The Evolution of the Worldwide Leaf Economic Spectrum (WLES) in Helianthus

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Plants from around the world vary considerably in their leaf morphological and physiological traits. Although some combinations of leaf traits are found repeatedly in nature, others are not. This suggests either that the observed trait combinations are economically advantageous for carbon gain and plant productivity in different habitats, and thus reflect adaptive evolution, or that these are the only trait combinations that are genetically possible. The project will test whether trait combinations identified as the Worldwide Leaf Economic Spectrum (WLES: leaf photosynthesis, nitrogen, thickness, and lifespan) reflect successful ecological and evolutionary solutions to different environments. First, the project will compare 27 species of sunflower species (Helianthus), to see whether particular trait combinations are robust when evolutionary relationships are accounted for, and whether they are associated with success in particular environments, and thus support adaptive evolution. Second, the project will test whether artificial selection under low nutrients results in trait combinations predicted by the WLES, and whether there are any genetic constraints. The expectation is that many trait combinations are possible (i.e. no genetic constraints) and that the WLES trait combinations found in nature and managed systems represent plant strategies that are the most successful compromises between rapid resource acquisition and greater resource conservation for different environments. A greater understanding of WLES leaf traits and their association with success in low resource habitats may contribute to the improvement of domesticated Helianthus annuus, which is a major oilseed crop with over 2 million acres in cultivation in the US. The results will also further the ability to predict which plants will be successful in natural and managed habitats as climates change. The study will provide unique training for high school students and future science teachers.