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

Abstract 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 chamaedrys ). 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.