CAN HEAT WAVES LEAVE A THERMAL LEAKY LEGACY? DYNAMICS OF LEAF MINIMUM CONDUCTANCE VARIATION DURING AND AFTER EXPOSURE TO HIGH TEMPERATURES, AND ITS IMPLICATIONS FOR PLANT SURVIVAL UNDER HOTTER-DROUGHT CONDITIONS

Abstract

In a species-specific manner, exposure to temperatures above a critical threshold (temperature of phase transition, Tp) can induce damage to the leaf cuticle which results in substantial rises in leaf minimum conductance (gleaf-res). Despite the implications of this increased residual water loss for species performance and survival, especially under hotter-drought conditions, little is known about the dynamics of gleaf-res variation after heat wave events (when temperatures fall below Tp). • Here, it was examined the gleaf-res variation before, during, and after the exposure to high temperatures in three Cerrado tree species. For this, multiple experiments were performed to compare the gleaf-res of leaves that were previously exposed to different temperatures for short or prolonged periods with others that were not submitted to thermal stress. • Leaves previously exposed to temperatures above their Tp had higher gleaf-res measured at 25°C when compared to those leaves that were not exposed to thermal stress, thus suggesting the existence of a “thermal leaky legacy” effect. Importantly, this legacy effect was found to be induced by short periods of heat stress and to increase proportionally with rising temperatures. On the other hand, despite the tendency of recovery over time, the gleaf-res of leaves that crossed their Tp remained higher than those that were not exposed to thermal stress even after 24 hours of storage, evidencing that the thermal-induced damages to the leaf cuticle cannot be fully repaired throughout the day. • Overall, our study highlights the threats that increased leaf water leaks during and after heat wave events may represent to plant species performance and survival under drought conditions.