Growth and development of native species of trees in response to long-term increases in atmospheric CO2 concentration were studied. Seedlings of two competing perennials, Pinustaeda L. and Liquidambarstyraciflua L., were obtained from germinated seeds and grown through one complete growing season at 350, 500, and 650 μL•L−1 CO2. The plants were grown in CO2 controlled greenhouses under natural photoperiods and light regimes, with temperature controlled to simulate mean local climate. Stem length and basal stem diameter increased with increasing CO2 in both species. Liquidambarstyraciflua maintained size dominance in all concentrations. The dry weights of stems, roots, and leaves increased in both species. In P. taeda, however, the seedlings reached maximum size at 500 μL•L−1 while L. styraciflua continued to increase up to 650 μL•L−1. Liquidambarstyraciflua produced significantly more branches and leaves at the higher CO2 concentrations than at 350 μL L−1. Differences in plant shape and responses in growth rate of these two naturally competing tree species suggest that continuing atmospheric CO2 enrichment could affect future interactions between the species and might produce changes in community composition.

SummaryIf atmospheric carbon dioxide concentration continues to increase, plant growth and crop yield could be affected. New Yorker and Better Boy cultivars of tomato (Lycopersicon esculentum) were used to investigate possible intraspecific variation in the response of crop species to increased CO2. Because precipitation and temperature are predicted to change with the increasing atmospheric CO2concentration, the response of the two cultivars to the interaction between CO2and water stress was also examined. Seeds of the two cultivars were germinated and grown under controlled environmental conditions, in either 350 or 675 μ1 CO2/1.The plant water status of the two cultivars was inherently different but was little affected by the CO2concentration when the plants were well watered. When water was withheld for 5 days the total leaf water potential and osmotic potential decreased in both CO2treatments but less rapidly in high CO2than in low. Under low CO2total leaf water potential decreased to a lower value than osmotic potential. The differences were due, at least in part, to the reduced stomatal conductance and transpiration rate under high CO2.Increased CO2ameliorated the detrimental effects of drought stress on plant growth. The results indicate that increased CO2could differentially affect the relative drought resistance of species cultivars.

The interaction of CO2 enrichment and drought on water status and growth of pea plants was investigated. Pisum sativum L. (cv. Alaska) plants were grown from seeds in growth chambers using 350 and 675 μl I1 CO2, a photon flux density of 600 μmol M‐2 S‐1, a 16 h photoperiod and a temperature regime of 20/14°C. The drought treatment was started at the beginning of branch initiation and lasted for 9 or 11 days. The water status of the plants was monitored daily by measuring total leaf water potential and stomatal conductance. The total leaf water potential of well‐watered plants was not affected by the CO2 level. Under draughting conditions total leaf water potential decreased, with a slower decrease under the high CO2 regime, due, at least in part, to reduced stomatal conductance. Upon rewatering, total leaf water potential and stomatal conductance recovered within one day. High CO2 counteracted the reduction in height and, to some extent, leaf area that developed in low CO2 unwatered plants. Additional CO2 had no effect on branch number and did not prevent the complete inhibition of branch development that resulted from drought stress. Removing the drought conditions resulted in a rapid recovery of the internal water status and also a rapid recovery of most, but not all, plant growth parameters.

