title: Repeated freeze-thaw cycles induce embolism in drought stressed conifers (Norway spruce, stone pine).
abstract: Freezing and thawing lead to xylem embolism when gas bubbles caused by ice formation expand during the thaw process. However, previous experimental studies indicated that conifers are resistant to freezing-induced embolism, unless xylem pressure becomes very negative during the freezing. In this study, we show that conifers experienced freezing-induced embolism when exposed to repeated freeze-thaw cycles and simultaneously to drought. Simulating conditions at the alpine timberline (128 days with freeze-thaw events and thawing rates of up to 9.5 K h(-1) in the xylem of exposed twigs during winter), young trees of Norway spruce [Picea abies (L.) Karst.] and stone pine (Pinus cembra L.) were exposed to 50 and 100 freeze-thaw cycles. This treatment caused a significant increase in embolism rates in drought-stressed samples. Upon 100 freeze-thaw cycles, vulnerability thresholds (50% loss of conductivity) were shifted 1.8 MPa (Norway spruce) and 0.8 MPa (stone pine) towards less negative water potentials. The results demonstrate that freeze-thaw cycles are a possible reason for winter-embolism in conifers observed in several field studies. Freezing-induced embolism may contribute to the altitudinal limits of conifers.
authors.affiliation: Institut f. Botanik, Universität Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria. stefan.mayr@uibk.ac.at
authors.forename: Stefan
authors.initials: S
authors.lastname: Mayr
authors.forename: Andreas
authors.initials: A
authors.lastname: Gruber
authors.forename: Helmut
authors.initials: H
authors.lastname: Bauer
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology*; D004190:Disasters; D005615:Freezing; D006358:Hot Temperature; D018547:Plant Stems / Q000033:anatomy & histology / Q000502:physiology*; D064028:Tracheophyta / Q000033:anatomy & histology / Q000502:physiology*; D014867:Water / Q000494:pharmacology / Q000502:physiology*
chemical_list: D014867:Water