LTREB: Testing Paradigms About Plant Functional Responses to Environmental Change

Long-term ecological experiments are needed that simulate the conditions of the future so that scientists can study their potential impacts on ecological communities. This study uses a 20-year old, field experiment, called BioCON, that raises the carbon dioxide concentrations in the atmosphere above prairie plant communities to levels that are expected to occur later in this century. The experiment is designed to study how higher carbon dioxide levels in the atmosphere affects the growth of different kinds of plants. The experiment is also designed to understand how the availability of soil nitrogen, an important nutrient that plants need to grow, influences the ability of plants to take up higher levels of carbon dioxide during photosynthesis. Data from the study will be made publicly available through the Cedar Creek, Long Term Ecological Research website. BioCON is visited by over 2500 K-12 students and teachers annually, including teachers of Native American students. College students work and learn how to carry out their own research projects in BioCON each summer. New K-12 lesson plans as well as videos for the sustainability science themed YouTube Channel MinuteEarth will be developed that specifically feature new knowledge gained from BioCON.

Through continued measurements of functional group and functional group mixture responses to carbon dioxide (CO2) and nitrogen treatments, this study will test two kinds of hypotheses. The first set uses a functional trait classification framework to develop predictions regarding direct functional group responses to eCO2 and N (i.e., responses expected in the absence of soil-mediated feedbacks, species interactions, or interactions with stochastic or directional changes in climate). The second set posits that long-term outcomes will diverge from predictions based on expected direct responses because of modifying processes, involving physiological acclimation, functional group effects on aboveground and belowground resource supply and soil pH, and interactions between treatments and variation in climate. The long-lived perennials in BioCON have not yet equilibrated in their response to CO2 and N, exhibiting interactions with year-to-year variation in climate and generating soil-mediated feedbacks. In BioCON, across 20 years, C4 species have become increasingly productive under high CO2 whereas the benefit of CO2 has gradually disappeared for C3 species, contradicting current theory. Understanding these divergent responses and whether they will continue is a major focus of the study, along with understanding the role of functional groups with respect to other long-term processes relevant to ecosystems under global environmental change, including productivity, decomposition, nutrient cycling, and water fluxes.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.