EXPLORING THE HIDDEN THREAT OF GASEOUS POLLUTANTS USING RICE (ORYZA SATIVA L.) PLANTS IN PAKISTAN

Three rice (Oryza sativa L.) varieties (Basmati-Pak, Basmati-370 and IRRI-9) of Pakistan were grown for their entire life cycle in open top field chambers to investigate the impacts of ambient ozone (O3), nitrogen dioxide (NO2), and sulphur dioxide (SO2) on the biomass, growth physiology, and yield. The treatments were charcoal filtered air (FA), unfiltered air (UFA) and ambient air (AA). O3, NO2, and SO2 concentrations recorded at the experimental site were 75, 29 and 18 ppb as 8 h daily mean, respectively. Microclimate conditions inside and outside the chamber environment remained virtually similar. All the rice cultivars showed severe depression in biomass (20-30%) due to reductions in number of tillers (20-27%) and leaves per plant (21-29%) during vegetative growth phase with maximum reductions seen in both Basmati-370 and IRRI-9 in UFA treatments compared with FA. These reductions were primarily due to decreased transpiration rate (10-20%), stomatal conductance (12-23%), net photosynthetic rate (9-22%) and photosynthetic efficiency (6-12%) of plants in UFA. Yield losses in total seed weight per plant in UFA were more or less similar in IRRI-9 (37%) and Basmati-370 (36%), followed by lower reduction in cv. Basmati-Pak (29%). Reductions in number of panicles per plant (18-25%), filled seeds per panicles (8-11%), seeds weight per panicle (13-17%) and 1000-seeds weight (5-8%) in UFA contributed significantly towards greater yield depression. Percent seed sterility was also higher in UFA and AA treatment plants. Starch contents of seeds in UFA were reduced by 14%, 19% and 21% in Basmati-Pak, Basmati-370 and IRRI-9, respectively when compared to FA control.