Photosynthesis and Growth Response of Red Spruce and Loblolly Pine to Soil-Applied Lead and Simulated Acid Rain

Abstract

Abstract Soils from red spruce (Picea rubens Sarg.) and loblolly pine (Pinus taeda L.) stands were amended with either 0, 150, 300, 600 or 1200 mg/kg Pb as PbCl2. Six-month-old spruce and six-week-old pine seedlings were planted in their respective native soils and treated for 19 weeks with simulated rain of either pH 4.5 or 3.0. Rain was applied directly to the soil at a rate of 1.5 cm per week. Net photosynthesis, height, and needle, shoot, and root dry weights were measured at the completion of the experiment. In both soils, pH decreased and nitrate concentration increased with the application of a simulated rain solution of pH 3.0. Despite these changes in soil chemistry, simulated rain pH had no significant effect on the growth of either species. Red spruce photosynthesis was 35% higher; however, at a pH of 3.0. Loblolly pine photosynthesis was not affected by solution pH. Growth and photosynthesis of red spruce were inhibited even at the 150 mg/kg Pb level, with additional Pb resulting in increasing inhibition. Growth of loblolly pine seedlings was less sensitive to Pb, and decreased only at the higher concentrations. Loblolly pine photosynthesis exhibited no decline even at the highest Pb level. These results suggest that both red spruce and loblolly pine are more sensitive to soil Pb than to acid precipitation. In addition, loblolly pine appears to be more tolerant of Pb than red spruce, when both species are grown in their respective native soils. For. Sci. 33(3):668-675.