Isotopic evidence of full and partial myco-heterotrophy in the plant tribe Pyroleae (Ericaceae).

Botanists and mycologists have long debated the potential for full myco-heterotrophy in the achlorophyllous Pyrola aphylla (Ericaceae). Here we address the ecophysiology of this putative myco-heterotroph and two other closely related green species in the tribe Pyroleae (Pyrola picta and Chimaphila umbellata). The stable isotopes of carbon and nitrogen (delta13C and delta15N) were analysed from 10 populations of Pyroleae species in California and Oregon, USA. For all populations isotope signatures were tested for significant differences between P. aphylla, green pyroloids, surrounding autotrophs and obligate myco-heterotrophs. Throughout all populations P. aphylla was most similar to myco-heterotrophs that associate with ectomycorrhizal fungi in its 13C signature (average enrichment epsilon13C = 6.9 +/- 0.9 per thousand) and even more enriched in 15N than many previously recorded myco-heterotrophic species (average enrichment epsilon15N = 18.0 +/- 2.2 per thousand). The two green Pyroleae species were not enriched in 13C compared with the autotrophic understory (C. umbellata average enrichment epsilon13C = -0.5 +/- 1.0 per thousand and P. picta average epsilon13C = 0.3 +/- 1.4 per thousand) and their 15N signatures were similar to myco-heterotrophs that associate with ectomycorrhizal fungi (C. umbellata average enrichment epsilon15N = 10.6 +/- 1.6 per thousand and P. picta average epsilon15N = 10.6 +/- 1.9 per thousand). This is the first study to analyse the isotope signatures of P. aphylla from a wide geographic region and our results confirm the variable trophic strategies of adult plants within the Pyroleae and the myco-heterotrophic status of P. aphylla.