PARENT SESSION
Oral Session # 45: Plant Ecology III: Plant - Water Relations I.
Presiding: R Giuliani
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.

Effects of water and nitrogen on community structure in tallgrass prairie.

Collins, Scott^*,1, Johnson, Loretta², Koelliker, James², Knapp, Alan², ¹ University of New Mexico, Albuquerque, NM² Kansas State University, Manhattan, KS

ABSTRACT- Recent evidence suggests that limiting resources may interact to affect vegetation structure in many plant communities. Tallgrass prairie vegetation has been shown to be co-limited by nitrogen, water and light. We used two long-term field experiments at Konza Prairie Biological Station to investigate the individual and combined effects of water and nitrogen additions on plant community structure and dynamics in this tallgrass prairie. Results from a 12-year irrigation experiment designed to minimize water limitation during the growing season showed that water alone had little impact on plant community structure, including changes in species richness or abundance of functional groups. However, abundance of Panicum virgatum increased significantly, while Andropogon gerardii abundance declined slightly, in irrigated lowlands. In a second experiment, we added three levels of water and four levels of nitrogen to upland and lowland vegetation. After only 4 years, forb and total richness declined with increasing N addition, grass richness declined with increasing water addition, but there were no significant water by nitrogen interactions. Again, P. virgatum abundance increased, whereas abundance of A. gerardii declined, in fertilized and watered lowlands. These results show that nitrogen and water act somewhat similarly, but independently, to shift the competitive balance among dominant grasses in this tallgrass prairie.

Key words: Nitrogen, Tallgrass prairie, Species diversity, Water