Diurnal pattern of leaf extension in Salix viminalis relates to the difference in leaf turgor before and after stress relaxation.

Diurnal variations in leaf extension and turgor relaxation were measured in young willow leaves (Salix viminalis L.). Turgor relaxation was calculated from measurements of xylem water potential and osmotic potential of whole, detached leaves that were incubated, without loss of water, under controlled conditions. There were clear diurnal variations in leaf extension and in leaf turgor relaxation and the diurnal pattern of the difference in leaf turgor before and after relaxation was in phase with that of leaf extension. The extent to which leaf turgor after relaxation may be related to threshold turgors for growth and the possible importance of leaf turgor during leaf extension are discussed.