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Starch -- Summary
In reviewing the literature, it is clear that CO2-induced starch accumulation is occurring 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. Studying the same species, Kainulainen et al. (1998) reported a significant enhancement in needle starch concentrations after three-years of atmospheric CO2 enrichment to 300 ppm above ambient. Similar results have also 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.

In another study, Liu et al. (2005) found that the combined effects of elevated CO2 and ozone (O3) acting together produced a significant increase in leaf non-structural carbohydrates of 3- and 4-year-old European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst) seedlings under both mixed and monoculture conditions, which result was similar to what was observed under CO2 enrichment alone. Hence, they concluded that "since the responses to the combined exposure were more similar to elevated pCO2 than to elevated pO3, apparently elevated pCO2 overruled the effects of elevated pO3 on non-structural carbohydrates."

Also studying the combined effects of elevated carbon dioxide and ozone were Kostiainen et al. (2006), who examined fast-growing silver birch (Betula pendula Roth) clones that were grown out-of-doors at Suonenjoki, Finland, in open-top chambers maintained at ambient and 1.9x ambient CO2 concentrations in combination with ambient and 1.5x ambient O3 concentrations.

Among their various findings, the researchers reported that the elevated CO2 treatment increased trunk starch concentration by 7%. Recognizing that "the concentration of nonstructural carbohydrates (starch and soluble sugars) in tree tissues is considered a measure of carbon shortage or surplus for growth (Korner, 2003)," the Finnish researchers stated that the "starch accumulation observed under elevated CO2 in this study indicates a surplus of carbohydrates produced by enhanced photosynthesis of the same trees (Riikonen et al., 2004)." In addition, they report that "during winter, starch reserves in the stem are gradually transformed to soluble carbohydrates involved in freezing tolerance (Bertrand et al., 1999; Piispanen and Saranpaa, 2001), so the increase in starch concentration may improve acclimation in winter." Considering this response, it can be appreciated that the ongoing rise in the air's CO2 content should be a boon to silver birch (and likely many other trees) in both summer and winter in both pristine and ozone-polluted air.

It should also be noted that elevated CO2 concentrations 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 concentration, 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).

It is therefore likely that 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 under a variety of stressful situations.

Bertrand, A., Robitaille, G., Nadeau, P. and Castonguay, Y. 1999. Influence of ozone on cold acclimation in sugar maple seedlings. Tree Physiology 19: 527-534.

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.

Korner, C. 2003. Carbon limitation in trees. Journal of Ecology 91: 4-17.

Kostiainen, K., Jalkanen, H., Kaakinen, S., Saranpaa, P. and Vapaavuori, E. 2006. Wood properties of two silver birch clones exposed to elevated CO2 and O3. Global Change Biology 12: 1230-1240.

Liu, X.-P., Grams, T.E.E., Matyssek, R. and Rennenberg, H. 2005. Effects of elevated pCO2 and/or pO3 on C-, N-, and S-metabolites in the leaves of juvenile beech and spruce differ between trees grown in monoculture and mixed culture. Plant Physiology and Biochemistry 43: 147-154.

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.

Piispanen, R. and Saranpaa, P. 2001. Variation of non-structural carbohydrates in silver birch (Betula pendula Roth) wood. Trees 15: 444-451.

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.

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.

Riikonen, J., Lindsberg, M.-M., Holopainen, T., Oksanen, E., Lappi, J., Peltonen, P. and Vapaavuori, E. 2004. Silver birch and climate change: variable growth and carbon allocation responses to elevated concentrations of carbon dioxide and ozone. Tree Physiology 24: 1227-1237.

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.

Last updated 26 September 2012