Needle flavonoids and population differentiation in the Abies section Nobilis Engelm

Abstract

The Abies section Nobilis Engelm. consists of two high-elevation tree species that grow in the mountains of Washington, Oregon and California. The two varieties of A.magnifica A.Murray grow south of A.procera Rehd. One of these varieties, A.magnifica var.shastensis Lemm., is intermediate in some characteristics and locations between the two "typical" species. The goal of this thesis was to clarify species and population differentiation in the section Nobiiis. To this end, nine populations of mature and twelve populations of immature trees were collected along a north-south transect that cut through most of the range of the section. The flavonoids were extracted from dried needle samples selected from each of the sample trees, and a flavonoid profile was determined for each tree. These individual tree profiles were used to prepare a composite flavonoid profile for the whole section. Sixty-four probable flavonoid compounds occurred in the sample trees, of which forty-seven were at least partially identified. Twenty-four variable compounds were chosen for analysis. Variation was assessed using product-moment correlation co-efficients, frequency histograms, principal components analysis, weighted-pair-group cluster analysis, discriminant analysis and cladistic analysis. These different statistical techniques allowed comparison between the different interpretations of population variation. Four factors appear to underly the pattern of population variation in the Abies section Nobilis : (1) evolution of the section under the diverse and changing conditions that have prevailed in the Pacific Northwest and California since the Oligocene epoch; (2) hybridization between morphologically, ecologically and/or chemically differentiated populations of trees within the section; (3) the presence of a genetically variable gene pool in the section as a consequence of these two factors; and (4) the expression of a portion of that variability as adaptation to different stages of forest succession. A.procera is an early-successional species with a gene pool that is more uniform than A.magnifica, which is essentially a late-succession or climax species. Flavonoid differentiation between these two species is not as distinct as has been observed in the Abies section Balsamea Engelm. Aprocera tends to exhibit acetylated monoglycosides consistently whereas A.magnifica does not, and A.magnifica tends to accumulate glycosides of dihydrokaempferol and taxifolin where A.procera does not. These differences apparently have been obscured somewhat by variation between the flavonoid complement of mature and immature trees, by migration and fragmentation of the range of the section Nobilis since the Oligocene epoch, and by hybridization within the section. The needle flavonoid results reported by this thesis, supported by published ecological, morphological and terpene data, confirm the current recognition of three taxa in the section. However, the variety shastensis exhibits enough differentiation to warrant further investigation into separation of that taxon into three or four separate taxa: (^) A. procera x A.magnifica; (2) relictual populations of A.magnifica var.shastensis in Tulare County, California and the Klamath Mountains of California and Oregon; and (3) A.magnifica var.shastensis from the North Coast Ranges of California.