Photosynthetic acclimation in tomato plants grown in high CO2

The effects of prolonged CO₂ enrichment of tomato plants on photosynthetic performance and Calvin cycle enzymes, including the amount and activity of ribulose-1,5-bisphosphate carboxylase (RuBPco), were determined. Also the light-saturated rate of photosynthesis (P_max) of the 5th leaf throughout leaf development was predicted based on the amount and kinetics of RuBPco. With short-term CO₂ enrichment, i.e. only during the photosynthesis measurements, P_max of the young leaves did not increase while the leaves reaching full expansion more than doubled their net rate of CO₂ fixation. However, with longer-term CO₂ enrichment, i.e. growing the crop in high CO₂, the plants did not maintain this photosynthetic gain. Compared with leaves of plants grown in normal ambient CO₂ the high CO₂-grown leaves, when almost fully expanded, contained only about half as much RuBPco protein and P_max in 300 and 1000 vpm CO₂ was similarly reduced.The loss of RuBPco protein may be a factor associated with the accelerated fall in P_max since P_max was close to that predicted from the amount and kinetics of RuBPco assuming RuBP saturation. Acclimation to high CO₂ is fundamentally different from acclimation to high light. In contrast to acclimation to high light, acclimation to high CO₂ does not usually involve an increase in photosynthetic machinery so the synthesis and maintenance costs (as indicated by the dark respiration rate) are generally lower.     

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     

Effects of Certain Inhibitors on Photorespiration by Wheat Leaf Segments

The effect on the carbon metabolism of wheat leaf segments ofcertain inhibitors of photorespiration was studied. Sodium 2-hydroxy-3-butynoatesupplied for 40 min resulted in accumulation of ¹⁴C in glycolicacid with only a 7% inhibition of photosynthesis; when suppliedfor 90 min, photosynthesis was inhibited by 47%. When ¹⁴CO₂was replaced by 1000 vpm ¹²CO₂, radioactivity in glycine decreasedbut increased more rapidly in sucrose with less release of ¹⁴CO₂.Isonicotinyl hydrazide (INH) inhibited photosynthesis from ¹⁴CO₂by 50% and glycine replaced sucrose as the main product. When,after 15 min, ¹⁴CO₂ was replaced by 150 vpm ¹²CO₂, in the presenceof INH less ¹⁴CO₂ was released, ¹⁴CO in glycine decreased moreslowly, and less [¹⁴CO]sucrose accumulated. Glycidate (potassium2,3-epoxypropionate) at 2 mM had no effect on photosyntheticrate and little effect on carbon metabolism; 20 mM glycidateinhibited photosynthesis by 64% and resulted in less radioactivityin glycine, more in phosphate esters, and less ¹⁴CO₂ released.When photosynthesis was measured in 1000 vpm CO₂ the inhibitorsgave smaller effects on metabolism than during photosynthesisfrom 150 vpm ¹⁴CO₂ but 20 mM glycidate still resulted in a 42%inhibition of photosynthesis. When U- [¹⁴CO]glycerate was appliedto leaf segments in air with 320 vpm ¹⁴CO₂ the total uptakeof glycerate was not changed by the inhibitors. INH and glycidateboth decreased the amount of glycerate metabolised. More ¹⁴COaccumulated in glycine in the presence of INH and in phosphateesters and serine in the presence of glycidate. Hydroxybutynoateincreased the production of glycolate from glycerate but didnot affect the total amount of glycerate metabolised. Although all three inhibitors affected photorespiratory metabolismnone stimulated photosynthesis. The results are consistent withthe main release of CO₂ in photorespiration arising from theconversion of glycine to serine.     

Photosynthesis of Stands of Tomato, Cucumber and Sweet Pepper Measured in Greenhouses under Various CO2-concentrations

