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Effects of irradiance and temperature on the chlorophyll fluorescence characteristics
結果顯示黃色甘藷葉綠素含量較低，葉綠素a/b值較高。將三種葉色之甘藷合併分析顯示，Fo( 最小螢光放射量 )、Fm( 最大螢光放射量 )、Fv/Fm( PSII最大光化學潛能 )等三者與葉綠素含量均呈曲線正相關，其中以黃葉甘藷之Fo、Fm及Fv/Fm均較低。隨著光度增加，P(光化學消散佔吸收光能的比例)會逐漸變小，D( 螢光消散熱消散佔所有吸收光能之比例 )則逐漸增加，而E (過多的能量佔所有吸收能量的比例 )變化較P及D為小且較不規則。但在相同光度下，光合作用較高的葉片，其P較高，D較低，E也會較少。除了光合速率特低(<5 μmol m-2 s-1)之葉片外，三種葉色之甘藷其Pn會隨電子傳遞速率(rate of electron transport)上升而增加，此增加之幅度會隨光合速率增加而加大。若將同種葉色、不同施肥量之甘藷葉片合併分析時，其光合速率與電子傳遞速率間回歸方程式之斜率以綠葉最大、紫葉次之、黃葉最小。三種甘藷在未照光前之Fv/Fm均為0.8左右。但照以高光(2000 μmol m-2 s-1)2小時後，其Fv/Fm會降低，P1200<5 μmol m-2 s-1之葉片，其Fv/Fm可降至0.3~0.5，但P1200>5 μmol m-2 s-1之葉片其Fv/Fm大致持平，此持平階段之Fv/Fm平均值以紫葉較高(0.70±0.02)、綠葉次之(0.66±0.02)、黃葉最小(0.59±0.02)。綜合以上結果得知黃葉甘藷之PSII效能對光度較紫葉及綠葉敏感。
探討在不同溫度下，不同植物之Tc值(在黑暗下快速增溫(1℃ min-1)時，Fo急遽增加時的臨界溫度)差異很大。9種溫帶原產植物之Tc值在冬季 (1~2月)為37~46℃，夏季則為32~48℃，而熱帶原產CAM及4種C4型植物之Tc值，在冬季及夏季分別為為41~47℃及45~46℃，其餘12種則分別為25~47℃及35~48℃。比較所有供試植物冬夏兩季Tc值之差異，得知溫帶原產C3植物之差異小於1.9℃，而熱帶原產CAM、C4及C3植物之差異則分別為-0.75℃、2.49±1.14℃(SD)及9.45±5.69℃。此外，將葉片以45℃處理20分鐘，再放置室溫1小時後，發現熱帶原產物種之Fo及Fv/Fm較不易受到高溫之影響，而溫帶原產C3植物則變化很大，從容易受到影響到不容易受到影響之物種均有，而且發現除了柳橙之外，將溫帶原產C3及熱帶原產CAM及C4型植物合併分析時Tc與RFvm(45℃處理後Fv/Fm之變化比率)呈顯著正相關。但是熱帶原產C3型植物其Tc值變化很大，但是RFvm卻很相近。由以上結果顯示，Tc值可比較熱帶原產CAM、C4及溫帶原產C3型植物之耐熱性，但可能無法作為熱帶原產C3型植物耐熱性指標。然而，相同植物在不同季節對溫度具有很高的可塑性，且經高溫馴化亦有相同結果，故Tc值可作為相同植物之耐熱指標。
Abstract In order to understand the effects of irradiance and temperature on the chlorophyll fluorescence characteristics among plant species, 3 varieties of sweet potato with different leaf color (yellow, green and purple), and 17 species of tropical origin as well as 9 species of temperate origin plants were used as materials. The results indicated that yellow sweet potato showed lower chlorophyll (chl) content and higher chl a/b ratio in leaves. When merged together the results measured from 3 sweet potato leaves to statistical analysis, it was found that Fo (minimum chlorophyll fluorescence), Fm (maximum chlorophyll fluorescence) and Fv/Fm (variable chlorophyll fluorescence) increased curvelinearly with the increase in chl content. It also found that P (fraction of light absorbed in PSII antennae that is utilized in photosynthetic electron transport) decreased gradually, and D (fraction of light absorbed in PSII antennae that is dissipated via thermal energy dissipation in the antennae) increased gradually with light increasing. While E (fraction of excess absorbed in PSII antennae) varied very lesser than P and D, and it not related to light intensity. Under the same light intensity, the leaves with higher rate of Pn showed higher P, and lower D and E. Expect the leaf with extremely low Pn (<5 μmol m-2 s-1), Pn increased with the increase in ETR. The slope of Pn increasing with rate of electron transport was higher in the leaf with higher Pn. When merged together all the data to statistical analysis measured from 3 sweet potato varieties with different levels of nitrogen applied, the order of the slope of regression equation between Pn and ETR was green > purple > yellow. The predawn Fv/Fm of three sweet potato is about 0.8. However, when illuminated with 2000 μmol m-2 s-1 (PPFD) for 2 hours, Fv/Fm of the leaves with extremely low Pn declined to 0.3~0.5, while that of other leaves were 0.7±0.02 for purple variety, 0.66±0.02 for green variety and 0.59±0.02 for yellow variety. This result indicated that actual PSII efficiency in yellow leaf sweet potato is most sensitive to light, followed by green, and then by purple leaf variety. When leaves were linearly heated from room temperature to the final temperatures of 45-50℃ with about 1℃ min-1 graduation in darkness, the temperature at which the F0 occurs increased sharply (critical temperature, Tc) varied largely with species. Nine of the temperate origin species ranged their Tc between 37-46℃ in winter (Jan.-Feb.), and ranged 32-48℃ in summer. While those of 1 tropical origin CAM and 4 C4 species were 41-47℃ and 45-46℃, and those for 12 tropical origin C3 species were 25-47℃and 35-48℃, respectively. The difference of Tc between two seasons in the same species for temperate origin C3 species were less than 1.9℃, while those for tropical origin CAM, C4 and C3 species were —0.75℃, 2.49±1.40(SD) and 9.45±5.95℃, respectively. When the leaves were exposed to 45℃ for 20 min and then accumulated in dark room for 1 hr, both F0 and Fv/Fm of temperate origin species with lower Tc were more influenced than those of tropical origin C4 and CAM species. On the contrary, other temperate origin species and all the tropical origin CAM and C4 species showed higher Tc, and their F0 and Fv/Fm were insensitive to high temperature in winter. Therefore, it showed significant correlation between their RFv/m (the ratio of Fv/Fm before and after 45℃ treatment) and Tc. However, the tropical origin C3 species were less sensitivity of F0 and Fv/Fm at 45℃ treatment in spite of showing largely variation of Tc among species, thus no significant correlation could be found between their RFv/m and Tc. It could be concluded that comparing the temperate origin C3 as well as tropical origin C4 and CAM species, Tc of tropical origin C3 species was hard to estimate their heat tolerance among species. However, they showed higher plasticity in the same species during different seasons or temperature treatments, so their Tc probably suited to estimate the degree of temperature accumulation in the same species. As a conclusion, chlorophyll fluorescence measurement is a non-invasive technique could provide fast and convenient data, is a powerful tools for ecophysiological syudy. Key words: Light, temperature, chlorophyll fluorescence, photosynthesis, photochemical quenching, heat tolerance, Tc.
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