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Title: SEEDLING RESPONSE TO ELEVATED CO2 IN FIVE EPIGEAL SPECIES

Author
item Tischler, Charles
item Polley, Herbert
item Johnson, Hyrum
item PENNINGTON, R - ROCHE MOLECULAR BIOCHEM

Submitted to: International Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Carbon dioxide concentration in the atmosphere is expected to double by the year 2050. Because plants use carbon dioxide in the process of photosynthesis to grow, this change may have important effects on the rate at which some plants grow. Some researchers have reported that doubled carbon dioxide does not increase the rate of plant growth until several weeks or even months after the plants emerge from the soil. We studied this question by growing five broadleaf plant species in normal air and in an atmosphere in which carbon dioxide was doubled. We found that increases in total plant weight in the high carbon dioxide atmosphere could be observed as early as three days after the seedlings came up. All the plants we studied had cotyledons (seed leaves) that turned green and carried on photosynthesis. Plants in which early responses are not observed do not have cotyledons which turn green and carry on photosynthesis. This suggests that the way a plant develops in nature as it germinates and begins to grow may have a big influence on how it responds to elevated carbon dioxide during the first month or two. The important result of our experiments is the finding that different kinds of seedlings will not all respond the same way to increases of carbon dioxide in the atmosphere.

Technical Abstract: Evidence from numerous sources suggests that atmospheric CO2 concentration has increased over the last 200 years and will continue to increase in the foreseeable future. Much research effort is being directed toward predicting the effects of this change on terrestrial vegetation. We focused on effects of elevated CO2 (700 uL L-1) on seedling growth characteristics of five C3 species having epigeal germination morphology, which differed by a factor of 20 in seed mass. The species and their respective seed mass ranges were: bagpod sesbania (Sesbania vesicaria, 0.23-0.26 g), cotton (Gossypium hirsutum var. Coker 317, 0.12-0.13 g), mesquite (Prosopis glandulosa, 0.041-0.048 g), cucumber (Cucumis sativus L. cv. Straight-8, 0.026-0.030 g), and hemp sesbania (Sesbania exaltata, 0.012-0.013 g). We observed stimulations in total biomass in the elevated CO2 environment for all species by three days after emergence, which is contrary to published reports that more time is required for a detectable response of seedlings to elevated CO2. Growth analyses indicated that no single growth parameter predicted the responses of the various species to elevated CO2. Maximum area of cotyledonary leaves was a better predictor of total biomass (at day 16) than was initial (day zero) seedling mass. Our data suggests that future increases in atmospheric CO2 will greatly improve the seedling stage competitive ability of C3 epigeal species with expanding (photosynthetic) cotyledons.