Effect of Salinity on Growth, Nodulation and Nitrogen Yield of Chickpea (Cicer arietinum L.)

Chickpea cultivar ILC 482 was inoculated with salt-tolerantRhizobium strain Ch191 in solution culture with different saltconcentrations added either immediately with inoculation or5 d later. The inhibitory effect of salinity on nodulation ofchickpea occurred at 40 dS m^–1 (34.2 mol m^–3 NaCl)and nodulation was completely inhibited at 7 dS m^–1 (61.6mol m^–3 NaCl); the plants died at 8 dS m^–1 (71.8mol m^–3 NaCl). Chickpea cultivar ILC 482 inoculated with Rhizobium strain Ch191^spcstrwas grown in two pot experiments and irrigated with saline water.Salinity (NaCl equivalent to 1–4 dS m^–1) significantlydecreased shoot and root dry weight, total nodule number perplant, nodule weight and average nodule weight. The resultsindicate that Rhizobium strain Ch191 forms an infective andeffective symbiosis with chickpea under saline and non-salineconditions; this legume was more salt-sensitive compared tothe rhizobia, the roots were more sensitive than the shoots,and N₂ fixation was more sensitive to salinity than plant growth. Key words: Cicer arietinum, nodulation, N₂ fixation, Rhizobium, salinity     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Partitioning and Utilization of Carbon and Nitrogen in Nodulated Roots and Nodules of Chickpea (Cicer arietinum) Grown at Two Moisture Levels

The partitioning and utilization of carbon (C) and nitrogen(N) in nodulated roots and nodules of chickpea (Cicer arietinumL.) was studied at two moisture levels at 10-d intervals 40–140d after sowing (DAS). More C was used in respiration and lessin growth of nodulated roots and nodules under water stresscompared to controls during all growth stages except at theearly vegetative stage. Similarly, less nitrogen was investedin dry matter of both nodules and nodulated roots under stress,except during the vegetative stage where more nitrogen was used.Calculated over the entire growth period, as much as 14 and20% of the total nitrogen and 3 and 4% of the total carbon fixedby the plant was lost to the rooting medium under controlledand stressed conditions, respectively. The efficiency of nitrogen fixation with respect to net C utilizationwas maximal during seed filling under both control and stressconditions However, the efficiency of nitrogen fixation wasalways greater under drier conditions. Carbon, chickpea (Cicer arietinum L.), nitrogen, nitrogen fixation, partitioning     

Preliminary characterization of 1-aminocyclopropane-1-carboxylate oxidase properties from embryonic axes of chick-pea (Cicer arietinum L.) seeds

For a deeper understanding of the germination of chick–pea(Cicer arietinum) seeds, which is dependent upon ethylene synthesis,a crude extract containing authentic ACC oxidase (ACCO) activitywas isolated in soluble form from the embryonic axes of seedsgerminated for 24 h. Under our optimal assay conditions (200mM HEPES at pH 7.0, 4µM FeS0₄, 6 mM Na–ascorbate,1 mM ACC, 20% 0₂, 3% CO₂ , and 10%glycerol) this enzyme was5–fold more active than under the conditions we used initiallyin the present work. The enzyme has the following K_m: 28 µMfor ACC (approximately 4–fold less than in vivo), 1.2%for O₂ (in the presence of an optimal CO₂ concentration of 3%),and 1% for CO₂ in the presence of O₂ (20%). The enzyme is inhibitedby phenanthroline (PNT) (specific chelating agent of ferrousion), and competitively inhibited (K₁, =0.5 mM) by 2–aminoisobutyricacid (AIB), and the enzymatic activity was not detectable inthe absence of CO₂. Under optimal assay conditions, the enzymehas two optimum temperatures (28 C and 35 C) and is inhibitedby divalent metal cations (Zn²⁺> CO²⁺>Ni²⁺>Cu²⁺>Mn²⁺>Mg²⁺) and by salicylic acid, propylgallate, carbonyl cyanidem–chlorophenyl hydrazone (CCCP), dinitrophenol (DNP),and Na–benzoate. The in vitro ACCO activity which we recoveredin soluble form is equivalent to approximately 80–85%of the apparent activity evaluated in vivo. Key words: ACC oxidase, Cicer arietinum, ethylene, germination, seeds     

