南印度型培地茅耐遮蔭性之研究

Abstract

台灣地區地震發生頻繁，山坡地表嚴重裸露，再加上雷豪雨的沖刷、山坡地不當的過度開發及工業與生活污水的不當處理和排放等，不僅使得土壤極易流失與劣化，水資源更遭受污染，故在種種環境日益惡化的壓力之下，水土保持與環境復育的工作刻不容緩。而培地茅健壯的生長及生理特性，不僅可以作為坡地保固之材料，更適合作為廢棄荒地生態復育工程的先驅植物。然而，台灣夏季雖然炎熱，但夏日午後常見的熱雷雨所帶來的雲層、春夏之際梅雨季節長達數天乃至數週的滯留鋒面及空氣懸浮微粒的遮蔽效應對需要高日照量的培地茅之影響不容忽視。本研究即針對現有的27種培地茅品系做遮蔭逆境之篩選。以田間及人工照明室內遮蔭處理的葉部生長型態（葉厚及比葉鮮重）、葉綠素相關測值（葉綠素計讀值、以N,N-dimethylformamide所萃取出的總葉綠素含量、葉綠素a含量、葉綠素b含量及葉綠素ab比值）及溫室內遮蔭處理之光合潛力（光飽和點、光飽和光合作用速率、光補償點及暗呼吸作用速率）為度測標準，探討此27種培地茅品系在遮蔭逆境下的改變及其面對遮蔭逆境所表現出來的可塑性，甚至觀察比較是否本身即具有在基因型上耐遮蔭逆境之可能性指標，以期在實際生態復育、水土保持及遺傳育種上能更有效的被開發利用。 然而，本試驗所針對的一些偵測性狀特徵，雖然在遮蔭處理下大致都表現出相關學理上所應該呈現的趨勢，即培地茅的葉片變得較薄、比葉鮮重降低，葉綠素相關測值含量皆增加，在光合潛力上也因遮蔭逆境之影響而降低。但這些性狀特徵都不足以作為判斷一品系是否具有耐遮蔭性之統一指標。在所有偵測性狀之可塑性比較上，或可呈現該品系面對遮蔭逆境下所做的應對能力之探討及適應遮蔭逆境優劣之參考，但有些品系對不同性狀之可塑性反應不一致，可見遮蔭逆境所能影響的層面廣泛，不太能針對某一方面來單獨的探討其耐受性，特別是本試驗所偵測的培地茅皆屬同一物種。此外，試驗亦將所偵測的性狀特徵與培地茅遺傳距離樹狀分枝圖相做比較，但亦未發現有任何一項量測值與用來估算遺傳歧異度的DNA分子標記有相關。 遮蔭逆境是一種長期累積的效應，特別是針對根系發達，地下部組織旺盛，且株叢龐大，地上部分蘗多而繁密的培地茅而言。本試驗雖仍未發現培地茅耐遮蔭性之可能性指標，但其中也有許多值得再討論與改進之處，供作日後繼續篩選其他可能的耐遮蔭性指標性狀試驗設計之參考。

The landscape in Taiwan is suffering naturally from frequent earthquake and storm and thus becoming highly vulnerable to erosion. The human activities including over-exploitation in the mountain area further worsen the situation. The effluent from the industry and urban development pollute the water supply is getting seriously. Hence, the recognition of the erosion control and restoration of the environment is prevailed in the general public. The vetiver grass with extensive root system and strong stems is suitable as pioneer species for the degraded soil and water and been used in many applications. The regular tropical storm happened in the afternoon in summer has significant impact on the intensity and amount of the light that vetiver received. The prolonged rainy season during the end of spring and smog from the air pollution has also contribute to the reduction of light available to vetiver. Thus the study of effect of shading on vetiver becomes a major issue. Twenty seven lines of vetiver were used in the study. The response of leaf morphology and chlorophyll content to the shade treatments conducted in the field and artificial lighting in phytotron were evaluated. The photosynthesis characteristics including light saturation point, light compensation point, light-saturated photosynthetic rate and dark-respiration rate were measured in the greenhouse. The results indicated general agreement with published hypothesis and principles, but discrepancies were also identified. One of the primary interests in this study was to identify traits suitable for selection for shade tolerant genotypes and the evaluated traits were proved to be unable to provide unambiguous results. The study of shade tolerance is complicated by the perennial nature of vetiver grass. It should be investigated further.