A CO2 Concentrating System in Leaves of Higher C3-Plants Predicted by a Model Based on RuBP Carboxylase/Oxygenase Kinetics and 14CO2/12CO2 Exchange

Mächler, F., Lehnherr, B., Schnyder, H. and Nösberger,J. 1985. A CO₂ concentrating system in leaves of higher C₃-plantspredicted by a model based on RuBP carboxylase/oxygenase kineticsand ¹⁴CO₂/¹²CO₂ exchange.–J. exp. Bot. 36: 1542–1550. A model is presented which compares the ratio of the two activitiesof the enzyme nbulose bisphosphate carboxylase/oxygenase asdetermined in vitro with the ratio of photosynthesis to photorespirationin leaves as determined from differential ¹⁴CO₂/¹²CO₂ uptakeor from CO₂ compensation concentration. Discrepancies betweenmeasurements made in vitro and in vivo are attributed to theeffect of a CO₂ concentrating system in the leaf cells. Interferencefrom dark respiration is discussed. A CO₂ concentrating systemis postulated which is efficient mainly at low temperature andlow CO₂ concentration. Key words: —Photosynthesis, photorespiration, ribulose bisphosphate carboxylase/oxygenase     

The Effect of External pH on the Apparent CO2 Affinity of Chlorella saccharophila

The carbon dioxide compensation point of the unicellular greenalga, Chloretla saccharophila, was determined in aqueous mediumby a gas chromatographic method. Compensation points decreasedmarkedly from 63 cm³ m^–3 at an external pH of 4.0 to 3.2cm³ m^–3 at pH 8.0 and were not affected by the O₂ concentrationof the medium. The calculated CO² concentration required tosupport the half-maximum photosynthetic rate of the algal cellsranged from 6.0 mmol m_–3 at an external pH of 60 to 1.5mmol m^–3 at pH 8.0 and these values were not affectedby O₂ concentration. The K_m(CO₂) of nbulose-l,5-bisphosphatecarboxylase isolated from cells grown either at pH 4.0 or pH8.0 was determined to be 64 mmol m^–3. These results indicatethat loss of CO₂ by photorespiration does not occur in C. saccharophilacells at acid pH and the disparity between the apparent affinityfor CO₂ of the intact cells and that of the carboxylase indicatesthe operation of a ‘CO₂ concentrating mechanism’in this alga at acid pH. Key words: Acidophilic alga, bicarbonate transport, Chlorella saccharophila, compensation point, CO₂ affinity, PH, RuBP carboxylase     

Role of carbonic anhydrase in photosynthetic CO2 fixation in Chlorella

Chlorella vulgaris 11h cells grown in air enriched with 4% CO₂(high-CO² cells) had carbonic anhydrase (CA) activity whichwas 20 to 90 times lower than that of algal cells grown in ordinaryair (containing 0.04% CO₂, low-CO₂ cells). The CO₂ concentrationduring growth did not affect either ribulose 1,5-bisphosphate(RuBP) carboxylase activity or its Km for CO₂. When high-CO₂ cells were transferred to low CO₂ conditions,CA activity increased without a lag period, and this increasewas accompanied by an increase in the rate of photosynthetic¹⁴CO₂ fixation under ¹⁴CO₂-limiting conditions. On the otherhand, CA activity as well as the rate of photosynthetic ¹⁴CO₂fixation at low ¹⁴CO₂ concentrations decreased when low-CO₂cells were transferred to high CO₂ conditions. Diamox, an inhibitor of CA, at 0.1 mM did not affect photosynthesisof low-CO₂ cells at high CO₂ concentration (0.5%). Diamox inhibitedphotosynthesis only under low CO₂ concentrations, and the lowerthe CO₂ concentration, the greater was the inhibition. Consequently,the CO₂ concentration at which the rate of photosynthesis attainedone-half its maximum rate (Km) greatly increased in the presenceof this inhibitor. When CO₂ concentration was higher than 1%, the photosyntheticrate in low-CO₂ cells decreased, while that in high-CO₂ cellsincreased. Fractionation of the low-CO₂ cells in non-aqueous medium bydensity showed that CA was fractionated in a manner similarto the distribution of chlorophyll and RuBP carboxylase. These observations indicate that CA enhances photosynthesisunder CO₂-limiting conditions, but inhibits it at CO₂ concentrationshigher than a certain level. The mechanism underlying the aboveregulatory functions of CA is discussed. ¹This work was reported at the International Symposium on PhotosyntheticCO₂-Assimilation and Photorespiration, Sofia, August, 1977 (18).Requests for reprints should be addressed to S. Miyachi, RadioisotopeCentre, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received December 11, 1978; )     

