Photosynthetic Use Efficiency of Macroelements, Water, and Light by Lactuca sativa (L.) under Contamination of Soil with Lead

The effect of soil contamination with lead (50 and 250 mg Pb²⁺ per 1 kg of dry soil weight) on the rate of photosynthetic assimilation of CO₂ (A_n), the content of major macronutrients in leaves, photosynthetic use efficiency of nitrogen (PNUE), phosphorus (PPUE), potassium (PKUE), water (PWUE), and light (α) in lettuce plants of the variety Medvezhye Ushko was studied under controlled environmental conditions. A negative effect of the metal ion on photosynthetic rate A_n was revealed, which was associated with the decreases in chlorophyll content, PNUE, PPUE, PKUE, and the α value. The quantum efficiency of PSII reaction (F_v/F_m) decreased but still remained within the range typical of photosystem normal functioning. No pronounced influence of lead on the content of macronutrients in plant leaves was found. In Pb-treated plants, the decrease in PNUE, PPUE, and PKUE was accompanied by the increase in leaf mass to leaf area ratio, which reflects close structural and functional relationships during plant adaptation to stressful conditions of heavy-metal soil pollution. It was shown that lead, even in the highest concentration applied (250 mg/kg soil), affected neither the transpiration rate nor the photosynthetic water use efficiency in plants.