GROWTH-RESPONSES OF TOMATO PLANTS TO LOW CONCENTRATIONS OF SULFUR-DIOXIDE AND NITROGEN-DIOXIDE

Forty-five-day-old plants of Lycopersicon esculentum were exposed to 0.1 PPM SO2, 0.2 ppm NO2 and 0.1 PPM SO2 + 0.2 ppm NO2 for 4 h daily for 50 days. Plant height, number of leaves, total leaf area, total leaf biomass, total shoot biomass and total plant biomass were increased by these low dosages. When exposed to either NO2 or SO2 alone, relative growth rate, net assimilation rate, leaf production rate and specific leaf area increased initially but declined after exposure for longer times. Both SO2 and NO2 reduced root growth and resulted in a low root:shoot ratio. Number of leaves, total leaf area, total leaf biomass and leaf area duration increased up to 30 days of both SO2 and NO2 exposure, indicating that the tomato plants in response to SO2 and NO2 allocated a greater proportion of its photoassimilates for growth and development of photosynthetic organs. Chlorophyll concentration increased initially but declined after exposure for longer periods. Foliar N and SO42--S content increased in plants exposed to NO2 and SO2, respectively. P content was reduced following exposure to SO2 and NO2 alone or in combination. The study suggests that low dosages of pollutants are fertilizing the plants, promoting vegetative growth at the expense of reproductive growth.