The potential use of elemental content of saxicolous lichens as bioindicators of nitrogen deposition in the central and southern California mountains

Abstract

High elevation and arid wilderness areas generally lack epiphytic lichen species used for air quality biomonitoring. We assessed the potential of saxicolous lichens to serve as bioindicators of nitrogen (N) and sulfur (S) deposition by examining relationships among deposition, environmental variables, and elemental concentrations in the saxicolous lichens Umbilicaria phaea (n = 51), Rhizoplaca melanophthalma (n = 20), and the epiphytic lichen Letharia vulpina (n = 16) in the southern Sierra Nevada (SN) and San Bernardino Mountains (SBM) of California, USA. Lichen samples were collected between 2013 and 2019 in 31 plots between 180 and 3330 m elevation. These samples were analyzed for concentrations of 23 elements, including N and S. Signal-to-noise ratios were high comparing the variation among plots to within plots and within samples for N and S concentrations of the Umbilicaria phaea samples. While Umbilicaria phaea N and S concentrations were correlated with modeled N and S deposition estimates, Rhizoplaca melanophthalma and Letharia vulpina N and S concentrations were not. Subsequent principal components analysis and cluster analysis of the Umbilicaria phaea dataset revealed differences in elemental profiles between the SN and SBM, with the SBM samples having higher concentrations of most elements, including heavy metals. Additionally, the first two principal components explained most of the variation (61 %) in elemental content and had strong relationships to latitude, longitude, N and S deposition, and precipitation. We conclude that the elemental profile of Umbilicaria could be used to assess N and S deposition for areas in the western USA that lack suitable epiphytic lichen species.