Localized temperature adaptation of cottonwoods from elevational ecoregions in the Rocky Mountains.

摘要

To investigate temperature adaptation of cool-climate trees, we studied 14 cottonwood genotypes from riparian (streamside) zones in three ecoregions differing in elevation in the Rocky Mountains of Alberta, Canada. Black cottonwoods (Populus trichocarpa) were collected from the higher, cooler montane and intermediate (aspen) parkland, and narrowleaf cottonwoods (P. angustifolia) were collected from the lower, warmer fescue prairie. The genotypes were grown in growth chambers under three temperature regimes reflecting the ecoregion variation. Sapling growth (dry weight) varied significantly across temperatures and for the genotypes from within and particularly across the ecoregions. Significant temperature . genotype interactions further indicated differentiation of the temperature response. Growth of the montane clones increased by 209% between 15/10 and 20/15.C and was 37% lower at 25/20.C. In contrast, genotypes from the lower ecoregions grew more slowly at the cool and intermediate temperatures (59 and 58% of montane) and then demonstrated constant (-3% parkland) or slightly increased (+16% prairie) growth at 25/20.C. This suggests the existence of P. trichocarpa ecotypes, localized populations with different temperature responses. This differentiation may explain our previous observation of comparable growth across these ecoregions despite substantial temperature variation, and the existence of ecotypes would produce a range of responses to climate warming that should produce an upward shift of the mountain ecoregions.