Species level patterns in ¹³C and ¹⁵N abundance of ectomycorrhizal and saprotrophic fungal sporocarps

Abstract

Abstract• The natural abundance of 13 C ( δ 13 C) and 15 N ( δ 15 N) of saprotrophic and ectomycorrhizal (ECM) fungi has been investigated on a number of occasions, but the significance of observed differences within and between the two trophic groups remains unclear.• Here, we examine the influence of taxonomy, site, host and time upon isotopic data from 135 fungal species collected at two forest sites in Sweden.• Mean δ 13 C and δ 15 N values differed significantly between ECM and saprotrophic fungi, with only a small degree of overlap even at the species level. Among ECM fungi, intraspecific variation in δ 15 N was low compared with interspecific and intergeneric variation. Significant variation due to site, year and host association was found.• At broad scales a number of factors clearly influence δ 13 C and δ 15 N values making interpretation problematic. We suggest that values are essentially site-specific within the two trophic groups, but that species-level patterns exist potentially reflecting ecophysiological attributes of species. The species is therefore highlighted as the taxonomic level at which most information may be obtained from fungal δ 13 C and δ 15 N data.

Stratégie saprophyte ou symbiotique durant le développement d’ascocarpes de truffes dans une truffière à chêne vert. Une réponse basée sur l’abondance naturelle du 13C et du 15N

“…For example, I. fastigiata displayed a low nitrogen natural abundance (δ 15 N of 2.0% ), while A. strobiliformis displayed a high natural abundance (δ 15 N of 13.5% ). These results are congruent with those of several research teams (Gebauer and Dietrich, 1993, Henn and Chapela, 2001Kohzu et al, 1999;Taylor et al, 2003;Trudell et al, 2004;Zeller et al, 2007) who all observed high 15 N abundance in ectomycorrhizal fungi sporophores. The three Tuber species displayed a high δ 15 N value (9.3 to 10.4% ).…”

“…As reported by several authors (Gebauer and Taylor, 1999;Henn and Chapela, 2001;Hobbie et al, 1999Hobbie et al, , 2001Högberg, 1997;Kohzu et al, 1999;Taylor et al, 2003, Trudell et al, 2004Zeller et al, 2007), δ 13 C values differed between sporophores of saprotrophic and ectomycorrhizal fungi. Sporophores of the two saprotrophic fungi from the Châteauvert site showed a 13 C enrichment compared to their substrates.…”

“…Fungal sheaths were 2.4 to 6.4% enriched compared to the root core. Other studies have confirmed that sporophores of ectomycorrhizal fungi are often more enriched in 15 N than sporophores of saprotrophic fungi, whereas sporophores of saprotrophic fungi are almost always enriched in 13 C compared to sporophores of ectomycorrhizal fungi (Hobbie et al, 1999;2002;Kohzu et al, 1999;2000;Taylor et al, 2003;Trudell et al, 2004). Lilleskov et al (2002) demonstrated that isotope signatures reflect ecophysiological functions.…”

“…Although the relative contribution of the C and N sources and the different internal processes involved in the fractionation of 13 C and 15 N remain unclear, it appears that the analysis of natural abundance of C and N isotopes could provide insight into the respective trophic roles of saprotrophic versus ectomycorrhizal fungi (Gebauer and Taylor, 1999;2005;Högberg et al, 1996;Kohzu et al, 1999;Taylor et al, 2003;Trudell et al, 2004;Zeller et al, 2007).…”

Stable isotope evidence for the saprotropic status of the truffle Schenella pityophilus

“…Stable isotope ratios of N and C differ between ectomycorrhizal and saprotrophic fungi with the general trend showing mycorrhizal fungi enriched in 15 N and depleted in 13 C relative to saprotrophic fungi (Hobbie et al 1999;Högberg et al 1999;Hobbie et al 2001;Hobbie & Horton 2007;Whitridge & Southworth 2005;Hobbie and Högberg 2012). Surveys comparing the isotope ratios of saprotrophic and mycorrhizal fungi at particular sites have focused on epigeous fungi with a low fraction of hypogeous species, i.e., 0/45 (Hobbie et al 2001); 1/135 (Högberg et al 1999;Taylor et al 2003); 1/34 (Hobbie and Agerer 2010) and 0/152 species (Trudell et al 2004). While trophic status might determine the C and N isotopic ratios of both epi-and hypogeous fungi, other factors such as differences in outgassing of volatile compounds, in biomass and nitrogen composition, and in exploration types support the importance of determining isotope ratios for hypogeous fungi (Hobbie and Agerer 2010;D'Auria et al 2013).…”