Ecotypic variation in root respiration rate among elevational populations ofAbies lasiocarpa andPicea engelmannii.

Small trees ofAbies lasiocarpa (Hook.) Nutt. andPicea engelmannii Parry were collected along two elevational transects in the central Rocky Mountains, and the effects of low temperature on their root respiration activity were measured after growth in cool and warm soil temperature treatments.Picea engelmannii roots respired significantly faster than those ofA. lasiocarpa, and trees of both species collected from high elevations respired significantly faster than those from lower elevations. The mean Q10 and mean activation energy of respiration were 2.0 and 47.2 kJ mol-1, respectively; they did not differ between transects, species, elevations of collection, or the soil temperature treatments. The results suggest ecotypic differentiation has occurred along these transects resulting in higher root respiration rates at higher elevations.