Direct and Maternal Effects of Elevated CO2on Early Root Growth of GerminatingArabidopsis thalianaSeedlings

Individuals ofArabidopsis thaliana, collected in different naturalpopulations, were grown in controlled and elevated CO₂in a glasshouse.Following germination, root growth of progeny of different linesof these populations was studied in control and elevated atmosphericCO₂. No significant direct effect of atmospheric CO₂concentrationcould be demonstrated on root growth. An important parentaleffect was apparent, namely that root length and branching weredecreased in seeds collected from a mother plant which had beengrown in elevated CO₂. This was correlated with smaller seeds,containing less nitrogen. These parental effects were geneticallyvariable. We conclude that CO₂may affect plant fitness via parentaleffects on seed size and early root growth and that the geneticvariability shown in our study demonstrates thatArabidopsispopulationswill evolve in the face of this new selective pressure.Copyright1998 Annals of Botany Company Root growth, root branching, seed, elevated CO₂, natural population,Arabidopsis thaliana, parental effect.     

Temporal and Nutritional Influences on the Response to Elevated CO2 in Selected British Grasses

To investigate the duration of the CO₂ response and its interactionwith mineral nutrition, CO₂-enrichment experiments were performedon four British grasses of differing ecology and functionaltype: Arrhenatherum elatius (L.) Beauv., Festuca ovina L., Festucarubra L. and Poa annua L. Naturally-lit, glasshouse cabinetswere used, with a non-limiting water supply and a daytime meantemperature of 18 °C. Two CO₂ treatments were maintainedat nominal concentrations of 350 and 700 vpm and were combinedfactorially with two levels of balanced mineral nutrition atconductivities of 0·1 and 1 mS cm^-1. Harvests took placeat planting-out, and at 16, 37 and 58 d thereafter. Fitted curves were used to derive instantaneous values of totaldry weight, relative growth rate (RGR), shoot weight fraction(SWF) and unit shoot rate (USR) for all combinations of species,CO₂ level, nutrient level and time of harvesting. At the higher nutrient level there was a reasonably close agreementwith previous estimates of the CO₂ response in the four species.The response, if any, most often arose from an increase in USRbeing accompanied by a less than proportionate decline in SWF.Responses were sustained throughout the period studied. At thelower nutrient level, all species showed a CO₂ response initially,but this declined at a rate which was inversely related to theCO₂-responsiveness of the species at the higher nutrient level. The underlying ontogenetic drift appeared to be markedly towardsadjustment in SWF and away from that of USR. However, this driftwas retarded, suspended or even reversed by low-nutrient conditionsand/or by high CO₂ responsiveness in the species itself.Copyright1995, 1999 Academic Press Climate change, CO₂ enrichment, plant strategies, mineral nutrition, growth analysis, relative growth rate, shoot weight fraction, unit shoot rate, functional equilibria     

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     

Genotypic variation in response of quaking aspen (Populus tremuloides) to atmospheric CO2 enrichment

Enriched atmospheric CO₂ alters the quantity and quality of plant production, but how such effects vary among plant genotypes is poorly known. We evaluated the independent and interactive effects of CO₂ and nutrient availability on growth, allocation and phytochemistry of six aspen (Populus tremuloides Michx.) genotypes. One-year-old trees, propagated from root cuttings, were grown in CO₂-controlled glasshouses for 64 days, then harvested. Foliage was analyzed for levels of water, nitrogen, starch, phenolic glycosides and condensed tannins. Of seven plant growth/allocation variables measured, four (biomass production, stem growth, relative growth rate and root:shoot ratio) exhibited marginally to highly significant CO₂ 2 genotype interactions. CO₂ enrichment stimulated growth of some genotypes more than others, and this interaction was itself influenced by soil nutrient availability. In addition, enriched CO₂ increased the magnitude of the among-genotype variance for four of the growth/allocation variables. Of six foliar chemical constituents analyzed, CO₂-mediated responses of two (the phenolic glycoside tremulacin and condensed tannins) varied among genotypes. Moreover, enriched CO₂ increased the magnitude of among-genotype variance for four of the chemical variables. Given the importance of these growth and chemical characteristics to the biological fitness of aspen, this research suggests that projected atmospheric CO₂ increases are likely to alter the genetic structures and evolutionary trajectories of aspen populations.     

