The present work was carried out to investigate the impact of coal smoke emissions on the overall growth performance cambial activity and the consequent wood production of Syzygium cumini (L.) Skeels growing at various distances (0.5 km, 2 km, 6 km, 9 km and 15 km) from the point source of pollution i.e. the Badarpur Thermal Power Station (BTPS) in Delhi. Growth performance was assessed by analyzing its carbon assimilation capacity and biochemical alterations as evident in the leaf tissue of the stressed trees and by investigating the effect of these metabolic alterations on the meristematic activity of vascular cambium, and the consequent wood development under a gradient of pollution regime.

          The following conclusions can be drawn from the present investigation regarding the changes that S. cumini trees experienced due to coal-smoke pollutants present in the air.

          SO2, NO2 and TSPM values were maximum at the most polluted site (6 km away) whereas at site V the values were below the permissible limit. Visible injury symptoms due to air pollutants were not observed at any of the sites and in any of the seasons. The stomata were smaller at site III (6 km) than at the other sites. Their size was maximum in pre-monsoon and minimum in post-monsoon season. The size of stomatal aperture declined up to a distance of 6 km. Stomatal index (SI) touched the minimum at site III. The SI was positively correlated with nitrogen content and vessel width. The concentration of photosynthetic pigments were lowest at site III and recovered thereafter. Carotenoid content also exhibited a similar trend. The total chlorophyll content was severely affected by TSPM & SO2 concentrations. Chlorophyll content did influence strongly the net photosynthetic rate, NR activity rate, protein content and nitrogen content. The sulphur content and sugar content remained negatively related to each other throughout the year. The sulphur content went parallel to pollution load. The S content was negatively correlated with chlorophyll and net photosynthetic rate in the monsoon months. The span of cambial activity in S. cumini was of about 6½ to 7 months at different sites. However, pollution stress delayed the cambial reactivation for about 2 months at site III. Xylem differentiation preceded phloem production. Curiously, the span of xylem production was longer than phloem under the pollution stress. The annual quantum of wood produced was consequently greater in trees at the polluted sites. Relative proportion of vessels in the wood was relatively low under pollution stress. Width of vessel elements was also smaller at the polluted sites, but their length increased with the degree of pollution. Wood fibres were shorter at the polluted sites, compared to those at the reference site. A high degree of negative correlation emerged between vessel length and fibre length. The photosynthetic rate was inversely proportional to the pollution load. It was positively correlated with nitrogen content. The stomatal conductance dropped to its lowest at the most polluted site. It maintained a positive relationship with sugar content throughout the year. The NR activity rate ran counter to the pollution load. It bore a significant positive correlation with chlorophyll content, sugar content and nitrogen content but a negative correlation with nitrate content. Contrary to NR activity, nitrate content was maximum at site III and minimum at the non-polluted site throughout the year. It was negatively correlated to photosynthetic rate, chlorophyll content and nitrogen content. A linear negative correlation was observed between the amount of total nitrogen and the pollution load. A significant positive correlation existed between sugar content and NR activity rate.