The response of lichens to changes in isotopic composition and concentration of atmospheric sulphur: a reciprocal transplant experiment

Abstract

Industrial and technological developments of the past 100 years have resulted in significant perturbations to the global sulphur cycle. The use of biomonitors, such as lichens, for quantifying environmental changes has grown in importance over the last decades and offers promising developments for the understanding of global elemental cycles. -- The present study was designed to investigate the response of lichens to changes in atmospheric sulphur conditions, as measured by changes in sulphur isotopic composition and concentration in lichen thalli. A reciprocal transplant of lichen thalli was performed between a "polluted" and "unpolluted" site, with respect to sulphur sources and concentration. Samples were collected monthly for a period of 18 months. -- Multiple regression with periodic functions was used to model the observations. All lichens showed a gradual change in isotopic composition and concentration toward the values at the transplant site, but did not reach local conditions. No long-term trend was discernible for sulphur concentration measurements in lichens transplanted to the polluted site, probably due to a significant increase in sulphur concentrations at that site over the course of the experiment. Seasonal trends were identified at both sites, and at the polluted site appeared to be closely related to anthropogenic sulphur emission patterns. Some sources of seasonal variation at the unpolluted site were unidentifiable, but influences from anthropogenic sources were identified, and influences from biogenic sources suggested. The mechanics of relocation did not affect lichen responses. It is likely that distinguishing between the organic and inorganic fractions of sulphur would have helped in interpreting results.