Elucidating the nutritional dynamics of fungi using stable isotopes

Abstract

Mycorrhizal and saprotrophic (SAP) fungi are essential to terrestrial element cycling due to their uptake of mineral nutrients and decomposition of detritus. Linking these ecological roles to specific fungi is necessary to improve our understanding of global nutrient cycling, fungal ecophysiology, and forest ecology. Using discriminant analyses of nitrogen (delta(15)N) and carbon (delta(13)C) isotope values from 813 fungi across 23 sites, we verified collector-based categorizations as either ectomycorrhizal (ECM) or SAP in > 91% of the fungi, and provided probabilistic assignments for an additional 27 fungi of unknown ecological role. As sites ranged from boreal tundra to tropical rainforest, we were able to show that fungal delta(13)C (26 sites) and delta(15)N (32 sites) values could be predicted by climate or latitude as previously shown in plant and soil analyses. Fungal delta(13)C values are likely reflecting differences in C-source between ECM and SAP fungi, whereas (15)N enrichment of ECM fungi relative to SAP fungi suggests that ECM fungi are consistently delivering (15)N depleted N to host trees across a range of ecosystem types.

Carbon and Nitrogen Metabolism in Mycorrhizal Networks and Mycoheterotrophic Plants of Tropical Forests: A Stable Isotope Analysis

“…1, A and D). Even if considerable variation may occur depending on the N source (Gebauer and Taylor, 1999), this contrasted with the 15 N enrichment usually reported in ectomycorrhizal fungi (Hobbie et al, 2001;Mayor et al, 2009). AMF were enriched in 15 N as compared with tree mycorrhizal roots (+3.01‰ on average) and all green leaves (+1.02‰), but often not significantly (Fig.…”

“…Third, stable isotope abundances were used as a major indicator to indirectly support the role of ectomycorrhizal fungi as a food source (Gebauer and Meyer, 2003). Compared with their host trees, ectomycorrhizal fungi are enriched in 13 C and 15 N (Gebauer and Dietrich, 1993;Hobbie et al, 2001;Mayor et al, 2009). In contrast, transfer from fungi to MH plants does not modify 13 C and 15 N abundances (or only slightly increases 15 N abundance; Trudell et al, 2003).…”

Detecting intraannual dietary variability in wild mountain gorillas by stable isotope analysis of feces

“…While represented by only a single sample, the very positive δ 13 C value of fungus falls within the range of previously reported saprotrophic fungi δ 13 C values and is more positive than cultivated representatives of the genus by only 1-2‰ (72,73). Isotopic variability among gorilla foods suggests it may be possible to detect similar source separation among the diets of other primates and forest-dwelling mammals.…”

Species-dependent partitioning of C and N stable isotopes between arbuscular mycorrhizal fungi and their C3 and C4 hosts

“…Moreover, in leek treatments, AMF spores were not always 13 C-enriched as compared with host shoots. Similarly, ECM fungi sometime fail to modify plant d 13 C after inoculation (Handley et al, 1993), although they derive more photosynthates from hosts than AMF (Bryla and Eissenstat, 2005;Smith and Read, 2008) and are considerably more 13 C-enriched (Mayor et al, 2009;Hobbie et al, 2012). This suggests that in both AMF and ECM symbioses, C partitioning between the fungus and the plant does not directly (or solely) explain how mycorrhizal inoculation changes plant d 13 C.…”