Energetic Costs of Tissue Construction in Yellow-poplar and White Oak Trees Exposed to Long-term CO2Enrichment

Two methods were used to estimate construction costs for leaves,stems, branches and woody roots of yellow-poplar (LiriodendrontulipiferaL.) trees grown at ambient (35 Pa) and elevated (65Pa) CO₂for 2.7 years and trees of white oak (Quercus albaL.)grown at these same CO₂partial pressures for 4 years. Samplecombustion in a bomb calorimeter combined with measurementsof ash and nitrogen content provided the primary method of estimatingtissue construction costs (W_G; g glucose g^-1dry mass). Thesevalues were compared with a second, simpler method in whichcost estimates were derived from tissue ash, carbon and nitrogencontent (V_G). Estimates of W_Gwere lower for leaves, branchesand roots of yellow-poplar and for leaves of white oak grownat elevated compared with ambient CO₂partial pressures. TheseCO₂-induced differences in W_Granged from 3.7% in yellow-poplarroots to 2.1% in white oak leaves. Only in the case of yellow-poplarleaves, however, were differences in V_Gobserved between CO₂treatments.Leaf V_Gwas 1.46 g glucose g^-1dry mass in ambient-grown treescompared with 1.41 g glucose g^-1dry mass for CO₂-enriched trees.Although paired-estimates of W_Gand V_Gclustered about a 1:1 linefor leaves and branches, estimates of V_Gwere consistently lowerthan W_Gfor stems and roots. Construction costs per unit leafarea were 95 g glucose m^-2for yellow-poplar trees grown at ambientCO₂and 106 g glucose m^-2for trees grown at elevated CO₂partialpressures. No differences in area-based construction costs wereobserved for white oak. Whole-plant energy content was 1220g glucose per tree in ambient-grown white oak compared with2840 g glucose per tree for those grown at elevated CO₂partialpressures. These differences were driven largely by CO₂-inducedchanges in total biomass. We conclude that while constructioncosts were lower at elevated CO₂partial pressures, the magnitudeof this response argues against an increased efficiency of carbonuse in the growth processes of trees exposed to CO₂enrichment. Bomb calorimeter; construction costs; elevated CO₂; energy allocation; global change; growth respiration; heat of combustion; respiration; Liriodendron tulipifera; Quercus alba     

Variation of Phosphoenolpyruvate Carboxylase Activity in Dunaliella Associated with Changes in Atmospheric CO2 Concentration

In Dunaliella tertiolecta, D. bioculata and D. viridis the activitiesof phosphoenolpyruvate carboxylase and carbonic anhydrase werehigher in the cells grown in ordinary air (low-CO₂ cells) thanin those grown in air enriched with 1–5% CO₂ (high-CO₂cells), whereas in Porphyridium cruentum R-1 there was no differencein phosphoenolpyruvate carboxylase activity between these twotypes of cells. Apparent K_m(NaHCO₃) values for photosynthesisin low-CO₂ cells of all species tested were smaller than thosein high-CO₂ cells. Most of the ¹⁴C was incorporated into 3-phosphoglycerate,sugar mono- and di-phosphates during the initial periods ofphotosynthetic NaH¹⁴CO₃ indicating that both types of cellsin D. tertiolecta are C₃ plants. (Received May 27, 1985; Accepted June 25, 1985)     

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     

Growth of White Clover, Dependent on N2 Fixation, in Elevated CO2 and Temperature

