溫度誘導光抑制對痲瘋樹幼苗光生理指標之影響

Abstract

痲瘋樹（Jatropha curcas L.），為目前世界上認為最具開發潛力之新興能源作物，為大戟科痲瘋樹屬落葉灌木或小喬木，性喜光，原產熱帶美洲，今廣泛分佈在亞洲、非洲之熱帶及亞熱帶地區，因此冬季與早春低溫仍會抑制其生長與發育。為了瞭解痲瘋樹在不同溫度下受光抑制脅迫之生理反應，本論文以痲瘋樹扦插繁殖幼苗為材料，研擬步驟，逐一探討，包括調查低溫寒害對痲瘋樹色素生合成與植生相關指數之影響；探討不同溫度強光脅迫下，對痲瘋樹螢光相關參數、光化學反射指數以及植生指數之影響；另探討高低溫持續期與強光脅迫對痲瘋樹光生理指標之影響。 結果顯示低溫寒害造成痲瘋樹葉片老化，葉色由綠轉黃而褐，葉片葉綠素及類胡蘿蔔素(Car)含量逐漸減少。反射光譜顯示葉片寒害過程中，可見光波段反射率呈現增加，而近紅外光波段反射率呈現減少的趨勢。以近紅外光波段如750 nm反射率與紅光臨界705 nm反射率來計算植生指數，並與葉片葉綠素含量進行迴歸分析，可得到葉綠素含量估算模式(R2 > 0.9)；以531、570 nm反射率計算光反射指數PRI則與Car含量有顯著相關(R2 > 0.85)。 痲瘋樹幼株在不同溫度處理後強光脅迫下，除外觀表現差異，在葉片反射光譜上亦有明顯變化，如綠光波段與近紅外光、光生理指數等；另一方面，葉片之葉綠素螢光(chlorophyll fluorescence)，亦可反應植株當時的生理狀態。本研究進行痲瘋樹幼株不同溫度試驗（7、14、21、28、35、42℃），處理24小時後測定以反射光譜計算常態化差異植生指數(NDVI, normalized difference vegetation index)、並於1,800 μmolm-2s-1 PPFD光強照光前、後計算光化學反射指數(PRI，photo-chemical reflectance index)及葉綠素螢光，以期瞭解痲瘋樹於不同溫度下其光生理指標之變化。試驗結果顯示，不同溫度處理下其NDVI值約為0.7~0.8，無顯著差異；而42℃高溫處理組，照光前PSII最大光化學潛能(Fv/Fm)、ΦPSII、ETR、qP與PRI值均顯著下降，NPQ值顯著上升，其中PSII最大光化學潛能下降幅度更達40~50%，而7℃低溫處理組各螢光參數在照光後的趨勢大致與42℃相似。高低溫持續期後強光脅迫實驗則延續前項不同溫度實驗，將7、42℃處理天數持續期改為1、2、3天，並測量葉綠素螢光參數、光飽和曲線參數、手持式光生理指數，結果顯示，三天內NDVI值皆無差異，三天內照光前後PRI值變動量以42℃較多，7℃的淨同化速率(Pn)在第二天即近於0，而42℃則在第三天才顯著下降，整體表現以42℃之耐受性較高，又綠素螢光之ΦPSII和Pn有高度相關性(R2 > 0.754, P < 0.0001)。 總結本研究顯示利用反射光譜計算植生指數及光化學反射指數，非破壞性地估算痲瘋樹葉片葉綠素、類胡蘿蔔素含量之變化，為有效可行的方法，並且以迅速又方便的葉綠素螢光亦可代表淨同化速率(Pn)變化趨勢，進而快速監測痲瘋樹在不同溫度環境之生理狀況。

Physic nut (Jatropha curcas L.) is one of the main crops which could provide biodiesel as an energy crop. It origins from tropical America and widely distributes in tropical and subtropical areas of Asia and Africa. Low temperatures in winter and early spring will inhibit the growth and development of physic nut. To understand the physiological responses such as photoinhibition of physic nut at different temperatures with high light intensity, cut stems of physic nut were used for propagation in this research. First, the pigment contents and the reflectance spectral properties of yellowing leaves subjected to winter cold stress. Second, chlorophyll fluorescence, photochemical reflectance index and vegetation index at different temperatures with high light intensity were evaluated. Third, photo-physiological indexes of young plants of physic nut treated at 7 or 42℃ for 1,2 and 3 days was tested. In the first experiment, the regression analysis of pigment contents and vegetation indexes by spectral reflectance was applied.When the leaves were senescent and yellow, the Chl and Car contents decreased significantly with the yellowing levels. The reflectance spectra showed that the reflectance of visible band was increased and the reflectance of NIR band was decreased. The normalized difference vegetation index (NDVI) was calculated by reflectance at 705 nm and 750 nm and significantly correlated with Chl concentrations (correlation R2 > 0.9). The photo-chemical reflectance index (PRI) was calculated by reflectance at 531 nm and 570 nm and significantly correlated with Car concentrations (correlation R2 > 0.85). Second, the young plants of physic nut under different temperatures with high light intensity would show different morphologies, photo-physiological index, reflectance spectral properties, and chlorophyll fluorescence also could represent different physiological status. In this study the physic nut plants were treated in dark environment at 7,14,21,28,35 and 42℃ for one day. The NDVI calculated by reflectance spectra showed no difference between all temperature treatments with the values between 0.7 to 0.8. The PRI calculated by reflectance spectra and chlorophyll fluorescence were measured before and after 1,800 μmolm-2s-1 PPFD light treatment. The results showed that levels of Fv/Fm,ΦPSII,ETR,qP and PRI decreased, and NPQ increased significantly at 42℃ before light treatment. Levels of Fv/Fm were decreased significantly to 40 to 50%. The trend of chlorophyll fluorescence of physic nut at 7℃ under 1,800 PPFD equals to those tested at 42℃. Third, young plants of physic nut were tested at 7 or 42℃ treatment for 1,2 and 3 days. The results showed that NDVI had no difference between all temperatures and day durations. The PRI variation before and after illumination were higher in the 42℃ treatment for 1,2 and 3 days than those in the 7℃ treatments. The net CO2 assimilation rate (Pn) approached zero at 7℃ for the second day, and the Pn decreased significantly at 42℃ for the third day. Physic nut was more tolerant at 42℃ than 7℃. The ΦPSII of chlorophyll fluorescence was significantly correlated with Pn (R2 > 0.754, P < 0.0001). From the results, we could use the NDVI and PRI, calculated by reflectance spectra, to estimate the contents of Chl and Car in the young plants of physic nut. We could also quickly monitor the physiological status of physic nut plants at different temperatures by the levels of chlorophyll fluorescence for the high correlation between ΦPSII and Pn.