Effect of Simulated Acid Rain on Chlorophyll and Carotenoid Content of Sunflower (Helianthus annuus L.) Leaves

The effects of simulated acid rain (SAR) of different pH [distilled water – 7.0 (control), 5.7, 4.5 and 3.0] were studied on chlorophyll and carotenoid content using sunflower (Helianthus annuus L.) cv. ‘Morden’ as the test system. Test plants were sprayed with 30 ml acid rain solution/plant at weekly intervals starting from two leaved stage till initiation of flowering in the early morning under natural environment. In case of control, the total chlorophyll content at the peak growth stage was recorded 1.947 mg g⁻¹ FW. The SAR application showed a decreasing trend in the total chlorophyll content of leaves with increasing acidity of SAR. Chlorophyll a and b contents followed a similar trend in change as was observed in the case of total chlorophyll. Carotenoids at a peak growth stage were recorded maximum in control (0.683 mg g⁻¹ FW) and declined gradually in SAR-treated plants reaching minimum (0.496 mg g⁻¹) at pH 3.0. Chl a: b ratio at peak growth was recorded 4.02 in control. The chlorophyll a: b ratio showed reduction to 3.79 at pH 5.7; however at pH 4.5 and 3.0, the chlorophyll a: b ratio slightly increased to 3.89 and 3.99, respectively. Simulated acid rain application did not affect total chlorophyll: carotenoid ratio.