NMR imaging of root water distribution in intact Vicia faba L plants in elevated atmospheric CO₂

The effect of elevated atmospheric CO 2 on water distribution in the intact roots of Vicia faba L. bean seedlings grown in natural soil was studied noninvasively with proton ( 1 H) nuclear magnetic resonance (NMR) imaging. Exposure of 24‐d‐old plants to atmospheric CO 2 ‐enriched air at 650 cm 3 m −3 produced significant increases in water imaged in upper roots, hypogeal cotyledons and lower stems in response to a short‐term 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 CO 2 (350 m 3 m −3 ), and stem shrinkage and increased stomatal resistance. The results suggest that inhibition of transpiration caused by elevated CO 2 does not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO 2 environments may be a mitigating factor in assessing deleterious effects of greenhouse changes on crops during periods of dry climate.