香莢蘭幼苗不同節位葉片光合作用路徑的轉變研究

Studies on the Transition of Photosynthetic Pathways in Leaves at Different Nodes of Vanilla planifolia Andrews Plantlets

香莢蘭（Vanilla planifolia Andrews）為國際重要的香料作物，在國外具有悠久的栽培歷史。臺灣近幾年開始引進栽種，而目前國內仍缺乏相關的生理生態研究。香莢蘭為厚葉型蘭花，其一般被認為進行景天酸代謝（crassulacean acid metabolism，CAM）光合作用路徑，具有晚上打開氣孔固定二氧化碳，並在日間進行卡爾文循環轉化為碳水化合物的能力。本試驗檢測香莢蘭扦插苗不同葉片的整日氣體交換變化，第2、6片葉（葉齡分別為3和15日）的二氧化碳固定高峰發生在白天，表現C3光合作用路徑特徵；第10、14片葉（葉齡分別為27和39日）的二氧化碳固定高峰則在傍晚並持續至夜晚都有高表現，表現CAM光合作用路徑特徵。同一植株繼續培養40日後，觀察到第16片葉（葉齡為43日）葉片雖然白天仍有較高的碳固定率，夜晚也開始有碳固定發生，證明在發育過程中葉片成熟度影響C3轉換成CAM的現象發生。葉綠素螢光檢測發現第16片葉相異的不可調控的非光化學能量淬滅量子產率（non-regulated non-photochemical quenching，ΦNO）與電子傳遞速率（electron transport rate，ETR）表現，顯示不同葉片相異的生理機制可能與C3和CAM的表現策略有關。在極端氣候加劇的未來，深入了解香莢蘭的生理生態特性有助於栽培上做更適當的管理。

Vanilla planifolia Andrews is a globally important spice with a long history of cultivation. It was introduced to Taiwan and cultivated in recent years. However, there is no study on its plant ecophysiology. Vanilla is a thick-leaved orchid which had been recognized exhibiting crassulacean acid metabolism (CAM) photosynthetic pathway. CAM plants uptake CO2 mainly at night and assimilate CO2 in the Calvin cycle during the daytime. In this study, we investigated the gas exchange in leaves of different nodes of vanilla rooted cuttings. The CO2 uptake peaks of the 2nd and 6th leaves (with leaf ages 27 and 39 days) occurred during the day, exhibiting the C3 photosynthetic pathway. Conversely, the 10th and 14th leaves (with leaf ages 27 and 39 days) showed CO2 uptake peaks from dusk to night, exhibiting the CAM photosynthetic pathway. After 40 days of growth, the 16th leaves (with leaf ages 43 days) became mature and showed higher carbon fixation during the daytime along with nighttime. This indicated a progressive shift from C3 to CAM as leaves approaching maturity. Chlorophyll fluorescence measurements revealed that the 16th leaves exhibited distinct patterns of non-regulated non-photochemical quenching (ΦNO) and electron transport rate (ETR), suggesting that the different physiological mechanisms in various leaves may be related to the strategies of expressing C3 or CAM. A better understanding of the ecophysiology in vanilla will provide fundamental knowledge for the cultivation management, especially in the face of extreme weather and global climate changes.