Impact of auto exhaust emission on seed germination and seedling growth behavior of senna alata (l.) roxb.- (candle bush) an important medicinal and ornamental flowering tree

Abstract

Automobile exhaust emission are a dominant source of urban environmental pollution due to movement of high traffic density and believed to have detrimental negative impact on plant growth rapidly since last couple of decades. This study describe the effects of autoexhaust emission on the seed germination and seedling growth behavior of Senna alata (L.) Roxb. (Ringworm) flowering tree growing as street tree in different road side of the city of Karachi. The effects of automobile exhaust emission on the seed germination and early seedling growth performance of S. alata was recorded. The auto emission showed negative effects on seedling height, leaf area (sq. cm), total plant fresh weight, total plant dry weight, root dry weight, stem dry weight, leaf dry weight, root / shoot ratio for fresh weight and root / shoot ratio for dry weight of S. alata growing in polluted sites (Tariq Road, Bahadurabad, Khalid Bin Waleed Road, Gulshan-e-Iqbal Gulshan-e-Iqbal) of city as compared to Karachi University Campus (Cleaner site). The seeds of S. alata collected from the Karachi University campus, which is considered as control site showed better percentage of seed germination and seedling growth as compared to the seeds of the same species collected from the different polluted areas of the city. A high percentage of decrease in seed germination was found for the seeds collected from the Tariq Road, followed by Bahadurabad, Khalid Bin Waleed Road and Gulshan-e-Iqbal Gulshan-e-Iqbal as compared to control. Seedling length was also highly decreased for seeds of same species collected from Tariq Road as compared to control. High percentage of decrease in seedling dry weight was found for seeds of same species collected from Tariq Road, Bahadurabad, Khalid Bin Waleed Road, and Gulshan-e-Iqbal Gulshan-e-Iqbal as compared to control. Root growth of S. alata was significantly decreased in the polluted seedlings as compared to control. According to tolerance test it was observed that seedling growth of S. alata showed lowest percentage of tolerance to auto exhaust emission were in order of samples collected from Gulshan-e-Iqbal>Bahadurabad>Khalid Bin Waleed Road>Tariq Road as compared to relatively clean area (University campus).