Frost Sensitivity of Subalpine Plants in the Colorado Rocky Mountains: The Effects of Seasonality, Water Content, and Phylogeny

Abstract

Our study examined the frost sensitivities of subalpine flowering plants near the Rocky Mountain Biological Laboratory, in Gothic, CO. Most studies on the impacts of climate change have focused on the effects of temperature warming and how it affects species. Our study examined the frost sensitivities of 22 subalpine flowering species in the Colorado Rocky Mountains. To our knowledge, previous studies have only examined frost sensitivity in regards to non-flowering plants in an ecological context. Our three hypotheses were (1) seasonal – species that flower early are more resistant to frost, (2) water content – species with low water content and species with high water content are more susceptible to frost damage, and (3) phylogenetic – species that are more closely related will have similar tolerances to frost. To test the seasonal and phylogenetic hypotheses we collected plant tissue (flowers, leaves, and buds), wrapped them in aluminum foil, and placed them in a temperature chamber which simulated a nighttime frost event using liquid CO2 as the cooling agent. In order to test for water content we collected plant tissue in the morning prior to 0800 hours, weighed samples initially for wet weight, dried for 48 hours at 60-65°C, and weighed again to acquire dry weight. Water content was found by subtracting dry weight from wet weight. Our results show a high amount of variability in the potential mechanisms for frost resistance. At the community level, neither the seasonality nor the phylogenetic hypotheses were supported. We did find support for the water content hypothesis, revealing that species containing the least and the most amount of water were more sensitive to frost than those containing intermediate amounts of water. However, among congener pairs we saw mixed support for both our seasonality and phylogenetic hypotheses, indicating that seasonality and phylogeny can play a role among some taxa but not among others. Frost appears to be highly variable among subalpine plant species in the Colorado Rocky Mountains, which has important implications for predicting the continued effects of global climate change in this ecosystem.

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