AbstractAtmospheric carbon dioxide and irradiance are important factors affecting growth and yield of plants. Due to the wide variation in irradiance in natural plant stands and the reportedly increasing carbon dioxide concentration in the global atmosphere, it is essential to study the interacting effects of these factors on the growth and production of crop plants. Growth analysis techniques were used to study the interaction of atmospheric CO2 concentration (350 and 675 µl/l) and photosynthetic photon flux density (PPFD) (600 and 1200 µEM−2 s−1)on four species (including both seed and root crops) grown in controlled environment chambers of the Duke University Phytotron. The plants were soybean (Glycine max L. Merr.), radish (Raphanus sativus L.), sugarbeet (Beta vulgaris L.), and corn (Zea mays L.). Total dry matter production increased in all species of plants and at all growth stages with both increased CO2 concentration and PPFD levels, and the maximum dry matter was produced at the highest combined levels of CO2 and PPFD. The dry weight increase varied between the different species and between plant parts within a species. High levels of CO2 and PPFD caused a greater increase in net assimilation rate in the plants during early growth stages than in later stages because the first two or three young, rapidly growing leaves were very efficient photosynthetic organs. A high CO2 or PPFD level resulted in decreasing leaf area ratios with increasing plant age for all the species due to a rapid increase in stem and root growth later in fruit production, and to a decreasing specific leaf area.Corn, having the C4 pathway of photosynthesis, showed less response to increased CO2 and PPFD than the three C3 species. Increasing the atmospheric CO2 concentration from 350 to 675 µl/liter at low and high PPFD levels produced dry matter increases of 72.7 and 76.4%, respectively, in soybean, and 18.9 and 18.6%, respectively, in corn at 50 days after planting. None of the species tested were light saturated at levels available in the standard fluorescent and incandescent lighting as is shown by the increased growth when higher PPFD levels were obtained with a combination of multivapor and sodium lamps.

Soybean ( Glycine max Merr.), tomato ( Lycopersicon esculentum Mill.), and marigold (Tagetes erects L.) produced 21%, 19% and 8% more dry weight, respectively, after 9 weeks when arcillite (Turface) was added to a gravel-venniculite medium. The addition of arcillite increased the available moisture holding capacity by 40%.

SummaryGrowth and yield components of a semi-dwarf spring wheat (Triticum aestivumL., cv. GWO 1809) were determined under three different atmospheric CO2a concentrations (350, 675 and 1000 μ1/1) in controlled environment chambers of the Duke University Phytotron. CO2 enrichment enhanced tiller and head emergence and increased the number of head-producing tillers and the total dry weight of the plants. Total leaf area, stem height and root/shoot ratio of the plants were greater at high CO2concentrations than at low. Net assimilation rate (NAR) increased with increasing CO2concentration and decreased with plant size. There was little effect of CO2enrichment on leaf weight ratio (LWR) and leaf area ratio (LAR) and no significant effect on specific leaf area (SLA). The weight and number of seeds were significantly higher with increasing CO2concentration. The results of this study provide evidence that important changes in plant growth and development may occur during the next century if global CO2enrichment continues. Some of these changes would have important ecological impact in natural and managed ecosystems in the future.

Water status and growth responses of wheat (Triticum aestivum L. [GWO-1809]) to increased CO2 concentration and water stress were studied in controlled-environment chambers. Plants were grown in 350 μl/ liter or 1,000 μl/liter CO2 at similar temperature, irradiance, and photoperiod conditions. Groups of plants were subjected to water stress by withholding irrigation for one or two cycles of treatment. In most treatments, decreasing leaf water potential was correlated with decreasing osmotic potential. In leaves grown in both low and high CO2 concentrations, the osmotic potentials were lower during the second stress cycle than during the first cycle. The stomata of plants in the low CO2 concentration closed at a higher leaf water potential than those in the high CO2 concentration. Stem and head production was greater in plants grown in high CO2 concentrations than those grown in low CO2, perhaps the result of turgor-pressure maintenance as leaf water potential decreased. In controlled-environment chambers, wheat plants adapted to water stress, apparently because of high CO2 concentration and repeated stress cycles.

AbstractMost previous studies on the influence of CO2 concentration on plant growth have investigated the effect of atmospheric CO2 enrichment alone. Little attention has been given to possible interactions between CO2 enrichment and nutrient supply. The objective of this study was to characterize the long‐term effects of atmospheric CO2 enrichment on growth components of wheat (Triticum aestivum L.) grown under different nutritional levels.Growth and yield responses of spring wheat (cv. GWO1809) to two (350 and 675 ppm) CO2 and four (full strength, 1/2, 1/8, or 1/16 strength Hoagland's solution No. 1) nutritional levels were measured in controlled environment chambers at day/night temperature of 26/20 C. Plants were grown from seed and were irrigated with respective nutrient solutions three times daily until maturity.Plants grown in a 675 ppm CO2 atmosphere produced more total dry matter at each nutrient level compared to those grown in 350 ppm CO2. The root:shoot ratio decreased with increased nutritional level in both CO2 concentrations. Total weight and number of seeds produced in high CO2 were greater than those produced in low CO2 under similar nutrition. In low CO2, seed weight and number increased with each increase in nutrient concentration up to the one‐half strength level and then decreased with full strength. In high CO2, however, increasing the nutritional level from one‐half to full strength did not decrease seed weight and number significantly. As the plants grew older, the increments of increase in total plant dry weight during harvest intervals were always greater in plants grown in 675 ppm CO2 than those grown in 350 ppm CO2.