Effects of Sodium Chloride Stress on Callus Cultures of Cicer arietinum L. cv. BG-203: Growth and Ion Accumulation

Growth and ion accumulation were measured in callus culturesof Cicer arietinum L. cv. BG-203, grown on media supplementedwith 0–200 mol m^–3 NaCl. Fresh and dry weights decreasedat concentrations ranging from 100–200 mol m^–3,the reduction being greater during the third and fourth weeksof culture. Slight stimulation of growth was observed at 25and 50 mol m^–3 NaCl. There was also a decrease in tissuewater content (fresh weight: dry weight) at 100–200 molm^–3 NaCl. The concentration of Na⁺ and Cl^– in thetissue increased with increasing salinity of the medium. Mostof the accumulation of these ions occurred by the first weekwhile significant growth inhibition became apparent by onlythe third week of culture. Tissue K⁺ and Mg²⁺ decreased withincreasing salinization, the decrease being greater in K⁺ levels.Levels of Ca²⁺, however, were maintained throughout the experimentalrange. Key words: Cicer arietinum, NaCl stress, Callus cultures, Ion accumulation     

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     

Root Distribution, Growth, Respiration, and Hydraulic Conductivity for Two Highly Productive Agaves

Cultivated Agave mapisaga and A. salmiana can have an extremelyhigh above-ground dry-weight productivity of 40 Mg ha^–1yr^–1. To help understand the below-ground capabilitiesthat support the high above-ground productivity of these Crassulaceanacid metabolism plants, roots were studied in the laboratoryand in plantations near Mexico City. For approximately 15-year-oldplants, the lateral spread of roots from the plant base averaged1.3 m and the maximal root depth was 0.8 m, both considerablygreater than for desert succulents of the same age. Root andshoot growth occurred all year, although the increase in shootgrowth at the beginning of the wet season preceded the increasein growth of main roots. New lateral roots branching from themain roots were more common at the beginning of the wet season,which favoured water uptake with a minimal biomass investment,whereas growth of new main roots occurred later in the growingseason. The root: shoot dry weight ratio was extremely low,less than 0.07 for 6-year-old plants of both species, and decreasedwith plant age. The elongation rates of main roots and lateralroots were 10 to 17 mm d^–1, higher than for various desertsucculents but similar to elongation rates for roots of highlyproductive C₃ and C₄ agronomic species. The respiration rateof attached main roots was 32 µmol CO₂ evolved kg^–1dry weight s^–1 at 4 weeks of age, that of lateral rootswas about 70% higher, and both rates decreased with root age.Such respiration rates are 4- to 5-fold higher than for Agavedeserti, but similar to rates for C₃ and C₄ agronomic species.The root hydraulic conductivity had a maximal value of 3 x 10^–7ms^–1 MPa^–1 at 4 weeks of age, similar to A. deserti.The radial hydraulic conductivity from the root surface to thexylem decreased and the axial conductivity along the xylem increasedwith root age, again similar to A. deserti. Thus, although rootsof A. mapisaga and A. salmiana had hydraulic properties perunit length similar to those of a desert agave, their highergrowth rates, their higher respiration rates, and the greatersoil volume explored by their roots than for various desertsucculents apparently helped support their high above-groundbiomass productivity Key words: Crassulacean acid metabolism, productivity, root elongation rate, root system, water uptake     

N2 Fixation and the Respiratory Costs of Nodules, Nitrogenase Activity, and Nodule Growth and Maintenance in Fiskeby Soyabean