The rate of net photosynthesis (P) of whole plant stands oftomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativusL.) and sweet pepper (Capsicum annuum L.) was measured in sixlong-term experiments in large greenhouses under normal operatingconditions and CO₂-concentrations between 200 and 1200 µmolmol^-1. The objective was to quantify the responses to lightand carbon dioxide and to obtain data sets for testing simulationmodels. The method of measuring canopy photosynthesis involvedan accurate estimation of the greenhouse CO₂ balance, usingnitrous oxide (N₂O) as tracer gas to determine, on-line, theexchange rate between greenhouse and outside air. The estimatedrelative error in the observed P was about ± 10%, exceptthat higher relative errors could occur under particular conditions. A regression equation relating P to the photosynthetically activeradiation, the CO₂ concentration and the leaf area index explained83-91% of the variance. The main canopy photosynthesis characteristicscalculated with the fitted regression equations were: canopyP_max 5-9 g m^-2 h^-1 CO₂ uptake; ratio P_max/LAI 1·5-3 gm^-2 h^-1; light compensation point 32-86 µmol s^-1 m^-2;light use efficiency (quantum yield) at low light 0·06-0·10µmol µmol^-1 and CO₂ compensation point 18-54 µmolmol^-1. The results were related to the prevailing conditions.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, CO₂, CO₂ balance, CO₂ use efficiency, cucumber, _{Cucumis sativus} L., glasshouse, greenhouse, light use efficiency, Lycopersicon esculentum Mill., sweet pepper, tomato, tracer gas     

Growth at elevated CO2 leads to down-regulation of photosynthesis and altered response to high temperature in Quercus suber L. seedlings

The effects of growth at elevated CO₂ on the response to hightemperatures in terms of carbon assimilation (net photosynthesis,stomatal conductance, amount and activity of Rubisco, and concentrationsof total soluble sugars and starch) and of photochemistry (forexample, the efficiency of excitation energy captured by openphotosystem II reaction centres) were studied in cork oak (Quercussuber L.). Plants grown in elevated CO₂ (700 ppm) showed a down-regulationof photosynthesis and had lower amounts and activity of Rubiscothan plants grown at ambient CO₂ (350 ppm), after 14 monthsin the greenhouse. At that time plants were subjected to a heat-shocktreatment (4 h at 45C in a chamber with 80% relative humidityand 800–1000 mol m^–2 s^–1 photon flux density).Growth in a CO₂-enriched atmosphere seems to protect cork oakleaves from the short-term effects of high temperature. ElevatedCO₂ plants had positive net carbon uptake rates during the heatshock treatment whereas plants grown at ambient CO₂ showed negativerates. Moreover, recovery was faster in high CO₂-grown plantswhich, after 30 min at 25C, exhibited higher net carbon uptakerates and lower decreases in photosynthetic capacity (A_max aswell as in the efficiency of excitation energy captured by openphotosystem II reaction centres (F_vJF_m than plants grown atambient CO₂. The stomata of elevated CO₂ plants were also lessresponsive when exposed to high temperature. Key words: Elevated CO₂, temperature, acclimation, photosynthesis, Quercus suber L.     

Response of Soybean Canopy Photosynthesis to CO2 Concentration, Light, and Temperature

Photosynthetic rates of outdoor-grown soybean (Glycine max L.Merr. cv. Bragg) canopies increased with increasing CO₂ concentrationduring growth, before and after canopy closure (complete lightinterception), when measured over a wide range of solar irradiancevalues. Total canopy leaf area was greater as the CO₂ concentrationduring growth was increased from 160 to 990 mm³ dm^–3.Photosynthetic rates of canopies grown at 330 and 660 mm³ CO₂dm^–3 were similar when measured at the same CO₂ concentrationsand high irradiance. There was no difference in ribulose bisphosphatecarboxylase/oxygenase (rubisco) activity or ribulose 1,5-bisphosphate(RuBP) concentration between plants grown at the two CO₂ concentrations.However, photosynthetic rates averaged 87% greater for the canopiesgrown and measured at 660 mm³ CO₂ dm^–3. A 10°C differencein air temperature during growth resulted in only a 4°Cleaf temperature difference, which was insufficient to changethe photosynthetic rate or rubisco activity in canopies grownand measured at either 330 or 660 mm³ CO₂ dm^–3. RuBP concentrationsdecreased as air temperature during growth was increased atboth CO₂ concentrations. These data indicate that the increasedphotosynthetic rates of soybean canopies at elevated CO₂ aredue to several factors, including: more rapid development ofthe leaf area index; a reduction in substrate CO₂ limitation;and no downward acclimation in photosynthetic capacity, as occurin some other species. Key words: CO₂ concentration, soybean, canopy photosynthesis     

Effect of Light Intensity, Carbon Dioxide Concentration, and Leaf Temperature on Gas Exchange of Spray Carnation Plants