Clonal plants of white clover (Trifolium repens L ), whollydependent on N₂ fixation, were grown for 6 weeks in controlledenvironments providing either (C680 regime) 23/18 °C day/nighttemperatures and a CO₂, concentration of 680 µmol mol^–1,or (C340 regime) 20/15 °C day/night temperatures and a CO₂,concentration of 340 µmol mol^–1 During the firsthalf of the experimental period the C680 plants grew fasterthan their C340 counterparts so that by week 3 they were twicethe weight this 2 1 superiority in weight persisted until theend of the experiment The faster initial growth of the C680plants was based on an approx 70 % increase in leaf numbersand an approx 30 % increase in their individual area Initially,specific leaf area (cm2 g^–1 leaf) was lower in C680 thanin C340 leaves but became similar in the latter half of theexperiment Shoot organ weights, including petioles and stolons,reflected the C680 plant's better growth in terms of photosyntheticsurface Throughout, C680 plants invested less of their weightin root than C340 plants and this disparity increased with timeAcetylene reduction assays showed that nitrogenase activityper unit nodule weight was the same in both C680 and C340 plantsBoth groups of plants invested about the same fraction of totalweight in nodules Nitrogen contents of plant tissues were similarirrespective of growth regime, but C680 expanded leaves containedslightly less nitrogen and their stolons slightly more nitrogenthan their C340 counterparts However, C680 leaves containedmore non-structural carbohydrate Young, unshaded C680 leavespossessed larger palisade cells, packed more tightly withinthe leaf, than equivalent C340 leaves The reason for the C680regime's loss of superiority in relative growth rate duringthe second half of the experiment was not clear, but more accumulationof non-structural carbohydrate, constriction of root growthand increased self-shading appear to be the most likely causes Trifolium repens, white clover, elevated CO₂, elevated temperature, growth, N₂ fixation, leaf structure     

Influence of Temperature on the Ratio of Ribulose Bisphosphate Carboxylase to Oxygenase Activities and on the Ratio of Photosynthesis to Photorespiration of Leaves

Lehnherr, B., Mächler, F. and Nösberger, J. 1985.Influence of temperature on the ratio of ribulose bisphosphatecarboxylase to oxygenase activities and on the ratio of photosynthesisto photorespiration of leaves.—J. exp. Bot. 36: 1117–1125. Rates of net and gross photosynthesis of intact white cloverleaves were measured by infrared gas analysis and by short termuptake of ¹⁴CO₂ respectively. Ribulose bisphosphate carboxylaseoxygenase (RuBPCO) was purified from young leaves and kineticproperties investigated in combined and separate assays. Theratio of carboxylase to oxygenase activities was compared withthe ratio of photosynthesis to photorespiration at various temperaturesand CO₂ concentrations. The ratio of photosynthesis to photorespiration at 30 Pa p(CO₂)was consistent with the ratio of carboxylase activity to oxygenaseactivity when each was measured above 20 °C. However, theratio of photosynthesis to photorespiration increased with decreasingtemperature, whereas the ratio of carboxylase to oxygenase activitywas independent of temperature. This resulted in a disagreementbetween the measurements on the purified enzyme and intact leafat low temperature. No disagreement between enzyme and leafat low temperature occurred, when the ratio of photosynthesisto photorespiration was determined at increased CO₂ concentrations. The results suggest an effect of low temperature and low CO₂concentration on the ratio of photosynthesis to photorespirationindependent of the enzyme. Key words: Ribulose bisphosphate carboxylase oxygenase, photorespiration, temperature     

Long Term Effects of High CO2 Concentration on Photosynthesis of Water Hyacinth (Eichhornia crassipes (Mart.) Solms)