Response of Photosynthesis, Stomatal Conductance and Water Use Efficiency to Elevated CO2 and Nutrient Supply in Acclimated Seedlings of Phaseolus vulgaris L.

Plants of Phaseolus vulgaris L were grown from seed in open-topgrowth chambers at present day (350 µmol mol^–1)and double the present day (700 µmol mol^–1) atmosphericCO₂ concentration with either low (L, without additional nutrientsolution) or relatively high (H, with additional nutrient solution)nutrient supply Measurements of assimilation rate, stomatalconductance and water use efficiency were started 17 d aftersowing on each fully expanded, primary leaf of three plantsper treatment Measurements were made in external CO₂ concentrations(C₂) of 200, 350, 450, 550 and 700 µmol mol^–1 andrelated to both C_a and to C₁, the mean intercellular space CO₂concentration Fully adjusted, steady state measurements weremade after approx 2 h equilibration at each CO₂ concentration The rate of CO₂ assimilation by leaves increased and stomatalconductance decreased similarly over the range of C_a or C₁ inall four CO₂ and nutrient supply treatments but both assimilationrate and stomatal conductance were higher in the high nutrientsupply treatment than in the low nutrient treatment The relationbetween assimilation rate or stomatal conductance and C₁ wasnot significantly different amongst plants grown in present-dayor elevated CO₂ concentration in either nutrient supply treatment,i e there was no evidence of down regulation of photosynthesisor stomatal response Increase in CO₂ concentration from 350to 700 µmol mol^–1 doubled water use efficiency ofindividual leaves in the high nutrient supply treatment andtripled water use efficiency in the low nutrient supply treatment The results support the hypothesis that acclimation phenomenaresult from unbalanced growth that occurs after the seed reservesare exhausted, when the supply of resources becomes growth limiting CO₂ enrichment, Phaseolus vulgaris L., net CO₂ assimilation rate, stomatal conductance, water use efficiency     

Effects of Light and CO2 on Net Photosynthesis Rates of Stands of Aubergine and Amaranthus

Net photosynthetic rates per unit ground area for plant standsof Solanum melongena L. var. esculentum (aubergine) and Amaranthuscaudatus L. var. edulis (grain amaranth) were measured over10 min intervals in an airtight, glass, controlled-environmentcabinet for a range of light flux densities provided by thediurnal variation in daylight. Light response curves for photosynthesisof stands, grown at ambient CO₂ concentration, were definedat 400, 800 and 1200 vpm CO₂. Light compensation points for these stands were around 20-30J m^-2 s^-1 and decreased slightly at higher CO₂ concentrations.For aubergine, a C₃ species, the short-term effects of CO₂ enrichmentwere to increase the initial slope as well as the asymptoteof the light response curve, reducing light saturation at moderateto high light flux densities; but for amaranthus, a C₄ species,saturation was less apparent and CO₂ enrichment scarcely increasedphotosynthesis except at light flux densities above 150 J m^-2s^-1. The canopies intercepted 93-98% of incident light. The efficiencyof utilization of intercepted light in photosynthesis (µgCO₂ J^-1) increased from zero at the light compensation pointto a maximum at an optimum light flux density of about 100 Jm^-2 s^-1 (the optimum rose a little with CO₂ enrichment) anddecreased slightly with further increase in light. Maximum utilizationefficiencies at 400 vpm CO₂ were 8-9 µg CO₂ J^-1. Enrichmentto 1200 vpm did not affect the peak utilization efficiency ofthe C₄ amaranthus, but increased that aubergine to 12·2µg CO₂ J^-1 (equivalent to some 14% when using the heatof combustion of plant dry matter to convert to the dimensionlessform). This is among the highest recorded efficiencies of lightutilization for stands, and relates to the exceptionally favourableenvironment, with optimal control of CO₂ concentration, humidity,temperature, water supply and mineral nutrition.Copyright 1993,1999 Academic Press Amaranthus caudatus L. var. edulis, Solanum melongena L. var. esculentum, canopy photosynthesis, CO₂ enrichment, light interception, light utilization, photosynthetic efficiency     

Photosynthesis, Ribulose-1,5-bisphosphate Carboxylase and Leaf Characteristics of Nicotiana tabacum L. Genotypes Selected by Survival at Low CO2 Concentrations

