Osmoregulation in Cotton in Response to Water Stress : III. Effects of Phosphorus Fertility.

Cotton (Gossypium hirsutum) (L.) was grown in a sand and nutrient solution system at two levels of phosphorus (0.5 and 5.0 millimolar). Within each phosphorus treatment, plants were either watered daily or acclimated to water stress by subjection to several water stress cycles.Stress acclimation increased leaf starch at the low phosphorus level, but not at the high phosphorus level. High phosphorus increased leaf sucrose and glucose concentration in both acclimated and nonacclimated plants, but had little effect on osmotic adjustment or the relationship between turgor and water potential.In nonacclimated plants, high phosphorus increased both leaf conductance and photosynthesis at high water potentials. In acclimated plants, high phosphorus increased photosynthesis but decreased conductance, thus increasing water use efficiency at the single leaf level.