The photosynthetic response to CO₂ concentration, light intensityand temperature was investigated in water hyacinth plants (Eichhorniacrassipes (Mart.) Solms) grown in summer at ambient CO₂ or at10000 µmol(CO₂) mol^–1 and in winter at 6000 µmol(CO₂)mol^–1 Plants grown and measured at ambient CO₂ had highphotosynthetic rate (35 µmo1(CO₂) m^–2 s^–1),high saturating photon flux density (1500–2000) µmolm^–2 s^–1 and low sensitivity to temperature in therange 20–40 °C. Maximum photosynthetic rate (63 µmol(CO₂)m^–2 s^–1) was reached at an internal CO₂ concentrationof 800 µmol mol^–1. Plants grown at high CO₂ in summerhad photosynthetic capacities at ambient CO₂ which were 15%less than for plants grown at ambient CO₂, but maximum photosyntheticrates were similar. Photosynthesis by plants grown at high CO₂and high light intensity had typical response curves to internalCO₂ concentration with saturation at high CO₂, but for plantsgrown under high CO₂ and low light and plants grown under lowCO₂ and high light intensity photosynthetic rates decreasedsharply at internal CO₂ concentrations above 1000 µmol^–1. Key words: Photosynthesis, CO₂, enrichment, Eichhornia crassipes     

Regeneration of Ribulose 1,5-bisphosphate and Ribulose 1,5-bisphosphate carboxylase/oxygenase Activity Associated with Lack of Oxygen Inhibition of Photosynthesis at Low Temperature

The nature of the lack of oxygen inhibition of C₃-photosynthesisat low temperature was investigated in white clover (Trifoliumrepens L.). Detached leaves were brought to steady-state photosynthesisin air (34 Pa p(CO²), 21 kPa p(O₂), balance N₂) at temperaturesof 20°C and 8°C, respectively. Net photosynthesis, ribulose1,5-bisphosphate (RuBP) and ATP contents, and ribulose 1,5-bisphosphatecarboxylase/oxygenase (RuBPCO) activities were followed beforeand after changing to 2·0 kPa p(O₂). At 20°C, lowering p(O₂) increased net photosynthesis by37%. This increase corresponded closely with the increase expectedfrom the effect on the kinetic properties of RuBPCO. Conversely,at 8°C net photosynthesis rapidly decreased following adecrease in p(O₂) and then increased again reaching a steady-statelevel which was only 7% higher than at 21 kPa p(O₂). The steady-staterates of RuBP and associated ATP consumption were both estimatedto have decreased. ATP and RuBP contents decreased by 18% and33% respectively, immediately after the change in p(O₂) suggestingthat RuBP regeneration was reduced at low p(O₂) due to reducedphotophosphorylation. Subsequently, RuBP content increased again.Steady-state RuBP content at 2·0 kPa p(O₂) was 24% higherthan at 21 kPa p(O₂). RuBPCO activity decreased by 22%, indicatingcontrol of steady-state RuBP consumption by RuBPCO activity. It is suggested that lack of oxygen inhibition of photosynthesisat low temperature is due to decreased photophosphorylationat low temperature and low p(O₂). This may be due to assimilateaccumulation within the chloroplasts. Decreased photophosphorylationseems to decrease RuBP synthesis and RuBPCO activity, possiblydue to an acidification of the chloroplast stroma. Key words: Oxygen inhibition, photosynthesis, ribulose bisphosphate carboxylase/oxygenase     

Effect of Elevated CO2 on the Photosynthesis, Respiration and Growth of Perennial Ryegrass

Single, seed-grown plants of ryegrass (Lolium perenne L. cv.Melle) were grown for 49 d from the early seedling stage ingrowth cabinets at a day/night temperature of 20/15 C, witha 12 h photoperiod, and a CO₂ concentration of either 340 or680µI 1^–1 CO₂. Following complete acclimation tothe environmental regimes, leaf and whole plant CO₂ effluxesand influxes were measured using infra-red gas analysis techniques.Elevated CO₂ increased rates of photosynthesis of young, fullyexpanded leaves by 35–46% and of whole plants by morethan 50%. For both leaves and whole plants acclimation to 680µI^–1 CO₂ reduced rates of photosynthesis in bothCO₂ regimes, compared with plants acclimated to 340µll^–1. There was no significant effect of CO₂ regime onrespiration rates of either leaves or whole plants, althoughleaves developed in elevated CO₂ exhibited generally lower ratesthan those developed in 340µI I^–1 CO₂. Initially the seedling plants in elevated CO₂ grew faster thantheir counterparts in 340µI I^–1 CO₂, but this effectquickly petered out and final plant weights differed by onlyc. 10%. Since the total area of expanded and unexpanded laminaewas unaffected by CO₂ regime, specific leaf area was persistently13–40% lower in elevated CO₂ while, similarly, root/shootratio was also reduced throughout the experiment. Elevated CO₂reduced tissue nitrogen contents of expanded leaves, but hadno effect on the nitrogen contents of unexpanded leaves, sheathsor roots. The lack of a pronounced effect of elevated CO₂ on plant growthwas primarily due to the fact that CO₂ concentration did notinfluence tiller (branch) numbers. In the absence of an effecton tiller numbers, any possible weight increment was restrictedto the c. 2.5 leaves of each tiller. The reason for the lackof an effect on tillering is not known. Key words: Lolium perenne, ryegrass, elevated CO₂, photosynthesis, respiration, growth, development     

