PARENT SESSION

Symposium S1D Photosynthesis and global change
Monday August 30th, 2004 10:20 AM-12:20 PM Room 510B
Chair: Dave Layzell and Neil Baker
Co-Chair: Don Ort

The response of plant carbohydrates to elevated CO₂. What have we learned from FACE studies? Alistair Rogers^{*,1, 2}, Elizabeth Ainsworth^{2, 4}, Stephen Long^{2, 3}, ¹ Environmental Sciences Department, Upton, NY, USA² Department of Crop Sciences, Champaign, IL, USA⁴ ICG-III, Julich, Germany³ Department of Plant Biology, Champiagn, IL, USA

ABSTRACT- 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 ([CO₂]). Carbohydrates are the product of photosynthetic cells, and the substrate for sink metabolism. However, carbohydrates are not just substrates, changes in the composition and pool size of foliar carbohydrates have the potential to communicate source-sink balance and the role of carbohydrates in the regulation of the expression of many plant genes has been established. Free Air CO₂ Enrichment (FACE) technology enables plants to be grown in their natural environment at a controlled elevated [CO₂] without the restrictions on rooting volume and alterations to the microclimate common in many controlled environment studies. As FACE technology was emerging, understanding of the link between carbohydrates and plant responses to growth at elevated [CO₂] was increasing. However, it was unclear whether the hypotheses that were being refined in model systems would hold up when tested in open-air field experiments. Over ten years of FACE experiments have provided the answer. In addition to growth at elevated [CO₂] manipulation of nitrogen supply and source-sink balance through partial defoliation and single gene substitution have been used to test the overarching hypothesis, that carbohydrates will accumulate in source leaves when photosynthesis exceeds the capacity of sinks to utilize photosynthate. Data are presented from several FACE experiments that include a pasture grass, a broad-leaf crop and tree species. Key indicators of sink-limitation are discussed and rules governing the response of foliar carbohydrates to growth in a future elevated [CO₂] atmosphere are presented.

KEY WORDS: elevated CO₂, FACE, carbohydrates