Abstract Detail

The evolution of functional traits in plants: is the giant still sleeping?

Duong, Fiona [1], Medeiros, Juliana [2].

Keep expecting the unexpected: leaf midrib anatomy and branch architecture define a surprising functional trade-off within ecologically diverse genus Rhododendron.

Selection acts at the whole-plant level, such that the fitness value of individual traits should be better understood in the context of other co-occurring traits. Across ecologically diverse genus Rhododendron, lower specific leaf area (SLA) is associated with smaller stem xylem vessels, higher branch-level variation in SLA, larger branch leaf areas, and evergreen phenology, while root traits show virtually no relationship with SLA. Little is known, however, about how SLA, branch architecture, or root traits might relate to leaf anatomy and gas exchange rates in Rhododendron.
For evergreen, semi-evergreen and deciduous species we used phylogenetic least squares to investigate the relationship of SLA and phenology to leaf anatomy and gas exchange for plants growing at Holden Arboretum. We also used phylogenetic principal component analysis (ppca) to determine relationships to previously published data on branch-level leaf properties, stem xylem and root traits for the same plants measured in this study.
Leaf anatomy was determined by phenology: compared to evergreens, deciduous leaves had proportionately more epidermis, less palisade, and larger leaf midrib xylem vessels. Higher SLA and deciduous phenology were associated with higher net assimilation rates under favorable conditions, but lower rates following a polar vortex year. Our ppca showed that SLA is positively correlated with vessel diameter, but more-so for stem than leaf midrib xylem. Orthogonal to SLA, midrib vessel diameter showed a strong negative correlation with branch-level variation in SLA, and palisade proportion, but a strong positive relationship to specific root length. In addition, root traits showed stronger correlation to leaf size and leaf number per branch, compared to SLA or leaf anatomy. All traits were highly similar in deciduous species, while evergreens were only similar in SLA. Semi-evergreens were intermediate in SLA, but distinguishable by their root and branch-level traits.
For Rhododendron, variation in leaf anatomy and gas exchange largely matches expectations based on leaf economics, but leaf midrib xylem and root traits are coordinated with branch-level variation in SLA, not with mean SLA. High similarity in leaf, branch and root traits among deciduous species may reflect their strikingly similar climate associations. In contrast, a wide range of leaf anatomy, root and branch-level traits among evergreen Rhododendron may explain their high climatic diversity, irrespective of the similarity in their leaf resource acquisition strategies. Our work adds new insight into whole-plant economics by demonstrating that functional trade-offs within genus Rhododendron include dimensions not captured by commonly measured leaf economics traits.

1 - Washington State University, 1100 N Western Ave, Wenatchee, WA, 98801
2 - The Holden Arboretum, Ecology And Evolutionary Biology, 9500 Sperry Rd, Kirtland, OH, 44094, United States

Water relations
plant architecture
economics spectrum.

Presentation Type: Colloquium Presentations
Number: 0010
Abstract ID:262
Candidate for Awards:None

Copyright © 2000-2019, Botanical Society of America. All rights reserved