© 1997 Heron Publishing—Victoria, Canada
Relationships between gas exchange adaptation of Sitka × interior spruce genotypes and ribosomal DNA markers
Shihe Fan, Steven C. Grossnickle and Ben C. S. Sutton
Forest Biotechnology Centre, B.C. Research, Inc., 3650 Westbrook Mall, Vancouver, B.C. V3S 2L2, Canada / Received February 10, 1996
Summary
Adaptive physiological changes were investigated in seven populations of Sitka (Picea sitchensis (Bong.) Carr.) × interior spruce (P. glauca (Moench) Voss × P. engelmannii Parry ex Engelm.) spanning the Nass–Skeena transition zone in British Columbia, Canada. Each population was represented by
an Si rDNA index that was calculated from the relative optical densities on a gel autoradiogram of five ribosomal DNA bands
characteristic of Sitka spruce and interior spruce. This index estimates the proportion of the genome contributed by interior
spruce. Physiological adaptations were assessed by gas exchange parameters measured under both well-watered and drought conditions.
Under well-watered conditions, Sitka spruce populations had higher maximal photosynthesis at saturating light and ambient
CO2, higher quantum yield at the light compensation point, and higher dark respiration than interior spruce populations. Sitka
spruce populations also reached maximal photosynthesis at lower photosynthetically active radiation and higher CO2 concentrations, and had higher stomatal densities that resulted in lower stomatal limitations to photosynthesis than interior
spruce populations. In contrast, interior spruce populations exhibited greater drought tolerance than Sitka spruce populations.
Their gas exchange rates declined at a slower rate in response to drought. They maintained higher gas exchange rates in response
to moderate to severe drought (predawn plant water potentials = –1.5 MPa), and their photosynthetic rates recovered faster
when they were rewatered after exposure to drought. Comparison of the seven populations indicated that physiological parameters
were significantly related to the Si rDNA index. An increase in Si rDNA index was associated with proportional changes in
physiological measurements, suggesting that genetic interchange among species with contrasting ecological adaptations can
enhance the environmental adaptation of natural populations.
Keywords:
DNA analysis, drought, Picea engelmannii, Picea glauca, Picea sitchensis.
