Structural differences between aerial and terrestrial roots of 28 <i>Dendrobium</i> germplasms

ABSTRACT Dendrobium , a genus within the Orchidaceae family, encompasses species and cultivars renowned for their ornamental appeal, as well as their notable medicinal and edible properties. During ex situ conservation and domestication efforts, epiphytic Dendrobium plants can develop both aerial and terrestrial roots; however, there is still a lack of studies focusing on these two root types in the process of conservation cultivation. In this study, we examined 28 Dendrobium germplasms, focused on two root regions (the mature zone and the root tip), analysing their aerial and terrestrial root types, and comparing their structural traits and developmental processes. We discovered that terrestrial roots are more costly to develop than aerial roots, with thicker velamen, cortex, and stele. Vessel density and total vessel area varied among species, sometimes being higher in aerial roots and sometimes in terrestrial roots. Furthermore, we observed that a similar correlation exists among the root anatomy of aerial and terrestrial roots. Overall, both aerial and terrestrial types of roots exhibited similar patterns in development, with velamen and stele proportions changing inversely during growth. These findings contribute to our understanding of Dendrobium root systems, aiding their conservation and management.