Growth and Yield of Wheat under CO2Enrichment and Water Stress1

Growth and yield responses of a semi‐dwarf spring wheat (Triticum aestivumL.; cv. GWO 1809) to two CO2concentrations and two water stress regimes were studied in controlled environment chambers of the Duke Univ. Phytotron. Groups of plants in low (350 ppm), or high (1,000 ppm) CO2environments were subjected to water stress By withholding irrigation starting at the 10th day after the beginning of anthesis. A second drying cycle beginning 5 days after termination of the first cycle was also given to some of the plants. Water potential of the flag leaves of the main stem of the plants in each CO2environment reached a minimum of −13 bars at the end of the first drying cycle and −17 bars at the end of the second cycle. Under well‐watered conditions high CO2enhanced the rate of tiller production by 43% and significantly increased grain yield, total dry matter, and number and size of the grains. As water stress developed, the osmotic potentials of the high CO2. plants decreased at a faster rate and resulted in maintenance of higher turgor pressures at the end of each stress cycle compared to the low CO2plants. Osmotic potentials of the leaves of both high and low 2plants decreased faster in the second drying cycle than in the first. Significantly fewer and smaller grains were produced on the plants grown under water stress in both CO2concentrations compared to unstressed plants. In general, high CO2plants under water stress conditions had a grain yield and total dry matter production equal to the unstressed, low CO2plants. Thus, CO2enrichment increased the yield potential of the water limited wheat plants due probably to osmotic adjustment by an increased concentration of solutes in their leaves.