How does rising atmospheric CO2 affect marine organisms?

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Agriculture (Species -- Other) -- Summary
Atmospheric CO2 enrichment generally increases crop productivity under non-stressful growth conditions.  Stanciel et al. (2000), for example, reported that peanuts grown at 800 and 1200 ppm CO2 produced more pods, heavier pods, and greater seed dry weights than plants grown at 400 ppm CO2.  In fact, the harvest index of the peanuts, or the ratio of seed dry weight to total pod dry weight, increased by 19 and 31% for plants grown at 800 and 1200 ppm CO2, respectively.  And in another experiment, Greaves and Buwalda (1996) observed that a 200-ppm increase in the air's CO2 concentration boosted rates of net photosynthesis in kiwifruit vines by 75%.

Atmospheric CO2 enrichment also stimulates the growth of crops under stressful environmental conditions.  De Luis et al. (1999), for example, reported that water-stressed alfalfa plants grown at 700 ppm CO2 produced 2.6 and 2.3 times more biomass than plants grown in air containing 400 ppm CO2 under water-stressed and well-watered conditions, respectively.  Similarly, Fangmeier et al. (2000) found that a 290-ppm increase in the air's CO2 content increased total grain yield in barley by 48 and 31% in low and high soil nitrogen regimes, respectively.  Furthermore, when the ambient air temperature was increased by 4C, Aloni et al. (2001) observed a 75% reduction in bell pepper pollen germination; but when the elevated air temperature treatment was accompanied by a 450-ppm increase in the atmospheric CO2 concentration, the depression in germination was completely alleviated.  In addition, the high temperature-induced 68% reduction in seed number per fruit became a mere 9% reduction with concurrent atmospheric CO2 enrichment.

To summarize, experimental data from a variety of different crops suggest that as the air's CO2 content continues to rise, we can expect to see improvements in the growth and productivity of nearly all types of agricultural plants in nearly all situations.

References
Aloni, B., Peet, M., Pharr, M. and Karni, L.  2001.  The effect of high temperature and high atmospheric CO2 on carbohydrate changes in bell pepper (Capsicum annuum) pollen in relation to its germination.  Physiologia Plantarum 112: 505-512.

De Luis, J., Irigoyen, J.J. and Sanchez-Diaz, M.  1999.  Elevated CO2 enhances plant growth in droughted N2-fixing alfalfa without improving water stress.  Physiologia Plantarum 107: 84-89.

Fangmeier, A., Chrost, B., Hogy, P. and Krupinska, K.  2000.  CO2 enrichment enhances flag leaf senescence in barley due to greater grain nitrogen sink capacity.  Environmental and Experimental Botany 44: 151-164.

Greaves, A.J. and Buwalda, J.G.  1996.  Observations of diurnal decline of photosynthetic gas exchange in kiwifruit and the effect of external CO2 concentration.  New Zealand Journal of Crop and Horticultural Science 24: 361-369.

Stanciel, K., Mortley, D.G., Hileman, D.R., Loretan, P.A., Bonsi, C.K. and Hill, W.A.  2000.  Growth, pod and seed yield, and gas exchange of hydroponically grown peanut in response to CO2 enrichment.  HortScience 35: 49-52.