Mycorrhizal colonization patterns of three Bletia species in a natural forest reserve in Michoacán, Mexico.

Mexico is the diversity center of the subtribe Bletinnae, resulting in a great richness of species in this territory. While the country possesses a great taxonomic knowledge of its orchid flora, little is known about the interactions with their mycorrhizal fungi. The present work aimed generating a description of the mycorrhization patterns in the mature roots of three terrestrial orchids of the Bletia genus: B. roezlii, B. punctata and B. purpurata. The mycorrhiza characterization was performed on several roots collected, and they were evaluated on several disturbance and site quality sites in a Pinus forest at the Natural Reserve Barranca del Cupatitzio located in the Michoacan State. The mycorrhizal intensity and extension were recorded during the plant flowering season (July to November 2008). A high heterogeneity among the intensity and extension of mycorrhization was recorded for both intra- and interspecies. However, these variables had different values as responses of the species to habitat transformation. A major proportion of partially digested pelotons were found in all of the segments, showing active nourishment by the orchids during the flowering period. The orchid B. roezlii was significantly more colonized and showed no differences in mycorrhizal intensity or extension that could be related to perturbation or site quality. For B. purpurata, the highest mycorrhizal colonization was observed at conserved sites, and for B. punctata, a significantly lower colonization at the more perturbed site also was found. Surprisingly, root length was significantly different among sites for all species. Differences were attributed to root enlargement to acquire more minerals as a consequence of reduced mycotrophy, leading to a major distribution of carbon to the roots as a result of an increase in light availability. It is possible that mycorrhizal colonization plays a role in the abundance and persistence of orchid habitat transformation. However, more in depth studies on mycorrhizal phenology, associated endophytes and soil nutrients are needed to better understand orchid sensitivity to disturbances and their vulnerability to habitat transformation.