GROWTH AND STOMATAL BEHAVIOR OF HYDROPONICALLY CULTURED POTATO (SOLANUM-TUBEROSUM L) AT ELEVATED AND SUPER-ELEVATED CO2

Potato cultivars Denali and Norland were grown in a controlled environ ment under low irradiance and CO2 partial pressures of 50, 100, 500, a nd 1000 Pa. The highest CO2 partial pressures, 500 and 1000 Pa, reduce d tuber yield when compared to 100 Pa CO2. Upper canopy stomatal condu ctance was greatest at the higher CO2 partial pressures (500 and 1000 Pa) for both cultivars, and conductance of Denali was consistently hig her than Norland. Stomatal conductance tended to decline sooner with p lant age at 50 and 100 Pa CO2 than at 500 and 1000 Pa. Water uptake wa s also greatest at the higher CO2 partial pressures, which resulted in lowest water-use efficiencies at 500 and 1000 Pa. These observations suggest that stomatal function under very high CO2 partial pressures ( 500-1000 Pa) does not follow known patterns observed at moderate parti al pressures (50-100 Pa). Although there is little concern about CO2 p artial pressures reaching extreme levels in the natural environment, t his information should be useful for controlled environments or space life support systems (e.g. space vehicles or habitats), where CO2 part ial pressures of 500-1000 Pa are common.