Essential oils enhanced by ultra-high carbon dioxide levels from Lamiaceae species grown in vitro and in vivo

The growth (fresh weight), morphogenesis (leaves, roots and shoots) and essential oil composition of mint (Mentha sp. L.) and thyme (Thymus vulgaris L.) plants were determined after 8 weeks under 350, 1,500, 3,000, 10,000 and 30,000 µmol mol^-1 CO₂. Plants were grown in vitro on basal medium (BM) consisting of Murashige and Skoog salts and 0.8% agar that contained either 0 or 3% sucrose under a 16-h (day)/8-h (night) photoperiod at a light intensity of 180 µmol s^-1 m^-2 or in soil in a greenhouse under conditions of natural sunlight. Ultra-high CO₂ levels (i.e. ́,000 µmol mol^-1 CO₂) substantially increased fresh weights, leaves, shoots and roots for all plants compared to plants grown under ambient air (350 µmol mol^-1 CO₂) both in vivo and in vitro. For both species, 10,000 µmol mol^-1 CO₂ was the optimum concentration to obtain the largest growth and morphogenesis responses under in vitro conditions, while the 3,000- to 10,000-µmol mol^-1 CO₂ range provided the largest yields for soil-grown plants. Essential oil composition (i.e. monoterpenes, piperitonone oxide and limonene from mint and aromatic phenol and thymol from thyme) from the shoot portion of plants grown at all CO₂ levels was analyzed in CH₂Cl₂ extracts via gas chromatography. Higher levels of secondary compounds occurred in vitro when cultures were grown under ultra-high CO₂ levels than in ambient air. The concentration of thymol, a major secondary compound in thyme plants grown on BM containing sucrose, was 317-fold higher at 10,000 µmol mol^-1 CO₂ than in plants grown under ambient air conditions with the same BM. The levels of secondary compound in in-vitro-grown plantlets exposed to ultra-high CO₂ concentrations exceeded those occurring in plants grown in the greenhouse under the same CO₂ levels. Substantially higher levels of secondary compound occurred in plants under ultra-high CO₂ levels on BM containing sucrose than on BM lacking sucrose or in soil. Thymol levels in thyme plants grown on BM containing sucrose were 3.9-fold higher at 10,000 µmol mol^-1 CO₂ than in shoots grown on BM without sucrose under the same CO₂ levels. High positive correlations occurred between thymol concentrations and CO₂ levels, fresh weights, shoots, roots and leaves when thyme shoots were grown on BM with sucrose. High positive correlations for thyme shoots grown on BM without sucrose only occurred between thymol concentrations and CO₂ levels, fresh weights, shoots and leaves. No positive correlations between thymol concentrations and CO₂ levels or any growth or morphogenesis responses occurred for thyme shoots when grown in soil.     

Responses of shoot and root gas exchange, leaf blade expansion and biomass production to pulses of elevated C02 in hydroponic wheat

Short-term effects of elevated CO₂ during the early life phaseof plants may have long lasting consequences for growth andbiomass in later periods. We exposed hydroponically grown wheatseedlings to 5 d pulses of elevated CO₂ while leaf expansiongrowth as well as shoot and root gas exchange were measuredsimultaneously and continuously. Shoot photosynthesis, night-timeshoot respiration and below-ground respiration (largely by roots)roughly doubled when atmospheric CO₂ concentration was doubled.An interruption of CO₂ enrichment caused CO₂ assimilation andrespiration to return to control levels. However, while theresponse of photosynthesis was immediate, that of respirationshowed a hysteresis of about 3 d. Since shoot biomass increasedat elevated CO₂ (with no change in allocation pattern) equalfluxes per shoot or root system after a return to control CO₂concentrations indicate substantial downward adjustment of thecapacity for CO₂ fixation and release in high-CO₂ grown plants.Leaf expansion growth was completely unaffected by CO₂ enrichment,whereas tiller initiation was significantly increased (doubledin 18 d). We conclude that leaf growth in these wheat plantswas already carbon-saturated at ambient CO₂ concentration atoptimum mineral nutrient supply. The stimulation of growth ofwhole plants was exclusively due to enhanced tillering duringthis very early part of the life of these wheat plants. Key words: Allocation, atmospheric carbon dioxide enrichment, growth, photosynthesis, respiration, tillering, Triticum aestivum     

