Identifying factors which modify the effects of ambient ozone on white clover (Trifolium repens) in Europe

This paper describes results of experiments carried out by participants of the UN/ECE ICE-Crops to investigate the dose response of plants to long-ter m ozone exposure. The data were analysed to determine the influences of cli matic and geographical factors upon this dose response. Members of the ICP- Crops carried out experiments at 12 sites in Europe, covering a geographica l range from Jokioinen, Finland, to Milan, Italy, to generate the database used in this study. The effects of ozone were determined using N-(2-(2-oxo- 1-imidazolidinyl)ethyl)-N'phenylurea (ethylene diurea; EDU) as a protectant against ozone damage. Thus, the ratio of biomass in EDU-treated plants to untreated plants indicated the severity of ozone damage. Simple linear regr ession produced a low r(2) of 0.16 for the dose response. Analysis of the r esiduals identified three groups in the data depending on their mean residu al values. Re-plotting the data into separate dose responses for these thre e groups produced improvements in the r(2) values to 0.33, 0.36 and 0.36, f or Groups 1 to 3, respectively. The data were subsequently used to train ar tificial neural network (ANN) models to determine the factors that caused t he scatter within the dose response. Vapour pressure deficit and temperatur e were found to be important influences on the dose response whereas longit ude, year and altitude were weaker influences. Inclusion of these factors i n the ANN model increased the r(2) of the model to 0.79. (C) 1998 Elsevier Science Ltd. All rights reserved.