Phalaenopsis can absorb urea directly through their roots

Phalaenopsis cultivars are epiphytic orchid plants with high economic value, largely produced across the world as potted plants or cut flowers. The goal of this experiment is to show if aseptic (in vitro) Phalaenopsis plants can absorb urea with their roots. Young in vitro Phalaenopsis plants were transferred aseptically to a growth medium (solid or liquid) where the three forms of nitrogen (nitrate, ammonium and urea) are equally present and where only one form at a time is marked with (15)N. The (15)N analysis of the younger leaves of each plant shows that urea and ammonium are the two preferred forms of nitrogen absorbed, with respectively 47% and 41% of the total amount, while nitrate is only absorbed to a level of 12%. The medium analysis revealed that no urea hydrolysis occurred before root absorption. Phalaenopsis roots, probably because of the special nature of velamen, can absorb large amounts of nitrogen directly in urea form. This experiment suggests that the medium of Phalaenopsis in vitro plants could advantageously contain a large proportion of nitrogen in urea form, and that this concept could probably be applied to fertilizer solutions used in growing Phalaenopsis pot plants and other orchids species.