higherat 7°C compared with 17°C, attributable mainly to higherconcentrations of NO^–₃ glutamine and proline. The resultsare discussed in terms of acclimatory and other responses shownby the NO^–₃ transport system under conditions of limitingNO^–₃ supply and low root temperature. Key words: Brassica napus, nitrate supply, efflux, influx, root temperature, xylem exudate