LATITUDINAL VARIATION IN MORPHOLOGICAL TRAITS OF NEEDLE LEAVES OF PINUS AND ITS RELATION TO ENVIRONMENTAL AND PHYLOGENETIC SIGNALS

Traits of angiosperm leaves are a common source of paleoclimate data whereas the traits of coniferous needle leaves have seldom been considered. The richness in morphological traits of angiosperm leaves, as compared to coniferous needle leaves, is one reason for their higher attractiveness. Yet also coniferous foliage may prove useful for providing environmental data. In this study, we analyze global patterns of the interspecific variation of various morphological traits of 103 species of the genus Pinus with latitude (as a surrogate of broad-scale environmental gradients). Trait variation partitioning was applied to separate phylogenetic and environmental signals.

For all considered traits, high latitudinal correlations were related to a decrease in the pure phylogenetic signal and to an increase in the phylogenetically structured environmental variation (PSEV), whereas the pure environmental signal was almost negligible. The data therefore indicate a high tendency for phylogenetic niche conservatism for Pinus. Strong latitudinal correlations were, however, found for the needle length/width ratio, with the purely phylogenetic component being lowest. Needle length/width ratio decreases with increasing latitude, with similar trends for different taxonomic species subsets and geographic regions. Needle shape appears therefore to be a trait that is "fine-tuned" by adaptation to environment within phylogenetic constraints.