Eight cultivars of Lycopersicon esculentum (tomato) and six cultivars of Lactuca sativa (lettuce) were subjected to CO2-enriched air (1000 μ11−1) containing 0.7 or 0.9 μll−1 nitrogen oxides (NOx).
CO2 enrichment without NO2 significantly increased the dry weight of all tomato (35–81%) and lettuce cultivars (25–101%). In six of the eight tomato cultivars the dry weight was reduced by the addition of NOx. The mean relative growth rate (RGR) decreased by 4–19% depending on the cultivar. This meant that the benefit of CO2 enrichment was almost completely eliminated in most of the cultivars. Marginal leaf necrosis appeared in some of the cultivars, while in others no visible injury developed. None of the lettuce cultivars was significantly affected by the addition of NO x.