GENETIC-VARIATION OF ECOPHYSIOLOGICAL TRAITS IN RED ALDER (ALNUS-RUBRA BONG)

We examined the genetic variation of ecophysiological traits within an d among 40 red alder (Alnus rubra Bong.) provenances (two families per provenance) in a common-garden experiment in the summer of 1993. The provenances were representative of the entire species range in British Columbia, Canada. We found significant genetic variation among proven ances (P < 0.001) in photosynthetic rate (A), mesophyll conductance (g (m)), transpiration rate (E), stomatal conductance (g(sw)), stomatal s ensitivity to water vapour pressure deficit (SENS(VPD)), intercellular to ambient CO2 concentration ratio (C-i/C-a), and midday xylem water potential (psi). Photosynthetic water-use efficiency, however, did not differ significantly among provenances. There were no significant dif ferences between families within provenance for any of these variables . A weak but significant geographic trend was detected in ecophysiolog ical traits: psi, A, g(m), and E increased, and SENS(VPD) decreased, f rom southeast to northwest. Photosynthetic rate, E, g(m), g(sw) and ps i were positively related to each other, but negatively correlated wit h SENS(VPD). C-i/C-a, was negatively correlated with g(sw). These corr elations indicate that red alder might have undergone genetic differen tiation in drought resistance.