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 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     

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     

Humidity Pretreatment Affects the Responses of Stomata and CO2 Assimilation to Vapor Pressure Difference in C3 and C4 Plants

Experiments were carried out to investigate the long-term influenceof humidity on the short-term responses of stomata and CO₂ assimilationto vapor pressure difference in Oryza sativa (rice, C₃ species)and Panicum maximum (green panic, C₄ species). Plants were grownfor four weeks in growth chambers set at 35% and 85% relativehumidity at 25C air temperature, 38+2 Pa CO₂ partial pressureand 1,700µmol m^-2s^-1 photon flux density. Soil was saturatedwith water in both humidity treatments. Low humidity pretreatmentscaused low leaf conductance and low rates of transpiration andCO₂ assimilation in O. sativa, but small changes in stomatalresponses to humidity and in CO₂ assimilation were found inP. maximum. From the short-term gas exchange experiments, itwas noted that the responsiveness of leaf conductance to vaporpressure difference were affected by humidity pretreatmentsin O. sativa, whereas unaffected in P. maximum. In O. sativameasurements of CO₂ assimilation as a function of internal CO₂partial pressure (A-Ci curve) indicated that low humidity pretreatmentsreduced the CO₂ assimilation at high internal CO₂ partial pressure,but the initial slope of the A-Ci curve was unaffected. Furthermore,plant characteristics such as total dry weight and leaf areaof plants subjected to low umidity were lower than plants subjectedto high humidity. The reductions in O. sativa, however, werelarger than in P. maximum. Stomatal frequency from low humiditygrown plant was higher than that from high humidity grown plantsin both species although there is no significant difference.The data indicated that if the short term inhibition of netCO₂ assimilation at a high vapor pressure difference was imposedduring vegetative growth, the photosynthetic biochemistry andthe resultant plant growth were largely depressed in O. sativa,a C₃ species. (Received May 26, 1992; Accepted November 2, 1992)     

Influence of Temperature and O2 Concentration on Photosynthesis and Light Activation of Ribulosebisphosphate Carboxylase Oxygenase in Intact Leaves of White Clover (Trifolium repens L.)

Detached leaves of white clover (Trifolium repens L.) were keptfor 1 h under various conditions of temperature, oxygen concentrationand light intensity. Rates of photosynthesis were measured whereappropriate and then ribulosebisphosphate carboxylase oxygenase(RuBPCO) was extracted rapidly and its initial activity measuredimmediately. The extracted activity increased with increased intensity ofillumination of the leaves. Where leaves were pretreated atlow light intensity, the lower the temperature of the leavesthe higher the extracted activity of RuBPCO. At high light intensitytemperature did not affect the activity of subsequently extractedRuBPCO but the light intensity which was necessary for maximumactivity increased with temperature. Activity of RuBPCO fromleaves pretreated in the dark was least when CO₂ was low andtemperature high. Leaves, pretreated at low temperatures andhigh light intensity in 20% O₂, yielded higher activity in extractsthan leaves pretreated under similar conditions but in 2% O₂.A relatively weak temperature response of photosynthesis atlow irradiances was associated with a decrease in extractableRuBPCO activity with increasing temperature. A strong temperaturedependence of the oxygen inhibition of photosynthesis was associatedwith lower extractable RuBPCO activity in leaves pretreatedat low oxygen concentration at low temperatures. With leavesfrom plants grown at low temperatures prior to treatment ofleaves, oxygen inhibition of photosynthesis was less temperaturedependent and activity of RuBPCO in extracts was not decreasedby low O₂ at low temperatures. Differences in the activationof RuBPCO appear to influence photosynthesis and account foran absence of oxygen inhibition of photosynthesis at low temperaturesin plants grown in warm conditions. Key words: Ribulosebisphosphate carboxylase oxygenase activation, Photosynthesis, Temperature, O₂ effect, White clover     

