桶柑葉片光合作用特徵之研究

Studies on Photosynthetic Characteristics of Tankan (Citrus tankan Hay.) Leaves

本試驗探討多項因子對桶柑淨光合作用速率的影響，以期對桶柑光合成能力有進一步認識。以可控制環境因子的開放式光合作用測定系統，測得溫室栽培盆株葉片之暗呼吸速率為1.0 μ mol/m²．s，光補償點20～40 μ E/m²．s，光量子產量（quantum yield；Φ） 0.025 μ mol C02/ μ mol PPFD，而在光度400～500 μ E/m²．s以上、葉溫29～34°C間、蒸氣壓差1.20 KPa之內時擁有較大光合成能力，約6～7 μ mol/m²．s 。以LI-6200可攜式光合作用測定系統調查田間植株葉片光合成能力，光合成能力之日變化趨勢約在上午八時達到最高，為11.0～12.0μ mol/m²．s，午間有下降現象，氣孔導度則在上午七時最高，為0.30 mol/m²．s；不論枝條屬性，當年生葉片光合成能力遠大於上年生葉片，顯示當年生葉片為果實生長之主要供源，但當年生不同葉齡營養枝葉片間光合成能力沒有差異。

Some factors affecting the net photosynthetic rates (Pn) of Tankan leaves were investigated, Pn values of glass-house grown potted plants were measured in an open gas analysis system under controlled environmental conditions. At 28°C the dark respiration rate was 1.0 μ mol/m²．s, quantum yield (Φ) was 0.025 μ molCO₂ /μ mol PPFD. The maximum Pn value, 6.0~7.0 μ mol/m²．s, occurred at PPFD above 400~500 μ E/m²． s, leaf temperature between 29~34°C, and vapor pressure deficit (VPD) less than 1.2 KPa. Diurnal changes of field-grown trees were measured in a LI-6200 portable photosynthesis system. The maximum Pn value, 11~12μ mol/m²．s, occurred at 8:00 LST and the maximum value of stomatal condcutance (g s), 0.30 mol/m²．s, occurred at 7:00 LST. The Pn values of the leaves with different ages on current shoots were not significantly different, but were siginiflcantly higher than those on one-year old shoots. The results suggest that assimilate supply to the growing fruits were mainly derived from the current-year leaves.