Effects of acidic rain and ozone on nitrogen fixation and photosynthesis in the lichen Lobaria pulmonaria (L.) Hoffm.

Abstract

The lichen Lobaria pulmonaria was subjected to ozone fumigations at 118, 235 and 353 μg/m 3 and simulated acidic rain at pH levels of 2.6, 4.2 and 5.6 for 5 days (M, W, F, M, W) during a 10-day period. Acidic rain at pH 2.6 caused significant reductions in nitrogen fixation and gross photosynthesis of 100 and 90%, respectively, and thallus bleaching was apparent. There were no significant differences between the pH 5.6 and 4.2 treatments in either gross photosynthesis or nitrogen fixation, and the color of the lichen thalli was unchanged. The effect of O 3 on nitrogen fixation and photosynthesis over the range of concentrations used was not significant, but there was a trend toward reduced nitrogen fixation with increasing O 3 concentration. There were no significant O 3-acidic rain interactions. The threshold for response to rain acidity for L. pulmonaria lies between pH 2.6 and 4.2, and the acidity of wet deposition in parts of the United States may fall in this range.