Sulfur Dioxide and Nitrogen Dioxide Meet Growth, Gas Exchange, and Water Relations of Potato Plants

The effects of SO 2 and NO 2 , singly and in combination, on the growth and physiology of nontuberizing Solarium tuberosum L. `Russet Burbank' plants were studied in controlled conditions. Plants were exposed to 0.11 μl SO 2 and/or 0.11 μl NO 2 /liter for 24 hours a day up to 10 days. Statistically significant effects were observed mainly in the SO 2 + NO 2 treatments compared with the control plants. Leaf area was reduced from day 2 onward, and root fresh and dry weights were reduced from day 4 onward. Significant reductions in leaf and stem dry weights occurred on day 6. Net CO 2 exchange rates were reduced for SO 2 exposed compared with control plants beginning on day 3, while water loss rates were increased with SO 2 + NO 2 beginning on day 3. The increases in water loss rate were possibly due to the development of cuticular injury observed as abaxial glazing on the upper and middle canopy leaves. Leaf osmotic potential (π) of plants with SO 2 + NO 2 became more negative within the first 24 hours of the exposure. This reduction was accompanied by an increase in reducing sugar concentration. Xylem water potential was reduced in the mature and expanding leaflets by day 2 of the SO 2 + NO 2 exposure. The most sensitive aspect of the action of SO 2 + NO 2 appeared to be the increase in reducing sugars that affected osmotic potential in the leaves. Considering the retardation of root growth, these data suggest that the pollutant gases may have interfered with partitioning of dry matter from the leaves to the roots.