TILLERING AND LEAF AREA OF WINTER BARLEY EXPOSED TO SULPHUR DIOXIDE IN THE FIELD

Effects of sulphur dioxide (SO2) on growth and flowering of SO2-tolerant and non-tolerant genotypes of Phleum pratense

The objective of this study was to compare the growth and interaction of clipping and sulphur dioxide (SO(2)) exposure on SO(2)-tolerant and non-tolerant genotypes of Phleum pratense at two field sites along an SO(2)-concentration gradient. Sulphur-dioxide-tolerant and non-tolerant genotypes of Phleum pratense were identified from indigenous populations that had been collected along the same SO(2)-concentration gradient in southern Alberta, Canada. Physiological differences between the two genotypes were confirmed by supplying leaves with (14)CO(2) and examining the assimilate partitioning between the genotypes. For the field experiment, clones of each genotype and seedlings grown from commercial seed were planted at two different field sites along an SO(2)-emission gradient. There were no differences in growth between the genotypes at the two field sites after the first year except that the SO(2)-tolerant clones had a greater percentage of root length colonised by vesicular-arbuscular (VA) mycorrhizal fungi. After the second growing season, there was a significant decrease in the number of inflorescences produced by plants exposed to SO(2), particularly by the non-tolerant genotype. The added stress of defoliation appeared to increase the sensitivity of flowering to SO(2), again particularly in the non-tolerant genotype. The results of the field study showed that flowering as opposed to vegetative plant growth was more sensitive to long-term low-concentration SO(2) exposure and that this sensitivity was compounded by the stress interaction of defoliation.

The effects of long-term open-air fumigation with SO2 on a field crop of broad bean (Vicia faba L.): III. Quantitative analysis of damage components

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.

Growth responses of barley exposed to SO2

Barley (Hordeum vulgare ev. Schooner) plants were exposed to 4, 42, 121, 256 or 517 nl 1^-l SO₂ to investigate the relationship between the exposure concentration of SO² and growth. The plants were exposed from 14 days old, in open-top chambers for 4 h day^-1 (10.00-14.00 h) for 79 days. The concentration-response curves established illustrated a small growth stimulation (approx. 10%) at 42 nl 1^-1 and a growth inhibition at 121 nl 1^1- or greater. The growth reduction was generally proportional to the exposure concentration at concentrations above 42 nl 1^-1 Sulphur concentration in the shoot increased linearly with ambient SO₂ concentration.

Yield responses of different crop species to long-term fumigation with sulphur dioxide in open-top chambers

Potted plants of commercial cultivars of rape (Brassica napus L., cv. 'callypso'), summer barley (Hordeum vulgare L., cvs. 'arena' and 'hockey') and bush beans (Phaseolus vulgaris L., cvs. 'rintintin' and 'rosisty') were continuously exposed in open-top chambers to sulphur dioxide (SO(2)) for the whole growing season in order to assess effects of this pollutant on growth and various yield parameters. Treatments consisted of charcoal-filtered air (CF) and CF supplemented with four levels of SO(2), resulting in mean exposure concentrations (microg m(-3)) of approximately 8, 50, 90, 140 and 190. With the exception of the 1000 seeds weight, which was slightly reduced, dry matter production and yield parameters of rape remained unaffected by all SO(2) concentrations or were even stimulated. Compared to CF vegetative growth of both bean cultivars was reduced by 10-26% at all SO(2) levels; however, with significant effects only for cv. 'rintintin'. While all SO(2) additions reduced significantly the yield (dry weight of pods) of the bean cultivar 'rosisty' between 17% and 32%, cv. 'rintintin' showed a significant reduction of up to 42% only at the two highest pollutant concentrations. Dry matter production of the barley cultivars was mainly impaired at SO(2) concentrations > 100 microg m(-3) with a reduction of 30-52%. While nearly all yield parameters of cv. 'hockey' reacted similar to the dry matter production, the yield of cv. 'arena' was reduced already at the low SO(2) levels. At a treatment concentration of 90 microg SO(2) m(-3) a significant yield loss of 30% was recorded. A reduction of the 1000 grains weight mainly contributed to these yield losses observed for both barley cultivars. From these results, it may be assumed that SO(2) concentrations within the range 50-90 microg m(-3) are potentially phytotoxic to some crop species.

The effects of long-term open-air fumigation with SO2 on a field crop of broad bean (Vicia faba L.) I. Depression of growth and yield

In an open-air Held exposure system for the controlled release of air pollutants, broad bean (Vida faba L.) crops were exposed to elevated SO₂ concentrations in three growing seasons, in order to analyse the effects on crop growth under field conditions. The treated plots were exposed to a mean concentration of 165μgm^-3 in 1985, 62μgm ^-3 in 1986 and 74μgm^-3 in 1988. The background concentration was about 10μ m^-3 . A reasonably uniform distribution of SO₂ concentration was obtained over an area of 8m × 8m and concentrations exceeding the target concentration were rare. In 1985 and 1988, the growth rate of the crop was depressed at the end of the pod-filling period. This resulted in a reduction of total dry-matter production of 17% in 1985 and 9% in 1988, and a seed yield reduction of 23% in 1985 and 10% in 1988. In 1986, dry matter growth was not analysed up to the end of the growing season due to a severe infection of Botrytis fabae (Choclate spot disease) infection in the control plot in the middle of the pod-filling period. Slight B. fabae infections in the control plots only were also observed in 1985 and 1988. In all experiments no significant reductions of dry matter growth were observed in the vegetative and early reproductive phases.