Growth Response and Drought Susceptibility of Red Spruce Seedlings Exposed to Simulated Acidic Rain and Ozone

Abstract

Abstract One-year-old seedlings of red spruce were exposed to O3 (≤0.025 or 0.10 μl 1-1, 4 h d-1, 3 d wk-1) in combination with simulated rain (pH 5.6 or 3.0, 1 h d-1, 2 d wk-1, 0.75 cm h-1) for 10 weeks. After pollutant treatments, seedlings were subjected to two successive drought cycles. Whole-plant fresh weight increment (FWT) and dry weight were reduced after O3 exposure, whereas FWT and shoot height growth were increased after simulated rain exposure at pH 3.0 compared to pH 5.6. No interaction between O3 and rain treatments was observed for any growth variable measured. Foliar concentrations of K and S were greater in seedlings exposed to simulated rain at pH 3.0 compared with those at pH 5.6. Root hydraulic conductivity was highest in seedlings exposed to 0.10 μl 1-1 O3 + pH 3.0 rain solution compared with all other treatments after the first drought cycle. There were no significant O3 effects on net photosynthesis (Pn), transpiration or water-use efficiency prior to the drought cycles. However, during the second drought cycle, Pn was more sensitive to branch water potential in seedlings exposed to 0.10 μl 1-1 O3 + pH 3.0 solution compared with seedlings exposed to low O3 + pH 5.6 solution. For. Sci. 36(2):265-275.