AbstractAlaska pea plants (Pisum sativum L.) were grown at 0.10 vol% and 0.035 vol% CO2 to determine the effects of high CO2 concentration upon plant growth and apical dominance. The results showed that a 0.10 vol% CO2 atmosphere significantly increased the rate of lateral branch, flower bud, flower and fruit development over an environment with 0.035 vol% CO2. At plant maturity, however, there were no significant differences in the number of branches or fruits produced at the different CO2 levels. Thus, no evidence was obtained for the loss of apical dominance at the CO2 concentrations tested. Root dry weight was significantly greater in plants grown at 0.10 vol% CO2 than in those grown at 0.035 vol% CO2 and leaf dry weight was significantly lower. However, no significant differences were found in total plant dry weight production at plant maturity.

Growth and yield responses of a semi‐dwarf spring wheat (Triticum aestivum L.; cv. GWO 1809) to two CO2 concentrations and two water stress regimes were studied in controlled environment chambers of the Duke Univ. Phytotron. Groups of plants in low (350 ppm), or high (1,000 ppm) CO2 environments were subjected to water stress By withholding irrigation starting at the 10th day after the beginning of anthesis. A second drying cycle beginning 5 days after termination of the first cycle was also given to some of the plants. Water potential of the flag leaves of the main stem of the plants in each CO2 environment reached a minimum of −13 bars at the end of the first drying cycle and −17 bars at the end of the second cycle.Under well‐watered conditions high CO2 enhanced the rate of tiller production by 43% and significantly increased grain yield, total dry matter, and number and size of the grains.As water stress developed, the osmotic potentials of the high CO2. plants decreased at a faster rate and resulted in maintenance of higher turgor pressures at the end of each stress cycle compared to the low CO2 plants. Osmotic potentials of the leaves of both high and low 2 plants decreased faster in the second drying cycle than in the first.Significantly fewer and smaller grains were produced on the plants grown under water stress in both CO2 concentrations compared to unstressed plants. In general, high CO2 plants under water stress conditions had a grain yield and total dry matter production equal to the unstressed, low CO2 plants. Thus, CO2 enrichment increased the yield potential of the water limited wheat plants due probably to osmotic adjustment by an increased concentration of solutes in their leaves.

Diurnal changes in net photosynthesis, dark respiration, specific leaf weight, leaf water potential, stomatal conductance, starch and soluble sugar concentrations, and the activities of malate dehydro- genase and glycollate oxidase were measured in soybeans grown in 23/23,26/20 and 29/17°C thermo- periods, to determine their relationship to thermoperiodic effects on plant growth. Soybean height and main stem leaf number were significantly higher under the constant daylnight (23/23°C) temperature regime. Leaf, stem and root dry weights, and specific leaf weight were all highest where the day/night temperature differential was greatest (29/17°C). Differences in net photosynthesis, dark respiration, starch and soluble sugar concentration, and malate dehydrogenase activity were small between the thermoperiod treatments. However, glycollate oxidase activity was higher under the constant-temperature conditions. Starch concentration, specific leaf weight, and glycollate oxidase activity all increased throughout the photoperiod and subsequently decreased through the dark period. Net photosynthesis declined throughout the photoperiod and both dark respiration and malate dehydrogenase activity peaked at the beginning of the dark period. Each of these diurnal responses was similar under each thermoperiod. Leaf water potential and stomatal conductance did not differ between thermoperiods.