Physiological and isotopic signals in epilithic mosses for indicating anthropogenic sulfur on the urban–rural scale

The strength and source of anthropogenic sulfur (S) deposition is an important area of research in both environmental and ecological disciplines. Here S concentration, stable isotope (δ34S) and photosynthetic pigments analyses were performed on epilithic mosses at Guiyang area (SW China) for investigating the distribution, origin and effect of urban-derived S at the urban–rural scale. Based on the variation of moss S, anthropogenic S was estimated to account for about 52% of total S in urban mosses and 35% in rural mosses within 30 km. The deposition of urban-derived S was biologically determined within 57 km from the urban center, but only 22% (about 24.4 × 106 kg-S annually) reached over 30 km, with 78% (about 85.9 × 106 kg-S) deposited within 30 km. δ34Smoss signatures suggested the major source of anthropogenic S was still from coal combustion, and comparable δ34Smoss values along the urban–rural transect suggested the inputs of urban-derived S into rural ecosystems. Unexpectedly, moss photosynthetic pigments did not show a decrease with S deposition, but express higher concentrations in the urban than in the rural. In contrast, correlations between moss photosynthetic pigments, and tissue nitrogen (N) and δ15N demonstrated a fertilizing effect of elevated N deposition on moss photosynthesis, which might buffer or offset the negative effect of S deposition on urban mosses. Collective evidences suggest that S% and δ34S in epilithic mosses provided useful information for determining anthropogenic S deposition on the urban–rural scale, but moss photosynthetic pigments may not be applicable for reflecting S loading under high N deposition.