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Title: THE EFFECT OF CO2 ENRICHMENT OF PHOTOSYNTHETIC RAS AND INSTANTANEOUS WATER USE EFFICIENCY OF ANDROPOGON GERARDII IN THE TALLGRASS PRAIRIE

Author
item ADAM, NEAL
item OWENSBY, C - KANSAS STATE UNIV
item HAM, J - KANSAS STATE UNIV

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: In order to predict the effect of higher atmospheric CO2 on rangelands, open-topped chambers were used to study the effects of CO2 enrichment on leaf-level photosynthetic rates of the big bluestem in the native tallgrass prairie ecosystem near Manhattan, Kansas, in a wet and a dry year. During the wet year, CO2 enrichment allowed plants to use less water while still photosynthesizing at rates similar to plants in ambient conditions. During the dry year, the CO2 enrichment allowed plants to maintain photosynthesis rates when stressed. This information is useful for incorporation into global climate models for use in predicting the effects of a future, higher-CO2 atmosphere on range plants and on the plants' use of water.

Technical Abstract: Open-topped chambers were used to study the effects of CO2 enrichment on leaf-level photosynthetic rates of the C4 grass Andropogon geradii in the native tallgrass prairie ecosystem near Manhattan, Kansas. Measurements were made during a year with abundant rainfall (1993) and a drought-stress year (1994). Treatments included no chamber, ambient CO2 (A); chamber with ambient CO2 (CA); and chamber with twice-ambient CO2 (CE). Measurements of photosynthesis were made at two-hour intervals, or at midday, on cloudless days throughout the growing season using an open-flow gas-exchange system. No significant differences in midday rates of photosynthesis or in daily carbon accumulation as a result of CO2 enrichment were found in the year with abundant precipitation. In the drought-stress year, midday rates of photosynthesis were significantly higher in the CE treatment than in the CA or A treatments throughout the season. Estimates of daily carbon accumulation also indicated that CO2 enrichment allowed plants to maximize carbon acquisition on a diurnal basis. The increased carbon accumulation was accounted for by greater rates of photosynthesis in the CE plots during midday. During the wet year, CO2 enrichment allowed plants to use less water while still photosynthesizing at rates similar to plants in ambient conditions. During the dry year, the CO2 enrichment allowed plants to maintain photosynthesis rates when stressed.