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item Sicher Jr, Richard
item Bunce, James

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Rising atmospheric carbon dioxide levels are an immediate concern for agriculture because carbon dioxide is the principal substrate for plant growth. It is currently not possible to accurately model photosynthesis or plant growth during long-term carbon dioxide enrichment. This is because plants grown in atmospheres enriched with carbon dioxide are capable of making various physiological adjustments. Most studies on this subject have made direct comparisons of plants grown at ambient and elevated carbon dioxide. Although acclimation responses to the carbon dioxide treatment have been reported, the mechanisms underlying plant responses to carbon dioxide enrichment remain elusive. In this study, we measured photosynthetic factors in potato leaves when plants were switched between ambient and elevated carbon dioxide levels. Results indicated that photosynthesis rates of plants switched from elevated to ambient carbon dioxide were almost completely deacclimated within three days. Conversely little or no evidence of photosynthetic acclimation was observed three days after plants were switched from ambient to elevated carbon dioxide. Also, there was a poor correlation between acclimation of photosynthesis and changes of leaf starch levels in potato leaves. We feel that this approach can be used to identify mechanistic factors involved in the onset of photosynthetic acclimation to elevated carbon dioxide.

Technical Abstract: Single leaf photosynthetic rates of potato [Solanum tuberosum (L.)] were studied in response to a reciprocal switch in ambient and elevated growth CO2. Plants were raised from individual tuber sections in controlled environment chambers at either ambient (36 Pa) or elevated (72 Pa) CO2. One half of the plants in each growth CO2 treatment were switched up or down to the opposite CO2 treatment 34 days after sowing. Net photosynthesis (Pn) rates and various leaf components were then measured at both 36 and 72 Pa CO2 34, 35, and 37 days after sowing. Three-day means of single leaf Pn rates, leaf starch, sucrose, glucose, initial and total Rubisco activity, Rubisco protein, chlorophyll (a+b), chlorophyll (a/b), a-amino N, and nitrate levels all differed significantly in the ambient and elevated CO2 treatments. Single leaf Pn rates were partially to completely deacclimated 3 days after elevated CO2 grown plants were shifted ddown, whereas much less evidence of photosynthetic acclimation was observe 3 days after ambient CO2 grown plants switched up. In a four-way comparison of the ambient, elevated, switched up, and switched down CO2 treatments 37 days after sowing, leaf starch, soluble protein, soluble carbohydrates, Rubisco protein and nitrate were the only photosynthetic factors that differed significantly. However, responses of the above photosynthetic factors to a reciprocal switch in the ambient and elevated growth CO2 were neither large enough nor closely correlated with CO2 treatment effects on Pn rates. Therefore, none of these photosynthetic factors were likely to be directly responsible for photosynthetic acclimation.