The respiratory effluxes of nodules and of roots of FiskebyV soyabean (Glycine max (L.) Merr.), grown in a controlled environment,were measured at intervals in air and 3% O₂ from shortly afterthe onset of N₂ fixation until plant senescence. The respiratoryburdens linked with nitrogenase plus ammonia metabolism, andnodule growth and maintenance, were calculated from gas exchangedata and related to the concurrent rates of N₂ fixation. The specific respiration rates of nodules increased to a maximumof 21 mg CO₂ g^–1 h^–1 at the time pods began development:the equivalent maximum for roots was c. 4.5 mg CO₂ g^–1h^–1. Maximum nodule and root respiration rates per plantwere attained about 25 d later at the time N₂ fixation peakedat 15 mg N d^–1 plant^–1. The relationship between nodule respiration and N₂ fixationindicated an average respiratory cost of 13.2 mg CO₂ mg^–1N until the last few days of plant development Separation ofnodule respiration into the two components: nitrogenase (+ NH₃metabolism) respiration and nodule growth and maintenance respiration,indicated that the latter efflux accounted for c. 20% of nodulerespiration while N₂ fixation was increasing and new noduletissue was being formed. When nodule growth ceased and N₂ fixationdeclined, this component of respiration also declined. The respiratorycost of nitrogenase activity plus the associated metabolismof NH₃ varied between 11 mg CO₂ mg^–1 N during vegetativeand early reproductive growth, to 12.5 mg CO₂ mg^–1 N duringthe later stages of pod development. Key words: N2 fixation, Respiration, Nodules, Nitrogenase     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: III. POST-ANTHESIS KINETICS OF NET NITRATE UPTAKE AND THE ROLE OF THE RELATIVE ROOT SIZE IN DETERMINING THE CAPACITY FOR NITRATE ACQUISITION

Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the ‘HN’ culture the relative rate of nitrate-Naddition (RA) was 0·08 d^–1 until day 48 and thendecreased stepwise to, finally, 0·005 d^–1 duringgrain-filling; the ‘LN’ culture received 45% ofthe nitrogen added in HN; the ‘CN’ culture was maintainedat RA 0·0375 d^–1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m^–3external nitrate. V_max (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative V_max (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·3–2·3d^–1 during vegetative growth to 0·1–0·7d^–1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m^–3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative V_max can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative V_max and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, V_max     

Waterlogging Tolerance Among a Diverse Range of Trifolium Accessions is Related to Root Porosity, Lateral Root Formation and 'Aerotropic Rooting'

Waterlogging tolerance, root porosity and root anatomy wereevaluated for 20 Trifolium accessions (species and sub-species,all annuals) selected from the eight Sections of the genus.Nine accessions were sensitive [relative growth rate (RGR) reducedby up to 80%] to waterlogging, nine accessions were tolerant(RGR not reduced), and in two accessions RGR increased (up to1.9-fold), when compared to drained controls. Growth of themain (i.e. tap) root axis was severely reduced in all accessionswhen waterlogged. Lateral roots formed the bulk of the rootsystem of tolerant accessions when grown in waterlogged soil.Lengths of the longest lateral roots were up to three-timeslonger than the main root axis. Root porosity varied from 0.7–12%among accessions when grown in aerated solution and from 1.1–15.5%in plants grown in hypoxic (0.031–0.045 mol O₂m^-3) solution.In some accessions aerenchyma formed by cell lysigeny; in othersit formed by schizogenous cell separation, or a combinationof both processes. O₂consumption rates of expanded lateral roottissues varied by up to 1.7-fold (on a mass basis) among thesix accessions tested and was reduced by an average of 24% forroots of plants grown in hypoxic solution prior to measurements.Accessions with the highest root porosity tended to have longerroots when grown in waterlogged soil. Three accessions formed‘aerotropic roots’ and the lateral root lengthsof these plants exceeded those of all other accessions, suggestingenhanced O₂movement to the submerged lateral root axis via theaerotropic roots. Waterlogging-tolerant accessions were identifiedin seven of the eight Sections in Trifolium, and the tolerantaccessions tended to be those with extensive lateral root systemsof relatively high porosity. Copyright 2001 Annals of BotanyCompany Waterlogging, Trifolium, aerenchyma, hypoxia, flooding, root respiration, clover, root anatomy, root porosity, pasture, aerotropic roots     

Maintenance and Growth Components of Carbon Dioxide Efflux from Growing Pea Fruits

Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s^–1 m^–2 photon flux density in a16 h photoperiod. The rate of CO₂ output per fruit increasedquickly from 0.005 to 0.018 mg CO₂ min^–1 during fruitelongation and subsequently more slowly to 0.030 mg CO₂ min^–1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO₂ g^–1 min^–1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO₂ g^–1 min^–1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g^–1 d. wt day^–1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg^–1 d. wt day^–1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg^–1 nitrogen day^–1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g^–1growth (equivalent to a conversion efficiency, Y_G, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration     

On the causes of interspecific differences in the growth-irradiance relationship for phytoplankton. Part I. A comparative study of the growth-irradiance relationship of three marine phytoplankton species: Skeletonema costatum, Olisthodiscus luteus and Gonyaulax tamarensis

