, Volume 71, Issue 3-4, pp 331-345

Response of eight tropical plants to enhanced ammonia deposition under field conditions prevalent with SO2 and NH3

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The impact of SO2 on the deposition of ammonia and the response of eight tropical tree species to excess deposition of ammonia was investigated. This was achieved by studying physiological aspects like total sugars, protein, nitrate reductace (NR) activity, organic/inorganic nitrogen ratio, specific leaf area and foliar injury in plants growing under field conditions prevalent with SO2 and NH3.

Analysis of water soluble substances present on foliar surfaces of the trees indicated enhanced NH4 + deposition and thereby result in enhanced foliar protein contents. Though the enhanced nitrogen was almost the same in different plants, the plants exhibited differential metabolic disturbances. Critical analysis of the results indicated three distinct types of plant response. Plants like Azadirachta indica, Acacia auriculiformis and Bambusa arundinaceae maintained enhanced total sugars and NR activity and incorporated excess NH4 + into proteins, thus enabling the plant to compensate/alleviate SO2 induced injury. Ficus benghalensis and Ficus religiosa maintained unaltered total sugars and NR activity and could partly incorporate NH4 + into proteins, thus modifying the SO2 impact to some extent. Dalbergia sissoo, Eucalyptus rostrata and Mangifera indica could not incorporate the excess NH4 +, mainly due to declined total sugars. The results indicate the ability of a plant to undergo species specific metabolic changes in order to cope with the excess nitrogen deposition, which may ultimately result in increasing or decreasing tolerance to SO2.