Germination niches and seed persistence of tropical epiphytic orchids in an urban landscape.

Urbanisation has contributed to significant biodiversity loss, yet, urban areas can facilitate biodiversity conservation. For instance, there is evidence of urban trees supporting natural establishments of orchids, the most species-rich plant family on Earth. However, the germination niches-which include both suitable biophysical conditions and orchid mycorrhizal fungus/fungi (OMF)-are not sufficiently known for most species, especially tropical epiphytic orchids. The fate of their dispersed seeds is poorly understood as well. We conducted fungal baiting and seed sowing experiments, next-generation sequencing, generalised linear models, and seed viability tests to detect and identify potential OMF, investigate biophysical factors that influenced OMF availability and orchid germination, and assess seed longevity. Ceratobasidiaceae- and Serendipitaceae-associated OMF were successfully detected in three of four orchid species. In general, orchid species and humus presence had significant effects on OMF availability. Orchid species and temperature were predictive of germination. Post-experiment viability tests revealed that one orchid species, Grammatophyllum speciosum Blume, may produce long-lived seeds. The results suggest that urban trees can support OMF and orchid germination, but both processes are limited by biophysical factors. This study also indicates the possibility of seed persistence among epiphytic species. As orchid germination niches are complex and tend to be unique to individual species, we do not encourage generalisations. In contrast, species-specific information can help formulate useful recommendations towards conservation.