Elevated carbon dioxide influences yield and photosynthetic responses of hydroponically-grown sweet potato

The response of 'TI-155' and 'Georgia Set' sweetpotato cultivars to elevated CO2 concentrations of 400 (ambient), 750 and 1000 mu mol mol(-1) were evaluated under controlled environment conditions using the nutrient film technique (NFT). Growth chamber conditions included photosynthetic photon flux (PPF) of 600 mu mol m(-2)s(-1), 14/10 light/dark period, and 70%+/-5% RH. Plants were grown using a modified half-Hoagland nutrient solution with a pH range of 5.5-6.0 and an electrical conductivity of 0.12 S m(-1). Gas exchange measurements were made using infrared gas analysis, an open-flow gas exchange system, and a controlled-climate cuvette. Photosynthetic (Pn) measurements were made at CO2 ranges of 50 to 1000 mu mol mol(-1). Storage root yield/plant increased with CO2 up to 750 but declined at 1000 mu mol mol(-1). Storage root dry matter (DM) and foliage dry weight increased with increasing CO2. Harvest index (HI) for both cultivars was highest at 750 mu mol mol(-1). The PPF vs Pn curves were typical for C-3 plants with saturation occurring at similar to 600 mu mol m(-2)s(-1). CO2 concentration did not significantly influence net Pn, transpiration, water-use-efficiency (WUE), and stomatal conductance. As measurement CO2 concentration increased, net Pn and WUE increased while transpiration and stomatal conductance decreased.