The Influence of Carbon Dioxide and Daily Photon-flux Density on Optimal Leaf Nitrogen Concentration and Root: Shoot Ratio

Using a cost-benefit model, the leaf nitrogen concentrationand root : shoot ratio that maximize whole-plant relative growthrate are determined as a function of the above-ground environment(integrated daily photon flux density and the concentrationof carbon dioxide at the site of fixation within the leaf).The major advantage of this approach is that it determines theadaptive significance of leaf physiology by considering thefunctional integration of leaves and roots. The predicted responseto increasing daily photon flux densities is an increase inoptimal leaf N concentration (N_opt) and a concomitant increasein root: shoot ratio. Increased carbon dioxide concentrations,on the other hand, reduce N_opt and only slightly change root:shoot ratio. The observed increase in leaf nitrogen concentrationfound in plants growing at high altitudes (low CO₂ partial pressure)is also predicted. Since these responses to light and CO₂ maximizethe whole-plant relative growth rate, the observed adjustmentsthat plants make to light and carbon dioxide concentration appearto be adaptive. We show that the relationship between photosynthesis and leafnitrogen concentration is complex and depends on the light andCO₂ levels at which photosynthesis is measured. The shape ofthis function is important in determining N_opt and the oppositeresponse of leaf nitrogen to light and carbon dioxide is shownto be the result of the different effects of light and CO₂ onthe photosynthesis-leaf nitrogen curve. Plant growth, photosynthesis, leaf nitrogen, biomass allocation, optimization, carbon dioxide light     

Effects of CO2 enrichment and intraspecific competition on biomass partitioning, nitrogen content and microbial biomass carbon in soil of perennial ryegrass and white clover

Seedlings of perennial ryegrass (Lolium perenne L. cv. Parcour)and white clover (Trifolium repens L. cv. Karina) grown at fivedifferent plant densities were exposed to ambient (390 ppm)and elevated (690 ppm) CO₂ concentrations. After 43 d the effectsof CO₂ enrichment and plant density on growth of shoot and root,nitrogen concentration of tissue, and microbial biomass carbon(C_mic) in soil were determined. CO₂ enrichment of Lolium perenneincreased shoot growth on average by 17% independent of plantdensity, while effects on root biomass ranged between -4% and+ 107% due to an interaction with plant density. Since tilernumber per plant was unaffected by elevated CO₂, the small responseof shoot growth to CO₂ enrichment was atributed to low sinkstrength. A significant correlation between nitrogen concentrationof total plant biomass and root fraction of total plant drymatter, which was not changed by CO₂ enrichment, indicates thatnitrogen status of the plant controls biomass partitioning andthe effect of CO₂ enrichment on root growth. Effects of elevatedCO₂ and plant density on shoot and root growth of Trifoliumrepens were not significantly interacting and mean CO₂-relatedincrease amounted to 29% and 66%, respectively. However, growthenhancement due to elevated CO₂ was strongest when leaf areaindex was lowest. Total amounts of nitrogen in shoots and rootswere bigger at 690 ppm than at 390 ppm CO₂. There was a significantincrease in C_mic in experiments with both species whereas plantdensity had no substantial effect. Key words: CO₂ enrichment, intraspecific competition, biomass partitioning, Lolium perenne, Trifolium repens, grassland     

A Model Allocating Growth Among Leaf Proteins, Shoot Structure, and Root Biomass to Produce Balanced Activity

A model is developed that considers the allocation of carbonand nitrogen substrates to a protein compartment in the shoots,shoot structural components, and root biomass. Inclusion ofa shoot-protein compartment allows variation in shoot-specificactivity to be modelled as a function of leaf nitrogen concentration.Allocation to the biomass compartments is controlled by twopartitioning variables that are defined by explicitly usingthe balanced activity hypothesis. The model produces balancedactivity where the shoot-specific activity, as well as rootand shoot biomass, vary in response to the above-ground (lightand CO₂) and below-ground (nitrogen) environments. The predictedpatterns of both root: shoot ratio and leaf nitrogen concentrationin response to environmental resource availability are qualitativelyconsistent with general trends observed in plants. Biomass allocation, plant growth, modelling, leaf nitrogen, root: shoot ratio, balanced activity     

