Acclimation to High CO(2) in Monoecious Cucumbers : I. Vegetative and Reproductive Growth

CO₂ concentrations of 1000 compared to 350 microliters per liter in controlled environment chambers did not increase total fruit weight or number in a monoecious cucumber (Cucumis sativus L. cv Chipper) nor did it increase biomass, leaf area, or relative growth rates beyond the first 16 days after seeding. Average fruit weight was slightly, but not significantly greater in the 1000 microliters per liter CO₂ treatment because fruit numbers were changed more than total weight. Plants grown at 1000 and 350 microliters per liter CO₂ were similar in distribution of dry matter and leaf area between mainstem, axillary, and subaxillary branches. Early flower production was greater in 1000 microliters per liter plants. Subsequent flower numbers were either lower in enriched plants or similar in the two treatments, except for the harvest at fruiting when enriched plants produced many more male flowers than the 350 microliters per liter treatments.     

Short-Term and Long-Term Responses of Crassulacean Acid Metabolism Plants to Elevated CO(2)

For the leaf succulent Agave deserti and the stem succulent Ferocactus acanthodes, increasing the ambient CO₂ level from 350 microliters per liter to 650 microliters per liter immediately increased daytime net CO₂ uptake about 30% while leaving nighttime net CO₂ uptake of these Crassulacean acid metabolism (CAM) plants approximately unchanged. A similar enhancement of about 30% was found in dry weight gain over 1 year when the plants were grown at 650 microliters CO₂ per liter compared with 350 microliters per liter. Based on these results plus those at 500 microliters per liter, net CO₂ uptake over 24-hour periods and dry weight productivity of these two CAM succulents is predicted to increase an average of about 1% for each 10 microliters per liter rise in ambient CO₂ level up to 650 microliters per liter.     

Minor Physiological Response to Elevated CO(2) by the CAM Plant Agave vilmoriniana

One-year-old plants of the CAM leaf succulent Agave vilmoriniana Berger were grown outdoors at Riverside, California. Potted plants were acclimated to CO₂-enrichment (about 750 microliters per liter) by growth for 2 weeks in an open-top polyethylene chamber. Control plants were grown nearby where the ambient CO₂ concentration was about 370 microliters per liter. When the plants were well watered, CO₂-induced differences in stomatal conductances and CO₂ assimilation rates over the entire 24-hour period were not large. There was a large nocturnal acidification in both CO₂ treatments and insignificant differences in leaf chlorophyll content. Well watered plants maintained water potentials of −0.3 to −0.4 megapascals. When other plants were allowed to dry to water potentials of −1.2 to −1.7 megapascals, stomatal conductances and CO₂ uptake rates were reduced in magnitude, with the biggest difference in Phase IV photosynthesis. The minor nocturnal response to CO₂ by this species is interpreted to indicate saturated, or nearly saturated, phosphoenolpyruvate carboxylase activity at current atmospheric CO₂ concentrations. CO₂-enhanced diurnal activity of ribulose bisphosphate carboxylase activity remains a possibility.     

Acclimation to High CO(2) in Monoecious Cucumbers : II. Carbon Exchange Rates, Enzyme Activities, and Starch and Nutrient Concentrations

Carbon exchange capacity of cucumber (Cucumis sativus L.) germinated and grown in controlled environment chambers at 1000 microliters per liter CO₂ decreased from the vegetative growth stage to the fruiting stage, during which time capacity of plants grown at 350 microliters per liter increased. Carbon exchange rates (CERs) measured under growth conditions during the fruiting period were, in fact, lower in plants grown at 1000 microliters per liter CO₂ than those grown at 350. Progressive decreases in CERs in 1000 microliters per liter plants were associated with decreasing stomatal conductances and activities of ribulose bisphosphate carboxylase and carbonic anhydrase. Leaf starch concentrations were higher in 1000 microliters per liter CO₂ grown-plants than in 350 microliters per liter grown plants but calcium and nitrogen concentrations were lower, the greatest difference occurring at flowering. Sucrose synthase and sucrose-P-synthase activities were similar in 1000 microliters per liter compared to 350 microliters per liter plants during vegetative growth and flowering but higher in 350 microliters per liter plants at fruiting. The decreased carbon exchange rates observed in this cultivar at 1000 microliters per liter CO₂ could explain the lack of any yield increase (MM Peet 1986 Plant Physiol 80: 59-62) when compared with plants grown at 350 microliters per liter.     

