A. Benowicz et al., Geographic pattern of genetic variation in photosynthetic capacity and growth in two hardwood species from British Columbia, OECOLOGIA, 123(2), 2000, pp. 168-174
Geographic patterns of intraspecific variations in traits related to photos
ynthesis and biomass were examined in two separate common garden experiment
s using seed collected from 26 Sitka alder (Alnus sinuata Rydb.) and 18 pap
er birch (Betula papyrifera Marsh.) populations from climatically diverse l
ocations in British Columbia, Canada. Exchange rates of carbon dioxide and
water vapour were measured on 2-year-old seedlings to determine the maximum
net instantaneous photosynthetic rate, mesophyll conductance, stomatal con
ductance, and photosynthetic water use efficiency. Height, stem diameter, r
oot and shoot dry mass and fall frost hardiness data were also obtained. Me
an population maximum photosynthetic rate ranged from 10.35 to 14.57 mu mol
CO2 m(-2) s(-1) in Sitka alder and from 14.76 to 17.55 mu mol CO2 m(-2) s(
-1) in paper birch. Based on canonical correlation analyses, populations fr
om locations with colder winters and shorter (but not necessarily cooler) s
ummers had higher maximum photosynthetic rates implying the existence of an
inverse relationship between leaf longevity and photosynthetic capacity. S
ignificant canonical variates based on climatic variables derived for the s
eed collection sites explained 58% and 41% of variation in the rate of phot
osynthesis in Sitka alder and paper birch, respectively. Since growing seas
on length is reflected in date of frost hardiness development, an intrinsic
relationship was found between photosynthetic capacity and the level of fa
ll frost hardiness. The correlation was particularly strong for paper birch
(r=-0.77) and less strong for Sitka alder (r=-0.60). Mean population bioma
ss accumulation decreased with increased climate coldness. These patterns m
ay be consequential for evaluation of the impact of climate change and exte
nsion of the growing season on plant communities.