16 The Response of Foliar Carbohydrates to Elevated [ CO 2 ]

Accumulation of foliar carbohydrates is one of the most pronounced and universal changes observed in the leaves of C3 plants grown at elevated CO2 concentration (e[CO2]). Carbohydrates are both the product of photosynthetic cells and the substrate for sink metabolism. However, carbohydrates are not just substrates; and the role of carbohydrates in regulation of the expression of many plant genes, and the activity of many key enzymes, is well established. As free air CO2 enrichment (FACE) technology was emerging, understanding of the link between carbohydrates and plant responses to growth at e[CO2] was increasing. However, it remained unclear whether the hypotheses that were being refined in model systems would hold up when tested in open-air field experiments. More than a decade of FACE experiments have provided the answer.