Effects of Ammonium to Nitrate Ratio in Culture Medium on Growth and Nutrient Absorption of Phalaenopsis Seedlings in Vitro

Abstract

The effects of NH₄⁺ : NO₃^- in culture medium on growth and nutrient absorption of Phalaenopsis seedlings in vitro were investigated. Leaf number decreased at 8 : 2 and 10: 0 of NH₄⁺ : NO₃^- (N ratio), and leaf area increased at 0 : 10 and 2 : 8 N ratios. Root number and root length were linearly decreased with increasing NH₄⁺ ratio. Consequently, possibility to control root growth by incubating on the medium with 2 : 8 N ratio without suppression of leaf growth was indicated. Although nitrogen absorption was not affected by N ratios between 0 : 10 and 4 : 6, P, K, Ca, and Mg absorption were remarkably decreased with increasing NH₄⁺ ratio. NH₄⁺ antagonistically inhibited Ca and Mg absorption. Thus, growth and nutrient absorption of Phalaenopsis seedling in vitro were promoted by incubating in culture medium containing NO₃^- as sole nitrogen source.