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Abstract
At high elevations, winter climatic conditions frequently cause excessive drought stress, which can induce embolism in conifer trees. We investigated the formation and repair of winter embolism in subalpine fir (Abies veitchii) growing near the timberline. We found a complete loss in xylem conductivity [100% percent loss of conductivity (PLC)] at the wind-exposed site (W+) and 40% PLC at the wind-protected site (W−). A PLC of 100% was far above the embolism rate expected from the drought-induced vulnerability analysis in the laboratory. At the W+ site, a PLC of 100% was maintained until May; this suddenly decreased to a negligible value in June, whereas the recovery at the W− site started in late winter and proceeded stepwise. The contrast between the two sites may have occurred because of the different underlying mechanisms of winter embolism. If most tracheids in the xylem of 100% PLC are air-filled, it will be difficult to refill quickly. However, embolism caused by pit aspiration could be restored rapidly, because aspirated pits isolate tracheids from each other and prevent the spread of cavitation. Although severe embolism may cause frost damage of needles, it may have a role in holding water within the stem.
Highlights
During winters, trees growing at high altitudes or latitudes are often exposed to conditions that are unfavourable to the plant’s water status[1]
As water in the xylem freezes, gases dissolved in water form bubbles that expand during subsequent thawing under the low water potential of xylem sap and result in embolism[11,14]
In the- present study, we monitored the intensity of winter desiccation, formation and repair of winter embolism, and water balance of the stem using a dendrometer in subalpine fir (Abies veitchii) growing near the timberline
Summary
Trees growing at high altitudes or latitudes are often exposed to conditions that are unfavourable to the plant’s water status[1]. The altitude limits of angiosperm tree species with large diameter-conduits are reportedly associated with their vulnerability for freeze–thaw-induced embolism[17,18]. Conifers with smaller conduits are reportedly more resistant to freeze– thaw-induced embolism than angiosperm tree species[17,19,20,21,22] This phenomenon provides an explanation for the dominance of conifers at high altitudes and latitudes[21]. The occurrence of xylem embolism during the winter months has frequently been demonstrated in conifers[23,24,25] This occurs because of excessive drought stress in combination with multiple freeze–thaw events[9]. The causes and consequences of winter embolism would be inferred by comparing A. veitchii trees at each site
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