THE EFFECTS OF OZONE AND CUTTING ON THE SPECIES COMPOSITION OF ARTIFICIAL GRASSLAND COMMUNITIES

1. Pots containing a mixture of the grasses Agrostis capillaris and Festuca rubra and the forbs Trifolium repens and Veronica chamaedrys were exposed to ozone in open-top chambers ventilated with charcoal-filtered air. Total ozone exposure ranged from 800 nl l(-1) h above 40 nl l(-1) to 15 000 nl l(-1) h above 40 nl l(-1). 2. Half of the pots in each chamber were cut fortnightly. Linear relationships were fitted between biomass or proportion of each species and ozone exposure. 3. In uncut pots T. repens biomass decreased with increasing ozone but biomass of F. rubra increased, so that total biomass was unaffected. 4. Trifolium repens also declined in cut pots, in which the proportional reduction of its biomass was much greater. Agrostis capillaris biomass increased with ozone in cut pots, so that again total biomass did not decline significantly. The response of proportion of forbs to ozone was significantly greater in cut pots. 5. It is concluded that ozone exposures experienced in the UK may potentially affect the species composition of semi-natural grasslands, that cumulative exposure above a threshold of 40 nl l(-1) may be used to express critical levels of ozone for such communities, and that cutting or grazing may influence community responses to ozone.