How does rising atmospheric CO2 affect marine organisms?

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Up-Regulation of Enzyme in Response to Elevated CO2
Hussain, M.W., Allen, L.H., Jr. and Bowes, G. 1999. Up-regulation of sucrose phosphate synthase in rice grown under elevated CO2 and temperature. Photosynthesis Research 60: 199-208.

What was done
Rice was grown for one season in controlled environment chambers receiving atmospheric CO2 concentrations of 330 and 660 ppm. In addition, plants were grown at daytime air temperatures of 25, 28, 31, 34, and 37C to determine the effects of elevated CO2 and temperature on the activity of sucrose phosphate synthase (SPS), which is a key enzyme involved in the production of sucrose.

What was learned
SPS activity was significantly higher in leaves of CO2-enriched plants relative to that measured in leaves of ambiently-grown plants. Twenty-one days after planting, for example, daytime SPS activity was 26 and 39% higher under saturating and unsaturating conditions (for the enzyme), respectively, when measured at elevated, as opposed to ambient, CO2. Averaged across the entire growing season, a similar pattern of CO2-induced up-regulation was observed in SPS activity; with CO2-enriched plants exhibiting 12 and 20% more activity than ambiently-grown plants under saturating and unsaturating enzymatic conditions, respectively. Similarly, SPS activity increased as air temperature rose from 25 to 34C, but not from 34 to 37C.

What it means
As the CO2 content of the air rises, rice plants will likely exhibit increased rates of photosynthesis and carbohydrate production. As carbohydrates accumulate in leaves, this source supply may exceed that of sink demands, thus triggering the down regulation of rubisco to optimize the utilization of limiting resources to help balance carbohydrate synthesis with carbohydrate usage. The present data suggest that a possible reallocation of nitrogen away from rubisco and into SPS resulted in increased SPS activity, thus leading to greater sucrose synthesis and export out of photosynthesizing leaves.

Reviewed 15 October 1999