Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 8/8/2002
Publication Date: N/A
Technical Abstract: The CO2 concentration of the atmosphere is rising at 0.4 percent per year and tropospheric ozone concentrations are rising even faster. Both have large direct effects on plants that will be further modified by rising temperatures. Although global change research has focused on the impacts of rising CO2, on future climate, the largest gap in predicting change over this century is knowing how vegetation will feedback on this change, and the extent to which crops may be adapted to this change. Despite genetic variation in plant responses to both gases neither classical plant breeding approaches nor natural selection has adapted plants to these changes in the atmosphere. Ozone currently costs US crop production more than $2 billion annually and is damaging natural ecosystems. The current understanding, and gaps therein, of the chain of effects from gene expression to an acclimated phenotype that result from long-term growth in elevated CO2 or ozone will be reviewed. In the short-term, elevated CO2 stimulates photosynthesis, due to both an increased velocity of carboxylation and an inhibition of oxygenation leading to photo respiration. Early laboratory studies suggested this initial stimulation of photosynthesis was short-lived, with little effect on plant production. Free-Air Concentration Enrichment (FACE) facilities, which simulate the future atmospheric composition over large areas of vegetation under open-air conditions, now show different results. Significant season-long increases in photosynthesis and production have found surprising changes in plant development. Nonetheless, observed increases in photosynthesis are still below theoretical expectations and the increase in a reproductive yield is less than that in photosynthesis. Negative feedbacks partly explained by carbohydrate and nitrogen effects on gene expression, suppression, and realization of the theoretical increase in a yield that elevated CO2 could allow. Initial studies with high doses of ozone suggest a multitude of acute changes and causes of decreased production. More realistic season-long exposures to the moderate increases observed in the field cause a chronic decrease in photo synthetic capacity largely due to decreased Rubisco. The experience with CO2 and ozone has implications for genomic approaches to other plant stresses.