The photosynthetic characteristics (responses to CO₂ and light),ribulose-1,5-bisphosphate carboxylase (Rubisco) properties,and the size and number of cells of the mesophyll of Nicotianatabacum L. leaves of genotypes selected for survival at lowatmospheric CO₂ concentrations are described. When grown inthe greenhouse with nutrient solutions, the total dry matterproduction of the selected genotypes was 23% greater than thatof the parent genotype; this increase was related to a greaternumber of mesophyll cells of smaller size in the selected plantscompared to the parent. However, it was not related to changesin the photosynthetic characteristics nor to Rubisco properties.These results suggest that the increased dry matter accumulationof the selected genotypes is not due to a reduction in photorespirationnor an increase in the CO₂ assimilation rates. Rather, the selectionof haploid tobacco plantlets in low CO₂ has resulted in plantswith greater leaf area (shown in previous work), due to theproduction of more cells of smaller size and to lower respirationrates per unit of leaf dry mass (previous work), thus increasinglight capture, reducing the loss of assimilates and increasingtotal plant dry matter production. Key words: Photosynthesis, ribulose-1,5-bisphosphate carboxylase, leaf anatomy, tobacco, genotypes     

Stomatal responses to a range of variables in two tropical tree species grown with CO2 enrichment

Seedlings of Maranthes corymbosa (Blume) and Eucalyptus tetrodonta(F. Muell) were grown with or without CO₂ enrichment (700µmolCO₂ mol^–1 The response of stomatal conductance (g₂) toleaf drying, exogenous absclslc acid and calcium ions was investigatedin M. corymbosa. Reciprocal transfer experiments were also conductedwhereby plants were grown in one treatment and then transferredto the other before g, was measured. Stomatal conductance in M. corymbosa was more sensitive (a greaterpercentage decline in g₂ per unit percentage decline in leaffresh weight) to leaf water status under conditions of CO₂ enrichmentcompared to ambient conditions. However, the rate of reductionof g₂ in response to exogenous abscisic acid was not influencedby CO₂ treatment. In contrast, the rate of reduction of g₂,in response to exogenous CaCl₂ was decreased under conditionsof CO₂ enrichment. Reciprocal transfer experiments showed that expo sure to CO₂enrichment results in a short-term, reversible decline in g₂,as a result of decreased stomatal aperture and a long-term,irreversible decline in g₂ as a result of a decreased stomataldensity. Seedlings of E. tetrodonta were used to investigate the responseof g₂ to light flux density, leaf-to-air vapour pressure difference(LAVPD), leaf internal CO₂ concentration (C₁ and temperature.Reciprocal transfer experiments were also conducted. CO₂ enrichmentdid not influence the pattern or sensitivity of response ofg to LAVPD and C in E. tetrodonta. In contrast, the slope ofthe response of g₂, to temperature decreased for trees grownunder elevated [CO₂]_a conditions and the equilibrium g₂ attainedat saturating light was also decreased for plants grown underelevated [CO_2a. conditions. Key words: Stomata, elevated CO₂, tropical trees     

Effects of Elevated Carbon Dioxide on Plant Biomass Production and Competition in a Simulated Neutral Grassland Community

Using open-top chambers, four prominent species (Lolium perenne,Cynosurus cristatus, Holcus lanatusandAgrostis capillaris) ofIrish neutral grasslands were grown at ambient and elevated(700 µmol mol^-1) atmospheric CO₂for a period of 8 months.The effects of interspecific competition on plant responsesto CO₂enrichment were investigated by growing the species ina four-species mixture. The results indicate that the speciesdiffer in their ability to respond to elevated CO₂. CO₂-enrichmenthad the largest effect on the biomass production ofH. lanatus,but substantial stimulations in biomass production were alsofound for the other three species. The CO₂-stimulation of biomassproduction forH. lanatuswas accompanied by increased tillering.In addition, reductions in specific leaf area were found forall species. Exposure to elevated CO₂increased the communitybiomass of the four-species mixture. This increase can be mainlyattributed to a significant increase in the biomass ofH. lanatusatelevated CO₂. No statistically-significant changes in speciescomposition of community biomass were found. However,H. lanatusdidincrease its share of community biomass at each of the harvests,with the other three species, mainlyL. perenne, suffering lossesin their shares at elevated CO₂. The results show that: (1)the species varied in their response to elevated CO₂; and (2)species composition in natural plant communities is likely tochange at elevated CO₂, but these changes may occur rather slowly.Much longer periods of exposure to elevated atmospheric CO₂maybe required to permit detection of significant changes in speciescomposition.Copyright 1998 Annals of Botany Company Carbon dioxide (CO₂) enrichment, competition, Lolium perenne,Cynosurus cristatus, Holcus lanatus, Agrostis capillaris, biomass, specific leaf area, tillering.     

