四種生長於台灣南部墾丁石灰岩地區之熱帶季風雨林主要組成樹種的初生幼苗:茄苳、皮孫木、樹青及鐵色,於1994年4月至10月問置於相對光量100%、50%、10%及2.5%四種遮蔭設備內,觀察其生長情形及的形態變化。其中100%代表全光下的光量,50%、10%及2.5%代表不同大小孔隙之光量,希望藉此試驗瞭解各樹種在不同林內光量環境下的生長及適應情形,並嚐試找出具有指標意義的形態性狀,提供野外觀察植物耐陰性之簡易可行的方法。 試驗結果發現,茄苳之生長表現隨著光度之增強而遞增,屬於需光性強之陽性樹種,基在2.5%相對光度處理下生長遲緩,生物量急劇下降至0.98g/株,僅10%相對光度處理之1/8。皮孫木在50%及10%相對光度下生長良好,在全光下有明顯光抑制造成的白化現象,在2.5%相對光度下呈生長停滯現象,屬於光度適應範圍較窄的樹種。樹青的生長表現隨著光量的增強而遞增,在10%及2.5%相對光度下亦能持續穩定的生長,生物量隨光度減弱而平緩下降,表現極佳之光適應能力。鐵色在50%相對光度下表現最佳生長,在其它3種光度處理下亦能維持穩定之生長,與樹青相同,表現了極佳的光適應能力,但在全光處理下的生長不如樹青。 在型態上,四個樹種之葉面積比隨光度的增加而遞減,單位面積葉重隨著光度增加而遞增,表示無論是陽性或耐蔭樹種均會産生陰葉及陽葉,但在不同光度處理下的葉面積比及單位面積比葉重的高低差距比(可塑性),需光性強之樹種與需光較低之樹種間並沒有顯著差異。相對苗高(除皮孫木外),均隨著光度之減弱而上升,且需光性強之茄苳及樹青亦表現了較強之可塑性,故相對苗高在不同光度處理下的變異較能反應出幼苗的耐蔭性,此一論點有待對更多的樹種做進一步的試驗,以評估其可靠性。各樹種根莖比均隨著光度之增強而遞增(茄苳2.5%相對光照處理除外),單位重葉綠素含量均隨著光度的增強而遞減,但需光性強之樹種與需光性較低之樹種間差異不顯著。
Seedling growth and morphology of four evergreen tree species from Renting limestone monsoon rain forest in southern Taiwan were studied in four simulated light intensities (100% 90% 10% 2.5% of fall sunlight) from April 1994 to October 1994. Bischofia javanica was found to be a exposure requiring species andgrew poorly in 2.5% full sunlight. Pisonia umbellifera was a narrow range exposure-adaptive species which showed great performance under 50% and 10% full sunlight but grow badly in 100% and 2.5% full sunlight. Pouteria obovata was found to be an exposure-adaptive species which showed the best growth performance under full sunlight but also grew well in 2.5% and 10% fall sunlight (shade-tolerant in lowlight levels). Drypetes littoralis was also an exposure-adaptive species which showed the best growth performance under 50% full sunlight but still grew well in 100% and 10% full sunlight, and was also shade-tolerant in 2.5% full sunlight. Both LAR (leaf area ratio) and SSLW (specific saturated leaf weight) were strongly correlated with light intensity. This phenomenon shows that any kind of tree species, either exposure-requiring or shade-tolerant, can have eon or shade leaves when grown in strung or weak light environments. The plasticity of relative height (height/root collar diameter) in significant difference between exposure-requiting and shade-tolerant species, so it was a good morphological parameter in judging shade tolerance of tree seedlings in this study. Root shunt ratio showed a positive correlation with light intensity. Chlorophyll contest per unit leaf weight showed a negative correlation with light intensity.
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