The rates of CO₂ assimilation by potted spray carnation plants(cv. Cerise Royalette) were determined over a wide range oflight intensities (45–450 W m^–2 PAR), CO₂ concentrations(200–3100 vpm), and leaf temperatures (5–35 °C).Assimilation rates varied with these factors in a way similarto the response of single leaves of other temperate crops, althoughthe absolute values were lower. The optimal temperature forCO₂ assimilation was between 5 and 10 °C at 45 W m^–2PAR but it increased progressively with increasing light intensityand CO₂ concentration up to 27 °C at 450 W m^–2 PARand 3100 vpm CO₂ as expressed by the equation TOpt = –6.47-h 2.336 In G + 0.031951 where C is CO₂ concentration in vpmand I is photo-synthetically active radiation in W m^–2.CO₂ enrichment also increased stomatal resistance, especiallyat high light intensities. The influence of these results on optimalization of temperaturesand CO₂ concentrations for carnation crops subjected to dailylight variation, and the discrepancy between optimal temperaturesfor growth and net photosynthesis, are discussed briefly     

Effects of CO2-Enrichment on the Growth of Young Tomato Plants in Low Light

Carbon dioxide-enrichment of young tomato plants grown in controlled-environmentcabinets at low light intensity (14 cal cm^–2 day^–1,visible radiation) increased their net assimilation rates and,initially, relative growth-rates. Subsequently, the relativegrowth-rate fell to near the rate of non-enriched plants, owingto a fall in leaf-area ratio associated with an increase inleaf dry weight/area. Sowing non-enriched plants a few daysearlier to reach the same total dry weight would not have producedidentical plants. The effects of CO₂-enrichment to 1000 vpm could be simulatedby increasing light intensity by approximately one third exceptthat the plants had shorter internodes than those in extra CO₂.This was a morphogenetic effect of light since CO₂-enrichmentitself produced slightly shorter plants than controls for anequivalent total dry weight. CO₂-enrichment did not change the dry-weight distribution inthe plants and had little effect on rate of leaf produoctionor the number of flower primordia. There were no indicationsthat beneficial effects of CO₂-enrichment operated other thanthrough increased photosynthesis.     

Measuring the Canopy Net Photosynthesis of Glasshouse Crops

A null balance method is described for measuring net photosynthesisof mature canopies of cucumber and other protected crops overperiods of 10 min in a single-span glasshouse (c. 9m x 18m inarea). Accuracy of control of the CO₂ concentration in the greenhouseatmosphere is within ±10 vpm of the normal ambient level(c. 350 vpm). The amounts of CO₂ used in canopy net photosynthesisare measured with linear mass flowmeters accurate to within±0.80g. The total errors incurred in measuring canopynet photosynthesis at an ambient CO₂ level are estimated tobe of the order of ± 1·2% in bright light (350W m^–2, PAR)and ±3·6% in dull light (100W m^–2, PAR). Measurements of the rates of net photosynthesis of a maturecanopy of a cucumber crop were made at near-ambient CO₂ concentrationsover a range (0–350 W m^–2) of natural light fluxdensities. A model of light absorption and photosynthesis applicableto row crops was used to obtain a net photosynthesis versuslight response curve for the cucumber crop. At a light fluxdensity of 350 W m^–2 the fitted value of canopy net photosynthesiswas 2.65 mg CO₂ m^–2s^–1 (equivalent to over 95 kgCO₂ ha^–1h^–1). The results are discussed in relationto the need for CO₂ supplements to avoid depletion in both ventilatedand unventilated glasshouses during late spring and summer. Key words: Glasshouse crops, cucumber, measurement, canopy photosynthesis, light, CO₂     

Acclimation of Lolium temulentum to enhanced carbon dioxide concentration

Acclimation of single plants of Lolium temulentum to changing[CO₂] was studied on plants grown in controlled environmentsat 20°C with an 8 h photoperiod. In the first experimentplants were grown at 135 µ;mol m^–2 s^–1 photosyntheticphoton flux density (PPFD) at 415µl l^–1 or 550µll^–1 [CO₂] with some plants transferred from the lowerto the higher [CO₂] at emergence of leaf 4. In the second experimentplants were grown at 135 and 500 µmol m^–2 s^–1PPFD at 345 and 575 µl l^–1 [CO₂]. High [CO₂] during growth had little effect on stomatal density,total soluble proteins, chlorophyll a content, amount of Rubiscoor cytochrome f. However, increasing [CO₂] during measurementincreased photosynthetic rates, particularly in high light.Plants grown in the higher [CO₂] had greater leaf extension,leaf and plant growth rates in low but not in high light. Theresults are discussed in relation to the limitation of growthby sink capacity and the modifications in the plant which allowthe storage of extra assimilates at high [CO₂]. Key words: Lolium, carbon dioxide, photosynthesis, growth, stomatal density     

