The influences of increased CO and water supply on growth, biomass allocation and water use efficiency of Sinapis alba L. grown under different wind speeds.

We examined how independent and interactive effects of CO concentrations, water supply and wind speed affect growth rates, biomass partitioning, water use efficiency, diffusive conductance and stomatal density of plants. To test the prediction that wind stress will be ameliorated by increased CO and/or by unrestricted water supply we grew Sinapis alba L. plants in controlled chambers under combinations of two levels of CO (350 ppmv, 700 ppmv), two water regimes and two wind speeds (0.3 ms, 3.7 ms). We harvested at ten different dates over a period of 60 days. A growth analysis was carried out to evaluate treatment effects on plant responses. Plants grown both in increased CO and in low wind conditions had significantly greater stem length, leaf area and dry weights of plant parts. Water supply significantly affected stem diameter, root weight and leaf area. CO enrichment significantly increased the rate of biomass accumulation and the relative ratio of biomass increase to leaf area expansion. High wind speed significantly reduced plant growth rates and the rate of leaf area expansion was reduced more than the rate of biomass accumulation. Regression analysis showed significant CO effects on the proportion of leaf and stem dry weight to total dry weight. A marked plant-age effect was dependent on water supply, wind speed and CO concentration. A reduced water supply significantly decreased the stomatal conductance, and water use efficiency significantly increased with a limited water supply, low wind and increased CO. We found significant CO x wind effects for water diffusion resistance, adaxial number of stomata and water use efficiencies and significant wind x water effect for water use efficiency. In conclusion, wind stress was ameliorated by growing in unrestricted water but not by growing in increased CO.