Author
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SICHER JR, RICHARD |
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Bunce, James |
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Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/2/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Current atmospheric carbon dioxide concentrations are expected to double during the next century because of the combined effects of deforestation and industrialization. The present investigation studied the effects of carbon dioxide enrichment on growth and leaflet gas exchange properties of potato plants grown in open-topped chambers in the field from 1996 to 1998. .The presence of developing potatoes (tubers) should constitute a major sin for the excess assimilates formed in the presence of elevated carbon dioxide. Developing tubers should prevent the feedback inhibition of photosynthesis that has been commonly observed in sink-limited small grain cereals, such as wheat. Average tuber yields were increased by 40 percent when the ambient carbon dioxide concentration was doubled. Consistent with increased yield, net rates of photosynthesis averaged over all measurement dates were 128 and 149 percent greater in the medium and high compared to the low carbon dioxide treatment, respectively. Leaflet water vapor exchange rates decreased when carbon dioxide concentrations were increased. Unlike wheat, there was a persistent enhancement of photosynthesis in potato under elevated carbon dioxide. Changes of photosynthesis in potato in response to carbon dioxide enrichment were independent of leaflet soluble protein levels. These results supported the hypothesis that large developing sinks promoted sustained high rates of photosynthesis. Our findings should be of interest to fellow researchers and to crop modellers. Technical Abstract: The photosynthetic responses of potato [Solanum tuberosum (L.)] to CO2 enrichment were studied in open-topped field chambers from 1996 to 1998. Plots were continuously fertilized with 1, 1.5 and 2 times ambient daytime CO2. These were low (L), medium (M) and high (H) CO2 treatments, respectively. Photosynthetic rates (Pn) and conductance to water vapor (gs) of upper canopy leaves were measured at 1 or 2 week intervals at the growth CO2 partial pressure and then Pn of plants in the L treatment was determined at 70 Pa CO2 (L70). Leaflet Pn averaged over all measurement dates were 128, 149 and 184 percent greater, respectively, in the M, H and L70 CO2 treatments, compared to plants in the L treatment. Changes of Pn in response to the L, M and H CO2 treatments were proportional to increases of internal CO2 (Ci) and mid-day gs was inversely related to growth CO2. The ratio of Pn at H compared to L70 was 0.81 when averaged over all measurement dates. Soluble protein, Rubisco protein and chlorophyll (a + b) were unaffected by CO2 treatment. Total Rubisco activity was decreased by CO2 enrichment but percent activation was similar in the L, M and H plots. Leaf starch was increased but sucrose, glucose and fructose were unaffected by CO2 treatment. The above findings indicated that negative photosynthetic acclimation to elevated CO2 was consistently observed in field-grown potato. A decrease of total Rubisco activity was potentially due to the presence of inhibitory compounds bound to the active site of the enzyme. The amount of photosynthetic acclimation observed here did not preclude a persistent enhancement of Pn under the elevated CO2 growth conditions. |
