Cucumber plants were cultured in a greenhouse and subjected to either well-watered or water deficit conditions that reduced leaf water potential to-0.6 MPa. Leaf gas exchange measurements were conducted using an open gas exchange system. Carbon dioxide assimilation (A) attained saturation at a photon flux density (PFD) of 1000 μmol·m-2·s-1 (400-700 nm). There were no significant differences in A at ambient temperatures between 16 and 34C. Water use efficiency decreased rapidly with increasing vapor-pressure deficits to 2.5 kPa. Water stressed plants had lower stomata1 conductances and CO2 assimilation rates. The decrease in A was only partially due to stomata1 closure. The A vs. intercellular CO (Ci) relationship for stressed leaves revealed a change in the CO, compensation point, and that nonstomatal factors were contributing to the decrease in A in stressed plants. Thus, feedback inhibition of A may have occurred through photoassimilate accumulation. The concentrations of sucrose and raffinose were higher, and the concentration of stachyose was lower in leaves of stressed than of well-watered plants.

The effects of water deficit and fruiting on leaf gas exchange and dry-matter production and partitioning in cucumber (Cucumis sativus L.) plants were evaluated in greenhouse and field experiments. Fruiting plants had higher photosynthetic rates (15.8 μmol·m-2·s-1) than defruited plants (12.7 μmol·m-2·s-1). Although stomatal conductance was lower in defruited plants, it accounted for only ≈35% of the assimilation rate (A) reduction. Under water deficit, defruiting caused a similar response in A, even though A was only ≈50% of that in watered plants. Fruiting and water deficits limited vegetative plant dry weight and total leaf area. In field experiments, removing flowers from the first four or eight nodes resulted in a higher count and fresh weight at harvest of only those pickling cucumber fruit that were irrigated.

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