Water relations in alfalfa (Medicago sativa L.) plants grown under high carbon dioxide concentration

The extent to which atmospheric CO2 enrichment may influence alfalfa (Medicago sativa L.) water relations under non-limiting conditions of water and nutrient supply is examined. During the 1994 and 1995 growing seasons water relations were studied by monitoring both predawn and midday water potentials, the daily trend of stomatal conductance, and the occurrence of osmotic adjustment. Midday water potential was higher in plants grown under CO2 enrichment in comparison with plants grown under ambient CO2, while stomatal conductance decreased. On the contrary, high CO2 treatment had no effect on predawn water potential. Furthermore, an osmotic adjustment was evident in well-watered alfalfa plants exposed to high CO2 although other factors such as plant age and/or period of growing season should be taken into account.