Effects of Warming and Altered Precipitation Regime on Managed Grassland Structure and Function

The proposed research will evaluate how managed grassland ecosystems respond to alterations in climate. The forage species that dominate these grassland systems have been selected for tolerance to climatic variability and herbivory, and they employ several strategies to accomplish these ecological feats (e.g., phenological plasticity, rapid maturation, production of secondary compounds, and associations with fungal endophtyes). The main obiective of this proposal is to determine if managed grassland response to climate change can be predicted based on known species-specific physiological traits. The over-arching hypotheses are that: 1) C4 and endophyte-infected C3 forage species will maintain higher rates of productivity under warmer, drier environmental conditions than endophyte-free C3 species; however, increases in secondary chemical production resulting from the increased dominance and activity of these species will alter the microbial community and slow nutrient cycling rates; and 2) These species-level responses will result in alterations in carbon and nitrogen storage within the plant-soil system. This research project will occur primarily in a managed grassland located at the University of Kentucky's Spindletop Agricultural Farm located near Lexington, KY; however, the regional component of the project will occur at sites scattered throughout the southeastern U.S. I will utilize three approaches in this study: 1) a field climate manipulation of precipitation and temperature conducted in a mixed species managed grassland; 2) a regional study evaluating endophyte effects on tall fescue carbon storage and microbial community across the southeastern U.S.; and 3) the compilation of a national forage variety trial database to further assess species-level responses to climate. In the climate manipulation, I will measure both ecosystem (e.g., above- and belowground net primary production, litter quality and decomposition rates, nitrogen mineralization rates, trace gas fluxes, and nutrient pools) and species-specific parameters (e.g., leaf water potentials, photosynthesis rates, secondary compound concentrations, and endophyte infection frequencies) in order to determine if ecosystem response to climate change is controlled by species traits. The second and third approaches will evaluate whether species-specific traits impact managed grassland function across broad geographic scales. This project will quantify the response of common, broadly utilized forage species and the managed grassland ecosystems they form to alterations in precipitation and temperature (Focus 1). It will also identify whether species-specific traits control carbon storage and flux in managed grasslands across the southeast. The resulting data and database will inform modeling efforts that attempt to predict the response of this ecosystem type to future alterations in climate.