Low intra-tree variability in resistance to embolism in four Pinaceae species

Abstract

Abstract& Key message Variability of embolism resistance within individual trees was assessed in four Pinaceae species by using a single method of measurement: the Cavitron. Contrary to what has been previously observed, our findings show a small variability in embolism resistance within and between organs. Indeed, we found (i) a lack of variability between branches within the crown, and (ii) that roots and trunks are either equally resistant or slightly more vulnerable to embolism than branches. This contradicts the vulnerability segmentation hypothesis proposed in the early 1990s. This paper also demonstrates that only few branches are necessary to determine the embolism resistance of a given tree. & Context Embolism formation in xylem has an important impact on plant growth and survival. Since most studies on xylem embolism resistance focus on branches, it remains questionable how the entire plant deals with embolism across organs. & Aims In this study, we aimed to evaluate the variability of embolism resistance within a given organ and between different organs within a single tree. & Methods Based on the Cavitron method, we estimated the intra-organ and the intra-plant variability of embolism resistance for four Pinaceae species. In addition, we compared pit anatomical characters for wood of all organs and species. & Results We found no variability of embolism resistance for a given organ within a tree. At the tree level, trunks and roots were either equally or more vulnerable to embolism than branches. For all species, organs that showed a similar range of embolism resistance presented similar torus-aperture overlap values. However, the least negative P 50 value for roots of Pinus pinaster was associated with the lowest torus-aperture overlap value. & Conclusion Our findings suggest that P 50 values are constrained within a particular organ and that intra-tree variation in embolism resistance is less substantial than previously reported. Moreover, our data do not support the vulnerability segmentation hypothesis which suggests that distal organs are more vulnerable to xylem embolism.

Plant resistance to drought depends on timely stomatal closure

“…The system has been simplified to consider only two resistances (rhizosphere and plant), making it easy to apply, with only one stem vulnerability curve and no need for assumptions concerning hydraulic segmentation, a phenomenon dependent on mechanisms that remain a matter of debate (Bouche et al . , ,b; Cuneo et al . ; Scoffoni et al .…”

Plant xylem hydraulics: What we understand, current research, and future challenges

“…Hydraulic conductivity measurements are usually performed with a 10–30 mM KCl solution to standardize for ionic effects on pit membrane flow resistance (Zwieniecki et al ; Gasco et al ; Nardini et al ). In some cases 1 mM CaCl 2 is added because of the additional presence of low levels of Ca +2 in sap (Bouche et al ). The added calcium ions can reduce sensitivity to KCl in some, but not all species (Nardini et al ).…”

Mapping xylem failure in disparate organs of whole plants reveals extreme resistance in olive roots

“…Seminal work proposed the existence of hydraulic 'segmentation' within the tissues of plants (Zimmermann, 1978), such that peripheral tissues were hypothesized to be the first to become cavitated during drought, thereby protecting more costly tissues, such as stems (Zimmermann, 1983;Tyree & Ewers, 1991). Recent work has suggested that the magnitude of segmentation in conifers (Bouche et al, 2016a) and herbaceous angiosperms (Skelton et al, 2017a) is very small (Bouche et al, 2016b), whereas there is some evidence that leaves (Charrier et al, 2016) and flowers (Zhang & Brodribb, 2017) of woody angiosperms are more vulnerable to cavitation than stems.…”