How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Growth Response of Radish to Super Atmospheric CO2 Enrichment
Schubert, B.A. and Jahren, A.H. 2011. Fertilization trajectory of the root crop Raphanus sativus across atmospheric pCO2 estimates of the next 300 years. Agriculture, Ecosystems and Environment 140: 174-181.

The authors write that "plant biomass is known to increase in response to elevated atmospheric CO2 concentration," but they state that "no experiments have quantified the trajectory of crop fertilization across the full range of CO2 levels estimated for the next 300 years," which Zachos et al. (2008) have suggested could extend all the way to a concentration of 1800 ppm if fossil fuel usage continues unabated.

What was done
In an attempt to obtain this information for a common food plant, Schubert and Jahren grew radishes (Raphanus sativus) from seed to maturity (a period of four months) in standard potting soil within eight growth chambers maintained at optimum temperature, humidity and soil water and fertility conditions in air of eight different CO2 concentrations (348, 388, 413, 426, 760, 1090, 1425 and 1791 ppm), after which they harvested the plants and determined their above- and below-ground biomass, both of which they found to be well described by a two-parameter rectangular hyperbola, "employing the method used by Hunt et al. (1991, 1993) for assessing the trajectory of the biomass response for 36 herbaceous species grown under CO2 levels ranging from 365 to 812 ppm."

What was learned
Going from the lowest to the highest CO2 concentration employed in their study, the two U.S. researchers found that above-ground biomass rose by a modest 58%, but that below-ground biomass rose by a phenomenal 279%, which trajectory "greatly exceeded a trajectory based on extrapolation of previous experiments for plants grown at CO2 < 800 ppm."

What it means
In the words of Schubert and Jahren, "if the below-ground biomass enhancement that we have quantified for R. sativus represents a generalized root-crop response that can be extrapolated to agricultural systems, below-ground fertilization under very high CO2 levels could dramatically augment crop production in some of the poorest nations of the world." And "needless to say," as they continue, "a doubling or tripling of below-ground crop tissue due to CO2 fertilization would be welcome on both a nutritional and economic basis."

Hunt, R., Hand, D.W., Hannah, M.A. and Neal, A.M. 1991. Response to CO2 enrichment in 27 herbaceous species. Functional Ecology 5: 410-421.

Hunt, R., Hand, D.W., Hannah, M.A. and Neal, A.M. 1993. Further responses to CO2 enrichment in British herbaceous species. Functional Ecology 7: 661-668.

Zachos, J.C., Dickens, G.R. and Zeebe, R.E. 2008. An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics. Nature 451: 279-283.

Reviewed 20 April 2011