Temporal variation in mycorrhizal diversity and C and N stable isotope abundance in the winter-green meadow orchid Anacamptis morio

• Many adult orchids, especially photoautotrophic species, associate with a diverse range of mycorrhizal fungi, but little is known of the temporal changes that may occur in the diversity and functioning of orchid mycorrhiza during vegetative and reproductive plant growth. • Temporal variations in the spectrum of mycorrhizal fungi and in stable isotope natural abundance were investigated in adult plants of Anacamptis morio, a wintergreen meadow orchid. • Anacamptis morio associated with mycorrhizal fungi belonging to Tulasnella, Ceratobasidium and a clade of Pezizaceae (Ascomycetes). When a complete growing season was investigated, multivariate analyses indicated significant differences in the mycorrhizal fungal community. Among fungi identified from manually isolated pelotons, Tulasnella was more common in autumn and winter, the pezizacean clade was very frequent in spring and Ceratobasidium was more frequent in summer. By contrast, relatively small variations were found in C and N stable isotope natural abundance, A. morio samples showing similar 15N enrichment and 13C depletion at the different sampling times. • These observations suggest that, irrespective of differences in the seasonal environmental conditions, the plant phenological stages and the associated fungi, the isotopic content in mycorrhizal A. morio remains fairly constant over time.