Abstract: A free-air CO₂ enrichment (FACE) experiment was conducted in 2001—2003 to study the effects of predicted higher CO₂ levels on the dry matter (DM) production and allocation in win-ter wheat variety Ningmai 9. The results showed that under FACE, the DM production had an in-crease of 10.8%, 31.6%, 40.5% and27.2% during the growth periods from sowing to wintering (Period 1), wintering to jointing (Period 2), jointing to booting (Period 3), and booting to heading (Period 4), respectively, but a decrease of 5.5% in the period from heading to grain maturity (Period 5). As a result, the final total biomass at maturity was increased by 13.6%. FACE had no significant effect on leaf area index (LAI) and net assimilation rate (NAR) in Period 1, but made the LAI in Period 2 increased obviously, and the NAR decreased dramatically in Period 3. Under FACE, the proportion of leaf to total aboveground DM decreased, while that of stem (including sheath) to total above-ground DM showed an opposite trend in the whole growth period. The percentage and total amount of soluble sugar and starch in the stem at grain-filling stage were also increased obviously under FACE.

Key words: River continuum characteristics, Xiangxi River, Epilithic algae