| Summary: | 碩士 === 臺灣大學 === 生態學與演化生物學研究所 === 98 === Azolla, a genus of aquatic fern, often turn reddish in winter or in hot summer due to the accumulation of anthocyanin. There are two species of Azolla in Taiwan, Azolla pinnata R. brown and Azolla japonica Fr. et Sav. A. japonica is often found turning red while reddish A. pinnata is not that common. In this study, I compared the ability of accumulating anthocyanin in these two species of Azolla under different light and temperature treatments. The ratio of variable to maximum fluorescence (Fv/Fm) was also measured to quantify the maximum PSⅡ quantum use efficiency. Under light illumination, reduction in Fv/Fm indicates photoinhibition. Following hypotheses were tested. (1) Azolla is susceptible to photoinhibition under high light and low temperature conditions. (2) Without anthocyanin accumulation, A. japonica exhibits greater photoinhibition than A. pinnata under high light and low temperature environments. (3) A. japonica accumulates more anthocyanin than A. pinnata under high light and low temperature conditions. (4) Anthocyanin accumulation can reduce the risk of photoinhibition in A. japonica.
The result revealed that both species had greater reduction in Fv/Fm values under high light environments than under shading conditions. The reduction in Fv/Fm was significantly higher at noon and the recovery of Fv/Fm was slower when plants were at lower air temperature (15/13℃) than at 25/20℃ and 35/30℃. A. japonica had equal or significantly lower Fv/Fm values than A. pinnata under high light environment. It indicates that A. japonica was more susceptible to photoinhibition than A. pinnata under some conditions.
High light and low temperature environments did induce Azolla to accumulate anthocyanin. The rate and content of anthocyanin accumulation was significantly faster or higher in A. japonica than in A. pinnata. Exposed Azolla with different amounts of anthocyanin to low temperature and high light, I found that Azolla with more anthocyanin had less reduction in Fv/Fm at noon and the recovery of Fv/Fm was faster than Azolla with less anthocyanin accumulation. This pattern was more apparent in A. japonica than in A. pinnata.
The results indicate that the accumulation of anthocyanin in Azolla, especially in A. japonica, can reduce the risk of plant being photoinhibited under high light and low temperature environment. Anthocyanin can also help Azolla’s photosynthetic efficiency to recover faster after being photoinhibited under low temperature. In comparison between two species, although A. japonica had higher anthocyanin content, it still suffered equal or higher photoinhibition level than A. pinnata under same light environment. The content of chlorophyll and anthocyanin are important factors determine the differential extent of photoinhibition between both species.
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