Three marine phytoplankton species (Skeletonema costatum, Olisthodiscusluteus andGonyaulax tamarensis) were grown in batch culturesat 15°C and a 14:10 L:D cycle at irradiance levels rangingfrom 5 to 450 µEinst m^–2 s^–1. At each irradiance,during exponential growth, concurrent measurements were madeof cell division, carbon-specific growth rate, photosyntheticperformance (both O₂ and POC production), dark respiration,and cellular composition in terms of C, N and chlorophyll a.The results indicate that the three species were similar withrespect to chemical composition, C:N (atomic) = 6.9 ±0.4, photo-synthetic quotient, 1.43 ± 0.09, and photosyntheticefficiency, 2.3 ±0.1 x 10^–3 µmol O₂ (µgChl a)^–1 h^–1 (µEinst m^–2 s^–1)^–1.Differences in maximum growth rate varied as the –0.24power of cell carbon. Differences in growth efficiency, werebest explained by a power function of Chl a:C at µ = 0.Compensation intensities, ranged from 1.1 µEinst m^–2s^–1 for S. costatum to 35 forG. tamarensis and were foundto be a linear function of the maintenance respiration rate.The results indicate that interspecific differences in the µ–Irelationship can be adequately explained in terms of just threeparameters: cell carbon at maximum growth rate, the C:Chl aratio (at the limit as growth approaches zero) and the respirationrate at zero growth rate. A light-limited algal growth modelbased on these results gave an excellent fit to the experimentalµ–I curves and explained 97% of the observed interspecificvariability. ¹Present address: Lamont-Doherty Geological Observatory Columbiaof University, Palisades, NY 10964, USA     

Effects of CO2 and Photosynthetic Photon Flux on Yield, Gas Exchange and Growth Rate of Lactuca Sativa L. 'Waldmann's Green'

Knight, S. L. and Mitchell, C. A. 1988. Effects of CO₂ and photosyntheticphoton flux on yield, gas exchange and growth rate of Lactucasativa L. ‘Waldmann’s Green'.—J. exp. Bot.39: 317–328. Enrichment of CO₂ to 46 mmol m^–3 (1 000 mm³ dm^–3)at a moderate photosynthetic photon flux (PPF) of 450 µmolm^–2 s^–1 stimulated fresh and dry weight gain oflettuce leaves 39% to 75% relative to plants at 16 mmol m^–3CO₂ (350 mm³ dm^–3). Relative growth rate (RGR) was stimulatedonly during the first several days of exponential growth. ElevatingCO₂ above 46 mmol m^–3 at moderate PPF had no further benefit.However, high PPF of 880–900 µmol m^–2 s^–1gave further, substantial increases in growth, RGR, net assimilationrate (NAR) and photosynthetic rate (Pn), but a decrease in leafarea ratio (LAR), at 46 or 69 mmol m^–3 (1000 or 1500 mm³dm^–3) CO², the differences being greater at the higherCO₂ level. Enrichment of CO₂ to a supraoptimal level of 92 mmolm^–3 (2000 mm³ dm^–3) at high PPF increased leaf areaand LAR, decreased specific leaf weight, NAR and Pn and hadno effect on leaf, stem and root dry weight or RGR relativeto plants grown at 69 mmol m^–3 CO₂ after 8 d of treatment.The results of the study indicate that leaf lettuce growth ismost responsive to a combination of high PPF and CO₂ enrichmentto 69 mmol m^–3 for several days at the onset of exponentialgrowth, after which optimizing resources might be conserved. Key words: Photosynthesis, relative growth rate, CO₂ enrichment     

Sources of Inorganic Carbon Acquired through CAM in Littorella uniflora (L.) Aschers

