Variation in stable carbon isotope discrimination among and within exotic conifer species grown in eastern Nebraska, USA

The study involved the measurement of stable-carbon isotope discrimination and specific leaf area on foliage of mature trees of 11 conifer species grown in a common-garden in eastern Nebraska, USA. Each species was represented by three to six trees from at least three populations. Carbon isotope discrimination differed significantly among species (F = 31.41, P < 0.0001) and among populations within species (F = 1.65, P < 0.035). Of the all Species, members of the Pinaceae family (Abies, Larix, Picea, Pinus, Pseudotsuga) had much higher discrimination (Delta = 18.87, SE = 0.08, n = 141) than species in the Cupressaceae family (Juniperus) (Delta = 16.26, SE = 0.12, n = 18). A deciduous conifer, Larix (Delta = 19.09, SE = 0.20, n = 16), did not differ significantly from evergreen members of the Pinaceae family. Although specific leaf area differed among species (F = 152.62, P < 0.0001), it was not correlated with discrimination (r = 0.24, P > 0.14). Annual height growth, specific leaf area, and annual precipitation of seed sources were intercorrelated (0.60 less than or equal to r less than or equal to 0.67, P < 0.01). No correlation was significant between Delta and the precipitation or evapotranspiration of the seed sources. The results indicate that these species have different genetic structures and acclimation processes. Selecting for better adapted genotypes based on carbon isotope discrimination must be species specific.