Functional traits of stress-tolerant Rhododendron species along tropical elevation gradients

Background/Question/Methods: Examination of plant functional traits along environmental gradients often reveal a shift in trait space, thus implying that ecological strategies may also change based on the environmental context. For instance, specific leaf area (SLA) generally declines with elevation, a pattern often attributed to increasing abiotic stress with elevation. However, abiotic conditions can also be stressful at lower elevations. Here, we address the question, what happens to patterns in trait space with elevation when considering plant species with a stress-tolerant ecological strategy? To address this, we used functional trait data on 160 tropical Rhododendron (Ericaceae) species grown in botanical garden greenhouses. Habitat information was obtained from botanical monographs and herbarium notes. We examined patterns of trait variation using linear regression models that accounted for growth form and edaphic specialization.

Results/Conclusions: We found that leaf area and seed tail length decreased with increasing elevation, yet many functional traits (SLA, thickness, toughness) changed little with elevation in terms of both trait means and variances. There was little difference in the traits of epiphytic versus terrestrial Rhododendron species. However, Rhododendron species that specialized in ultramafic (serpentine soil) habitat showed a decline in SLA with increasing elevation. Overall, Rhododendron species provide a unique perspective on how a stress-tolerant ecological strategy influences functional trait space across elevation gradients.