FORAGE QUALITY OF ANDROPOGON GERARDII ACROSS A PRECIPITATION GRADIENT

This study focused on the ecotypic variation in forage quality of Andropogon gerardii Vitman, a dominant C4 grass in North American grasslands and an important forage grass for native and introduced grazers. Ecotypes are genetic variations of a plant species adapted to local environmental conditions. Andropogon gerardii is represented by many local ecotypes across its range. Forage quality analyses quantify digestibility and nutrition of a plant sample and allow an assessment of nutritional value for grazers. The variability in forage quality among A. gerardii ecotypes is unknown. This study aimed to quantify variation in forage quality of A. gerardii collected across a precipitation gradient from eastern Colorado to southern Illinois in the North American grassland. Samples of A. gerardii plants in four distinct precipitation regions and three-remnant grassland populations within each region were sampled in July 2010 to assess differences in forage quality. In the field study, forage quality increased along an east to west gradient corresponding with a decrease in annual precipitation levels. A greenhouse study, conducted in April to September 2010, was used to test effect of varied precipitation on three A. gerardii ecotypes from distinct precipitation regions grown under controlled conditions. In the greenhouse experiment, plant maturity had significant effects on all forage measurements except lignin (ADF%). Forage quality was most directly connected to environmental conditions and forage maturity, with smaller differences among population sources. Of those tested here, southern IL ecotypes were the most adaptable to variations in precipitation, and will likely maintain high levels of forage quality under projected changes in precipitation resulting from climate change