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Title: Patterns in root traits of woody species hosting arbuscular and ectomycorrhizas: implications for the evolution of belowground strategies

Author
item Comas, Louise
item CALLAHAN, HILARY - Barnard College
item MIDFORD, PETER - Duke University

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2014
Publication Date: 7/4/2014
Citation: Comas, L.H., Callahan, H.S., Midford, P.E. 2014. Patterns in root traits of woody species hosting arbuscular and ectomycorrhizas: implications for the evolution of belowground strategies. Ecology and Evolution. 1-12. doi: 10.1002/ece3.1147

Interpretive Summary: Understanding trait differences among plants allows us to better understand plant functioning in the environment. We examined four root traits among 33 Northeastern US tree species forming two common types of fungal symbioses to determine how root systems of these plants differed and identify evolutionary forces shaping them. In three traits we found moderate signals indicating that a portion of the trait differences among plant species mirrored species evolution. Plants forming more ancient interactions with fungi had roots with lower branching intensity and thicker diameter than those forming more recently-evolved interactions. Moreover, fungal colonization was higher in plants with thicker roots and shorter length per unit mass, suggesting that plants evolved mechanisms to limit their interactions with symbiotic fungi as they evolved root traits that allowed them to explore soil more efficiently.

Technical Abstract: Despite large variation in root traits among species, we have limited understanding of how traits are related to diverse soil resource acquisition strategies. We examined root trait variation among 33 species co-existing in Northeastern US forests that form the two most common mutualisms with mycorrhizal fungi to further understand structures and functions of root traits and selection pressures shaping them. We quantified the phylogenetic signal (K statistic) in fine root morphology and architecture (specific root length (SRL), diameter, tissue density, and branching intensity) and used phylogenetically independent contrasts (PICs) to test whether taxa forming different mycorrhizal types had different root traits. There was phylogenetic signal in SRL, diameter and branching intensity (K = 0.44-0.68). Additionally, plants forming arbuscular mycorhizas (AMs) had roots with lower branching intensity and thicker diameter than those forming ectomycorrhizas (EMs) (rPIC = -0.77, 0.41). Because EM associations evolved recently and irregularly across plant phylogenies, differences between AM and EM hosts either imply recent selection pressures on root trait evolution with trade-offs to support different associations or linkages between EM evolution and root traits. Moreover, colonization was higher in species with thicker roots and lower in those with longer SRL (rPIC = 0.85, -0.87), suggesting evolutionarily-linked constraints.