Mycorrhizal association impacts fitness of epiphytic orchids in situ

The evolutionary association between mycorrhizae and plants has a long history, with effects on plant development that can be positive, negative, or neutral. In the case of some epiphytes, such as certain orchids, the interaction with mycorrhizal fungi is essential for seed germination, as these seeds rely on nutrients provided by the fungi. During the early developmental stages (protocorms and seedlings), this association is obligate. Although it has been suggested that the relationship remains important in later stages, substantial evidence is still lacking. Understanding this relationship is crucial to determine how mycorrhizae contribute to plant growth, reproduction, and survival under natural environmental conditions. The objective of this study was to determine the interaction between the degree of mycorrhizal colonization, the functional state of the pelotons (mycorrhizal colonization structures in the roots) and abiotic factors with reproductive success, seed viability, plant development, and survival of in situ Rhynchostele cervantesii across different developmental stages as a model system, thereby exploring the significance of this orchid-mycorrhizal association in post-germination stages. Mycorrhization was assessed in 100 plants (50 adults and 50 juveniles) during both the wet (WS) and dry (DS) seasons over 2 years by surveying peloton presence and density in the roots. We evaluated the correlations between peloton density and functional state (intact or digested), abiotic factors (light, relative humidity, and temperature) and the development of both juvenile and adult individuals of R. cervantesii under natural conditions. The relationship between mycorrhization with reproductive success, seed viability, plant growth, size, and survival were also evaluated. Plants with higher peloton densities exhibited increased seed viability, growth, and survival, particularly in juvenile individuals. Temperature negatively affected plant development, while relative humidity had a positive influence across both life stages. Juvenile plants showed stronger dependence on mycorrhizal interactions than adults. Mycorrhizal fungi play a vital role in promoting seed viability, growth, and survival of R. cervantesii in situ . Both biotic and abiotic factors shape the life cycle of epiphytic orchids, and conservation and management strategies should account for ontogenetic variation in mycorrhizal dependence, environmental sensitivity, and particularly early-stage vulnerability under changing climatic conditions.