Nitrogen and carbon isotope variability in the green-algal lichen Xanthoria parietina and their implications on mycobiont-photobiont interactions.

Andreas Beck,Christoph Mayr

doi:10.1002/ece3.417

Abstract

Stable isotope patterns in lichens are known to vary largely, but effects of substrate on carbon and nitrogen stable isotope signatures of lichens were previously not investigated systematically. N and C contents and stable isotope (δ15N, δ13C) patterns have been measured in 92 lichen specimens of Xanthoria parietina from southern Bavaria growing on different substrates (bark and stone). Photobiont and mycobiont were isolated from selected populations and isotopically analyzed. Molecular investigations of the internal transcribed spacer of the nuclear ribosomal DNA (ITS nrDNA) region have been conducted on a subset of the specimens of X. parietina. Phylogenetic analysis showed no correlation between the symbionts X. parietina and Trebouxia decolorans and the substrate, isotope composition, or geographic origin. Instead specimens grown on organic substrate significantly differ in isotope values from those on minerogenic substrate. This study documents that the lichens growing on bark use additional or different N sources than the lichens growing on stone. δ15N variation of X. parietina apparently is controlled predominantly by the mass fraction of the mycobiont and its nitrogen isotope composition. In contrast with mycobionts, photobionts of X. parietina are much more 15N-depleted and show less isotopic variability than mycobionts, probably indicating a mycobiont-independent nitrogen acquisition by uptake of atmospheric ammonia.

Highlights

Lichen growth is most notable on substrate, where almost no other organisms can grow, due to low or absent water storage in the environment or where some factor like low temperature excludes higher plants (e.g., Garvie et al 2008)
Relation between substrate and stable isotopes and element contents of Xanthoria parietina The isotope values of X. parietina show a large variability ranging from À16.0 to 1.2& for d15N and from À17.0 to À25.3& for d13C (Fig. 2). d13C values separate the lichens from both substrates. d15N values of bark lichens have a very broad range while those of lichens on minerogenic ground cover only part of that range, but do fall completely within values for bark samples, possibly indicating an extra depleted source for bark lichens that is not available to rock lichens
Xanthoria from minerogenic substrates are on average 4.3 and 2.6& enriched in d15N and d13C, respectively, relative to those growing on organic substrates

Summary

Introduction

Lichen growth is most notable on substrate, where almost no other organisms can grow, due to low or absent water storage in the environment or where some factor like low temperature excludes higher plants (e.g., Garvie et al 2008). Lichens colonize nutrientpoor substrates, and especially N-limitation seems to be a considerable limiting factor (Crittenden et al 1994; Nash 2008). The use of stable isotope techniques has become an important tool for ecophysiology and ecosystem research (e.g., Hogberg 1997; Dawson et al 2002; Post 2002), but was comparatively rarely applied to lichens. Krouse (1977) was among the first conducting stable isotope measurements on lichens and elucidated the uptake of atmospheric sulfur emissions using their d34S values. Since d34S values were repeatedly used to study the response of lichens to atmospheric sulfur pollution (e.g., Wiseman and Wadleigh 2002). The d13C and d15N values of lichens were in the focus of comparatively few studies so far. D13C values of lichens were found to vary broadly over a large range of habitats and species (e.g., Batts et al 2004), but d13C values of lichens appeared to be less variable within one lichen species, for example, Usnea antarctica Du

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