title: Patterns in root traits of woody species hosting arbuscular and ectomycorrhizas: implications for the evolution of belowground strategies.
abstract: Root traits vary enormously among plant species but we have little understanding of how this variation affects their functioning. Of central interest is how root traits are related to plant resource acquisition strategies from soil. We examined root traits of 33 woody species from northeastern US forests that form two of the most common types of mutualisms with fungi, arbuscular mycorrhizas (AM) and ectomycorrhizas (EM). We examined root trait distribution with respect to plant phylogeny, quantifying the phylogenetic signal (K statistic) in fine root morphology and architecture, and used phylogenetically independent contrasts (PICs) to test whether taxa forming different mycorrhizal associations had different root traits. We found a pattern of species forming roots with thinner diameters as species diversified across time. Given moderate phylogenetic signals (K = 0.44-0.68), we used PICs to examine traits variation among taxa forming AM or EM, revealing that hosts of AM were associated with lower branching intensity (r PIC = -0.77) and thicker root diameter (r PIC = -0.41). Because EM evolved relatively more recently and intermittently across plant phylogenies, significant differences in root traits and colonization between plants forming AM and EM imply linkages between the evolution of these biotic interactions and root traits and suggest a history of selection pressures, with trade-offs for supporting different types of associations. Finally, across plant hosts of both EM and AM, species with thinner root diameters and longer specific root length (SRL) had less colonization (r PIC = 0.85, -0.87), suggesting constraints on colonization linked to the evolution of root morphology.
authors.affiliation: Intercollege Graduate Program in Ecology, Department of Horticulture, The Pennsylvania State University 103 Tyson Bldg, University Park, Pennsylvania, 16802 ; USDA-ARS Water Management Research Unit 2150 Centre Avenue, Bldg D Suite 320, Fort Collins, Colorado, 80526.
authors.forename: Louise H
authors.initials: LH
authors.lastname: Comas
authors.affiliation: Department of Biological Sciences, Barnard College, Columbia University 3009 Broadway, New York City, New York, 10027.
authors.forename: Hilary S
authors.initials: HS
authors.lastname: Callahan
authors.affiliation: NESCent 2024 W. Main Street, Suite A200, Durham, North Carolina, 27705.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Midford
keywords: Comparative method; K statistic; mycorrhizal colonization; nutrient acquisition strategies; root architecture; root branching intensity; root diameter; root morphology; root tissue density; specific root length