Evolutionary Divergences in Root Exudate Composition among Ecologically-Contrasting Helianthus Species

• Published in: PloS one 2016-01, Vol.11 (1), p.e0148280
• Main Authors: Bowsher, Alan W, Ali, Rifhat, Harding, Scott A, Tsai, Chung-Jui, Donovan, Lisa A
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Amino acids; Availability; Biochemistry; Biological Evolution; Biology and Life Sciences; Carbon; Citric Acid - metabolism; Computer and Information Sciences; Divergence; Ecology; Ecosystem; Environmental conditions; Evolution; Evolutionary biology; Exudates; Exudation; Fumarates - metabolism; Gas chromatography; Gas Chromatography-Mass Spectrometry; Genetic aspects; Glucose - metabolism; Helianthus; Helianthus - classification; Helianthus - metabolism; Indigenous species; Malates - metabolism; Mass spectrometry; Mass spectroscopy; Medicine and Health Sciences; Metabolites; Morphology; Natural resources; Nitrogen; Nutrient availability; Nutrients; Nutrients in soil; Nutrition; Organic acids; Phylogeny; Physical Sciences; Physiological aspects; Plant biology; Plant Growth Regulators - metabolism; Plant roots; Plant Roots - metabolism; Principal Component Analysis; Research and Analysis Methods; Seedlings; Sibling species; Soil - chemistry; Soil fertility; Soil nutrients; Soil testing; Soils; Studies; Sunflowers
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0148280

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.