Light and CO2 responses of photosynthesis and chlorophyll fluorescence characteristics in bean plants after simulated acid rain

The effects of simulated acid rain on some chlorophyll fluorescence characteristics and photosynthetic gas exchange at different light intensities and CO₂ concentrations of bean plants were investigated. Measurements were carried out 3, 5 and 24 h after spraying. The results showed that a single acid rain (pH 1.8) treatment of bean plants reduced gas exchange, the maximal carboxylating efficiency and photochemical quenching. This treatment led also to increased CO₂ compensation point and non-photochemical quenching and changed the shape of CO₂ and light curves of photosynthesis. Both stomatal and non-stomatal factors contributed to the decreased photosynthetic rate, but their proportion changed with time of recovery of the photosynthetic ampparatus. Three hours after the treatment, the stomatal factors predominated in photosynthesis reduction, while during the next experimental period (5–24 h), mainly non-stomatal factors determined the decreased photosynthetic rate. It is suggested that the effects observed in consequence of acid rain treatment could be due to an increased intracellular accumulation of H⁺ and harmful ions contained in the cocktail. This probably led to impaired membrane permeability, enhancement of stroma acidity, uncoupled electron transport and insufficient accumulation of ATP and NADPH, which affected carbon metabolism.