The effects of long‐term open‐air fumigation with SO₂ on a field crop of broad bean (Vicia faba L.)

Abstract

SUMMARYEfTects of SO., 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.^ by leaves and for efTects 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 efTect 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 efTects of SO, on leaf photosynthesis explained an extra 10 "o of the observed yield loss (losses ranged from 7 to 17 "o of control yield). This small efTect was confirmed by field measurements which showed no detectable efTects of SO^ on leaf and canopy photosynthesis. Increased leaf respiration, which was observed in the 1988 experiment, explained another 10 °o of the observed yield reduction.Total SO2-sulphur uptake by the fumigated crop, which is an important component of dry deposition of SOg, was accurately simulated by the model.

Long-term effects of SO2 on plants, SO2 metabolism and regulation of intracellular pH

“…The fate of the airborne sulphur was analysed by relating the difference in accumulated sulphate-S to the difference in total-S between control and fumigated plants. The near 1:1 relationship indicates that only a very small amount of S0 2 was converted into organic sulphur, because it was shown in an earlier paper (Kropff, 1990) that the simulated uptake of sulphur from the air by the fumigated plants was close to the observed difference in sulphur content of the fumigated and control plants (Fig. 3).…”

“…Similiar effects on leaf area and dry matter production were observed in two preceding experiments conducted in 1985 and 1986 at the same location (Kropff et al, 1989a,b). Simulation analysis demonstrated that so2 effects on total dry matter production in all three experiments were mainly caused by the reduction of the green leaf area in the fumigated plots at the end of the growing period (Kropff, 1990) so2 effects on ionic composition Nitrate was not detected in any of the samples. Nitrogen fixation in the nodules appeared to be the most important nitrogen source, because about 450 kg N ha-t was taken up by the plants (1985 experiment at the same conditions), whereas only 50 kg nitrate-N ha-t and 68 kg ammonium N ha-t was available from the potting mixture and fertilizer.…”

“…In the open-air fumigation experiments with Vicia faba crops, at least 10 kg S ha -1 was taken up as so2 without growth reduction or visible injury (Kropff, 1990). The amount of protons produced in the leaves was ((10/32) X (2=) 625 mol H+ ha-\ which equals 52 mol H+ m -3 leaf, assuming (a) that all S0 2 is metabolized to sulphate resulting in the production of 2 mol H + ions per mol S0 2 (b) a leaf thickness 0.4 mm, and (c) an average Leaf Area Index over the growing period of 3.…”

“…The observed reductions in crop yield ranged from 7 to 17% mainly caused by chronic injury (macroscopic leaf damage appearing after long exposures) (Kropff, 1990). Subtle injury (direct effects on photosynthesis and respiration) were less important (Kropff, 1989;1990;Kropff and Goudriaan, 1989).…”

“…The observed reductions in crop yield ranged from 7 to 17% mainly caused by chronic injury (macroscopic leaf damage appearing after long exposures) (Kropff, 1990). Subtle injury (direct effects on photosynthesis and respiration) were less important (Kropff, 1989;1990;Kropff and Goudriaan, 1989). Because sulphur is an essential nutrient for plant growth, a mechanistic understanding of chronic S0 2 injury requires insight in the metabolism of S0 2 • Plants growing on soils which cannot meet the sulphur requirements for plant growth ' may use so2 as an additional source of sulphur (Olsen, 1957;Thomas et al, 1943;1944).…”