Differentiating Day from Night Effects of High Ambient [CO2] on the Gas Exchange and Growth of Xanthium strumarium L. Exposed to Salinity Stress

Sodium chloride, at a concentration of 88 mol m^-3in half strengthHoagland nutrient solution, increased dry weight per unit areaofXanthium strumarium L. leaves by 19%, and chlorophyll by 45%compared to plants grown without added NaCl at ambient (350µmol mol^-1) CO₂concentration. Photosynthesis, per unitleaf area, was almost unaffected. Even so, over a 4-week period,growth (dry weight increment) was reduced in the salt treatmentby 50%. This could be ascribed to a large reduction in leafarea (>60%) and to an approx. 20% increase in the rate ofdark respiration (Rd). Raising ambient [CO₂] from zero to 2000 µmol mol^-1decreasedRd in both control and salinized plants (by 20% at 1000, andby 50% at 2000 µmol mol^-1CO₂concentration) compared toRd in the absence of ambient CO₂. High night-time [CO₂] hadno significant effect on growth of non-salinized plants, irrespectiveof day-time ambient [CO₂]. Growth reduction caused by salt wasreduced from 51% in plants grown in 350 µmol mol^-1throughoutthe day, to 31% in those grown continuously in 900 µmolmol^-1[CO₂]. The effect of [CO₂] at night on salinized plants depended onthe daytime CO₂concentration. Under 350 µmol mol^-1day-time[CO₂], 900 µmol mol^-1at night reduced growth over a 4-weekperiod by 9% (P <0.05) and 1700 µmol mol^-1reduced itby 14% (P <0.01). However, under 900 µmol mol^-1day-time[CO₂], 900vs . 350 µmol mol^-1[CO₂] at night increasedgrowth by 17% (P <0.01). It is concluded that there is both a functional and an otiose(functionless) component to Rd, which is increased by salt.Under conditions of low photosynthesis (such as here, in thelow day-time [CO₂] regime) the otiose component is small andhigh night-time [CO₂] partly suppresses functional Rd, therebyreducing salt tolerance. In plants growing under conditionswhich stimulate photosynthesis (e.g. with increased daytime[CO₂]), elevated [CO₂] at night suppresses mainly the otiosecomponent of respiration, thus increasing growth. Consequently,in regions of adequate water and sunlight, the predicted furtherelevation of the world atmospheric [CO₂] may increase plantsalinity tolerance. Xanthium strumarium ; respiration; photosynthesis; salt stress; sodium chloride; carbon dioxide; atmosphere     

Effect of elevated CO2 on the utilization of light energy in Nothofagus fusca and Pinus radiata

