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Carbon Dioxide and Ozone Effects on Growth of a Legume‐Grass Mixture
Author(s) -
Johnson B. G.,
Hale B. A.,
Ormrod D. P.
Publication year - 1996
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1996.00472425002500040036x
Subject(s) - shoot , dry matter , carbon dioxide , ozone , chemistry , biomass (ecology) , phleum , forage , legume , zoology , horticulture , agronomy , perennial plant , botany , biology , organic chemistry
Atmospheric carbon dioxide (CO 2 ) and photochemical ozone (O 3 ) 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 CO 2 and O 3 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 CO 2 levels (350 and 700 µL/L) in controlled environment chambers and exposed to four weekly O 3 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 O 3 exposure. Total dry biomass of alfalfa and timothy was 50 and 40%, respectively, greater at 700 than at 350 µL CO 2 /L with low O 3 . Increasing peak O 3 concentration decreased alfalfa shoot dry biomass at 700 µL CO 2 /L but not at 350 µL/L and decreased root dry biomass at both CO 2 levels. In timothy, intermediate O 3 levels reduced shoot growth but the highest level of O 3 resulted in more shoot growth in the mixture at both CO 2 levels. Partitioning of dry matter to alfalfa roots was strongly retarded by increasing O 3 , particularly in the CO 2 ‐enriched environment, while timothy root growth was unaffected by O 3 . The enhancement of timothy shoot biomass in the mixture by exposure to the highest level of O 3 at either CO 2 level could not be fully explained by changes in competition between timothy and alfalfa in relation to differential O 3 tolerance.