Effects of CO(2) Concentration on Rubisco Activity, Amount, and Photosynthesis in Soybean Leaves

Growth at an elevated CO₂ concentration resulted in an enhanced capacity for soybean (Glycine max L. Merr. cv Bragg) leaflet photosynthesis. Plants were grown from seed in outdoor controlled-environment chambers under natural solar irradiance. Photosynthetic rates, measured during the seed filling stage, were up to 150% greater with leaflets grown at 660 compared to 330 microliters of CO₂ per liter when measured across a range of intercellular CO₂ concentrations and irradiance. Soybean plants grown at elevated CO₂ concentrations had heavier pod weights per plant, 44% heavier with 660 compared to 330 microliters of CO₂ per liter grown plants, and also greater specific leaf weights. Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) activity showed no response (mean activity of 96 micromoles of CO₂ per square meter per second expressed on a leaflet area basis) to short-term (~1 hour) exposures to a range of CO₂ concentrations (110-880 microliters per liter), nor was a response of activity (mean activity of 1.01 micromoles of CO₂ per minute per milligram of protein) to growth CO₂ concentration (160-990 microliters per liter) observed. The amount of rubisco protein was constant, as growth CO₂ concentration was varied, and averaged 55% of the total leaflet soluble protein. Although CO₂ is required for activation of rubisco, results indicated that within the range of CO₂ concentrations used (110-990 microliters per liter), rubisco activity in soybean leaflets, in the light, was not regulated by CO₂.     

Effects of High Atmospheric CO(2) and Sink Size on Rates of Photosynthesis of a Soybean Cultivar

The effect of sink strength on photosynthetic rates under conditions of long-term exposure to high CO₂ has been investigated in soybean. Soybean plants (Merr. cv. Fiskeby V) were grown in growth chambers containing 350 microliters CO₂ per liter air until pod set. At that time, plants were trimmed to three trifoliolate leaves and either 21 pods (high sink treatment) or 6 pods (low sink treatment). Trimmed plants were either left in 350 microliters CO₂ per liter of air or placed in 1000 microliters CO₂ per liter of air (high CO₂ treatment) until pod maturity. Whole plant net photosynthetic rates of all plants were measured twice weekly, both at 350 microliters CO₂ per liter of air and 1000 microliters CO₂ per liter of air. Plants were also harvested at this time for dry weight measurements. Photosynthetic rates of high sink plants at both measurement CO₂ concentrations were consistently higher than those of low sink plants, and those of plants given the 350 microliter CO₂ per liter of air treatment were higher at both measurement CO₂ concentrations than those of plants given the 1000 microliters CO₂ per liter of air treatment. When plants were measured under treatment CO₂ levels, however, rates were higher in 1,000 microliter plants than 350 microliter CO₂ plants. Dry weights of all plant parts were higher in the 1,000 microliters CO₂ per liter air treatment than in the 350 microliters CO₂ per liter air treatment, and were higher in the low sink than in the high sink treatments.     

Reversibility of Photosynthetic Inhibition in Cotton after Long-Term Exposure to Elevated CO(2) Concentrations

Cotton (Gossypium hirsutum L. cv Stoneville 213) was grown at 350 and 1000 microliters per liter CO₂. The plants grown at elevated CO₂ concentrations contained large starch pools and showed initial symptoms of visible physical damage. Photosynthetic rates were lower than expected based on instantaneous exposure to high CO₂.

A group of plants grown at 1000 microliters per liter CO₂ was switched to 350 microliters per liter CO₂. Starch pools and photosynthetic rates were monitored in the switched plants and in the two unswitched control groups. Photosynthetic rates per unit leaf area recovered to the level of the 350 microliters per liter CO₂ grown control group within four to five days. To assess only nonstomatal limitations to photosynthesis, a measure of photosynthetic efficiencies was calculated (moles CO₂ fixed per square meter per second per mole intercellular CO₂). Photosynthetic efficiency also recovered to the levels of the 350 microliters per liter CO₂ grown controls within three to four days.

Recovery was correlated to a rapid depletion of the starch pool, indicating that the inhibition of photosynthesis is primarily a result of feedback inhibition. However, complete recovery may involve the repair of damage to the chloroplasts caused by excessive starch accumulation. The rapid and complete reversal of photosynthetic inhibition suggests that the appearance of large, strong sinks at certain developmental stages could result in reduction of the large starch accumulations and that photosynthetic rates could recover to near the theoretical capacity during periods of high photosynthate demand.

     

Carbon and nitrogen limitations on soybean seedling development

Carbon and nitrogen limitations on symbiotically grown soybean seedlings (Glycine max [L.] Merr.) were assessed by providing 0.0, 1.0, or 8.0 millimolar NH₄NO₃ and 320 or 1,000 microliters CO₂/liter for 22 days after planting. Maximum development of the Rhizobium-soybean symbiosis, as determined by acetylene reduction, was measured in the presence of 1.0 millimolar NH₄NO₃ under both levels of CO₂. Raising NH₄NO₃ from 0.0 to 8.0 millimolar under 320 microliters CO₂/liter increased plant dry weight by 251% and Kjeldahl N content by 287% at 22 days after planting. Increasing NH₄NO₃ from 1.0 to 8.0 millimolar under 320 microliters CO₂/liter increased total dry weight and Kjeldahl N by 100 and 168%, respectively, on day 22. Raising CO₂ from 320 to 1,000 microliters CO₂/liter during the same period had no significant effect on Kjeldahl N content of plants grown with 0.0 or 1.0 millimolar NH₄NO₃. The maximum CO₂ treatment effects were observed in plants supplied with 8.0 millimolar NH₄NO₃, where dry weight and Kjeldahl N content were increased 64% and 20%, respectively. An increase in shoot CO₂-exchange rate associated with the CO₂-enrichment treatment was reflected in a significant increase in leaf dry weight and starch content for plants grown with 1,000 microliters CO₂/liter under all combined N treatments. These data show directly that seedling growth in symbiotically grown soybeans was limited primarily by N availability. The failure of the CO₂-enrichment treatment to increase total plant N significantly in Rhizobium-dependent plants indicates that root nodule development and functioning in such plants was not limited by photosynthate production.     

Photosynthetic Rates of Sporophytes and Gametophytes of the Fern, Todea barbara

The photosynthetic rates of intact sporophytes or gametophytes of the fern Todea barbara grown in sterile culture were measured using an infrared gas analyzer. Sporophytes consisted of single whole plants with roots and leaves grown in tubes of agar. Gametophytes were grown as several plants covering the surface of the agar. Sporophytes had photosynthetic rates at light saturation of 8.50 microliters CO₂ per hour per milligram dry weight and 1,300 microliters CO₂ per hour per milligram chlorophyll, whereas rates for gametophytes were lower, 2.36 microliters CO₂ per hour per milligram dry weight and 236 microliters CO₂ per hour per milligram chlorophyll.     

Alteration of Components of Leaf Water Potential and Water Content in Velvetleaf under the Effects of Long-Term Humidity Difference

Velvetleaf (Abutilon theophrasti Medik.) was grown in growth chambers set at 45 or 85% relative humidity at 30°C, CO₂ 350 microliters per liter and 1000 micromoles per square meter per second of photosynthetically active radiation. Soil water potential was maintained at −0.05 megapascal by subirrigation with half strength Hoagland solution. The third, fourth, and fifth leaves from the base of 21- and 25-day-old plants were used for pressure-volume measurements. Components of leaf water status including water potential (osmotic and potential associated with the apoplast), leaf water content (apoplasmic and symplasmic water), and elastic modulus of leaf tissue were determined. Results indicate: (a) persistent dry air generated leaves with lower water potential at a given relative water content than did humid air; (b) the higher total leaf water content in plants grown in dry air was related to an increase in apoplasmic water, whereas symplasmic water remained similar in both humidity treatments; (c) difference in leaf water potential between low and high humidity treatments was related to decreased potential associated with the apoplast but not to a change in cell wall elasticity.     