Influence of modified oxygen and carbon dioxide atmospheres on mint and thyme plant growth, morphogenesis and secondary metabolism in vitro

. Growth (fresh weight) and morphogenesis (production of leaves, roots and shoots) of mint (Mentha sp. L.) and thyme (Thymus vulgaris L.) shoots were determined under atmospheres of 5%, 10%, 21%, 32%, or 43% O₂ with either 350 or 10,000 µmol mol^-1 CO₂. Plants were grown in vitro on Murashige and Skoog salts, 3% sucrose and 0.8% agar under a 16/8-h (day/night) photoperiod with a light intensity of 180 µmol s^-1 m^-2. Growth and morphogenesis responses varied considerably for the two plant species tested depending on the level of O₂ administered. Growth was considerably enhanced for both species under all O₂ levels tested when 10,000 µmol mol^-1 CO₂ was added as compared to growth responses obtained at the same O₂ levels tested with 350 µmol mol^-1 CO₂. Mint shoots exhibited high growth and morphogenesis responses for all O₂ levels tested with 10,000 µmol mol^-1 CO₂. In contrast, thyme shoots exhibited enhanced growth and morphogenesis when cultured in ₁% O₂ with 10,000 µmol mol^-1 CO₂ included compared to shoots cultured under lower O₂ levels. Essential oil compositions (i.e. monoterpene, piperitenone oxide from mint and aromatic phenol, thymol from thyme) were analyzed from CH₂Cl₂ extracts via gas chromatography from the shoot portion of plants grown at all O₂ levels. The highest levels of thymol were produced from thyme shoots cultured under 10% and 21% O₂ with 10,000 µmol mol^-1 CO_2,and levels were considerably lower in shoots grown under either lower or higher O₂ levels. Higher levels of piperitenone oxide were obtained from mint cultures grown under ₁% O₂ with 10,000 µmol mol^-1 CO₂ compared to that obtained with lower O₂ levels.     

Physiology of Pinus strobus L. Seedlings Grown under High or Low Soil Moisture Conditions

White pine seedlings (Pinus strobus L.) were grown under highor low soil-moisture levels. The increase in the length andin the fresh weight of seedlings, respiration, photosynthesis,transpiration, translocation of photosynthate from shoots toroots, and bio-electric potentials between the tip and the baseof a stem were measured throughout the growing season from Aprilto October 1964. At both moisture levels the lowest translocation of recent photosynthatefrom shoots to roots occurred during early summer, or at thetime when the rate of root growth was the lowest and that ofthe shoot the highest. The specific activity of ¹⁴CO₂, respiredby the shoots of such plants remained high throughout the 8h of the experiment, indicating a continuous utilization ofrecent photosynthate as a respiratory substrate. On the otherhand, early and late in the growing season, when translocationof recent photosynthate from shoots to roots and the rate ofroot growth were high, the specific activity of ¹⁴CO₂, respiredby the shoots rapidly decreased during the 8 h of the experiment,indicating a drop in the utilization of recent photosynthateas respiratory substrate. The highest positive values for thepotential difference between the top and the base of the mainshoot also occurred in early summer or during the period ofhigh rates of transpiration per needle stomatal surface area.     

Models of the Use of Root-zone CO2 by Selected North American Isoetids

Sediment CO₂, entering via the roots, contributes a significantportion of the total carbon uptake for isoetids (small, evergreen,submersed, vascular plants). Laboratory studies of inorganiccarbon uptake via the roots and shoots by five isoetids wereused to model the use of root-zone CO₂. Simple first-order linearmodels accounted for at least 75 per cent of the variation inthe data for Gratiola aurea, Isoetes macrospora, Littorellauniflora and Lobelia dortmanna. For Eriocaulon septangulare,which relies almost exclusively on root-zone CO₂, models couldaccount for only about 62 per cent of the variation in root-zoneCO₂ use. For each species, we present the best fitting regressionof root-zone CO₂ use as a function of root- and shoot-zone CO₂concentrations. For the species studied, carbon uptake was not saturated atfield concentrations of root and shoot-zone CO₂. Maximum ratesof carbon uptake were lower for species that naturally occurredat greater depths, compared with species more common in shallowwater. At equal external CO₂ concentrations carbon entry perunit root surface area was several times more rapid than entryper unit shoot surface area for L. dortmanna. The entry ratesper unit root and shoot surface area were about equal for G.aurea and E. septangulare. Shoots were equally or more permeablethan the roots of L. uniflora and I. macrospora, a fact thatmay be related to the functioning of crassulacean acid metabolismin these plants. Carbon, CO₂, photosynthesis, isoetid, Eriocaulon septangulare, Gratiola aurea, Isoetes macrospora, Littorella uniflora, Lobelia dortmanna     

