Abstract Detail



Ericaceae: Systematics, Ecology and Evolution

Medeiros, Juliana [1].

Ecological and evolutionary implications of variable trait coordination across deciduous and evergreen lineages of genus Rhododendron.

Within the leaf economic spectrum, leaves with higher carbon investment per photosynthetic surface area are relatively slow-growing, but have higher stress resistance. Because physiological processes are often stringently coordinated, trait coordination should be highly conserved, such that species with slow-growing leaves should also have roots and wood with slow-growth attributes. Species life history, evolutionary history, or other leaf traits besides carbon investment could mediate leaf function, however, potentially resulting in variable trait coordination across growth environments, or over evolutionary time. Genus Rhododendron contains 900+ species from sub-tropical to alpine environments and representing a range of leaf economics. We explored trait–trait and trait–climate relationships for 20+ Rhododendron species with evergreen, deciduous, or semi-evergreen leaf habits. We accounted for phylogenetic relationships and within-species variation to investigate whether leaf, wood and root traits are coordinated as part of a whole-plant economics spectrum.  
Rhododendron exhibited expected leaf economics relationships, more carbon-rich leaves had significantly higher C:N and were associated with more stressful climates. But, all species had wood with low water transport capacity compared to most angiosperms. Thus, branch leaf area and gas exchange rates are likely constrained by wood anatomy. Clade-specific leaf-wood relationships suggest that the leaves of some acquisitive species may be hydraulically under-supplied, with implications for drought and heat tolerance in a warming world. High variability in leaf traits at the branch level could, however, compensate for xylem constraints on leaf function in evergreens and semi-evergreens. Root carbon investment also differed according to climate of origin and across growth environments, but roots differed within- and among-species even more than leaves. Also, the deciduous clade exhibited a strong negative relationship between carbon investments in leaf surface area versus root length, while evergreen clades showed a weaker positive or no relationship. We also found evidence that investment in root foraging scale vs. precision is a fundamental trade-off defining root variation among these species.  
Taken together, these results suggest that natural selection has shaped coordination between leaf, wood and root traits across genus Rhododendron. In addition, we show that morphological decoupling could lead to the unexpected patterns of leaf hydraulic function and microbial community diversity we have observed across Rhododendron species. Our work highlights the fact that deciduous leaves are not just short-lived versions of evergreen leaves, but rather deciduous, evergreen and semi-evergreen lineages have evolved fundamentally different approaches to the growth-stress trade-off, reflected in their different patterns of trait coordination.


1 - Holden Forests & Gardens, Research Department, 9500 Sperry Rd, Kirtland, OH, 44094, United States

Keywords:
Physiology
phylogenetic diversity
leaf economics.

Presentation Type: Colloquium Presentations
Number:
Abstract ID:234
Candidate for Awards:None


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