Effects of Water Stress on Photosynthesis and Carbon Partitioning in Soybean (Glycine max [L.] Merr.) Plants Grown in the Field at Different CO(2) Levels

The effects of water stress and CO₂ enrichment on photosynthesis, assimilate export, and sucrose-P synthase activity were examined in field grown soybean plants. In general, leaves of plants grown in CO₂-enriched atmospheres (300 microliters per liter above unenriched control, which was 349 ± 12 microliters per liter between 0500 and 1900 hours EST over the entire season) had higher carbon exchange rates (CER) compared to plants grown at ambient CO₂, but similar rates of export and similar activities of sucrose-P synthase. On most sample dates, essentially all of the extra carbon fixed as a result of CO₂ enrichment was partitioned into starch. CO₂-enriched plants had lower transpiration rates and therefore had a higher water use efficiency (milligrams CO₂ fixed per gram H₂O transpired) per unit leaf area compared to nonenriched plants. Water stress reduced CER in nonenriched plants to a greater extent than in CO₂-enriched plants. As CER declined, stomatal resistance increased, but this was not the primary cause of the decrease in assimilation because internal CO₂ concentration remained relatively constant. Export of assimilates was less affected by water stress than was CER. When CERs were low as a result of the imposed stress, export was supported by mobilization of reserves (mainly starch). Export rate and leaf sucrose concentration were related in a curvilinear manner. When sucrose concentration was above about 12 milligrams per square decimeter, obtained with nonstressed plants at high CO₂, there was no significant increase in export rate. Assimilate export rate was also correlated positively with SPS activity and the quantitative relationship varied with CER. Thus, export rate was a function of both CER and carbon partitioning.     

Acclimation of Two Tomato Species to High Atmospheric CO(2): II. Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase and Phosphoenolpyruvate Carboxylase

Lycopersicon esculentum Mill. cv Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO₂ concentrations (330 or 900 microliters per liter) for 10 weeks. The elevated CO₂ concentrations increased the initial ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity of both species for the first 5 weeks of treatment but the difference did not persist during the last 5 weeks. The activity of Mg²⁺-CO₂-activated Rubisco was higher in 900 microliters per liter for the first 2 weeks but declined sharply thereafter. After 10 weeks, leaves grown at 330 microliters per liter CO₂ had about twice the Rubisco activity compared with those grown at 900 microliters per liter CO₂. The two species showed the same trend to Rubisco declines under high CO₂ concentrations. The percent activation of Rubisco was always higher under high CO₂. The phosphoenolpyruvate carboxylase (PEPCase) activity measured in tomato leaves averaged 7.9% of the total Rubisco. PEPCase showed a similar trend with time as the initial Rubisco but with no significant difference between nonenriched and CO₂-enriched plants. Long-term exposure of tomato plants to high CO₂ was previously shown to induce a decline of photosynthetic efficiency. Based on the current study and on previous results, we propose that the decline of activated Rubisco is the main cause of the acclimation of tomato plants to high CO₂ concentrations.     

Prechilling of Xanthium strumarium L. Reduces Net Photosynthesis and, Independently, Stomatal Conductance, While Sensitizing the Stomata to CO(2)

Greenhouse-grown plants of Xanthium strumarium L. were exposed in a growth cabinet to 10 C during days and 5 C during nights for periods of up to 120 hours. Subsequently, CO₂ exchange, transpiration, and leaf temperature were measured on attached leaves and in leaf sections at 25 or 30 C, 19 C dew point of the air, 61 milliwatts per square centimeter irradiance, and CO₂ concentrations between 0 and 1000 microliters per liter ambient air. Net photosynthesis and stomatal conductance decreased and dark respiration increased with increasing duration of prechilling. The reduction in net photosynthesis was not a consequence of decreased stomatal conductance because the intercellular CO₂ concentration in prechilled leaves was equal to or greater than that in greenhouse-grown controls. The intercellular CO₂ concentration at which one-half maximum net photosynthesis occurred remained the same in prechilled leaves and controls (175 to 190 microliters per liter). Stomata of the control plants responded to changes in the CO₂ concentration of the air only slightly. Prechilling for 24 hours or more sensitized stomata to CO₂; they responded to changes in CO₂ concentration in the range from 100 to 1000 microliters per liter.     

