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Early Vessel Evolution and the Diversification of Wood Function: Insights from the Malagasy Canellales

Xylem vessels have long been proposed as a key innovation for the ecological diversification of angiosperms by providing a breakthrough in hydraulic efficiency to support high rates of photosynthesis and growth. However, recent studies demonstrated that angiosperm woods with structurally ‘primitive’ vessels did not have greater whole stem hydraulic capacities as compared to vesselless angiosperms. As an alternative to the hydraulic superiority hypothesis, the heteroxylly hypothesis proposes that subtle hydraulic efficiencies of primitive vessels over tracheids enabled new directions of functional specialization in the wood. However, the functional properties of early heteroxyllous wood remain unknown. We selected the two species of Canellales from Madagascar to test the heteroxylly hypothesis because Canellaceae (represented by <em>Cinnamosma madagascariensis</em>) produces wood with vessels of an ancestral form, while Winteraceae, the sister-clade (represented by <em>Takhtajania perrieri</em>) is vesselless. We found that heteroxylly correlated with increased wood functional diversity related mostly to biomechanical specialization. However, vessels were not associated with greater stem hydraulic efficiency or increased shoot hydraulic capacity. Our results support the heteroxylly hypothesis and highlight the importance integrating a broader ecological context to understand the evolution of vessels.

Identiferoai:union.ndltd.org:UTENN_/oai:trace.tennessee.edu:utk_gradthes-1648
Date01 May 2010
CreatorsHudson, Patrick Joseph
PublisherTrace: Tennessee Research and Creative Exchange
Source SetsUniversity of Tennessee Libraries
Detected LanguageEnglish
Typetext
Formatapplication/pdf
SourceMasters Theses

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