Phenology of roots and mycorrhiza in orchid species differing in phototrophic strategy.

• The mycorrhiza of orchids represents an energy source that may replace or supplement photosynthesis. Dependency on mycotrophy in adult life stages would thus be expected to be inversely related to the prevalence of phototrophic structures. • The phenology of underground parts and mycorrhizal infection were monitored in five terrestrial species differing in leaf phenology (and thus in phototrophic strategy): Goodyera pubescens (evergreen), Tipularia discolor (wintergreen), Galearis spectabilis and Liparis lilifolia (summergreen) and Corallorhiza odontorhiza (chlorophyll deficient), growing sympatrically in a North American deciduous forest. • Mycorrhizal infection was extensive in T. discolor roots and C. odontorhiza rhizomes. Only the proximal part of roots was infected in G. pubescens, and mycorrhizal colonisation was patchy in roots and tubers of G. spectabilis and localized in the rhizome in L. lilifolia. Mycotrophic roots were long-lived (1.5-3 yrs) determinate structures and mycorrhizal infection reached maximum intensity 2-6 months after development. Mycotrophy appeared to be active all year round in mature organs. • The phenology of mycotrophic roots and patterns of mycorrhizal infection were not related to the leafy season. The hypothesis that phototrophic and mycotrophic nutrition alternate through the seasons could not be confirmed.