Production of reactive oxygen species in Arabidopsis thaliana cell suspension cultures in response to an elicitor from Fusarium oxysporum: implications for basal resistance

The present understanding of ROS generation in the defence responseof Arabidopsis thaliana is reviewed. Evidence suggests thatthe apoplastic oxidative burst generated during basal resistanceis peroxidase-dependent. The ROS generated during this basalresistance may serve to activate NADPH oxidase during the R-gene-mediatedhypersensitive response. The processes involved in the productionof reactive oxygen species in A. thaliana cell suspension culturesin response to an elicitor from Fusarium oxysporum are investigatedin the present work. This system appears analogous to the productionof ROS during the basal resistance response in French bean,which is peroxidase-dependent. A panel of modulators effectivein other pathogen elicitor and plant cell systems has been usedto investigate the Arabidopsis signalling pathways and the plantcell responses involved. Thus as in other systems, an earlycalcium influx into the cytosolic compartment, a rapid effluxof K⁺ and Cl^–, and extracellular alkalinization of elicitedcell cultures has been found. However the alkalinization isnot sufficient to stimulate the apoplastic oxidative burst byitself, unlike in French bean, although vectorial ion fluxesare needed. A secretory component which is sensitive to monensinand N-ethylmaleimide and insensitive to brefeldin A may alsobe necessary for the release and provision of substrates forperoxidase-dependent generation of H₂O₂. Key words: Arabidopsis thaliana, calcium, elicitation, hydrogen peroxide, oxidative burst, secretion     

Effect of irradiance and vapour pressure deficit On stomatal response to CO2 enrichment of four tree species

The stomatal response of seedlings grown in 360 or 720 µmolmol^–1 to irradiance and leaf-to-air vapour pressure deficit(VPD) at both 360 and 720 µmol mol^–1 to CO₂ wasmeasured to determine how environmental factors interact withCO₂ enrichment to affect stomatal conductance. Seedlings offour species with different conductances and life histories,Cercis canadensis (L.), Quercus rubra (L.), Populus deltoides(Bartr. ex Marsh.) P. nigra (L.), and Pinus taeda (L.), weremeasured in hopes of identifying general responses. Conductanceof seedlings grown at 360 and 720 µmol mol^–1 CO₂were similar and responded in the same manner to measurementCO₂ concentration, irradiance and VPD. Conductance was lowerfor all species when measured at 720 than when measured at 360µmol mol^–1 CO₂ at both VPDs ({small tilde}1.5 and{small tilde}2.5 kPa) and all measured irradiances greater thanzero (100, 300, 600,>1600 µmol m^–2 S^–2)The average decrease in conductance due to measurement in elevatedCO₂ concentration was 32% for Cercis, 29% for Quercus, 26% forPopulus, and 11% for Pinus. For alt species, the absolute decreasein conductance due to measurement in CO₂ enrichment decreasedas irradiance decreased or VPD increased. The proportional decreasedue to measurement in CO₂ enrichment decreased in three of eightcases: from 0.46 to 0.10 in Populus and from 0.18 to 0.07 inPinus as irradiance decreased from>1600 to 100 µmolm^–2 s^–1 and from 0.35 to 0.24 in Cercis as VPD increasedfrom 1.3 to 2.6 kPa. Key words: Stomatal conductance, CO₂ enrichment, irradiance, vapour pressure deficit     

Effects of elevated carbon dioxide on three grass species from montane pasture II. Nutrient uptake, allocation and efficiency of use

