Desiccation time during drought is highly predictable across species of Eucalyptus from contrasting climates

Abstract

Summary Catastrophic failure of the water transport pathway in trees is a principal mechanism of mortality during extreme drought. To be able to predict the probability of mortality at an individual and landscape scale we need knowledge of the time for plants to reach critical levels of hydraulic failure. We grew plants of eight species of Eucalyptus originating from contrasting climates before allowing a subset to dehydrate. We tested whether a trait‐based model of time to plant desiccation tcrit, from stomatal closure gs90 to a critical level of hydraulic dysfunction Ψcrit is consistent with observed dry‐down times. Plant desiccation time varied among species, ranging from 96.2 to 332 h at a vapour‐pressure deficit of 1 kPa, and was highly predictable using the tcrit model in conjunction with a leaf shedding function. Plant desiccation time was longest in species with high cavitation resistance, strong vulnerability segmentation, wide stomatal‐hydraulic safety, and a high ratio of total plant water content to leaf area. Knowledge of tcrit in combination with water‐use traits that influence stomatal closure could significantly increase our ability to predict the timing of drought‐induced mortality at tree and forest scales.

Weak Tradeoff and Strong Segmentation Among Plant Hydraulic Traits During Seasonal Variation in Four Woody Species

“…However, as non-structural carbohydrates are fine-tuned (Choat et al, 2012;Bartlett et al, 2014;Delzon, 2015;Wang et al, 2018), synchronous seasonal changes in the embolism resistance traits of PS and TT lay a permanent foundation for hydraulic segmentation. The present study supported the HVSH and corroborated previous reports (Liu et al, 2015;Johnson et al, 2016;Blackman et al, 2019;Losso et al, 2019;Skelton et al, 2019). Strong segmentation among plant hydraulic traits between PS and TT could ensure year-round xylem functionality.…”

“…Thus, the annual tradeoffs between hydraulic efficiency and safety traits are unclear, several traits may have tradeoffs while others may not, on the whole plant hydraulic traits, the tradeoffs are weak. No consistent results have been reported in previous studies (Liu et al, 2015;Johnson et al, 2016;Blackman et al, 2019;Losso et al, 2019;Skelton et al, 2019). In a global metaanalysis, only ∼1/4 of the studies reviewed supported the safety-efficiency hypothesis while the remaining 3/4 did not (Gleason et al, 2016).…”

“…Numerous studies have focused on growing-season segmentation in distal plant organs including the leaves, branches, and roots. The time to desiccation is longest in species with strong embolism resistance and vulnerability segmentation which enable plants to adapt to complex environments (Johnson et al, 2016;Blackman et al, 2019;Losso et al, 2019;Skelton et al, 2019). Liu et al (2015) examined segmentation between leaflet laminae and compound leaf petioles in two compound leaf tree species during the growing season.…”

Adaptive plasticity in plant traits increases time to hydraulic failure under drought in a foundation tree

“…The significantly greater P88 in HRI-D saplings indicates a capacity to tolerate a greater level of water stress during drought in comparison with saplings from other population × treatment combinations. In support of these findings, Blackman et al (2019b) found a strong relationship between P50 and the time for saplings to desiccate from stomatal closure (Pgs90) to P88 (tcrit) in eight Eucalyptus species, with those exhibiting greater stem P50…”

Linking Forest Flammability and Plant Vulnerability to Drought

“…The eucalypts were sourced from a range of vegetation communities (wet sclerophyll forest, dry sclerophyll forest, grassy woodland and semiarid woodland). Further details of the study design and data were provided in Li et al [37], Li et al [38] and Blackman et al [39]. Images of the leaves of each species are provided in Figure S1.…”