Impacts of ozone on the growth and yield of field-grown winter wheat

Seed of winter wheat (Triticum aestivum L. cv Riband) was sown on 29 August 1992 in eight field plots. Four plots were exposed to elevated ozone (O-3) concentrations on 16 days between 29 August and 2 October 1992, for 6 h da y(-1), and on 27 days between 29 March and 24 August 1993, for 7 h day(-1). Mean daily O-3 concentrations were approximate to 30 and 80 nmol mol(-1) i n ambient and fumigated plots, respectively. Plants were sampled on 5 Novem ber (1992), 14 January, 16 February, 1 April, 25 May, 23 June and 24 August (1993). No visible symptoms of O-3 damage or premature senescence were obs erved at any time over the course of the experiment. Exposure to elevated O -3 decreased the above ground biomass by reducing plant density and individ ual plant relative growth rate. However, there was no significant influence of the pollutant on the growth of the root relative to the shoot. Assessme nt of yield characteristics at the final harvest revealed an O-3-induced de crease in the number of grains per ear, as a result of fewer grains per spi kelet and an increase in the number of infertile florets per spikelet. No s ignificant effects of the pollutant on the number of ears per plant, spikel ets per ear, or 1000 grain weight were found. As a result of the combined e ffects on the number of grains per ear and the decrease in plant density an d growth rate, O-3 exposure reduced grain and straw yields (tonnes ha(-1)) by 13 and 8%, respectively. However, no significant change in the partition ing of dry matter between the grain and the straw was observed in fumigated plots. The findings are discussed within the context of United Nation Econ omic Commission for Europe critical level guidelines for the protection of crop yields, in relation to their application to winter-sown crops. (C) 199 9 Elsevier Science Ltd. All rights reserved.