Agrostis capillaris L.⁴ Festuca vivipara L. and Poa alpinaL.were grown in outdoor open-top chambers at either ambient (340µmol mol^–1) or elevated (680 µmol^–1)CO² for periods from 79 to 189 d. Under these conditions thereis increased growth of A. caplllarls and P. alpina, but reducedgrowth of F. vivipara. Nutrient use efficiency, nutrient productivity(total plant dry weight gain per unit of nutrient) and nutrientallocation of all three grass species were measured in an attemptto understand their individual growth responses further andto determine whether altered nutrient-use efficiencies and productivitiesenable plants exposed to an elevated atmospheric CO₂ environmentto overcome potential limitations to growth imposed by soilfertility. Total uptake of nutrients was, in general, greater in plantsof A. capillaris and P. alpina (with the exception of N andK in the latter) when grown at 680 µmol mol^–1 CO₂.In F. vivipara, however, uptake was considerably reduced inplants grown at the higher CO₂ concentration. Overall, a doubling of atmospheric CO₂ concentration had littleeffect on the nutrient use efficiency or productivity of A.capillaris. Reductions in tissue nutrient content resulted fromincreased plant growth and not altered nutrient use efficiency.In P. alpina, potassium, magnesium and calcium productivitieswere significantly reduced and photosynthetic nitrogen and phosphorususe efficiencies were doubled at elevated CO₂ with respect toplants grown at ambient CO₂ F. vivipara grown for 189 d showedthe most marked changes in nutrient use efficiency and nutrientproductivity (on an extracted dry weight basis) when grown atelevated CO₂, F. vivipara grown at elevated CO₂ however, showedlarge increases in the ratio of non-structural carbohydrateto nitrogen content of leaves and reproductive tissues, indicatinga substantial imbalance between the production and utilizationof assimilate. Key words: Nutrient, allocation, nutrient use efficiency, grasses, nutrient productivity, elevated CO₂, cliniate change     

The Greenhouse Effect: Acclimation of Tomato Plants Growing in High CO2, Photosynthesis and Ribulose-1, 5-Bisphosphate Carboxylase Protein

Tomato plants were grown in solution culture in a controlledenvironment at 20 ?C with a 12 h photoperiod of 400 µmolquanta m^–2 s^–1 PAR with either normal ambient CO₂,approximately 340 vpm, or with 1000 vpm CO₂. The short- andlong-term effects of CO₂ enrichment on photosynthesis were determinedtogether with the levels of ribulose-1, 5-bisphosphate carboxylase(RuBPco) E.C. 4.1.1.39 [EC] protein and activity throughout leafdevelopment of the unshaded 5th leaf above the cotyledons. Thehigh CO₂ concentration during growth did not appreciably affectthe rate of leaf expansion or final leaf area but did increasethe fresh weight per unit area of leaf. With short-term CO₂enrichment, i.e. only during the photosynthesis measurements,the light-saturated photosynthetic rate (P_max) of young leavesdid not increase while those reaching full expansion more thandoubled their net rate of CO₂ fixation. However, with longerterm CO₂ enrichment, i.e. growing the crop in high CO₂, theplants did not maintain this photosynthetic gain. While theCO₂ concentration during growth did not affect the peak in P_maxmeasured in 300 vpm CO₂ or P_max in 1000 vpm CO₂, RuBPco proteinor its activity, the subsequent ontogenetic decline in theseparameters was greatly accelerated by the high CO₂ treatment.Compared with plants grown in normal ambient CO₂ the high CO₂grown leaves, when almost fully expanded, contained only approximatelyhalf as much RuBPco protein and P_max in 300 vpm CO₂ and P_maxin1000 vpm CO₂ were similarly reduced. The loss of RuBPco proteinmay be a major factor associated with the accelerated fall inP_max since it was close to that predicted from the amount andkinetics of RuBPco assuming RuBP saturation. In the oldest leavesexamined grown in high CO₂ additional factors may be limitingphotosynthesis since RuBPco kinetics marginally overestimatedP_max in 300 vpm CO₂ and the initial slope of photosynthesisin response to intercellular CO₂ was also less than expectedfrom the extractable RuBPco. Key words: Lycopersicon esculentum (Mill.) cv. Findon Cross, CO₂ enrichment, acclimation to high CO₂, photosynthesis, RuBPco protein and activity     

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 Effects of CO2 Enrichment and Nutrient Supply on Growth Morphology and Anatomy of Phaseolus vulgaris L. Seedlings

