| Abstract: | A system, designed by Snow and Tingey (1985) for ‘subjectingplants to reproducible water stress levels for extended periodsof time’, is considered. Modifications are also outlinedwhich enable water table heights to be maintained without theneed for complex float chambers. Sunflower plants (Helianthus annuus L. cv. Frankasol) were grownusing the system and these were either ‘well-watered’or subjected to water deficits. The temporal development ofwater deficits was closely monitored by regular psychrometricmeasurements of leaf water potential. Diurnal stomatal behaviour,mid-day abaxial stomatal conductance, and photosynthetic assimilationrates were also determined throughout the experiment, with growthanalysis at the end. A reduction in stomatal conductance occurred within 2–4d after the onset of a restriction in water supply. Data fromboth viscous flow and diffusion porometry suggested that stomatalclosure apparently began without a fall in bulk leaf water potential.Leaf water potentials of plants with a restricted supply ofwater did, however, subsequently decline during the early partof the experiment reaching values as low as –0.99±0.07 MPa after 14 d. No further reduction in bulk water potentialwas observed after a further 5 d, suggesting that a steady-statehad been reached. Corresponding values of leaf water potentialfor well-watered plants were about –0.60 ± 0.04MPa. Biomass determinations indicated the potential for quantifyingthe effects of water deficits, of controlled magnitudes, onrates of leaf production and expansion. However, the possibilityof physical limitations of root development—imposed bothby the plant container and also by the imposition of restrictedwater supplies—must be carefully considered when planningexperiments with this system. |