Changes in the Morphology of Roots and Leaves of Carob Seedlings Induced by Nitrogen Source and Atmospheric Carbon Dioxide

Carob seedlings were grown hydroponically for 9 weeks under360 and 800 µl l^-1CO₂. One of two nitrogen sources, nitrateor ammonium, was added to the nutrient medium at concentrationsof 3 mol m^-3. Root systems of the developing plants suppliedwith nitrate compared to those supplied with ammonium were characterizedby:(a)more biomass on the lower part of the root;(b)fewer lateralroots of first and second order;(c)longer roots;(d)higher specificroot length;(e)a smaller root diameter. The morphology of theroot systems of nitrate-fed plants changed in the presence ofelevated carbon dioxide concentrations, resembling, more closely,that of ammonium-fed plants. Total leaf area was higher in ammonium-than in nitrate-fed plants. Nitrate-fed plants had greater totalleaf area in the presence of high carbon dioxide than in normalCO₂, due to an increase in epidermal cell size that led to developmentof larger leaflets with lower stomatal frequency. The observedchanges in the morphology of roots and shoots agreed with theresults observed for total biomass production. Nitrate-fed plantsincreased their biomass production by 100% in the presence ofelevated CO₂compared to 15% in ammonium-fed plants, indicatingthat the response of carob to high CO₂concentrations is verydependent on the nitrogen source. Under elevated CO₂, nitrate-grownplants had a larger content of sucrose in both roots and shoots,while no significant difference was observed in the contentof sucrose in ammonium-grown plants, whether in ambient or enrichedcarbon dioxide. Hence, the differences in soluble carbohydratecontents can, at least partly, account for differences in rootand shoot morphology.Copyright 1997 Annals of Botany Company Ceratonia siliquaL.; carob; ammonium; carbohydrate; carbon dioxide; nitrate; morphology; sucrose     

Assimilate Partitioning in Red and White Clover Either Dependent on N2 Fixation in Root Nodules or Utilizing Nitrate Nitrogen

During vegetative growth in controlled environments, the patternof distribution of ¹⁴C-labelled assimilates to shoot and root,and to the meristems of the shoot, was measured in red and whiteclover plants either wholly dependent on N₂ fixation in rootnodules or receiving abundant nitrate nitrogen but lacking nodules. In experiments where single leaves on the primary shoot wereexposed to ¹⁴CO₂, nodulated plants of both clovers generallyexported more of their labelled assimilates to root (+nodules),than equivalent plants utilizing nitrate nitrogen, and thiswas offset by reduced export to branches (red clover) or stolons(white clover). The intensity of these effects varied with experiment.The export of labelled assimilate to growing leaves at the terminalmeristem of the donor shoot was not influenced by source ofnitrogen. Internode elongation in the donor shoot utilized nolabelled assimilate. Whole plants of white clover exposed to ¹⁴CO₂ on seven occasionsover 32 days exhibited the same effect on export to root (+nodules),which increased slightly in intensity with increasing plantage. Nodulated plants had larger root: shoot ratios than theirequivalents utilizing nitrate nitrogen. Trifolium repens, Trifolium pratense, red clover, white clover, nitrogen fixation, nitrate utilization, assimilate partitioning     

Effect of controlled carbon dioxide on in vitro shoot multiplication in Feronia limonia (L.) Swingle

