Impact of Nitrate and Ammonium ratio on Nutrition and Growth of two Epiphytic Orchids

Abstract Phalaenopsis and Dendrobium do not grow and flower well with 100% ammonium (NH4-N); and there are detailed studies on the effects of nitrate (NO3-N) and ammonium ratios on the flowering, but no information about accumulation of other nutrients and the effects of ammonium toxicity on orchids. For this reason, two experiments were carried out with orchids: Phalaenopsis ‘Golden Peoker’ and Dendrobium ‘Valentine’. Six months after acclimatization the plants were transplanted to individual plastic vessels and the treatments consisted of five ratios (%) of nitrate / ammonium (0/100, 25/75, 50/50, 75/25, 100/0). The sources of NO3-N and NH4-N were calcium nitrate and ammonium sulfate, respectively. After 12 months treatment, when the plants were beginning to issuance of flower stem, the accumulation of: N, P, K, Ca and Mg in the shoot and biometric variables were evaluated for both species. The NH4-N ratio of 40% and 50% of the total nitrogen benefited the growth of Phalaenopsis and Dendrobium, respectively. The application of higher proportions of ammonium resulted in decreased N, K, Ca and Mg absorption, index of green color and increased leakage of electrolytes in Phalaenopsis and Dendrobium. NH4-N proportions greater than 75% for 12 months caused toxicity in Phalaenopsis and Dendrobium.

摘要：蝴蝶兰（Phalaenopsis）与石斛兰（Dendrobium）在完全以铵态氮（ammonium, NH4-N）为唯一氮源时，生长与开花表现均不佳；目前已有诸多关于硝态氮（nitrate, NO3-N）与铵态氮配比对开花影响的详细研究，但尚未见关于其他养分累积情况以及铵态氮毒性对兰花影响的相关报道。为此，本研究以蝴蝶兰‘Golden Peoker’与石斛兰‘Valentine’为试材开展试验。植株驯化6个月后，被移栽至单独塑料容器中，试验设置5组硝态氮/铵态氮配比（%）处理：0/100、25/75、50/50、75/25、100/0。试验所用硝态氮与铵态氮的氮源分别为硝酸钙与硫酸铵。处理12个月后，待植株开始抽生花茎时，测定两个品种地上部的氮（N）、磷（P）、钾（K）、钙（Ca）与镁（Mg）累积量，并评估其生物性状指标。结果显示，铵态氮占总氮比例为40%时最利于蝴蝶兰生长，占比50%时最利于石斛兰生长。较高比例的铵态氮施用会降低蝴蝶兰与石斛兰对氮、钾、钙、镁的吸收量，降低其绿度指数，并增加电解质渗漏率。连续12个月施用占比超过75%的铵态氮，会导致蝴蝶兰与石斛兰出现铵态氮中毒症状。