Interactive effects of elevated ozone and carbon dioxide on growth and yield of leaf rust-infected versus non-infected wheat

Spring wheat (Triticum aestivumn L. cv. Turbo) was grown from seedling emer gence to maturity (129 days) in chambers simulating the physical climate an d ozone pollution of a field site in Northern Germany from 1 April to 31 Ju ly with a mean l-h daily maximum of 61.5-62.4 nl l(-1) ozone compared to a constant low level of 21.5-22.8 nl l(-1) ozone. The two ozone levels were c ombined with either a current (374.1-380.2 mu l l(-1)) or enriched (610.6-6 15.0 mu l l(-1)) CO2 atmosphere. Additionally, a leaf rust epidemic (Puccin ia recondita f. sp. tritici) was induced at tillering stage by repeated re- inoculations with the inoculum formed on the plants. Leaf rust disease was strongly inhibited by ozone, but largely unaffected by elevated CO2. Ozone damage on leaves was strongly affected by CO2 and infection. On infected pl ants, ozone lesions appeared 2-4 weeks earlier and were up to fourfold more severe compared to non-infected plants. Elevated CO2 did not delay the ons et of ozone lesions but it significantly reduced the severity of leaf damag e. It also enhanced the photosynthetic rate of flag leaves and increased th e water use efficiency, biomass formation and grain yield. The relative inc reases in growth and yield induced by CO2 were much larger on ozone-stresse d than on non-stressed plants. Both ozone and fungal infection reduced biom ass formation, number of grains per plant, thousand grain weight and grain yield; however, adverse effects of leaf rust infection were more severe. El evated CO2 largely equalized the negative effects of ozone on the photosynt hetic rate, growth and yield parameters, but was not capable of compensatin g for the detrimental effects of fungal infection. The data imply that the impact of ozone in the field cannot be estimated without considering the pr edisposing effects deriving from fungal infections and the compensating eff ects deriving from elevated CO2. (C) 2000 Elsevier Science Ltd. All rights reserved.