The effect of controlled carbon dioxide environment on in vitro shoot growth and multiplication in Feronia limonia (a tropical fruit plant, Family- Rutaceae) was studied. Carbon dioxide available in the ambient air of the growth room was insufficient for in vitro growth of the shoots alone. Also, the presence of sucrose only as the C-source in the medium (without CO₂), was found to be inadequate for sustainable growth and multiplication of shoots. The carbon dioxide enrichment promoted shoot multiplication and overall growth. The promotory effect of CO₂ was independent of the presence of sucrose in the medium. In the presence of both CO₂ and sucrose, an additive effect was observed producing maximum shoot growth. In the absence of sucrose a higher concentration of CO₂ (10.0)g m⁻³ was required to achieve photoautotrophic shoot multiplication comparable to ambient air controls. Highest leaf area per shoot cluster promoting shoot growth and multiplication was recorded under this treatment. Shoots growing on sucrose containing medium under controlled CO₂ environment of 0.6 g m⁻³ concentration evoked better response than ambient air controls (shoots growing on sucrose containing medium) in growth room. This treatment produced the overall best response. The present study highlighted the possibility of photoautotrophic multiplication which might prove useful for successful hardening and acclimatization in tissue culture plants.     

Effects of CO2 Enrichment at Different Irradiances on Growth and Yield of Wheat: II. EFFECTS ON KLEIBER SPRING WHEAT TREATED FROM ANTHESIS IN CONTROLLED ENVIRONMENTS IN RELATION TO EFFECTS ON PHOTOSYNTHESIS AND PHOTORESPI RATION

Spring wheat plants were grown in a cage with a glass roof untilthree days after anthesis and then subjected to treatments inconstant environment rooms with any one of all combinationsof four irradiances and two concentrations of carbon dioxide.The photoperiod was 16 h and day/night temperatures 19?C/14?C.Growth and yield of grain were saturated at the two brightestirradiances. Carbon dioxide enrichment from 350 to 1200 mm³dm^–3 increased shoot dry weight and grain yield at finalharvest at all irradiances, by averages of 10.5 (not significant)and 23.5 (significant) percent respectively. However, increasingthe irradiance from 150 to 613 µE m^–2 s^–1caused much larger yield increases (approximately 3-fold). Increasedgrain production by increased light was caused by both increasesin dry weight per grain and by increases in grain number perspikelet. The increase caused by CO₂ enrichment was mainly becauseof increased dry weight per grain. Increase in ear dry weightcaused by CO₂ enrichment took place between 30 and 60 d afteranthesis. The increase in shoot dry weight took place immediatelyafter exposure to increased CO₂ from 3 to 15 d after anthesis.Net photosynthesis by flag leaves on the main shoots was almostdoubled 16 d after anthesis by the CO₂ enrichment even thoughstomatal resistance was also doubled. However, this increasewas not reflected by a proportional increase in yield, probablybecause increased mutual shading by bigger stems and late tillersreduced total assimilation and because of increased respirationby the shoots. The increase in photosynthesis was not due toa decrease in photorespiration but to an increase in gross photosynthesis. Key words: CO₂enrichment, Photosynthesis, Photorespiration     

Dark Respiration of Several Varieties of Winter Wheat Given Different Amounts of Nitrogen Fertilizer

Carbon dioxide production in the dark by ears and by the restof the shoot of winter wheat grown in the field was measuredin 2 years during grain growth. The respiration rate per g d.wt of the ears was increased by nitrogen fertilizer. Ears ofthe semi-dwarf varieties Maris Fundin and Hobbit respired moreslowly than ears of Maris Huntsman and Cappelle-Desprez. Respirationrates of the rest of the shoot were unaffected by nitrogen orvariety. The amount of carbohydrate required to provide the CO₂ respiredduring the whole period of grain growth varied from 163 to 443g m^–2, or 42 to 76 per cent of the dry weight of the grain.More than half the CO₂ lost was respired by the ear. The additionof 180 kg N ha^–1, which increased grain yield by 78 percent in 1975, almost trebled the amount of CO₂ lost by the ears.The semi-dwarf varieties lost less CO₂ from ears and shootsthan did the taller ones, and had larger yields of grain. Respiration was also estimated from the difference between the¹⁴C contents of shoots sampled immediately after a 30 s exposureto ¹⁴CO₂ and at maturity. When 14C was supplied 10 days afteranthesis, the loss by maturity amounted to 16–28 per centof that initially absorbed by flag leaves and 40 per cent ofthat absorbed by the leaf below the flag leaf. Most of the lossoccurred in the first day. The loss of 14C by maturity was significantlyincreased by nitrogen fertilizer in 1975. Triticum aestivum L., wheat, respiration, nitrogen supply, fertilizer treatment     

Elevated [CO2] and nutrient status modified leaf phenology and growth rhythm of young Populus trichocarpa trees in a 3-year field study

