title: Evolutionary Divergences in Root Exudate Composition among Ecologically-Contrasting Helianthus Species.
abstract: Plant roots exude numerous metabolites into the soil that influence nutrient availability. Although root exudate composition is hypothesized to be under selection in low fertility soils, few studies have tested this hypothesis in a phylogenetic framework. In this study, we examined root exudates of three pairs of Helianthus species chosen as phylogenetically-independent contrasts with respect to native soil nutrient availability. Under controlled environmental conditions, seedlings were grown to the three-leaf-pair stage, then transferred to either high or low nutrient treatments. After five days of nutrient treatments, we used gas chromatography-mass spectrometry for analysis of root exudates, and detected 37 metabolites across species. When compared in the high nutrient treatment, species native to low nutrient soils exhibited overall higher exudation than their sister species native to high nutrient soils in all three species pairs, providing support for repeated evolutionary shifts in response to native soil fertility. Species native to low nutrient soils and those native to high nutrient soils responded similarly to low nutrient treatments with increased exudation of organic acids (fumaric, citric, malic acids) and glucose, potentially as a mechanism to enhance nutrition acquisition. However, species native to low nutrient soils also responded to low nutrient treatments with a larger decrease in exudation of amino acids than species native to high nutrient soils in all three species pairs. This indicates that species native to low nutrient soils have evolved a unique sensitivity to changes in nutrient availability for some, but not all, root exudates. Overall, these repeated evolutionary divergences between species native to low nutrient soils and those native to high nutrient soils provide evidence for the adaptive value of root exudation, and its plasticity, in contrasting soil environments.
authors.affiliation: Department of Plant Biology, University of Georgia, Athens, Georgia, United States of America.
authors.forename: Alan W
authors.initials: AW
authors.lastname: Bowsher
authors.affiliation: Department of Environmental Health Science, University of Georgia, Athens, Georgia, United States of America.
authors.forename: Rifhat
authors.initials: R
authors.lastname: Ali
authors.affiliation: Department of Genetics, University of Georgia, Athens, Georgia, United States of America.|Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia, United States of America.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Harding
authors.affiliation: Department of Genetics, University of Georgia, Athens, Georgia, United States of America.|Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia, United States of America.
authors.forename: Chung-Jui
authors.initials: CJ
authors.lastname: Tsai
authors.affiliation: Department of Plant Biology, University of Georgia, Athens, Georgia, United States of America.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Donovan
mesh_terms: D000222:Adaptation, Physiological; D005075:Biological Evolution; D019343:Citric Acid / Q000378:metabolism; D017753:Ecosystem; D005650:Fumarates / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D005947:Glucose / Q000378:metabolism; D006368:Helianthus / Q000145:classification / Q000378:metabolism*; D008293:Malates / Q000378:metabolism; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism*; D025341:Principal Component Analysis; D012987:Soil / Q000737:chemistry*
chemical_list: D005650:Fumarates; D008293:Malates; D010937:Plant Growth Regulators; D012987:Soil; D019343:Citric Acid; C030298:malic acid; C032005:fumaric acid; D005947:Glucose
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