Madsen, T. V. 1987. Sources of inorganic carbon acquired throughCAM in Littorella uniflora (L.) Aschers.—J. exp. Bot.38: 367–377. The CO₂ dynamics of the lacunal air and the relative contributionof external and internal CO₂ sources to dark CO₂ assimilationwas examined in the submerged aquatic CAM species Littorellauniflora (L.) Aschers. Refixation of internal CO₂, released by dark respiration, constitutedabout 30–35% of the total dark CO₂ assimilation. At aCO₂ concentration of 0·2 mol m^–3 around the leavesthe external CO₂ uptake through the roots increased from 45%of the total CO₂ uptake at 0·7 mol m^–3 CO₂ to 100%at 1·6 mol m^–3 and 3·1 mol m^–3 CO₂around the roots. The negligible importance of leaf CO₂ uptakeat high CO₂ concentrations around the roots was the result ofa causative high CO₂ concentration in the leaf lacunae. The CO₂ permeability of Littorella leaves was high relativeto root permeability. This has at least two ecological implications:(1) it enhances the potential diffusive release of CO₂ fromthe sediment C0₂-pool via the lacunal system of the plants.This loss of CO₂, however, was found to be greatly reduced byCAM activity of the plants. (2) The high permeability of theleaf surface to CO₂ exchange allows the plants to assimilateCO₂ from the water surrounding the leaves when the concentrationis high, i.e. during extensive epiphyte dark respiration. Thus,CAM tends to facilitate retension of a high CO₂ pool in thesediment-plant system and at the same time allows the plantsto exploit the water column CO₂ source when it is abundant.This result is in accordance with the general idea that CAMin aquatics constitute a carbon conserving mechanism. Key words: Aquatic macrophytes, dark CO₂ assimilation, inorganic carbon sources     

Effects of elevated CO2 concentrations on three montane grass species: III. Source leaf metabolism and whole plant carbon partitioning

Agrostis capillaris L.⁵, Festuca vivipara L. and Poaalpina L.were grown in outdoor open-top chambers at either ambient (340 3µmol mol^–1) or elevated (6804µmol mol^–1)concentrations of atmospheric carbon dioxide (CO₂) for periodsfrom 79–189 d. Photosynthetic capacity of source leaves of plants grown atboth ambient and elevated CO₂ concentrations was measured atsaturating light and 5% CO₂. Dark respiration of leaves wasmeasured using a liquid phase oxygen electrode with the buffersolution in equilibrium with air (21% O₂, 0.034% CO₂). Photo-syntheticcapacity of P. alpina was reduced by growth at 680 µmolmol^–1 CO₂ by 105 d, and that of F. vivipara was reducedat 65 d and 189 d after CO₂ enrichment began, suggesting down-regulationor acclimation. Dark respiration of successive leaf blades ofall three species was unaltered by growth at 680 relative to340 µmol mol^–1 CO₂. In F. vivipara, leaf respirationrate was markedly lower at 189 d than at either 0 d or 65 d,irrespective of growth CO₂ concentration. There was a significantlylower total non-structural carbohydrate (TNC) concentrationin the leaf blades and leaf sheaths of A. capillaris grown at680µmol mol^–1 CO₂. TNC of roots of A. capillariswas unaltered by CO₂ treatment. TNC concentration was increasedin both leaves and sheaths of P. alpina and F. vivipara after105 d and 65 d growth, respectively. A 4-fold increase in thewater-soluble fraction (fructan) in P. alpina and in all carbohydratefractions in F. vivipara accounted for the increased TNC content. In F. vivipara the relationship between leaf photosyn-theticcapacity and leaf carbohydrate concentration was such that therewas a strong positive correlation between photosynthetic capacityand total leaf N concentration (expressed on a per unit structuraldry weight basis), and total nitrogen concentration of successivemature leaves reduced with time. Multiple regression of leafphotosynthetic capacity upon leaf nitrogen and carbohydrateconcentrations further confirmed that leaf photosynthetic capacitywas mainly determined by leaf N concentration. In P. alpina,leaf photosynthetic capacity was mainly determined by leaf CHOconcentration. Thus there is evidence for down-regulation ofphotosynthetic capacity in P. alpina resulting from increasedcarbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positivelycorrelated in P. alpina and F. vivipara. Leaf dark respirationand soluble carbohydrate concentration of source leaves werepositively correlated in A. capillaris. Changes in source leafphotosynthetic capacity and carbohydrate concentration of plantsgrown at ambient or elevated CO₂ are discussed in relation toplant growth, nutrient relations and availability of sinks forcarbon. Key words: Elevated CO₂, Climate change, grasses, carbohydrate partitioning, photosynthesis, respiration     

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     

Vernalization in Chickpea (Cicer arietinum); Fact or Artefact?

