N-fixation rate determined after 12 weeks ozone exposure by
acetylene reduction assay (ARA) (Hewitt et al., 2014). A second,
previously unpublished ozone-exposure experiment, using the
same experimental set up and treatments, was conducted in year
2013 on clover/ryegrass pasture mesocosms using T. repens cv.
Crusader and Lolium perenne cv. Abermagic. L. perenne cv. Aber-
Magic was sown at a rate of 0.28 g per pot directly into 10 L pots
(27.5 cm diameter 22 cm height) filled with compost (John Innes
No. 2; J. Arthur Bowers, Lincoln, UK). The total nitrogen content of
soils ranged 1e3% (data not shown). T. repens cv. Crusader plants
were also propagated from seed, grown in the same compost in
plug-plant trays in an unheated glasshouse.