Effects of Atmospheric CO(2) Enrichment on the Growth and Mineral Nutrition of Quercus alba Seedlings in Nutrient-Poor Soil

One-year-old dormant white oak (Quercus alba L.) seedlings were planted in a nutrient-deficient forest soil and grown for 40 weeks in growth chambers at ambient (362 microliters per liter) or elevated (690 microliters per liter) levels of CO₂. Although all of the seedlings became severely N deficient, CO₂ enrichment enhanced growth by 85%, with the greatest enhancement in root systems. The growth enhancement did not increase the total water use per plant, so water-use efficiency was significantly greater in elevated CO₂. Total uptake of N, S, and B was not affected by CO₂, therefore, tissue concentrations of these nutrients were significantly lower in elevated CO₂. An increase in nutrient-use efficiency with respect to N was apparent in that a greater proportion of the limited N pool in the CO₂-enriched plants was in fine roots and leaves. The uptake of other nutrients increased with CO₂ concentration, and P and K uptake increased in proportion to growth. Increased uptake of P by plants in elevated CO₂ may have been a result of greater proliferation of fine roots and associated mycorrhizae and rhizosphere bacteria stimulating P mineralization. The results demonstrate that a growth response to CO₂ enrichment is possible in nutrient-limited systems, and that the mechanisms of response may include either increased nutrient supply or decreased physiological demand.     

Carbon Dioxide Exchange in Lichens : RELATIONSHIP BETWEEN NET PHOTOSYNTHETIC RATE AND CO(2) CONCENTRATION

The relationship between net photosynthesis and CO₂ concentration was investigated for four species of lichen using an infrared gas analyzer operating in a closed loop system. All species showed a linear relationship at low CO₂ levels (100 microliters per liter) with CO₂ saturation levels being in excess of 400 microliters per liter. Detailed studies of Sticta latifrons showed a strong influence of thallus water content which resulted in the net photosynthetic response at high water contents still being nearly linear at 1000 microliters per liter CO₂. Very low CO₂ compensation values (5 microliters per liter) were obtained under some conditions but the value varied between thalli and with thallus water content. The results differ from previous studies which reported low CO₂ saturation levels (200 microliters per liter) and no apparent effect of water content. It is suggested that some of these differences may result from the use of a discrete sampling injection infrared gas analyzer system in the earlier studies and an assessment is made of the influence of nonsaturating CO₂ levels, lack of cuvette ventilation, and data presentation for this technique.     

Increases in Phosphorus Requirements for CO(2)-Enriched Pine Species

Pinus radiata D. Don (half-sib families 20010 and 20062) and Pinus caribaea var hondurensis (an open-pollinated family) were grown for 49 weeks at seven levels of phosphorus and at CO₂ concentrations of either 340 or 660 microliters per liter, to establish if the phosphorus requirements differed between the CO₂ concentrations and if mycorrhizal associations were affected. When soil phosphorus availability was low, phosphorus uptake was increased by elevated CO₂. This may have been related to changes in mycorrhizal competition. When the phosphorus concentration in the youngest fully expanded needles was above 600 milligrams per kilogram the shoot weight of all pine families was greater at high CO₂ due to increases in rates of photosynthesis. More dry weight was partitioned to the stems of P. radiata family 20010 and P. caribaea. At foliar phosphorus concentrations above 1000 milligrams per kilogram (P. radiata) and 700 milligrams per kilogram (P. caribaea), growth did not increase at 340 microliters of CO₂ per liter. Soluble sugar levels in the same needles mirrored the growth response, but the starch concentration declined with increasing phosphorus. At 660 microliters of CO₂ per liter, shoot weight and soluble sugar concentrations were still increasing up to a foliar P concentration of 1800 milligrams per kilogram for P. radiata and 1600 milligrams per kilogram for P. caribaea. The starch concentrations did not decline. These results indicate that higher foliar phosphorus concentrations are required to realize the maximum growth potential of pines at elevated CO₂.     

