High Atmospheric CO2 Concentrations Research Articles

Influence of Elevated Carbon Dioxide on Water Relations of Soybeans

Soybean (Glycine max L. Merrill cv ;Bragg') plants were grown in pots at six elevated atmospheric CO(2) concentrations and two watering regimes in open top field chambers to characterize leaf xylem potential, stomatal resistance and conductance, transpiration, and carbohydrate contents of the leaves in response to CO(2) enrichment and water stress conditions. Groups of plants at each CO(2) concentration were subjected to water stress by withholding irrigation for 4 days during the pod-filling stage.Under well watered conditions, the stomatal conductance of the plants decreased with increasing CO(2) concentration. Therefore, although leaf area per plant was greater in the high CO(2) treatments, the rate of water loss per plant decreased with CO(2) enrichment. After 4 days without irrigation, plants in lower CO(2) treatments showed greater leaf tissue damage, lower leaf water potential, and higher stomatal resistance than high CO(2) plants. Stomatal closure occurred at lower leaf water potentials for the low CO(2) grown plants than the high CO(2) grown plants. Significantly greater starch concentrations were found in leaves of high CO(2) plants, and the reductions in leaf starch and increases in soluble sugars due to water stress were greater for low CO(2) plants. The results showed that even though greater growth was observed at high atmospheric CO(2) concentrations, lower rates of water use delayed and, thereby, prevented the onset of severe water stress under conditions of low moisture availability.

Effect of high atmospheric CO2 concentration on ?13 of algae

Effect of high atmospheric CO2 concentration on ?13 of algae

Mutants of the cruciferous plant Arabidopsis thaliana lacking glycine decarboxylase activity.

A mutant of Arabidopsis thaliana (L.) Heyn. (a small plant in the crucifer family) that lacks glycine decarboxylase activity owing to a recessive nuclear mutation has been isolated on the basis of a growth requirement for high concentrations of atmospheric CO2. Mitochondria isolated from leaves of the mutant did not exhibit glycine-dependent O2 consumption, did not release 14CO2 from [14C]glycine, and did not catalyse the glycine-bicarbonate exchange reaction that is considered to be the first partial reaction associated with glycine cleavage. Photosynthesis in the mutant was decreased after illumination under atmospheric conditions that promote partitioning of carbon into intermediates of the photorespiratory pathway, but was not impaired under non-photorespiratory conditions. Thus glycine decarboxylase activity is not required for any essential function unrelated to photorespiration. The photosynthetic response of the mutant in photorespiratory conditions is probably caused by an increased rate of glyoxylate oxidation, which results from the sequestering of all readily transferable amino groups in a metabolically inactive glycine pool, and by a depletion of intermediates from the photosynthesis cycle. The rate of release of 14CO2 from exogenously applied [14C]glycollate was 14-fold lower in the mutant than in the wild type, suggesting that glycine decarboxylation is the only significant source of photorespiratory CO2.