Vessel diameter polymorphism determines vulnerability-to-embolism curve shape

Abstract

Summary Sherwin Carlquist proposed several functional interpretations for vessel diameter, including that narrow vessels were hydraulically “safe” while wide diameter vessels were more vulnerable to embolism. He applied these ideas both across species and biomes, and within xylem tissue, where function of growth ring types was inferred from vessel diameter polymorphisms (occurrence of differing vessel diameter classes within a tissue). Following on Carlquist’s ideas, we were interested in evaluating if vessel diameter polymorphism could be linked to vulnerability-to-embolism curve shape. Vulnerability curves were fit with a model that included a continuous shape term (alpha). We predicted that high variation in vessel diameter would result in lower alpha (more r-shaped) curves whereas low variation would produce higher alpha (more s-shaped) curves, with potential for intermediate curve types. Our findings support Carlquist’s functional interpretations of vessel diameter. Vessel diameter polymorphism was strongly correlated to vulnerability curve shape. Homogeneous vessel diameters were associated with more s-shaped curves. As vessel diameter polymorphism increased, alpha declined and curves became more linear. High polymorphism was associated with r-shaped curves. There was no relationship between vessel length and curve shape. Vessel diameter was strongly correlated with a common estimate of embolism resistance (P50), with wider diameter vessels associated with increased vulnerability. Vulnerability curves show enormous variety in shape and scale, and both parameters are likely critical in understanding and predicting plant function. Carlquist’s ecological anatomy data, predictions, and functional inferences will continue to be valuable as we expand our understanding of structure–function links in plant anatomy.

Xylem cell size regulation is a key adaptive response to water deficit in Eucalyptus grandis

“…2015 ; Jacobsen et al. 2019 ; Jacobsen and Pratt 2023 ). Pit membranes are also affected by the thickness of the conduit walls, which improve the structural integrity of these structures and prevent stretching ( He et al.…”

Seasonal Cambial Activity and Formation of Secondary Phloem and Xylem in White Oaks (Quercus alba L.)

“…While narrow vessels have been accepted as safer against embolism caused by frost [40][41][42][43], the same is not true for embolism caused by drought [41,46], positing a problem. For decades, based on comparative wood anatomical studies, especially those championed by Carlquist [1,47,48], researchers have proposed that narrow vessels would be safer against drought embolism [49,50], such as the embolisms caused by frost. However, nowadays there is a heated debate among experimental wood anatomists, where one group's experiments seem to corroborate the hypothesis that narrow vessels are safer against drought embolism [49,50], while another's vehemently dispute that conclusion, demonstrating by their experiments that the decisive character promoting safety against drought embolism is the thickness of intervessel pit membranes [46].…”

“…For decades, based on comparative wood anatomical studies, especially those championed by Carlquist [1,47,48], researchers have proposed that narrow vessels would be safer against drought embolism [49,50], such as the embolisms caused by frost. However, nowadays there is a heated debate among experimental wood anatomists, where one group's experiments seem to corroborate the hypothesis that narrow vessels are safer against drought embolism [49,50], while another's vehemently dispute that conclusion, demonstrating by their experiments that the decisive character promoting safety against drought embolism is the thickness of intervessel pit membranes [46]. The narrow vessels of tropical ring-porous species were suggested to occur as a response to lack of water by the latter authors, impairing the full expansion of the cells [46].…”