Various cool treatments of imbibing seeds reduced the subsequenttimes taken to flower in two genotypes of chickpea (Cicer arietinumL.). These reductions were greater in the kabuli cv. Rabat thanin the desi accession ICC 5810. Nevertheless, in both genotypes,the hastening of flowering was entirely accounted for by thephotothermal time accumulated during each cool temperature pretreatment,provided it was recognized that the ceiling photoperiods wereapproximately 10 and 8 h d^–1, respectively; i.e. neithergenotype shows a true vernalization response. A thorough reevaluationof ‘ responsiveness to vernalization’ in the chickpeagermplasm might now be prudent. Cicer arietinum L, chickpea, vernalization, photothermal time, screening germplasm     

Activity of the Pentose Phosphate Pathway and Changes in Nicotinamide Nucleotide Content during Germination of Seeds of Cicer arietinum L.

Changes in the level of nicotinamide nucleotides, rate of ¹⁴CO₂output from [1^–14C] or [6¹⁴ C₆/C₁ ratios, glucose-6-phosphatedehydrogenase, 6-phosphogluconate dehydrogenase, and NAD kinaseactivities were determined during the first 72 h of germinationof seeds of Cicer arietinum L. The level of oxidized and reducedforms of nicotinamide nucleotides, together with the activityof glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase,NAD kinase, and C₆/C₁ ratios, suggest that the pentose phosphatepathway is activated during early germination in cotyledonsof chick pea seeds. The results obtained in embryonic axes seemsto indicate a lower participation of the PP pathway, probablydue to the development of the activity of the glycolytic-TCApathway.     

Components of Growth and Dark Respiration of Kikuyu (Pennisetum clandestinum Chiov.) at Various Temperatures

Growth and dark respiration were measured in dense, miniatureswards of kikuyu grass grown at constant temperatures of 15,20, 25 and 30 °C. Total respiration over the first 12 hof darkness was very high and CO² efflux per unit surface areavaried from 2.4 to 3.9 g CO₂ m^–2 h^–1 at 15 and 30°C respectively. Such rates were consistent with the correspondinglyhigh net growth rates of 24 and 63 g d. wt m^–2 d^–1and the heavy yields of herbage. When plants were kept in thedark, CO₂ efflux subsequently declined rapidly to a lower, constantrate which was taken to be the maintenance respiration rate.The half-life of the declining phase of respiration averaged10.9 and 6.0 h at 15 and 30 °C respectively, and was curvilinearlyrelated to the specific maintenance respiration rate (m). Therapid decline in respiration was consistent with the low concentrationsof total soluble carbohydrate and starch in the herbage. Valuesof m for lamina and top growth increased with temperature witha Q₁₀ of 2.6 and 1.42 respectively, but m of stems alone wasnot affected by temperature. Using results from this study forkikuyu and from McCree (1974) for sorghum and white clover,it was noted that all three species have similar m when grownat temperatures which are near their respective optimums forgrowth. Kikuyu, Pennisetum clandestinum, growth, respiration, temperature     

Root Aeration and Respiration in Young Mangrove Plants (Avicennia marina (Forsk.) Vierh.)

The roots of young plants of Avicennia marina (Forsk.) Vierh.grown under simulated tidal conditions were harvested so asto obtain the entire root system. The roots were subdividedand weighed and subsamples taken for manometric determinationof respiration rates at different temperatures. The supply capacityof the above-ground portion of the root system was determinedand the results compared in terms of supply and demand. Theoxygen consumption rate of the roots at 15°C was found tobe 1·69±0·07 µmol kg^–1 s^–1for cable roots and 3·27±0·12 µmolkg^–1 s^–1 for fine roots. The Q₁₀ for respirationwas 2·55 for oxygen consumption in both fine and cableroots, and for carbon dioxide production was 2·66 forfine roots and 3·04 for cable roots. The respiratoryquotient varied with temperature but was less than unity. Concentrationdifferences of between 1·8 mol m^–3 and 3·4mol m^–3 between the inside of root and the air were sufficientto permit aeration of the root system by diffusion alone, andthe aerenchyma contained sufficient oxygen to maintain aerobicconditions while the roots were covered with water. The effectof tide and seasonal temperature change on gas exchange, togetherwith the possibility of some form of carbon dioxide fixationwithin the root, are examined and the implications of theseeffects on growth and development are discussed. Key words: Mangrove, root aeration, respiration, aerenchyma