Relative sensitivity of leaf elongation and stomatal conductance of cucumber plants to changes in leaf and soil water potentials

Identification of drought-resistant cucumber genotypes and optimization of irrigation scheduling require an improved understanding of cucumber plant water relations. Stomatal conductance (ks), relative leaf elongation rate (RLER), and leaf water relations were examined on greenhouse-grown cucumber (Cucumis sativus L. 'Marketmore 80') over two drought cycles. Water was withheld from the entire root system of cucumber plants and ks, leaf length, leaf water (Psi(L)) and osmotic potential, and soil matric potential were measured periodically. In both drought cycles, ks decreased before, and RLER decreased after predawn Psi(L) began to decline. No osmotic adjustment was found after one drought cycle and slight osmotic adjustment (- 0.14 MPa) was observed in expanding leaves after a second drought cycle. Evidence for a nonhydraulic root signal in cucumber was examined in split-root experiments. Psi(L) was Similar in plants which received water to one (stress treatment) or to both halves (control treatment) of the root system. Stomatal conductance and RLER remained at control levels as soil water potential (Psi(L)) around half the root system declined to - 0.25 to - 0.30 MPa No convincing evidence for effects of root signals on ks and RLER at lower Psi(soil) was observed.