As the air's CO2 content continues to rise, nearly all of earth's vegetation will respond by exhibiting enhanced rates of photosynthesis and greater production of carbohydrates. Many of these carbohydrates will be exported from leaves to ultimately provide energy or carbon skeletons to facilitate increased biomass production. After such needs have been met, any remaining carbohydrates will likely be converted into starch and stored within leaves or roots for future use. Thus, the rising CO2 content of the air should boost starch concentrations within these specialized plant organs.
In reviewing the recent literature, it is clear that this scenario is being played out in a variety of different plants. In a study by Janssens et al. (1998), for example, a six-month period of atmospheric CO2 exposure of 700 ppm caused a 90% increase in root starch accumulation in Scots pine seedlings relative to control seedlings that were exposed to ambient CO2 concentrations of 350 ppm. Using the same species, Kainulainen et al. (1998) reported a significant enhancement in needle starch concentrations after three-years of atmospheric CO2 enrichment (+300 ppm). Similar results have been reported in tropical trees, where ten (Lovelock et al., 1998) and four (Wurth et al., 1998) species exhibited approximate doublings of their leaf starch contents in response to a doubling of the atmospheric CO2 content. In other tree studies, Rey and Jarvis (1998) also noted a 100% CO2-induced increase in leaf starch contents of birch seedlings exposed to an atmospheric CO2 concentration of 700 ppm, while Pan et al. (1998) reported a whopping 17-fold increase in this parameter for apple seedlings grown at an atmospheric CO2 concentration of 1600 ppm.
Elevated CO2 concentrations also increase starch concentrations within non-woody herbaceous plants. Reid et al. (1998), for example, documented a 148% increase in soybean leaf starch contents, due to a doubling of the atmospheric CO2 content, at both normal and elevated concentrations of ozone. And in another agricultural crop, exposure to 1000 ppm CO2 caused a 10-fold increase in leaf starch concentrations of potato (Ludewig et al., 1998).
Clearly, rising atmospheric CO2 levels will significantly boost starch production in plants, thereby increasing the availability of an important raw material that can be metabolized to help sustain enhanced growth.
References
Janssens, I.A., Crookshanks, M., Taylor, G. and Ceulemans, R. 1998. Elevated atmospheric CO2 increases fine root production, respiration, rhizosphere respiration and soil CO2 efflux in Scots pine seedlings. Global Change Biology 4: 871-878.
Kainulainen, P., Holopainen, J.K. and Holopainen, T. 1998. The influence of elevated CO2 and O3 concentrations on Scots pine needles: Changes in starch and secondary metabolites over three exposure years. Oecologia 114: 455-460.
Lovelock, C.E., Winter, K., Mersits, R. and Popp, M. 1998. Responses of communities of tropical tree species to elevated CO2 in a forest clearing. Oecologia 116: 207-218.
Ludewig, F., Sonnewald, U., Kauder, F., Heineke, D., Geiger, M., Stitt, M., Muller-Rober, B.T., Gillissen, B., Kuhn, C. and Frommer, W.B. 1998. The role of transient starch in acclimation to elevated atmospheric CO2. FEBS Letters 429: 147-151.
Pan, Q., Wang, Z. and Quebedeaux, B. 1998. Responses of the apple plant to CO2 enrichment: changes in photosynthesis, sorbitol, other soluble sugars, and starch. Australian Journal of Plant Physiology 25: 293-297.
Rey, A. and Jarvis, P.G. 1998. Long-Term photosynthetic acclimation to increased atmospheric CO2 concentration in young birch (Betula pendula) trees. Tree Physiology 18: 441-450.
Reid, C.D., Fiscus, E.L. and Burkey, K.O. 1998. Combined effects of chronic ozone and elevated CO2 on rubisco activity and leaf components in soybean (Glycine max). Journal of Experimental Botany 49: 1999-2011.
Wurth, M.K.R., Winter, K. and Korner, C. 1998. Leaf carbohydrate responses to CO2 enrichment at the top of a tropical forest. Oecologia 116: 18-25.