Response of Two Wheat Cultivars to CO(2) Enrichment under Subambient Oxygen Conditions

Two cultivars of wheat (Triticum aestivum L. cvs Sonoita and Yecora Rojo) were grown to maturity in a growth chamber within four sub-chambers under two CO₂ levels (350 or 1000 microliters per liter) at either ambient (21%) or low O₂ (5%). Growth analysis was used to characterize changes in plant carbon budgets imposed by the gas regimes. Large increases in leaf areas were seen in the low O₂ treatments, due primarily to a stimulation of tillering. Roots developed normally at 5% O₂. Seed development was inhibited by the subambient O₂ treatment, but this effect was overcome by CO₂ enrichment at 1000 microliters per liter. Dry matter accumulation and seed number responded differently to the gas treatments. The greatest dry matter production occurred in the low O₂, high CO₂ treatment, while the greatest seed production occurred in the ambient O₂, high CO₂ treatment. Growth and assimilation were stimulated more by either CO₂ enrichment or low O₂ in cv Yecora Rojo than in Sonoita. These experiments are the first to explore the effect of whole plant low O₂ treatments on growth and reproduction. The finding that CO₂ enrichment overcomes low O₂-induced sterility may help elucidate the nature of this effect.     

Effects of CO(2) Enrichment and Carbohydrate Content on the Dark Respiration of Soybeans

During the period of most active leaf expansion, the foliar dark respiration rate of soybeans (Glycine max cv Williams), grown for 2 weeks in 1000 microliters CO₂ per liter air, was 1.45 milligrams CO₂ evolved per hour leaf density thickness, and this was twice the rate displayed by leaves of control plants (350 microliters CO₂ per liter air). There was a higher foliar nonstructural carbohydrate level (e.g. sucrose and starch) in the CO₂ enriched compared with CO₂ normal plants. For example, leaves of enriched plants displayed levels of nonstructural carbohydrate equivalent to 174 milligrams glucose per gram dry weight compared to the 84 milligrams glucose per gram dry weight found in control plant leaves. As the leaves of CO₂ enriched plants approached full expansion, both the foliar respiration rate and carbohydrate content of the CO₂ enriched leaves decreased until they were equivalent with those same parameters in the leaves of control plants. A strong positive correlation between respiration rate and carbohydrate content was seen in high CO₂ adapted plants, but not in the control plants.

Mitochondria, isolated simultaneously from the leaves of CO₂ enriched and control plants, showed no difference in NADH or malate-glutamate dependent O₂ uptake, and there were no observed differences in the specific activities of NAD⁺ linked isocitrate dehydrogenase and cytochrome c oxidase. Since the mitochondrial O₂ uptake and total enzyme activities were not greater in young enriched leaves, the increase in leaf respiration rate was not caused by metabolic adaptations in the leaf mitochondria as a response to long term CO₂ enrichment. It was concluded, that the higher respiration rate in the enriched plant's foliage was attributable, in part, to a higher carbohydrate status.

     

The water relations of Verna Lemon trees from flowering to the end of rapid fruit growth

Lemon plants (Citrus limonum L. cv. Verna) were grown in the field under two different flood irrigation treatments. The dry treatment received four irrigations per year (March, July, September and November) and the wet treatment one monthly. The amounts of water applied per year for dry and wet treatments were 340.0 mm and 1020.0 mm, respectively. The effects of the two treatments on certain aspects of the plant water relations during the period between flowering and the end of rapid fruit growth (critical period) were studied. Soil matric potential (ψm) and leaf water potential (ψi) values in the dry treatment revealed development of water stress during the experimental period. The water supply in the wet treatment seems sufficient to achieve the crop water requirements. The g₁ values in July were higher in the wet than dry treatments. Pronounced oscillations in g₁ from sunrise to afternoon were found especially in the dry treatment.     

Effects of Atmospheric CO(2) Enrichment on Photosynthesis, Respiration, and Growth of Sour Orange Trees

Numerous net photosynthetic and dark respiratory measurements were made over a period of 4 years on leaves of 24 sour orange (Citrus aurantium) trees; 8 of them growing in ambient air at a mean CO₂ concentration of 400 microliters per liter, and 16 growing in air enriched with CO₂ to concentrations approaching 1000 microliters per liter. Over this CO₂ concentration range, net photosynthesis increased linearly with CO₂ by more than 200%, whereas dark respiration decreased linearly to only 20% of its initial value. These results, together with those of a comprehensive fine-root biomass determination and two independent aboveground trunk and branch volume inventories, suggest that a doubling of the air's current mean CO₂ concentration of 360 microliters per liter would enhance the growth of the trees by a factor of 3.8.