種植蝴蝶蘭之水苔介質酸化現象之研究

Abstract

台灣栽培蝴蝶蘭(Phalaenopsis spp.)之介質以水苔為主。隨著種植蝴蝶蘭的時間增長，水苔介質pH値逐漸下降，而造成此酸化現象的原因至今仍尚未釐清。介質pH值的變化會改變根域礦物元素有效性，導致植物營養缺乏或毒害，降低栽培品質。本論文探討造成介質酸化的原因，並嘗試瞭解介質酸化現象是否與蝴蝶蘭偏好的生長pH值範圍有關，進一步分析蝴蝶蘭的根部分泌物，以釐清介質酸化的肇因。 本研究以大白花蝴蝶蘭(Phal. Sogo Yukidian ‘V3’)為材料，分別對介質特性、肥料施用或植物本身等可能肇因進行試驗。結果顯示雖然施用肥料濃度增加，會降低介質的初始pH值，但施肥不是造成水苔介質持續酸化的主要原因。因為不論有無施肥，未種植蝴蝶蘭的水苔介質pH值皆隨時間增加而上升，而有種植蝴蝶蘭者之水苔介質pH值皆會下降。以不同介質栽培蝴蝶蘭，雖各種介質之pH值變化程度和過程不同，但pH値均呈下降的趨勢。綜合上述，蝴蝶蘭根部是造成水草介質持續酸化的主要原因。此外，雖然提高環境溫度可增進蝴蝶蘭營養生長，水苔照光處理可提升蝴蝶蘭根部品質，但兩者皆不會改變介質酸化趨勢。 為瞭解蝴蝶蘭是否偏好較低的pH值範圍而造成介質酸化，本試驗分別以水苔和養液淹灌栽培方式進行試驗，探求蝴蝶蘭偏好的生長pH範圍。水苔以較高濃度石灰水(12和24 g•L-1)處理者，蝴蝶蘭地下部生長較差，因此若欲使用石灰提高水苔初始的pH值，用量須低於12 g•L-1。而不同pH值養液栽培，栽植在高pH值養液(pH 9.0和pH 10.5)中的蝴蝶蘭根部品質較差，因此，蝴蝶蘭應較不適合生長在高pH值環境中。 進一步將前述淹灌栽培後回收之養液進行分析，期望可以辨識造成介質酸化的根部分泌物。結果顯示不論有無施肥，有種植蝴蝶蘭者，在HPLC分析結果中多出一個吸收波峰，此波峰的最大UV吸收值在200之下。而NMR分析結果顯示其結構為兩個以上醣類所組成的複合物，LC-MS-MS分析後推測其分子量應為526 amu。因此蝴蝶蘭的根部會分泌一分子量為526 amu的雙醣衍生物，但目前尚不能斷論其與介質酸化有關。 綜合上述，蝴蝶蘭為造成水苔介質酸化現象的主要原因，而蝴蝶蘭較不適合生長在高pH值環境中，否則根部生長不佳。目前發現蝴蝶蘭根部會分泌由雙醣構成，分子量為526 amu之衍生物，而其與介質酸化間的關係仍需進一步研究。

In Taiwan, growers usually use sphagnum moss as potting medium to plant Phalaenopsis. The pH of sphagnum moss medium decreases during the cultivation of Phalaenopsis and the causes of this phenomenon are still unknown. Generally, change of medium pH affects mineral effectiveness, which might lead to nutritional deficiency or toxicity, and consequently reduces plant quality. This study aims to explore the causes of medium acidification and to understand the relationship between medium acidification and the preferred pH range of Phalaenopsis. Moreover, root secretions of Phalaenopsis were analyzed, in order to clarify causes of medium acidification. This study aimed to realize if medium types, fertilizer application, and Phalaenopsis Sogo Yukidian ‘V3’ itself are related to the medium acidification. The results showed that the initial medium pH value decreased with increasing fertilizer concentration. However, fertilizer application was not the main cause of continuous medium acidification, since a gradual pH decrease occurred only when Phalaenopsis was planted. Although the patterns of pH change were different between medium types, all media pH decreased with time. Although higher temperature improved vegetative growth of Phalaenopsis and light-transmission clear pot increased the root quality of Phalaenopsis, both temperature and light transmission had no effect on medium acidification. In conclusion, Phalaenopsis is the main cause of continuous medium acidification. Some other experiments were conduced to understand the relationship between medium acidification and the preferred pH range of Phalaenopsis. The results showed that Phalaenopsis in sphagnum moss pretreated with higher concentrations of CaCO3 solution (12 and 24 g•L-1) had poor root growth. Therefore, when using lime to increase the sphagnum moss medium pH, the applied concentration should be less than 12 g•L-1. In ebb and flow culture with various pH, though only tested for one month, higher pH of solution (pH 9 and pH 10.5) also resulted in poor root quality. Thereby it is recommended that the cultivation of Phalaenopsis should avoid high rhizosphere pH. In order to find out what Phalaenopsis roots have secreted to acidify medium, cultural solution after growing Phalaenopsis for 14 days was analyzed. The results showed that when Phalaenopsis was planted, regardless of fertilization, one more absorbance peak was recorded in HPLC analysis compared with solution where no Phalaenopsis was planted. The maximum UV absorption of the additional peak was below 200 and the NMR results showed that at least two sugar moieties might have composed the disaccharide derivative, and the LC-MS-MS analysis showed the molecular weight was 526 amu. Therefore, the exudation of Phalaenopsis roots contained a disaccharide derivative with molecular weight of 526 amu. In summary, Phalaenopsis was the main cause of the continuous medium acidification. High pH environment should be avoided when cultivating Phalaenopsis. Presently, a disaccharides derivative with molecular weight of 526 amu secreted from Phalaenopsis root was detected, but its relationship to medium acidification needed further studies.