黑葉荔枝不同葉齡葉片形態與光合作用特性之研究

Studies on Leaf Morphology and Photosynthetic Characteristics at Various Ages of 'Hak lp' Litchi

荔枝葉片的下表皮才具有氣孔，成熟葉片的氣孔密度為3-4個／平方公厘。荔枝葉片葉肉組織內細胞的排列，除了在5天葉齡的幼葉排列非常緊密之外，其餘葉齡的葉肉組織都會發現有空隙的存在。葉片並無明顯維管束鞘的構造存在，上下表皮均有明顯的角質層。荔枝葉片葉綠素含量在5天葉齡時高於10天葉齡，之後便隨著葉齡增加而增加，葉齡20天後達一較穩定的值，葉齡50天後又隨葉齡之增加而上升，直至葉齡90天。荔枝不同葉齡的葉片在溫度27℃、二氧化碳350ppm、蒸氣壓差1.0kPa之內的條件下，光飽合點約400-500μmole photon/平方公尺•sec，光補償點在5-20μmole photon/平方公尺•sec之間，而與葉齡並無規律性關係存在；在光飽合點以上、二氧化碳350ppm、蒸氣壓差1.0kPa之內的條件下，光合成適溫在27℃至30℃之間。荔枝各個葉齡葉片之淨光合成速率均隨著蒸氣壓差的變大而降低。在600ppm範圍內，荔枝各個葉齡葉片之淨光合成速率均隨著二氧化碳濃度之增加而呈直線增加；荔枝各個葉齡葉片的二氧化碳補償點在40-450ppm之間，與葉齡並無明顯相關性存在。光呼吸率隨著葉齡的增加而逐漸下降；暗呼吸速率與葉齡則無明顯關系存在。

Litchi was hypostomatous with 3.4 stomata/mm^2 on mature leaf. Mature leaves was dorsiventral and all the mesophyll cells were loosely packed. There was no apparent structure of vasicular bundle sheath in the leaves. Thick cuticle layer was found on both abaxial and adaxial surfaces. The chlorophyll concentration of 5-day-old litchi leaves was higher than that of 10 day-old ones. Its concentration increased with increasing age to 20 day-old and maintain a plateau up to 50 days, and then increased again, until 90 days. The photosynthetic characteristics of litchi (cv. Hak IP) leaves at various ages were measured under the condition of 27℃, 350ppm CO2 and ＜1.0 kPa vapor pressure deficit (VPD). The light saturation point was about 400-500 μmole photon/m^2•sec of photosynthetic photon flux density (PPFD), the point of light compensation was about 5-20μmole photon/m^2 sec and their magnitude were not related with leaf age. Under the condition of PPFD is higher than light saturation point, 350ppm CO2, and ＜1.0kPa VPD, the optimum temperature for photosynthesis was between 27℃ and 30℃. No matter what was the age of leaf, all the net photosynthetic rate decreased with increasing VPD. In the range of 600ppm, the net photosynthetic rate of leaves with various ages increased linearly with the concentration of CO2. The CO2 compensation point was 40-150ppm and its concentration had no obvious relation with leaf age. The photorespiration rate decreased with increasing leaf age whereas dark respiration rate was not related with leaf age.