Variation in root functional traits of Neotropical epiphytic and terrestrial orchids along an elevational gradient

Assessing variation in root functional traits may offer novel insights into plant adaptations to changing environmental conditions. However, such studies, particularly on epiphytic species in tropical ecosystems, are still limited. Previous research has suggested that precipitation has a major impact on epiphyte survival and thus can be considered a candidate driver of epiphytic root trait variation, though compelling evidence is lacking. In this study, we investigated variation in 19 root functional traits in 43 epiphytic (36 species) and 14 terrestrial (7 species) orchids along an elevational gradient in Colombia and examined whether this variation is associated with differences in abiotic conditions. Contrary to previous studies, our findings did not associate trait variation with precipitation but revealed strong correlations with solar radiation, temperature, and water vapour pressure. The variation was particularly pronounced in traits related to the velamen radicum. Epiphytic and terrestrial orchids showed similar responses despite their different growth habits. Overall, these patterns suggest that higher sunlight and temperature conditions lead both orchid types to allocate more resources to root structures that mitigate abiotic stress, and highlight the role of other environmental factors in driving root trait variability.