Nasser Sionit

Response of an insect herbivore to host plants grown in carbon dioxide enriched atmospheres

Rising atmospheric carbon dioxide concentration is expected to increase plant productivity, but little evidence is available regarding effects on insect feeding or growth. Larvae of the soybean looper, a noctuid moth, were fed leaves of soybean plants grown under three carbon dioxide regimes (350, 500 and 650 μl·l-1). Larvae fed at increasingly higher rates on plants from elevated carbon dioxide atmospheres: 30% greater on leaves from the 650 μl·l-1 treatment than on leaves from the 350 μl·l-1 treatment. When variation in larval feeding was related to the leaf content of nitrogen and water, there was no significant remaining effect of carbon dioxide treatment. The principal effect on herbivores of increasing the carbon supply of leaves appeared to be reduction of leaf nutrient concentration. This study suggests that feeding by herbivores on the leaves of C3 plants may increase as the level of atmospheric carbon dioxide rises.

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.

Responses of C4 grasses to atmospheric CO2 enrichment

SummaryThe growth and photosynethetic responses to atmospheric CO2 enrichment of 4 species of C4 grasses grown at two levels of irradiance were studied. We sought to determine whether CO2 enrichment would yield proportionally greater growth enhancement in the C4 grasses when they were grown at low irradiance than when grown at high irradiance. The species studied were Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica, and Setaria faberi. Plants were grown in controlled environment chambers at 350, 675 and 1,000 μl 1-1 CO2 and 1,000 or 150 μmol m-2 s-1 photosynthetic photon flux density (PPFD). An increase in CO2 concentration and PPFD significantly affected net photosynthesis and total biomass production of all plants. Plants grown at low PPFD had significantly lower rates of photosynthesis, produced less biomass, and had reduced responses to increases in CO2. Plants grown in CO2-enriched atmosphere had lower photosynthetic capacity relative to the low CO2 grown plants when exposed to lower CO2 concentration at the time of measurement, but had greater rate of photosynthesis when exposed to increasing PPFD. The light level under which the plants were growing did not influence the CO2 compensation point for photosynthesis.