Data includes impacts on root nodule biomass, stomatal conductance, injury rates, and N-fixation in the white clover cultivar (T. repens cv. crusader). An ozone-exposure experiment was conducted in solardomes during the spring and summer of year 2012 on modern clover (Trifolium spp.) cultivars. The effects of ozone pollution (30, 35, 40, 45, 52, 67 parts per billion (ppb) treatment means) on the growth and functioning of the clover cultivars was investigated. Both cultivars had positive increases in ozone-injury rates, although stomatal conductance was unaffected by ozone exposure. Reductions in root nodule biomass and nodule number occurred in white clover, and red clover displayed an increase in nodule density. Nitrogen fixation rates were suppressed in white clover, which could have important implications for the sustainability of managed pasture. The work was carried out as part of a NERC funded PhD. Project number NEC04456. Full details about this dataset can be found at https://doi.org/10.5285/b63fbb6c-5030-43a1-b0ea-160bb5a83078