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Effects of SO2 on growth and production of broad bean, observed in three open-air fumigation experiments, were interpreted in terms of damage components with a mechanistic simulation model. The model consisted of an elementary model for crop growth, extended with submodels for the microclimate in the crop and with a submodel for uptake of SO2 by leaves and for effects on leaf photosynthesis. The major part of the observed reduction in total dry matter production could be explained by leaf injury observed in the oldest leaves of the fumigated plants at the end of the growing period. The effect consisted of dry matter loss through leaf abscission and a reduced growth rate at the end of the growth period due to reduction of the amount of absorbed radiation by the canopy. Direct effects of SO2 on leaf photosynthesis explained an extra 10% of the observed yield loss (losses ranged from 7 to 17% of control yield). This small effect was confirmed by field measurements which showed no detectable effects of SO2 on leaf and canopy photosynthesis. Increased leaf respiration, which was observed in the 1988 experiment, explained another 10% of the observed yield reduction. Total SO2-sulphur uptake by the fumigated crop, which is an important component of dry deposition of SO2, was accurately simulated by the model. [ABSTRACT FROM AUTHOR]

Faba bean crops (Vicia faba L.) were exposed to elevated SO2 concentrations in three different years in an open-air field exposure system for the controlled release of air pollutants. The treated crops were exposed to an average SO2 concentration of 165 μg m&sup-3; in 1985, 62 μg m&sup-3; in 1986 and 74 μg m&sup-3; in 1988. The ambient SO2 concentration was about 10 μg m&sup-3;. Plant height, number of internodes and number of pods were not affected by SO2. The specific leaf area was reduced in the plants exposed to SO2 at the end of the growing season. Leaf area development was strongly affected during the pod-filling period in 1985 and 1988 as a result of leaf injury and defoliation in the fumigated plots. In 1986 a similar trend in leaf area reduction was observed in the early reproductive phase. N and Mg content of the different organs was unaffected by SO2. The S content was strongly elevated in the leaves and pods of the fumigated plants, and the Ca content of the leaves was reduced by SO2. Chlorophyll content of different leaf numbers was unaffected by SO2. [ABSTRACT FROM AUTHOR]

Effects of SO 2 on growth and production of broad bean, observed in three open-air fumigation experiments, were interpreted in terms of damage components with a mechanistic simulation model. The model consisted of an elementary model for crop growth, extended with submodels for the microclimate in the crop and with a submodel for uptake of SO 2 by leaves and for effects on leaf photosynthesis. The major part of the observed reduction in total dry matter production could be explained by leaf injury observed in the oldest leaves of the fumigated plants at the end of the growing period. The effect consisted of dry matter loss through leaf abscission and a reduced growth rate at the end of the growth period due to reduction of the amount of absorbed radiation by the canopy. Direct effects of SO 2 on leaf photosynthesis explained an extra 10% of the observed yield loss (losses ranged from 7 to 17% of control yield). This small effect was confirmed by field measurements which showed no detectable effects of SO 2 on leaf and canopy photosynthesis. Increased leaf respiration, which was observed in the 1988 experiment, explained another 10% of the observed yield reduction. Total SO 2 -sulphur uptake by the fumigated crop, which is an important component of dry deposition of SO 2 , was accurately simulated by the model.