Plants of Phaseolus vulgaris were grown from seed in open-topgrowth chambers at the present (P, 350 µmol mol^–1)atmospheric CO₂ concentration and at an elevated (E, 700 µmolmol^–1) CO₂ concentration, and at low (L, without additionalnutrient solution) and high (H, with additional nutrient solution)nutrient supply for 28 d The effects of CO₂ and nutrient availabilitywere examined on growth, morphological and biochemical characteristics Leaf area and dry mass were significantly increased by CO₂ enrichmentand by high nutrient supply Stomatal density, stomatal indexand epidermal cell density were not affected by elevated CO₂concentration or by nutrient supply Leaf thickness respondedpositively to CO₂ increasing particularly in mesophyll areaas a result of cell enlargement Intercellular air spaces inthe mesophyll decreased slightly in plants grown in elevatedCO₂ Leaf chlorophyll content per unit area or dry mass was significantlylower in elevated CO₂ grown plants and increased significantlywith increasing nutrient availability The content of reducingcarbohydrates of leaves, stem, and roots was not affected byCO₂ but was significantly increased by nutrient addition inall plant parts Starch content in leaves and stem was significantlyincreased by elevated CO₂ concentration and by high nutrientsupply Phaseolus vulgaris, elevated atmospheric CO₂, CO₂-nutrient interaction, stomatal density, leaf anatomy, chlorophyll, carbohydrates, starch     

Effects of Different CO2 Environments on the Photosynthesis-Yield Relationship and the Carbon and Water Balance of a White Clover (Trifolium repens L. cv. Blanca) Sward

Effects of atmospheric CO₂ enrichment to a level above 600 parts10^–6 on leaf and canopy gas exchange characteristics wereinvestigated in Trifolium repens, using an open system for gasexchange measurement. The cuvettes of the system served as growthchambers, allowing continuous measurement in a semi-controlledenvironment of ±350 and ±600 parts 10^–6CO₂, respectively. Carbon balance data were compared with cropyield and effects on the canopy level were compared with measuredleaf responses of photosynthesis and stomatal behaviour. Photosyntheticstimulation by high CO₂ was stronger at the canopy level (103%on average) than for leaves (90% in full light), as a consequenceof accelerated foliage area development. The latter increasedabsolute water consumption by 16%, despite strong stomatal closure.The overall result was a 63% improvement in canopy water useefficiency (WUE), while leaf WVE increased almost 3-fold insaturating light. The stomatal response was such that, whilethe internal CO₂ concentration in the leaf, ch increased withrising atmospherical CO₂ concentration, c_a, ci/c_a was somewhatdecreased. Total canopy resistance, R_c, was generally lowerat high CO₂ levels, despite higher leaf resistance. Higher canopyCO₂ loss at night and faster light extinction in a larger-sizedhigh CO₂ canopy were major drawbacks which prevented a furtherincrease in dry matter production (the harvest index was increasedby a factor 1.83). Key words: CO₂ enrichment, canopy CO₂ exchange, carbon balance, water use efficiency, leaf and canopy resistance     

Nutrient Dilution by Starch in CO2-enriched Chrysanthemum

Increasing growth irradiance and CO₂ generally decreases foliarnutrient concentration on a dry weight basis and increases foliarstarch concentration. However, the extent to which starch concentrations‘dilute’ foliar nutrient concentrations when thelatter are expressed on a dry weight basis is not known. Todetermine the importance of differential starch accumulationin calculating nutrient concentrations on a dry weight basis,leaf nutrient and starch concentrations were measured in Chrysanthemum? morifolium ‘Fiesta’ (Ramat.) cuttings grown atthree irradiance levels and two CO₂ levels for eight weeks inboth winter and spring. On a dry weight basis, foliar concentrationsof most nutrients were lower in both seasons as a result ofthe elevated CO₂ and irradiance levels, and total dry weightswere higher. Per cent starch was greater at the high CO₂ levelin both seasons but was only greater at higher irradiances inthe winter experiment. When starch was subtracted from the leafdry weights, the differences between CO₂ and irradiance treatmentsdisappeared with respect to N, P, K, Ca, Mg, S, and B but notfor Fe, Mn, Zn, and Cu. Key words: CO₂ enrichment, starch, nutrients, irradiance     

