INFLUENCE OF SOIL TEMPERATURE ON ROOT RESPIRATION AND WATER UPTAKE OF SUBALPINE CONIFERS FROM LOW AND HIGH ELEVATIONS (ALPINE TIMBERLINE, ABIES LASIOCARPA, PICEA ENGELMAUNII, TREELINE, ROOT RESISTANCE)

Influences of low soil temperature on the root respiration and resistance to water uptake were compared among elevational populations of Abies lasiocarpa (Hook.) Nutt. and Picea engelmannii Parry. Small trees of both species were collected along two elevational transects in the central Rocky Mountains. Picea engelmannii roots respired significantly faster than those of A. lasiocarpa (p = 0.004), and trees of both species collected from high elevations respired significantly faster than those from lower elevations (p = 0.02), implying that ecotypic differentiation has occurred at these sites. Respiration activity was not significantly altered by changing the soil temperature in which they were grown (p = 0.24), which suggests that no acclimation to soil temperature occurred. The mean Q(,10) and mean activation energy of respiration were 1.99 and 47.2 kJ mol('-1), respectively; they did not differ between transects, species, or elevations of collection. Root resistances to water uptake increased significantly when soil temperatures were decreased from 10(DEGREES)C to 0(DEGREES)C. Abies lasiocarpa showed significantly greater increases in root resistance when temperatures were decreased below 10(DEGREES)C than did P. engelmannii (p = 0.008). No differences in root permeability at low soil temperatures were detected between trees of either species collected from low and high elevations. Root resistance of these two subalpine species is influenced less by cold soils than is the root resistance of lower elevation species investigated in other studies. The results suggest soil temperature can have a significant effect on the root physiology of subalpine trees and may thereby influence their growth and distribution at high elevations.