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Winter desiccation is believed to contribute to stress in coniferous trees growing at the treeline because cuticular conductance increases with altitude. To test whether winter desiccation occurs in high-altitude conifers of the Dolomites (NE Italian Alps), we measured minimum cuticular conductance ( g  min ), needle wettability (contact angle) and cuticle thickness in  Picea abies  (L.) Karst. and  Pinus cembra  L. needles from December to August. Samples were collected from adult trees along an altitudinal gradient from valley bottom (1050 m a.s.l.) to the treeline (2170 m a.s.l.). The treeline site is one of the highest in the area and is characterized by a generally low wind exposure. Altitude had no effect on  g  min  in either species. In  P. abies , large seasonal variations in  g  min  were recorded but no changes were related to needle age class.  Pinus cembra  had a low  g  min  and appeared to be efficient in reducing needle water losses. There was a significant increase in  g  min  with needle aging in  P. cembra  growing at low altitude that could be related to a shorter needle longevity compared with  P. abies . High contact angles (&gt; 110–120°) suggested the presence of tubular epicuticular waxes on needles of both species. Contact angles were higher (low wettability) in high-altitude needles than in low-altitude needles. By the end of winter, there was no difference in contact angles between needles in the windward and leeward positions. Wax structures transformed toward planar shapes as demonstrated by the decrease in contact angle from winter to summer. In both species, the cuticle was thicker in needles of high-altitude trees than in needles of low-altitude trees and there was no correlation between  g  min  and cuticle thickness. Because desiccation resistance did not decrease with altitude in either species, we conclude that they are not susceptible to winter desiccation at the tree line.

tree physiology

Minimum cuticular conductance and cuticle features of  Picea abies  and  Pinus cembra  needles along an altitudinal gradient in the Dolomites (NE Italian Alps)