Nitrogen and carbon stable isotope abundances support the myco-heterotrophic nature and host-specificity of certain achlorophyllous plants

Over 400 species of achlorophyllous vascular plants are thought to obtain all C from symbiotic fungi. Consequently, they are termed 'myco-heterotrophic.' However, direct evidence of myco-heterotrophy in these plants is limited. During an investigation of the patterns of N and C stable isotopes of various ecosystem pools in two old-growth conifer forests, we sampled six species of mycoheterotrophic achlorophyllous plants to determine the ability of stable isotope ratios to provide evidence of myco-heterotrophy and host-specificity within these symbioses. Dual-isotope signatures of the myco-heterotrophic plants differed from those of all other pools. They were most similar to the signatures of ectomycorrhizal fungi, and least like those of green plants. delta(15)N values of the myco-heterotrophic plants correlated strongly and positively with those of putative mycobionts. Used in conjunction with other techniques, N and C stable isotope ratios can be used to demonstrate myco-heterotrophy and host-specificity in these plants when other ecosystem pools are well characterized. They also appear promising for estimating the degree of heterotrophy in photosynthetic, partially myco-heterotrophic plants.