Relationships between gas exchange and carbon isotope discrimination of Sitka x interior spruce introgressive genotypes and ribosomal DNA markers.

Effects of hybridization on physiological performance were investigated in seven natural introgressive populations and one F(1) population of Sitka (Picea sitchensis (Bong.) Carr.) x interior spruce (P. glauca (Moench) Voss. x P. engelmannii Parry ex Engelm.). Each population was represented by a Sitka-interior spruce ribosomal DNA (Si rDNA) index that was calculated from the relative abundance of species-specific DNA polymorphisms. Gas exchange parameters were measured under well-watered conditions on current-year needle tissues, which were also analyzed for carbon isotope discrimination. Sitka spruce populations had higher gas exchange rates (net photosynthesis, stomatal conductance to water vapor), but lower carbon isotope discrimination values than interior spruce populations. The natural hybrid populations had intermediate values of these parameters consistent with their Si rDNA index. The F(1) population had gas exchange parameters resembling those of Sitka spruce populations, but its carbon isotope discrimination was skewed toward that of interior spruce populations. These results confirmed previous findings that physiological performance of introgressive hybrid spruce populations varied as their DNA constitution changed.