Effects of elevated CO2 concentration on growth, water use, yield and grain quality of wheat under two soil water levels

Wheat (Triticum aestivum L.) is one of the most important food sources in the world. The potential impacts of elevated CO2 on wheat yield and grain quality will have profound influences on the supply and nutritional value of wheat products as well as on many industrial sectors. A growth-chamber experiment was designed to estimate how soil moisture influences the potential effects of elevated CO2 concentration ([CO2]) on wheat growth, water use and grain yield. Spring wheat (T. aesrivum cv. Ganmai 8139) was grown in pots placed in controlled growth chambers and was subjected to two [CO2] (approximately 350 and 700 mul/l, respectively) and two soil water levels (80 and 40% of field water capacity (FWC), respectively). High [CO2] increased plant shoot dry weight by 89% under 80% FWC and by 53% under 40% FWC. Grain yield of wheat was markedly increased under elevated [CO2] with greater grain number and harvest index. The ratio of plant shoot dry weight to height was increased by 75% under high [CO2] at high soil moisture, and by 54% at low moisture. Water use efficiency of shoot (WUEs) and grain yield (WUEg) were increased under high [CO2] because the magnitude of the increase in shoot dry weight and grain yield was greater than that of the cumulative consumption of water under high [CO2] conditions. When wheat plants were under high [CO2] conditions and maintained at high moisture, the WUEs and WUEg were increased by 62 and 128%, respectively. Elevated [CO2] resulted in lower concentrations of mineral nutrients (N, P, K and Zn), lysine and crude protein in mature grains. This was probably caused by a dilution effect induced by great increment of carbohydrate in grains. The total quantity of mineral nutrients, lysine and crude protein accumulated in grains per hectare were still increased under high [CO2] due to increase in grain yield. Our results indicate that high [CO2] is beneficial to plant growth, wield and WUE, while grain quality was lowered under high [CO2] conditions as reflected by the increased crude starch content, and corresponding decreases in mineral nutrients, lysine and crude protein concentrations. The analysis of yield components suggested that the yield increase was mainly attributable to an increase in the number of grains. However, the effects of CO2 enrichment on plants depend on the availability of soil moisture, and plants may benefit more from CO2 enrichment when sufficient water is supplied. (C) 2004 Elsevier B.V. All rights reserved.