Complementary water and nutrient utilization of perianth structural units help maintain long floral lifespan in Dendrobium

Most orchids have high ornamental value with long-lived flower. However, the mechanisms by which orchids maintain floral longevity are poorly understood. Here, we hypothesized that long floral longevity in Dendrobium is maintained by high resource investment and complementary water and nutrient utilization in different structural units of the perianth. To test this hypothesis, we determined which water- and nutrient-related traits are correlated with flower longevity in twenty-three Dendrobium species or cultivars and examined the variations of the related traits during flower development of one long-lived cultivar. We found that floral longevity was correlated with dry mas per unit area of perianths and total flower biomass, which indicates that maintaining long floral longevity requires increased resource investment. During development of long-lived flowers, labella showed high capacity for water storage and nutrient reutilization, which can partly remedy high water demand and biomass investment. Sepals and petals, in contrast, had stronger desiccation avoidance and higher metabolic activity with lower biomass investment. These findings indicate that Dendrobium flowers maintain longevity by complementary water and utilization strategies in the sepals, petals and labella, with labella consuming more water and nutrients to extend flower display, while sepals and petals use a more conservative strategy.