H. Hellmers

Effects of different concentrations of atmospheric CO2 on growth and yield components of wheat

Growth and yield components of a semi-dwarf spring wheat ( Triticum aestivum L., cv. GWO 1809) were determined under three different atmospheric CO 2 a 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 CO 2 concentrations than at low. Net assimilation rate (NAR) increased with increasing CO 2 concentration and decreased with plant size. There was little effect of CO 2 enrichment 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 CO 2 concentration. The results of this study provide evidence that important changes in plant growth and development may occur during the next century if global CO 2 enrichment continues. Some of these changes would have important ecological impact in natural and managed ecosystems in the future.

EFFECTS OF ATMOSPHERIC CO2 CONCENTRATION AND WATER STRESS ON WATER RELATIONS OF WHEAT

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.

Carbon dioxide enrichment and water stress interaction on growth of two tomato cultivars

If 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 CO 2 . Because precipitation and temperature are predicted to change with the increasing atmospheric CO 2 concentration, the response of the two cultivars to the interaction between CO 2 and water stress was also examined. Seeds of the two cultivars were germinated and grown under controlled environmental conditions, in either 350 or 675 μ1 CO 2 /1. The plant water status of the two cultivars was inherently different but was little affected by the CO 2 concentration when the plants were well watered. When water was withheld for 5 days the total leaf water potential and osmotic potential decreased in both CO 2 treatments but less rapidly in high CO 2 than in low. Under low CO 2 total 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 CO 2 . Increased CO 2 ameliorated the detrimental effects of drought stress on plant growth. The results indicate that increased CO 2 could differentially affect the relative drought resistance of species cultivars.