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     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). I. Microclimate and Photosynthesis

Measurements of microclimate and photosynthesis of lucerne var.Europe were made in the field during the spring of 1976. Themaximum rate of canopy gross photosynthesis (14.3 g CO₂ m^–2h^–1, I = ) was 2.5 times greater than that of S 24 perennialryegrass at the same LAI. This difference was due to differencesin individual leaf photosynthesis. The photosynthetic rate ofthe youngest fully expanded leaf of lucerne remained constantthroughout the experimental period at 3.6 g CO₂ m^–2 h^–1(300 W m^–2). Measurements of soil water potential profiles indicated thatlucerne extracted water from the soil to a depth of at least800 mm, with a region of maximum uptake between 400 and 600mm. This capability, with a moderate mean leaf resistance of460 s m^–1, conferred a high assimilation efficiency onlucerne, with a mean water use efficiency of 34 g H₂O lost pergram of carbohydrate assimilated, compared with 200 g H₂O pergram of carbohydrate for S 24. Medicago sativa L, lucerne, photosynthesis, assimilation efficiency     

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     

Response of young barley plants to CO2 enrichment

Barley (Hordeum vulgare L. cv. Digger) was grown for 22 d inenclosed chambers with a CO₂ enrichment of 35, 155, 400 or 675µmol CO₂ mol1. CO₂ enrichment increased photosyntheticcapacity in the plants grown at either of the two highest levelsof pCO₂. A CO₂ enrichment of 675µmol CO₂ caused a significantincrement of shoot dry weight, whereas no changes were observedin fresh weight, chlorophyll or protein levels. At a light intensityof 860µmol m^–2s^–1 CO₂ enrichment caused photosyntheticcapacity to increase by 250%, whereas no effect was observedat 80 µmol m^–2 s^–1. Over time, photosynthesisdecreased by 70% independent of CO₂. A time-dependent increasein the level of extractable fructose was observed whereas totalextractable carbohydrate only changed slightly. Key words: Carbohydrates, CO₂ enrichment, Hordeum vulgare, photosynthesis, respiration     

Effects of temperature and CO2 concentration on photosynthetic CO2 fixation by Chlorella

The rates of photosynthetic ¹⁴CO₂ fixation by Chlorella vulgarisllh, grown under high CO₂, were determined between 4 to 37°Cwith air containing from 300 to 13,000 ppm ¹⁴CO₂. When the CO₂level was increased, both the rate of photosynthesis and theoptimum temperature for maximum photosynthesis increased. Themaximum photosynthetic rate was reached at 12°C with 300ppm ^l4CO₂. Among the photosynthetic products fromed at 300 ppm ¹⁴CO₂, glycolatedecreased greatly when the temperature was raised from 20 to30°C. At 3,000 ppm ¹⁴CO₂ an insignificant amount of glycolatewas formed at all temperatures, whereas ¹⁴C-incorporation intothe insoluble fraction, sucrose, and the lipid fraction wassignificantly higher than at 300 ppm ¹⁴CO₂. The ¹⁴C in sucrosewas greatly increased and the radioactivity in the insolublefraction decreased when the temperature was raised from 28 to36°C. (Received April 8, 1980; )     

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     

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     

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     

Photosynthesis and primary production of Microcystis aeruginosa Kutz. in Lake Kasumigaura

Seasonal changes in the photosynthesis and primary productionof Microcystis aeruginosa Kütz. were investigated in LakeKasumigaura during 1981–1982. Microcystis always showeda light-saturated photosynthesis-light curve. Both P_max andthe initial slope of the photosynthesis-light curve of Microcystisin early summer were very high, so it was concluded that Microcystisutilized both low and high light intensities efficiently. TheP_max of Microcystis was found to be a function of the watertemperature except in August and September. The linear regressionon the temperature-P_max relationship discontinued at 11°C,where the P_max value dropped; Microcystis did not photosynthesizebelow 4°C. The initial slope of the curve was also descendingbelow 11°C. It is suggested that Microcystis changes itsphysiological properties below 11°C. The highest value ofgross production calculated for M. aeruginosa was 5.4 gC m^–2d^–1 in July; the annual gross production was estimatedto be 300 gC m^–2year^–1 (i.e., 40% of the total primaryproduction in this lake).     

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