Productivity losses in barley attributable to ambient atmospheric pollutants in Pakistan

The productivity responses of four barley (Hordeum vulgare L.) cultivars (Haider-93, Haider-91, Jou-87, Jou-85) to air pollution were investigated during 2004-2005 season using open-top chambers with charcoal-filtered air (FA), unfiltered air (UFA) and unchambered field plots (AA) at a semi-urban site in Lahore, Pakistan. The 8 h daily mean O3, NO2 and SO2 in UFA remained 71, 30 and 16 ppb, respectively. In UFA, seed yield was drastically reduced in all the cultivars, 13% for Haider-93, 30% for Haider-91, 34% for Jou-87 and 44% for Jou-85 compared with FA plants. This impact in UFA was due to combined effects of reductions in number of ears per plant, seeds per ear and 1000-seed weight. A mid-season harvest of 9-weeks-old plants has revealed 16-25% and 7-15% reductions in plant fresh and dry weights, respectively, in UFA compared with counterparts grown in FA. Plants grown in UFA also showed significant reductions in stomatal conductance (6-12%), transpiration rate (20-27%), net photosynthetic rate (13-21%) and photosynthetic efficiency (8-9%). Nutritional quality of seeds was, however, not altered with respect to some minerals (Ca, Mg, K, P), and protein in all treatments, except for higher starch contents found in FA than both UFA and AA treatments. The yield losses attributable to the mix of pollutants and experienced in the urban fringe of Lahore are appreciably larger than expected. Their significance more widely in Pakistan needs to be assessed as a matter of priority, as population growth rates and emission levels are both rapidly increasing in the country.