CUR - The Council on Undergraduate Research

Shifts in Leaf Investment Strategies of Sunflowers Across Climatic Gradients in the Upper Midwest

Michael Bylander, Thu Nguyen, and Dr. Nora Mitchell, Department of Biology, University of Wisconsin – Eau Claire, 330 Phillips Hall, 101 Roosevelt Ave, Eau Claire WI 54701

The earth is undergoing a period of global warming, this warming period is impacting many organisms and ecosystems as changes in climate alter average precipitation and temperature. With carbon and other greenhouse gases continuing to increase each year, the strategies plants employ to stay competitive in their environments must continue to shift to face the changing climate. This research asks how plant leaf investment strategies vary across climatic gradients in the Upper Midwest, using sunflower (Helianthus) species as a model system. Understanding how sunflower leaf traits relate to differences in climate will help to predict how species distributions may change and how plants may respond to climate change. Our team collected data on three species of sunflower (H. grosseserratus, H. maximiliani, and H. giganteus) from 20 different sites across Wisconsin and Minnesota. We collected field measurements of leaf thickness, area, length, width, dry and wet mass. Specific leaf area (SLA) was calculated as a proxy for investment strategy, where higher SLA leaves are associated with faster growth strategies, and lower SLA leaves are associated with more conservative strategies.  SLA was analyzed against climate data (such as mean summer temperatures) to understand how strategies differ across regional climates. We found no evidence that SLA was related to precipitation, however, SLA was found to be inversely related to temperature. This finding could indicate a shift toward more conservative leaf investment strategies in areas experiencing higher average temperatures under future climate change.

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