Young individuals of a single clone of black cottonwood, in Iceland, were exposed for 3 years to elevated atmospheric CO₂ concentrations [CO₂] in whole-tree chambers at natural and high nutrient availability. No treatment effects were found at bud break or the start of shoot extension in spring. Autumn phenology was, however, affected both by elevated [CO₂] and changes in nutrient status. The time of annual growth cessation was linearly related to leaf nitrogen concentration, irrespective of CO₂ treatment. At low (natural) nutrient availability, elevated [CO₂] accelerated growth cessation and bud set, which reduced the period of active growth. An earlier and more pronounced leaf senescence and corresponding loss of photosynthetic capacity further decreased carbon acquisition in elevated [CO₂]. The negative [CO₂] effect on duration of shoot extension and leaf senescence existed, but was not as pronounced, when trees grew at higher nutrient availability. Improved nutrient availability extended the shoot extension period and delayed leaf senescence. It is suggested that trees grown in elevated [CO₂] altered their autumn phenology as an effect of a signal similar to that in trees growing at low nutrient availability, i.e. an imbalance between carbon and nitrogen sources. These alterations in autumn phenology may be important when predicting how trees will grow in a future CO₂ environment.     

Effects of Sucrose Concentration on the Photosynthetic Ability of Rose Shoots In Vitro

Reducing the concentration of sucrose in the culture mediumover successive subcultures has been tested as a method forincreasing the ability of rose shoots grown in vitro (Rosa cvsIceberg and Peace) to take up CO₂. Shoots maintained on ‘constant’10, 20 and 40 g I^–1 sucrose showed decreased levels ofCO² uptake at higher sucrose concentrations, although cv. Peacegrew least at 10 g l^–1 and showed correspondingly lowamounts of CO₂ uptake compared with 20 and 40 g l^–1. Bothcultivars died when sucrose was omitted from the medium. Assucrose concentration was reduced in the medium, so CO₂ uptakeof shoots initially cultured on 20 and 40 g l^–1 sucrosewas found to increase, although a concentration of 10 gl ^–1sucrose seemed to be limiting, below which the growth and chlorophylllevels of shoots declined. Rosa hybrid, rose, shoot culture in vitro, photosynthetic ability, sucrose, infra-red gas analysis     

Root to shoot ratio of crops as influenced by CO2

Crops of tomorrow are likely to grow under higher levels of atmospheric CO₂. Fundamental crop growth processes will be affected and chief among these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO₂ concentration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO₂ concentration will affect roots and shoots of crop plants proportionally. Since elevated CO₂ can induce changes in plant structure and function, there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO₂ on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability. Herein we review root to shoot allocation as affected by increased concentrations of atmospheric CO₂ and provide recommendations for further research. Review of the available literature shows substantial variation in R:S response for crop plants. In many cases (59.5%) R:S increased, in a very few (3.0%) remained unchanged, and in others (37.5%) decreased. The explanation for these differences probably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO₂ enrichment will add substantially to the global change response data base.Abbreviations R:S root to shoot ratio, dry weight basis     

Is Partitioning of Dry Weight and Leaf Area Within Dactylis glomerata Affected by N and CO2Enrichment?

We examined changes in dry weight and leaf area within Dactylisglomerata L. plants using allometric analysis to determine whetherobserved patterns were truly affected by [CO₂] and N supplyor merely reflect ontogenetic drift. Plants were grown hydroponicallyat four concentrations of in controlled environment cabinets at ambient (360 µll^–1) or elevated (680 µl l^–1) atmospheric[CO₂]. Both CO₂and N enrichment stimulated net dry matter production.Allometric analyses revealed that [CO₂] did not affect partitioningof dry matter between shoot and root at high N supply. However,at low N supply there was a transient increase in dry matterpartitioning into the shoot at elevated compared to ambient[CO₂] during early stages of growth, which is inconsistent withpredictions based on optimal partitioning theory. In contrast,dry matter partitioning was affected by N supply throughoutontogeny, such that at low N supply dry matter was preferentiallyallocated to roots, which is in agreement with optimal partitioningtheory. Independent of N supply, atmospheric CO₂enrichment resultedin a reduction in leaf area ratio (LAR), solely due to a decreasein specific leaf area (SLA), when plants of the same age werecompared. However, [CO₂] did not affect allometric coefficientsrelating dry weight and leaf area, and effects of elevated [CO₂]on LAR and SLA were the result of an early, transient stimulationof whole plant and leaf dry weight, compared to leaf area production.We conclude that elevated [CO₂], in contrast to N supply, changesallocation patterns only transiently during early stages ofgrowth, if at all. Copyright 2000 Annals of Botany Company Allometric growth, carbon dioxide enrichment, Cocksfoot, Dactylis glomerata L., dry weight partitioning, leaf area ratio, nitrogen supply, shoot:root ratio, specific leaf area     

