Rapid springtime leaf osmotic adjustment, but low late-seasonal and interannual variation in leaf turgor loss points in three temperate tree species

Leaf turgor loss point has been recognized as an important plant physiological trait explaining a species’ drought tolerance (πtlp). Less is known about the variation of πtlp in time and how seasonal or interannual differences in water availability are affecting πtlp as a static trait. I monitored the seasonal variation of πtlp during a drought year starting in early spring with juvenile leaves and assessed the interannual variation in πtlp of fully matured leaves among years with diverting water availability for three temperate broad-leaved tree species. The largest seasonal changes in πtlp occurred during leaf unfolding until leaves were fully developed and matured. After leaves matured, no significant changes occurred for the rest of the vegetation period. Interannual variation that could be related to water availability was only present in one of the three tree species. The results suggest that the investigated species have a rapid period of osmotic adjustment early in the growing season followed by a period of relative stability, when πtlp can be considered as a static trait.