Diurnal changes in embolism rate in nine dry forest trees: relationships with species-specific xylem vulnerability, hydraulic strategy and wood traits.

Abstract

Recent studies have reported correlations between stem sapwood capacitance (C(wood)) and xylem vulnerability to embolism, but it is unclear how C(wood) relates to the eventual ability of plants to reverse embolism. We investigated possible functional links between embolism reversal efficiency, C(wood), wood density (WD), vulnerability to xylem embolism and hydraulic safety margins in nine woody species native to dry sclerophyllous forests with different degrees of iso versus anisohydry. Substantial inter-specific differences in terms of seasonal/diurnal changes of xylem and leaf water potential, maximum diurnal values of transpiration rate and xylem vulnerability to embolism formation were recorded. Significant diurnal changes in percentage loss of hydraulic conductivity (PLC) were recorded for five species. Significant correlations were recorded between diurnal PLC changes and P50 and P88 values (i.e., xylem pressure inducing 50 and 88% PLC, respectively) as well as between diurnal PLC changes and safety margins referenced to P50 and P88. WD was linearly correlated with minimum diurnal leaf water potential, diurnal PLC changes and wood capacitance across all species. In contrast, significant relationships between P50, safety margin values referenced to P50 and WD were recorded only for the isohydric species. Functional links between diurnal changes in PLC, hydraulic strategies and WD and C(wood) are discussed.