The ectomycorrhizal status of Calostoma cinnabarinum determined using isotopic, molecular, and morphological methods

Calostoma cinnabarinum Corda belongs to the suborder Sclerodermatineae (Boletales), which includes many well-known ectomycorrhizal basidiomycetes, but the genus Calostoma has been described as saprotrophic. This study combines isotopic, molecular, and morphological techniques to determine the mode of nutrition of C. cinnabarinum. δ13C and δ15N measurements were compared among co-occurring C. cinnabarinum, ectomycorrhizal fungi, saprotrophic fungi, and ectomycorrhizal plants. Isotopic profiles of C. cinnabarinum resembled those of ectomycorrhizal fungi but not those of saprotrophic fungi. For molecular analyses, ectomycorrhizal root tips were extracted from soil cores collected beneath C. cinnabarinum fruit bodies. Nuclear ribosomal internal transcribed spacer (nrITS) sequences were obtained from ectomycorrhizal root tips using fungal-specific primers and screened against C. cinnabarinum nrITS sequences. Ectomycorrhizal root tips had nrITS sequences that matched C. cinnabarinum fruiting bodies. Root tips colonized by C. cinnabarinum were also described morphologically. Several morphological characters were shared between fruiting bodies and ectomycorrhizal root tips of C. cinnabarinum. Results of isotopic, molecular, and morphological analyses indicate that C. cinnabarinum is ectomycorrhizal. Molecular analysis and observations of plant associations suggest that C. cinnabarinum forms ectomycorrhizae with Quercus .