High‐resolution secondary ion mass spectrometry analysis of carbon dynamics in mycorrhizas formed by an obligately myco‐heterotrophic orchid

Mycorrhiza formation represents a significant carbon ( C ) acquisition alternative for orchid species, particularly those that remain achlorophyllous through all life stages. As it is known that orchid mycorrhizas facilitate nutrient transfer (most notably of C ), it has not been resolved if C transfer occurs only after lysis of mycorrhizal structures (fungal pelotons) or also across the mycorrhizal interface of pre‐lysed pelotons. We used high‐resolution secondary ion mass spectrometry ( nanoSIMS ) and labelling with enriched 13 CO 2 to trace C transfers, at subcellular scale, across mycorrhizal interfaces formed by R hizanthella gardneri , an achlorphyllous orchid. Carbon was successfully traced in to the fungal portion of orchid mycorrhizas. However, we did not detect C movement across intact mycorrhizal interfaces up to 216 h post 13 CO 2 labelling. Our findings provide support for the hypothesis that C transfer from the mycorrhizal fungus to orchid, at least for R . gardneri , likely occurs after lysis of the fungal peloton.