The effect of HNO₃ gas on the lichen Ramalina menziesii.
Authors:
Riddell, J. Nash, T.H. III Padgett, P. USDA, FS
Source:
Flora. 2008, v. 203, no. 1, p. 47-54.
NALT Subjects:
air pollution gases lichens nitric acid Lecanorales atmospheric deposition plant response forests population size nitrates environmental indicators indicator species pollutants nitrogen duration leachates potassium fumigation elevated atmospheric gases chlorophyll carbon summer urban areas California
Other Subjects:
Ramalina menziesii
Issue Date:
2008
Abstract:
Nitric acid (HNO₃) and ozone (O₃), secondary products of photochemical reactions of nitrogen oxides (NO(x)) and volatile organic compounds, are important pollutants in arid regions with large outputs from petrol combustion. In the Los Angeles (LA) air basin, nitrogen dry deposition rates in forests downwind of the urban areas can reach 35-40 kg ha-1 year-1, roughly equivalent to the amount of N used to fertilize agricultural fields. The marked decline in the lichen population of the LA air basin has previously been attributed to local O₃ concentration gradients, which overlaid the patterns of species extirpation. Recent research in the air basin has shown that nitrate (NO₃⁻) deposition gradients run parallel to the O₃ concentration gradient, and that deposition of NO₃⁻ and HNO₃ can have significant effects on forest health. Our research examines the effects of HNO₃ dry deposition on the lichen Ramalina menziesii Tayl. in an effort to understand the loss of lichen species in southern California, and increase the usefulness of lichens as biomonitors of nitrogen pollutants. We transplanted healthy R. menziesii thalli from a “pristine” location into fumigation chambers and exposed them to HNO₃ under humid and dry conditions, and moderate and high HNO₃ fumigations. R. menziesii thalli treated with HNO₃ in month-long fumigations experienced a significant decline in chlorophyll content and carbon exchange capacity compared to thalli in control chambers. Leachate conductivity, NO₃⁻ and K⁺ concentrations increased with HNO₃ fumigation levels and time. We conclude that R. menziesii has an unequivocally negative response to HNO₃ gas concentrations common to ambient summer conditions in the LA air basin.