Photosynthetic Assimilation of 14CO2 by Mature Brown Stems of the Tea Plant (Camellia sinensis L.)

The fixation of ¹⁴CO₂ by mature brown stems of the tea plantwas studied by supplying ¹⁴CO₂ to selected stems of pruned andintact plants for 24 h under field conditions. Utilization of¹⁴C assimilates for the production of new shoots was also examined.The photosynthetic nature of the fixation of ¹⁴CO₂ is demonstrated.The efficiency of this fixation was very low compared with thattaking place in leaves. The movement of labelled assimilatesfrom stem bark to the roots was inappreciable, whereas newlyemerged shoots on the pruned frame drew labelled assimilatesfrom stem bark.     

Studies in the Nutrition of Apple Rootstocks: III. Effects of Level of Magnesium Nutrition on Growth, Form and Mineral Composition

One-year rooted shoots of apple M. VII rootstock were grownfor a single season by spraying their roots continuously withnutrient solutions containing <3, 10, 45, and 135 ppm Mg.These treatments respectively produced plants with a severeMg deficiency (Mg₍₀₎), a mild deficiency (Mg₍₁₎), normal foliageand growth (Mg₍₂₎), and a high level of Mg (Mg₍₃₎). The effectof Mg nutrition on the leaves can explain most of the observedeffects on vegetative growth. Depression of growth of Mg₍₁₎)plants was not detected until late in the season although necrosis,typical of Mg deficiency, occurred on the lower leaves by mid-July.This loss of photosynthetic area of leaf was to a large extentcompensated for by increased efficiency of the remaining greenleaves; as the deficiency symptoms progressed, the loss of leaf,and therefore of carbohydrate production, predominated and totalgrowth was affected. The form of the plant was little altered. Symptoms were apparent on leaves of severely deficient Mg₍₀₎plants by late June, and reductions in growth and modificationsin form by August. The poor root systems and thin shoots arelargely attributed to loss of leaf rather than to the low Mgconcentration in these organs. No symptoms of toxicity developed on the Mg₍₃₎ plants althoughby the end of the season the total dry weights were less thanthose of the Mg₍₂₎ controls, and the plants also produced thickershoots. Plant dry weight, and more especially Mg uptake, increasedfrom Mg₍₀₎ to Mg₍₂₎ but above this level the gradient of Mguptake in relation to supply was less steep. The excess Mg takenup at the Mg(j) level led to the relatively lower weights ofthese plants. Much of the excess Mg accumulated in the leaves,especially in the older ones. Mg moved from, or accumulatedin, the lower leaves of the shoot according to the level ofMg supplied to the plants. Thus the shoot apex tended towardsnormality both in the concentration of Mg and in its growth. In general, growth of the plant, and of individual componentparts, governed the uptake of elements other than Mg, althoughmore K, Ca, and Mn and less Fe per unit of plant dry weightaccumulated at the lower levels of Mg than at the higher levels.     

Effects of Waterlogging on the Gibberellin Content and Growth of Tomato Plants

Flooding of tomato roots results in decreased stem growth. Wehave shown that flooding will reduce levels of gibberellins(GA) in the roots, shoots, and bleeding sap of tomato plants.The adventitious roots that appear on the third day of waterloggingmay be responsible for the production of GA that accumulatein the shoot after 3 to 4 days of flooding. The endogenous GAof tomato will stimulate stem growth of tomato plants. Initially,application of gibberellic acid (GA₃) will stimulate the growthof flooded plants to a greater extent than that of nonwaterloggedplants. It is suggested that one of the first effects of floodingis to reduce GA levels and so inhibit stem elongation. At alater stage of waterlogging GA₃ is less effective and otherfactors appear to inhibit shoot growth.