title: Does leaf shedding protect stems from cavitation during seasonal droughts? A test of the hydraulic fuse hypothesis.
abstract: During droughts, leaves are predicted to act as 'hydraulic fuses' by shedding when plants reach critically low water potential (Ψplant), thereby slowing water loss, stabilizing Ψplantand protecting against cavitation-induced loss of stem hydraulic conductivity (Ks). We tested these predictions among trees in seasonally dry tropical forests, where leaf shedding is common, yet variable, among species. We tracked leaf phenology, Ψplantand Ksin saplings of six tree species distributed across two forests. Species differed in their timing and extent of leaf shedding, yet converged in shedding leaves as they approached the Ψplantvalue associated with a 50% loss of Ksand at which their model-estimated maximum sustainable transpiration rate approached zero. However, after shedding all leaves, the Ψplantvalue of one species, Genipa americana, continued to decline, indicating that water loss continued after leaf shedding. Kswas highly variable among saplings within species and seasons, suggesting a minimal influence of seasonal drought on Ks. Hydraulic limits appear to drive diverse patterns of leaf shedding among tropical trees, supporting the hydraulic fuse hypothesis. However, leaf shedding is not universally effective at stabilizing Ψplant, suggesting that the main function of drought deciduousness may vary among species.
authors.affiliation: Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA.|Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancon, Panama.
authors.forename: Brett T
authors.initials: BT
authors.lastname: Wolfe
authors.affiliation: Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Sperry
authors.affiliation: Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA.|Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancon, Panama.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Kursar
mesh_terms: D055864:Droughts; D005740:Gases / Q000378:metabolism; D008954:Models, Biological; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology*; D018547:Plant Stems / Q000033:anatomy & histology / Q000502:physiology*; D054046:Plant Stomata / Q000502:physiology; D012621:Seasons; D013045:Species Specificity; D013997:Time Factors; D014197:Trees / Q000502:physiology; D014867:Water / Q000502:physiology
chemical_list: D005740:Gases; D014867:Water
keywords: drought deciduousness; hydraulic limitation; hydraulic segmentation hypothesis; leaf abscission; leaf phenology; seasonally dry tropical forest; xylem cavitation