兩種紅樹林物種對鹽水淹沒的光合反應與C3-CAM轉化

Photosynthetic responses of two mangrove species to salinity immersion and C3-CAM conversion

紅樹林生態系統容易受到潮汐的影響，每當海平面上升時，植物會處在鹽度增加以及潮汐淹沒的環境中。為了解適應不同潮位高度的紅樹林鹽分淹水的光合作用，本試驗在不同鹽度（（千分之20）和（千分之40））與淹水處理下測量水筆仔（Kandeliao-bovate，Liu & Yong）與紅海欖（Rhizophora stylosa, Griffith）的氣體交換和葉綠素螢光參數。結果顯示水筆仔能適應淹水壓力並在這些條件下生理表現優於紅海欖。而紅海欖處於淹水和低CO_2濃度處理1週後，在夜晚裡能吸收CO_2，並在清晨時葉片酸度較高，顯示淹水和低CO_2濃度等多重逆境可能誘發紅海欖的景天酸代謝（crassulacean acid metabolism）的特徵，與景天酸代謝型植物一致。

Mangrove ecosystems are vulnerable to rising sea levels. When the sea level rises, plants are exposed to increased salinity as well as tidal submergence. In this study, Kandelia obovata Sheue, Liu & Yong and Rhizophora stylosa Griffith were subjected to different salinity ((20 per mille) and (40 per mille)) and immersion treatments to understand their photosyn-thesis responses to salinity immersion in mangroves and adaptability to different tidal elevations, gas exchange, and chlorophyll fluorescence parameters. K. obovata adapted to immersion stress and outperformed R. stylosa under these conditions, indicating that the colonization ability of K. obovata took place in the immersive conditions. Immersion and low CO_2 concentration stresses might enable R. stylosa to adapt to darkness for CO_2 absorption and exhibit leaf acidity in the early morning. Accordingly, R. stylosa exposed to immersion and low CO_2 concentration for one week could adapt to darkness and successfully absorb CO_2. This phenomenon was consistent with that observed in crassulacean acid metabolism (CAM)-type plants, which fix CO_2 at night and exhibit leaf acidity in the early morning. Our results demonstrate that R. stylosa displays distinct CAM characteristics under 40‰of salinity and immersion stress.