Frost drought in conifers at the alpine timberline: xylem dysfunction and adaptations

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  • Abstract. Drought stress can cause xylem embolism in trees when the water potential (W)in the xylem falls below specific vulnerability thresholds. At the alpine timberline, frostdrought is known to cause excessive winter embolism unless xylem vulnerability ortranspiration is sufficiently reduced to avoid critical W.We compared annual courses of W and embolism in Picea abies, Pinus cembra, Pinus mugo,Larix decidua, and Juniperus communis growing at the timberline vs. low altitude. In addition,vulnerability properties and related anatomical parameters as well as wood density (Dt) andwall reinforcement (wall thickness related to conduit diameter) were studied. This allowed anestimate of stress intensities as well as a detection of adaptations that reduce embolismformation.At the alpine timberline, W was lowest during winter with corresponding embolism rates ofup to 100% in three of the conifers studied. Only Pinus cembra and Larix decidua avoidedwinter embolism due to moderate W. Minor embolism was observed at low altitude where thewater potentials of all species remained within a narrow range throughout the year. Withinspecies, differences in W50(W at 50% loss of conductivity) at high vs. low altitude were lessthan 1 MPa. In Picea abies and Pinus cembra, W50was more negative at the timberline while,in the other conifer species, W50was more negative at low altitude. Juniperus communisexhibited the lowest (6.4 6 0.04 MPa; mean 6 SE) and Pinus mugo the highest W50(3.34 60.03 MPa). In some cases, Dtand tracheid wall reinforcement were higher than in previouslyestablished relationships of these parameters with W50, possibly because of mechanicaldemands associated with the specific growing conditions.Conifers growing at the alpine timberline were exposed to higher drought stress intensitiesthan individuals at low altitude. Frost drought during winter caused high embolism rateswhich were probably amplified by freeze–thaw stress. Although frost drought had a largeeffect on plant water transport, adaptations in hydraulic safety and related anatomicalparameters were observed in only a few of the conifer species studied.

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    © 2006 the Ecological Society of America. This version of this article is open access and can be downloaded and shared. The original author(s) and source must be cited.
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    • Mayr, S., Hacke, U., Schmid, P., Schweinbacher, F., and Gruber, A. (2006). Frost drought in conifers at the alpine timberline: xylem dysfunction and adaptations. Ecology, 87(12), 3175–3185.
  • Link to related item[3175:FDICAT]2.0.CO;2