Nutrient acquisition of an underground and mycoheterotrophic orchid

Background and Aims Most species of orchids become autotrophic after the formation of the first leaf develops; however, some mycoheterotrophic species remain achlorophyllous at maturity and non-photosynthetic throughout their entire life cycles, depending on fungal associations for survival. However, the mechanisms governing carbon and nitrogen exchange between mycoheterotrophic plants and their associated fungi remain largely unexplored in neotropical regions. Studies with mycoheterotrophic orchids from tropical regions and different subfamilies contribute to a better understanding of the nutrition mode of these plants, and allow evaluation of the role that morphological and anatomical characteristics play in the mycoheterotrophic way of life. Methods Samples of different individuals of Pogoniopsis schenckii were fixed and subjected to standard anatomical techniques for light microscopy, histochemical tests, transmission and scanning electron microscopy and stable isotope analysis. Key Results P. schenckii exhibits two distinct root types: one with acute apex and another with a rounded apex. Fungal hyphae were found in all roots but were not organized into typical pelotons; instead, they were distributed throughout the epidermis and cortex, including within cells associated with starch storage. Our isotopic results suggest that P. schenckii acquires carbon and nitrogen through its symbiotic fungi from the soil. Conclusions The root system of P. schenckii exhibits two root morphotypes that differ in size, apex shape, and anatomy. The observed patterns of 13C and 15N abundances in P. schenckii suggest that this mycoheterotrophic orchid is associated with ectomycorrhizal fungi. Additionally, we described two trends in the degradation of the semi-coiled hyphae found within the epidermal and cortical cells of the two root morphotypes of this mycoheterotrophic species.