Sarah Evans GDPE PhD Dissertation Defense
Friday, April 6, 2012, 01:00 PM
Natural and Environmental Sciences Building, Room A304

Global circulation models predict that in the future, grasslands will experience more summer drought and more intense rainfall patterns (more drought and floods). In these systems, the availability of water strongly controls ecosystem function, but grassland plants are also highly resistant to water stress, so it is unclear how changes in precipitation will alter carbon and nitrogen dynamics and the microorganisms that control them. Shifts in these factors with new rainfall patterns could alter how much we expect changes in precipitation to alter grassland ecosystem function, and potentially, alter the trajectory of climate change through soil-atmosphere feedbacks to greenhouse gases. In my dissertation, I used regional climate gradients and lab studies coupled to field rainfall manipulations to examine the effects of predicted rainfall patterns. I first examined the general controls over carbon and nitrogen storage in grasslands by testing whether models developed in US grasslands could accurately describe relationships between climate and biogeochemical dynamics in similar grasslands in China. I also used rainfall manipulations in the US Great Plains to examine how historical precipitation patterns shape the contemporary response of biogeochemical cycling and microbial communities to water. I found that long-term drought significantly alters nitrogen cycling such that nitrogen may be more vulnerable to loss when rainfall returns. Microbial communities were also sensitive to precipitation shifts, and, contrary to current assumptions, the response of these communities to moisture was influenced by these organisms’ precipitation history. This suggests that overall, even though grasslands are resistant to drought, extreme shifts in precipitation are likely to alter grassland ecosystems in the future. My work shows that these changes will be accompanied by shifts in nitrogen cycling and history-dependent functional changes in microbial communities that could alter predictive relationships between precipitation and grassland dynamics under future climates.

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Event Contact: Jeri Morgan can be reached at (970) 491-4373

Sponsored by the Graduate Degree Program in Ecology.