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Testing the growth – cold tolerance trade-off in willows : a phylogenetic approach

It is hypothesized that cold-tolerance in plants has a significant cost that constrains growth. However, tests of this hypothesis have not previously considered the biogeographic and evolutionary history of species. Using a phylogenetic approach, we propose to test for correlated evolution in growth rate and cold tolerance in 35 species of the willow family (Salicaceae). We will investigate mechanisms of cold tolerance and metabolic costs in this clade, which includes species that may have unexpectedly high cold tolerance due to their history as well as fast growth rates. We hypothesize that in the absence of cold stress, there is little metabolic cost to maintaining a genetic capacity to tolerate cold. If correct, this result would indicate that cold tolerance does not necessarily impose constraints on growth as previously thought. This work has implications for modeling plant responses to climate change and for generating sustainable, fast-growing plant communities for biofuel production.