Leaf habit and plant architecture integrate whole-plant economics and contextualize trait-climate associations within ecologically diverse genus Rhododendron

Plant resource strategies negotiate a trade-off between fast growth and stress resistance, characterized by specific leaf area (SLA). How SLA relates to leaf structure and function or plant climate associations remains open for debate, and leaf habit and plant architecture may alter the costs versus benefits of individual traits. We used phylogenetic canonical correspondence analysis and phylogenetic least squares to understand the relationship of anatomy and gas exchange to published data on root, wood, architectural and leaf economics traits and climate. Leaf anatomy was structured by leaf habit and carbon to nitrogen ratio was a better predictor of gas exchange than SLA. We found significant correspondence of leaf anatomy with branch architecture and wood traits, gas exchange corresponded with climate, while leaf economics corresponded with climate, architecture, wood and root traits. Species from the most seasonal climates had the highest trait-climate correspondence, and different aspects of economics and anatomy reflected leaf carbon uptake versus water use. Our study using phylogenetic comparative methods including plant architecture and leaf habit provides insight into the mechanism of whole-plant functional coordination and contextualizes individual traits in relation to climate, demonstrating the evolutionary and ecological relevance of trait-trait correlations within a genus with high biodiversity. Leaves negotiate a trade-off between fast growth and stress resistance, but the timing and arrangement of plant parts may alter the costs and benefits of individual leaf traits within a given climate. Using phylogenetically informed analyses to investigate leaf traits related to carbon and water relations we found that correspondence between traits and climate was strongest in highly seasonal climates and that leaf carbon uptake versus water use are defined by different aspects of leaf morphology and anatomy. Our study shows that plant architecture and leaf habit contextualize individual traits in relation to climate, demonstrating the evolutionary and ecological relevance for suites of traits and mechanisms of whole-plant coordination within a genus with high biodiversity.