Effect of SO2 - NO2 fumigation on wooden tree seedlings in open top chamber system

The present study has been performed on one year old tree saplings of <i>Azadirachta indica</i> (L.), <i>Cassia siamea</i> (L.), <i>Dalbergia sissoo</i> (Roxb.), <i>Eucalyptus rostrata</i> (L.), <i>Mangifera indica</i> (L.) and <i>Schyzygium cumini</i> (L.) in order to assess the effect of exposure of SO₂-NO₂, alone and combination of two gases. Tree saplings have been exposed to an average of 495 <i>&#956;</i>g m^-3 SO<sub2</sub> and 105 <i>&#956;</i>g m^-3 NO₂ for 40 d at the rate of 4 h d^-1 during 10:00 am to 01:00 pm in OTC. Total chlorophyll, specific leaf area (SLA), nitrate reductase (NR) activity, foliar protein, free proline content and free amino acids (AAs) of foliage have been the plant parameters, taken into consideration to evaluate the effect of gaseous exposure. Exposure of two gases has caused reduction in total chlorophyll content (<i>P</i> < 0.05, 0.01). Physiological and biochemical process has been seemed to be altered noticeable due to the combined effect of SO₂ + NO₂ followed by SO₂ alone (<i>P</i> < 0.05, 0.01). NO₂ mediated stress has produced, stimulatory and inhibitory responses in tree saplings. Results reveal that tree saplings have been attempted to absorb the NO₂ through N assimilation pathway. <i>E. rostrata</i>, <i>C. siamea</i> have been emerged as moderate tolerant to SO₂ mediated stress followed by <i>A. indica</i>. Response pattern of <i>S. cumini</i>, <i>M. indica</i> and <i>D. sissoo</i> set them as good indicators of SO₂-NO₂ exposure. Effects of two gases on tree saplings have been found to be synergistic.