THE INFLUENCE OF ELEVATED CO2 ON NONSTRUCTURAL CARBOHYDRATE DISTRIBUTION AND FRUCTAN ACCUMULATION IN WHEAT CANOPIES

We grew 2.4 m2 wheat canopies in a large growth chamber under high pho tosynthetic photon flux (1000 mumol m-2 s-1) and using two CO2 concent rations, 360 and 1200 mumol mol-1. Photosynthetically active radiation (400-700 nm) was attenuated slightly faster through canopies grown in 360 mumol mol-1 than through canopies grown in 1200 mumol mol-1, even though high-CO2 canopies attained larger leaf area indices. Tissue fr actions were sampled from each 5-cm layer of the canopies. Leaf tissue sampled from the tops of canopies grown in 1200 mumol mol-1 accumulat ed significantly more total non-structural carbohydrate, starch, fruct an, sucrose, and glucose (p less-than-or-equal-to 0-05) than for canop ies grown in 360 mumol mol-1. Non-structural carbohydrate did not sign ificantly increase in the lower canopy layers of the elevated CO2 trea tment. Elevated CO2 induced fructan synthesis in all leaf tissue fract ions, but fructan formation was greatest in the uppermost leaf area. A moderate temperature reduction of 10-degrees-C over 5 d increased sta rch, fructan and glucose levels in canopies grown in 1200 mumol mol-1, but concentrations of sucrose and fructose decreased slightly or rema ined unchanged. Those results may correspond with the use of fructosyl -residues and release of glucose when sucrose is consumed in fructan s ynthesis.