Growth and nutritive quality of Poa pratensis as influenced by ozone and competition

Interspecific plant competition has been hypothesized to alter effects of early-season ozone (O-3) stress. A phytometer-based approach was utilized to investigate O-3 effects on growth and nutritive quality of Poa pratensis grown in monoculture and in mixed cultures with four competitor-plant species (Anthoxanthum odoratum, Achillea millefolium, Rumex acetosa and Veronica chaniaedrys). Mesocosms were exposed during April/May 2000-2002 to charcoal-filtered air + 25 ppb O-3 (control) or non-filtered air + 50 ppb O-3 (elevated O-3). Biomass production was not affected by O-3, but foliar injury symptoms were observed in May 2002. Early-season O-3 exposure decreased relative food value of P. pratensis by an average of 8%, which is sufficient to have nutritional implications for its utilization by herbivores. However, forage quality response to O-3 was not changed by interspecific competition. Lack of injury and nutritive quality response in P. pratensis harvested in September may reflect recovery from early-season O-3 exposure. (c) 2005 Elsevier Ltd. All rights reserved.