Winter water relations of native and introduced evergreens in interior Alaska

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Abstract
In view of wintertime browning of needles of pines introduced in Alaska, winter desiccation damage was suspected. However, examination of field xylem water potentials and relative water contents indicated little water stress in pine needles but severe stress in sunny native spruce (Picea glauca) needles and slightly less stress in shaded needles. Spruce were typical of drought tolerant plants, exhibiting field xylem water potentials of -10 to -40 bars and field relative water contents of 88-99%, closing stomates at water contents of 71-92% and maintaining cuticular conductances from 0.013-0.088 cm s-1. In contrast, pines were drought avoiding, exhibiting field xylem water potentials of 0 bars and field water contents of 100%, keeping stomates closed all winter, and maintaining cuticular conductances from 0-0.033 cm s-1 and 0-0.074 cm s-1 in lodgepole pine and yellow pine, respectively. Needles of all species photosynthesized at temperatures from 0-10.degree. C with rates in spruce being 10 times those in yellow pine and 3 times those in lodgepole pine. While spruce needles had significantly more carbohydrate reserves at the end of the winter than did pine needles, the latter were apparently not severely carbohydrate depleted.