Growth responses of tomato plants to low concentrations of sulphur dioxide and nitrogen dioxide

Abstract

Forty-five-day-old plants of Lycopersicon esculentum were exposed to 0.1 ppm SO 2, 0.2 ppm NO 2 and 0.1 ppm SO 2 + 0.2 ppm NO 2 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 NO 2 or SO 2 alone, relative growth rate, net assimilation rate, leaf production rate and specific leaf area increased initially but declined after exposure for longer times. Both SO 2 and NO 2 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 SO 2 and NO 2 exposure, indicating that the tomato plants in response to SO 2 and NO 2 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 SO 2− 4-S content increased in plants exposed to NO 2 and SO 2, respectively. P content was reduced following exposure to SO 2 and NO 2 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.