Quantification of stress adaptation by laser-induced fluorescence spectroscopy of plants exposed to engine exhaust emission and drought

The effects of drought and petrol engine exhaust pollutants, such as SO2 and NO2 and suspended particulate matter (SPM), on the photosynthetic activity of colocasia [Colocasia esculenta (L.) Schott], kacholam (Kaempferia galanga L.) and tapioca (Manihot esculenta Crantz) plants were studied from in vivo laser-induced chlorophyll fluorescence (LICF) spectra. An open-top chamber (OTC) of 2.5 m diameter and 3 m height incorporating an air-filtering unit was developed for this study. Plants grown inside the OTC were exposed to exhaust emissions from a two-stroke Birla Yamaha genset for 10 d, while a control group was maintained outside. Gaseous pollutants and SPM present inside the OTC during the exposure period were measured with a high-volume air sampler. The steady-state LICF spectra of the control and treated plants were recorded in the 650–750-nm region. Fluorescence induction kinetics (Kautsky effect) was also recorded during the stress period from dark-adapted intact plant leaves at the chlorophyll bands of 685 and 730 nm. The vitality indexes (Rfd-685 and Rfd-730) and stress adaptation index (Ap) derived from the induction kinetics were utilised along with the chlorophyll fluorescence intensity ratio (F685 /  F730) for evaluation of stress-induced changes in plants. It has been observed that F685 /  F730 ratio increased for all plants inside the OTC whereas the Rfd-685, Rfd-730 and Ap values showed a downward trend with increasing pollution stress. As compared to colocasia and tapioca, kacholam plants showed higher resistance to exhaust emission and water stress as well as better capacity to regain its photosynthetic functioning on removal of the stress. Results of this study demonstrate the capability of stress adaptation index for early quantification of the functional impairment of photosynthetic apparatus in different species of plants due to air pollution and drought stresses.