Effects of sulfur dioxide and ozone on Ulmus americana seedlings. II. Carbohydrates, proteins, and lipids

The effects of SO2 (2 ppm for 6 h), O3 (0.9 ppm for 5 h), and SO2–O3 mixtures (2 ppm SO2 and 0.9 ppm O3 for 5 h followed by SO2 for 1 h) were studied on metabolite contents of 4-month-old, actively growing and quiescent Ulmus americana L. seedlings. Effects on metabolite contents in leaves, stems, and roots were examined 24 h, 1 week, and 5 weeks after exposure to pollutants for actively growing seedlings, and 24 h and 1 week for quiescent seedlings. Fumigations caused significant reduction in total nonstructural carbohydrate and protein contents of actively growing seedlings within 24 h after fumigation. By the end of 5 weeks, however, carbohydrate and protein contents of new (< 1 cm long at the time of fumigation) leaves were comparable with those of control plants, indicating that capacity of new leaves to function was restored. The adverse effects of pollutants on metabolites of older leaves (> 1 cm long) of actively growing seedlings persisted throughout the 5-week period. Changes in lipid contents of actively growing seedlings were small and in most cases not significant. Exposure to pollutants decreased lipid contents of quiescent seedlings (up to 28%); this decrease was much lower than reduction in carbohydrates or proteins (up to approximately 65%). Metabolite contents of both actively growing and quiescent seedlings were reduced most by SO2–O3, an intermediate amount by SO2, and least by O3 treatment.