Red beech (Nothofagus fusca (Hook. F.) Oerst.; Fagaceae) andradiata pine (Pinus radiata D. Don; Pinaceae) were grown for16 months in large open-top chambers at ambient (37 Pa) andelevated (66 Pa) atmospheric partial pressure of CO₂, and incontrol plots (no chamber). Summer-time measurements showedthat photosynthetic capacity was similar at elevated CO₂ (lightand CO₂-saturated value of 17.2 µmol m^–2 s^–1for beech, 13.5 µmol m^–2 s^–1 for pine), plantsgrown at ambient CO₂ (beech 21.0 µmol^–2 s^–1,pine 14.9 µmol m^–2s^–1) or control plants grownwithout chambers (beech 23.2 µmol m^–2 s^–1,pine 12.9 µmol m^–2 s^–1). However, the higherCO₂ partial pressure had a direct effect on photosynthetic rate,such that under their respective growth conditions, photosynthesisfor the elevated CO₂ treatment (measured at 70 Pa CO₂ partialpressure: beech 14.1 µmol m^–2 s^–1 pine 10.3)was greater than in ambient (measured at 35 Pa CO₂: beech 9.7µmol m^–2 s^–1, pine 7.0 µmol m^–2s^–1) or control plants (beech 10.8 µmol m^–2s^–1, pine 7.2 µmol m^–2 s^–1). Measurementsof chlorophyll fluorescence revealed no evidence of photodamagein any treatment for either species. The quantity of the photoprotectivexanthophyll cycle pigments and their degree of de-epoxidationat midday did not differ among treatments for either species.The photochemical efficiency of photosystem II (yield) was lowerin control plants than in chamber-grown plants, and was higherin chamber plants at ambient than at elevated CO₂. These resultssuggest that at lower (ambient) CO₂ partial pressure, beechplants may have dissipated excess energy by a mechanism thatdoes not involve the xanthophyll cycle pigments. Key words: Carotenoids, chlorophyll fluorescence, photosynthesis, photoinhibition, photoprotection, xanthophyll cycle     

Influence of High CO2Partial Pressure on Nitrogen Use Efficiency of the C4Grasses Panicum coloratum and Cenchrus ciliaris

Australia's tropical grasslands are dominated by C₄grasses,characterized by their unique biochemistry and anatomy. Twonaturalized C₄grasses (Panicum coloratum and Cenchrus ciliaris)were used to investigate whether high CO₂partial pressure [p(CO₂)] influences photosynthetic nitrogen use efficiency andplant nitrogen use efficiency (PNUE and NUE respectively). Plantswere grown for 30 d with four levels of N at p(CO₂) of 38 or86 Pa. PNUE was calculated from leaf CO₂assimilation rates (A)and leaf N concentrations, and NUE from total leaf N contentand plant dry mass. At each p(CO₂), PNUE and NUE were greaterfor C. ciliaris than for P. coloratum due to higher A and drymass combined with lower leaf N concentrations. Elevatedp (CO₂)increased PNUE of C. ciliaris only. This effect was due to lowerleaf N concentrations (area basis). At high p(CO₂), NUE of C.ciliaris was also greater. This resulted from a 1.6-fold stimulationof dry mass by high p(CO₂). Although dry mass of P. coloratumwas increased 1.2-fold by elevated p(CO₂), its NUE was unaffected.Leaf transpiration rates were halved at elevated p(CO₂), andwe suggest that this factor plays a major role in the growthresponse of C₄grasses to high p(CO₂). Copyright 2001 Annalsof Botany Company Panicum coloratum, Cenchrus ciliaris, nitrogen use efficiency, elevated CO₂, leaf N concentration, growth, photosynthesis     

Effect of elevated CO2 and nutrient status on growth, dry matter partitioning and nutrient content of Poa alpina var. vivipara L.

Poa alpina var. vivipara L. was grown in an atmosphere containingeither 340 or 680 µmol CO₂ mol^–1 within controlledenvironment chambers. The available nutrient regime was variedby altering the supply of nitrogen and phosphorus within a completenutrient solution. At a high, but not low, N and P supply regime,elevated CO₂ markedly increased growth. Differences betweennutrient supply, but not atmospheric CO₂ concentration, alteredthe allometric relations between root and shoot. Net photosynthesisof mature leaf blades and leaf N and P concentration were reducedin plants grown at the elevated CO₂ concentration. The question was asked: is it possible to ascribe all of theseeffects to elevated CO₂ or are some due to nutrient deficiencycaused by dilution with excess carbon? Several criteria, includingthe nutrient content of sink tissue, root:shoot allometry andthe use of divalent cations to estimate integrated water flowsare suggested in order to make this distinction. It is concludedthat only at a low supply of N and P₁ and elevated CO₂ concentration,was low leaf N concentration due to induced nutrient deficiency.The data are consistent with a model where the capacity of sinksto use photosynthetically assimilated carbon sets both the rateof import into those sinks (and thus rate of export from sourceleaves) and the rate of photosynthesis of source leaves themselves. Key words: Poa alpina L., growth, photosynthesis, carbohydrate, export, nitrogen, phosphorus