How does rising atmospheric CO2 affect marine organisms?

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Interactive Effects of Temperature and CO2 on Birch
Wayne, P.M., Reekie, E.G. and Bazzaz, F.A. 1998. Elevated CO2 ameliorates birch response to high temperature and frost stress: implications for modeling climate-induced geographic range shifts. Oecologia 114: 335-342.

What was done
The authors grew yellow birch seedlings in controlled environment glass cabinets that received combinations of either 400 or 800 ppm atmospheric CO2 and day/night air temperatures of 26/21 or 31/26C for about two months, in order to determine the interactive effects of CO2 and temperature on several plant growth and physiological parameters.

What was learned
Elevated CO2 stimulated net photosynthesis in seedlings by approximately 48% regardless of temperature. This additional carbon increased seedling biomass at elevated CO2 by 60% and 227% relative to plants grown at 400 ppm CO2 at normal and high air temperatures, respectively. At ambient CO2, high temperature reduced total biomass by 73%. At elevated CO2, however, biomass was reduced by only 43%, indicating that elevated CO2 partially compensates for the negative effects of high temperature on overall growth. This beneficial phenomenon results, in part, from CO2-induced changes in several physiological parameters. Respiratory carbon loss, for example, typically increases with temperature; and at ambient CO2, it rose by 174% in going from the low temperature regime to the high temperature regime; but at elevated CO2, it increased by only 13%, indicating that elevated CO2 reduces this growth-retarding process. In addition, because elevated CO2 reduced transpiration by 25 and 36% at normal and high air temperatures, respectively, plant water-use efficiency increased by 52 and 94% at the low and high temperatures. Thus, the CO2-induced modifications of these parameters helped reduce the negative impact of high temperature on overall growth. On another note, plants grown at 26/21C and ambient CO2 concentration exhibited approximately 30% less bud survivorship following exposure to simulated winter temperatures than plants grown at 31/26C. At elevated CO2, however, the differences in bud survivorship between the two temperature regimes were marginal (5-10%), indicating that elevated CO2 made dormant buds less susceptible to freezing stress.

What it means
As the concentration of CO2 in the atmosphere continues to rise, yellow birch seedlings should exhibit increased rates of net photosynthesis, even at higher temperatures, thereby facilitating increased biomass production. With more CO2 in the air, the beneficial reduction in transpiration and the concomitant rise in water-use efficiency may allow this species to expand its range southward into regions where high summer temperatures and limited rainfall currently discourage its presence. Similarly, yellow birch may also expand northwards, as the additional CO2 may make seedlings more tolerant to freezing temperatures.

Reviewed 1 November 1998