Compensatory Roles of Nitrogen Uptake and Photosynthetic N-use Efficiency in Determining Plant Growth Response to Elevated CO2: Evaluation Using a Functional Balance Model

We used a modified functional balance (FB) model to predictgrowth response of Helianthus annuus L. to elevated CO₂. Modelpredictions were evaluated against measurements obtained twiceduring the experiment. There was a good agreement between modelpredictions of relative growth rate (RGR) responses to elevatedCO₂and observations, particularly at the second harvest. Themodel was then used to compare the relative effects of biomassallocation to roots, nitrogen (N) uptake and photosyntheticN-use efficiency (PNUE) in determining plant growth responseto elevated CO₂. The model predicted that a rather substantialincrease in biomass allocation to root growth had little effecton whole plant growth response to elevated CO₂, suggesting thatplasticity in root allocation is relatively unimportant in determininggrowth response. Average N uptake rate at elevated comparedto ambient CO₂was decreased by 21–29%. In contrast, elevatedCO₂increased PNUE by approx. 50% due to a corresponding risein the CO₂-saturation factor for carboxylation at elevated CO₂.The model predicted that the decreased N uptake rate at elevatedCO₂lowered RGR modestly, but this effect was counterbalancedby an increase in PNUE resulting in a positive CO₂effect ongrowth. Increased PNUE may also explain why in many experimentselevated CO₂enhances biomass accumulation despite a significantdrop in tissue nitrogen concentration. The formulation of theFB model as presented here successfully predicted plant growthresponses to elevated CO₂. It also proved effective in resolvingwhich plant properties had the greatest leverage on such responses.Copyright 2000 Annals of Botany Company Elevated CO₂, functional balance model, Helianthus annuus L., N uptake, photosynthetic nitrogen use efficiency, root:shoot ratio     

A Mutant of Arabidopsis thaliana That Defines a New Locus for Glycine Decarboxylation

A novel photorespiratory mutant of Arabidopsis thaliana, designatedgld2, was isolated based on a growth requirement for abnormallyhigh levels of atmospheric CO₂. Photosynthetic CO₂ fixationwas inhibited in the mutant following illumination in air butnot in atmosphere containing 2% O₂. Photosynthetic assimilationof ¹⁴CO₂ in an atmosphere containing 50% O₂ resulted in accumulationof 48% of the soluble label in glycine in the mutant comparedto 9% in the wild type. The rate of glycine decarboxylationby isolated mitochondria from the mutant was reduced to 6% ofthe wild type rate. In genetic crosses, the mutant complementedtwo previously described photorespiratory mutants of A. thalianathat accumulate glycine during photosynthesis in air due todefects in glycine decarboxylase (glyD, now designated gld1)and serine transhydroxymethylase (stm). Because glycine decarboxylaseis a complex of four enzymes, these results are consistent witha mutation in a glycine decarboxylase subunit other than thataffected in the gld1 mutant. The two gld loci were mapped tochromosomes 2 and 5, respectively. ³Present address: Department of Crop and Soil Sciences, MichiganState University, East Lansing, MI 48824, U.S.A. ⁴Present address: Department of Applied Bioscience, Facultyof Agriculture, Hokkaido University, Kita-Ku, Sapporo, 060 Japan ⁵Present address: Department of Biology, Carnegie Institutionof Washington, 290 Panama Street, Standford, CA 94305, U.S.A.     

Delay in the Response of Stomata to Abscisic Acid in CO2-free Air

Abscisic acid (10^–5 M) was fed via their petioles to leavesdetached from well watered plants of Xanthium strumartum, whilethe intercellular spaces were flushed with air of known CO₂content. A closing response to ABA occurred in the presenceor absence of CO₂, and the stomata responded to CO₂ whetheror not ABA was supplied to the leaves. A factorial experimentrevealed no interaction between CO₂ and ABA, and suggested thattheir effect on the rate of closure was purely additive. Theonly evidence of interdependence between the two corn poundswas a delay in the response to ABA in C0 air, which was moremarked in a high light intensity. A hypothesis which is consistentwith the data is that ABA induces stomatal closure by interferingwith the energy supply required for the active transport processeson which guard cell turgor depends. The inhibitory action ofABA takes longer in CO₂-free air because, in the absence ofCO₂ fixation, energy is available from chioroplasts as wellas mitochondria.