© 2005 Heron Publishing—Victoria, Canada
Stomatal characteristics of riparian poplar species in a semi-arid environment
David W. Pearce (1, 2), Sandra Millard (1), Douglas F. Bray (1) and Stewart B. Rood (1)
1. Department of Biological Sciences, University of Lethbridge, Lethbridge, Alberta, T1K 3M4, Canada / 2. Corresponding author (pearce@uleth.ca) / Received October 29, 2004; accepted May 15, 2005; published online November 8, 2005
Summary
Several native poplar species meet at the margins of their natural distributions in southern Alberta, Canada. In this semi-arid
area, poplars are obligate riparian species but they occupy several intergrading ecoregions. Populus deltoides Bartr. ex Marsh predominates in the warmest and driest eastern prairie ecoregions; P. balsamifera L. occupies the cooler and wetter western parkland and montane ecoregions; and P. angustifolia James and hybrids between the species occur in the intermediate grassland ecoregions. We investigated stomatal characteristics
of these poplars in 51 genotypes collected across the range of ecoregions and grown in a semi-arid common garden. Stomatal
length differed among genotypes within species but did not differ among species, ranging from 19 to 22 µm. Total stomatal
densities (adaxial plus abaxial) differed among genotypes within species but were similar among species (290–420 stomata mm–2). Single-surface stomatal densities differed among species and consequently, the ratio of adaxial:abaxial stomatal density
also differed, ranging from 0.94 for P. deltoides to 0.27 for P. balsamifera, with intermediate stomatal density ratios in P. angustifolia and hybrids. In a subsequent study of a subset of the same genotypes, stomatal density was correlated with stomatal conductance
(r2 = 0.75) and the conductance ratios differed among species in the same manner as the stomatal density ratios. We conclude
that: (1) diverse poplar genotypes respond similarly to a semi-arid environment by producing comparatively small and dense
stomata; (2) differences in stomatal density underlie differences in stomatal conductance and differences among species in
stomatal density ratio or conductance ratio may reflect adaptation to climatic differences among ecoregions; and (3) there
is substantial variation in stomatal characteristics within and among species and hybrids in this area that could be useful
for the selection and breeding of poplars adapted to different climatic conditions.
Keywords:
adaptation, amphistomaty, Populus, stomatal conductance, stomatal density.
