This study presents novel evidence that 15N natural abundance can be used as a robust indicator to detect pollutant nitrogen in natural plant communities. Vegetation from the heavily polluted industrial area of Cubatão in São Paulo State, SE Brazil, was strongly 15N depleted compared to plants at remote sites. Historic herbarium samples from Cubatão were significantly less 15N depleted than extant plants, indicating that 15N depletion of vegetation is associated with present-day nitrogen pollution in Cubatão. The heavy load of nitrogenous atmospheric pollutants in Cubatão provides a nitrogen source for plants, and strongly 15N depleted air NH3 is likely to contribute to plant and soil 15N depletion. Epiphytic plants from Cubatão were extremely 15N depleted (average -10.9‰) contrasting with epiphytes at remote sites (averages -1.0‰ and -3.0‰). Nitrogen isotope composition of vegetation provides a tool to determine input of pollutant nitrogen into plant communities. The strong isotopic change of epiphytes suggests that epiphytes are particularly sensitive biomonitors for atmospheric pollutant nitrogen.
Keywords: 15N natural abundance; Atlantic rain forest; Epiphytes; Historic samples; Nitrogen pollution.