Carbon Dioxide and Ozone Effects on Growth of a Legume-Grass Mixture
- B. G. Johnson,
- B. A. Hale and
- D. P. Ormrod *
Atmospheric carbon dioxide (CO2) and photochemical ozone (O3) have been increasing in the biosphere and will continue to do so with further industrialization and burning of fossil fuels. The purpose of this study was to examine the interaction of CO2 and O3 on plant growth and aboveground competition using a forage mixture of alfalfa (Medicago sativa L.) and timothy (Phleum pratense L.). Mixtures were grown at two CO2 levels (350 and 700 µL/L) in controlled environment chambers and exposed to four weekly O3 episodes of 8-h duration with peak daily concentrations of 0.03, 0.08, 0.13, or 0.18 µL/L on Days (d) 21, 28, 35, and 42 after seeding. Roots of individual plants were in separate containers. The plants were harvested 2 d after the final O3 exposure. Total dry biomass of alfalfa and timothy was 50 and 40%, respectively, greater at 700 than at 350 µL CO2/L with low O3. Increasing peak O3 concentration decreased alfalfa shoot dry biomass at 700 µL CO2/L but not at 350 µL/L and decreased root dry biomass at both CO2 levels. In timothy, intermediate O3 levels reduced shoot growth but the highest level of O3 resulted in more shoot growth in the mixture at both CO2 levels. Partitioning of dry matter to alfalfa roots was strongly retarded by increasing O3, particularly in the CO2-enriched environment, while timothy root growth was unaffected by O3. The enhancement of timothy shoot biomass in the mixture by exposure to the highest level of O3 at either CO2 level could not be fully explained by changes in competition between timothy and alfalfa in relation to differential O3 tolerance.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © . .