NMR IMAGING OF ROOT WATER DISTRIBUTION IN INTACT VICIA-FABA L PLANTS IN ELEVATED ATMOSPHERIC CO2

The effect of elevated atmospheric CO2 on water distribution in the in tact roots of Vicia faba L. bean seedlings grown in natural soil was s tudied noninvasively with proton (H-1) nuclear magnetic resonance (NMR ) imaging. Exposure of 24-d-old plants to atmospheric Co2-enriched air at 650 cm3 m-3 produced significant increases in water imaged in uppe r roots, hypogeal cotyledons and lower stems in response to a short-te rm drying-stress cycle. Above ground, drying produced negligible stem shrinkage and stomatal resistance was unchanged. In contrast, the same drying cycle caused significant depletion of water imaged in the same upper root structures in control plants subject to ambient CO2 (350 m 3 m-3), and stem shrinkage and increased stomatal resistance. The resu lts suggest that inhibition of transpiration caused by elevated CO2 do es not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO2 environments may be a mitigating factor in assess ing deleterious effects of greenhouse changes on crops during periods of dry climate.