Climatic Variability and Ecosystem Response: Precipitation Patterns, Soil Moisture Dynamics, and Productivity in Tallgrass Prairie

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Climatic variability is a key driver of ecosystem structure and function in grasslands, and climate models suggest that variability in rainfall, temperature, and other climatic parameters will increase because of global climate change. However, there is uncertainty about future rainfall patterns, with some models predicting increased, others decreased growing season rainfall and soil moisture. Any shifts in rainfall quantity or frequency will change rainfall variability, and several lines of evidence suggest that variability may as important as the total quantity of rainfall in regulating tallgrass prairie net primary productivity. Indeed, increases in rainfall variability, even with no change in rainfall quantity, have the capacity to reduce plant performance and productivity and may cause shifts in tallgrass prairie community composition, because of unavoidable physiological and morphological limitations on plant abilities to track and adjust to varying resources. The objective of the research described in this proposal is to experimentally determine the impact of variability in rainfall patterns on above- and belowground grassland productivity, using tallgrass prairie as a model system. We will impose decreases and increases in variability in rainfall inputs on microcosms containing common tallgrass prairie grasses and forbs, by experimental watering at sixteen different quantity and frequency combinations. Measurements will focus on soil moisture dynamics, photosynthetic performance, canopy development, root growth dynamics, plant reproduction, and above and belowground net primary productivity. The overarching hypothesis tested by this experiment is that variability is a key driver of tallgrass prairie productivity, and the experiment will examine several specific hypotheses about the relationships between rainfall quantity and frequency and productivity in grasses and forbs. This knowledge will broaden our understanding of the regulation of grassland productivity, and will have implications for research on productivity/diversity relationships, fire/grazer interactions, terrestrial carbon dynamics, atmosphere/vegetation feedbacks, and interactions among climatic elements in global change scenarios (rainfall, temperature, and elevated CO2). An accurate understanding of these issues is crucial to predicting climate change impacts on grasslands and developing proactive conservation and management plans for these endangered systems.