鳳凰木的植物相剋作用潛能之研究

Abstract

鳳凰木(Delonix regia (Boj) Raf.)係熱帶的豆科植物，經常在此植物下，其地被植物種類少，且生物量相當低。依田野的觀察及測定，此地被植物稀少的原因非物理因數如光、水或營養物質的競爭所致，而可能是由於鳳凰木的落葉或其代謝物質抑制地被植物的相剋作用所致。?證明此相剋作用，本研究以生物分析、色層分析、掃描式電子顯微鏡及組織切片等方法來證明鳳凰木植物相剋作用潛能。 將掉落的鳳凰木花、葉、枝條以不同百分比萃取的水溶萃取液如1％、2％、3％、4％、5％，分別對萵苣、苜蓿、白菜、油菜作生物分析以比較其植物毒性程度。其結果顯示花水溶萃取液在1％時抑制白菜根生長達81.5％，抑制油菜、萵苣根生長達77.6％及70.1％，其次是枝條及葉的水溶萃取液，而鳳凰木樹下的土壤及其根圈土或腐葉土之水溶萃取液之植物毒性不顯著，顯示植物毒性表示於花、葉、枝條等部位。一般言之，藿香薊常生長在陽光充足的棲地，偶而也在陰暗地方，但在具相當光度之鳳凰木樹下卻不常見，作者選用上述萃取液做一系列探討卻發現無明顯抑制現象，此原因有待進一步探討。對另二種陰地植物如日本柳葉箬、雷公根的毒性程度則較明顯，由此顯示陰地植物被抑制的現象與植物相剋作用有關。 ?進一步瞭解植物毒物植對植物根生長抑制之機制，作者選用白菜種子以鳳凰木水溶萃取液做生物分析處理後以掃描式電子顯微鏡觀察發現白菜種子根發育明顯受毒物質抑制，根冠細胞有嚴重剝落現象。 經HPLC之分析，本研究經鑑得鳳凰木中之植物毒物質有gallic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzaldehyde, chlorogenic acid, 4-hydroxybenzoic acid, 3,5-dinitrobenzoic acid, 3,4-dihydroxyhydrocinnamic acid等，尚有未被鑑定之類黃素及其它物質亦可能?植物相剋物質。 本研究結果證明鳳凰木抑制樹下地被植物生長與鳳凰木所產生之次階代謝物質及其中所含之植物毒物質有關。鳳凰木所產生之次階代謝物及其中所含之植物毒物質亦影響其土壤中之微生物相。

Delonix regia (Boj.) Raf. plantation in Tainan, southern Taiwan, exhibits a unique pattern of weed exclusion beneath canopy. The pattern has been particularly pronounced in the area where a substantial amount of D. regia litter has accumulated on the ground. Field data showed that the phenomenon was due primarily not to physical competition, involving light, soil moisture and nutrients, but due to an allelopathic interaction. Aqueous extracts fallen leaves, branches, flowers of D. regia showed significantly phytotoxic effects on many test species, including lettuce (Lactuca sativa), alfalfa (Medicago sativa), pickled cabbage (Brassica chinensis) and Brassica campestris L. subsp. napus Hook. f. & Anders. var. nippo-oleifera Mak. The aqueous extracts of the flower of D. regia revealed the highest phytotoxicity. In order to further understand the inhibition of phytotoxic effect, seeds of Brassica campestris were soaked in the aqueous extracts for various time period and the seedings of B. campestris were observed by scanning electron microscopy. Injury in seedings of the tested plants were shown by deteriorated epidermis and abnormally swelling of the seedings. The allelopathic substances isolated from D. regia leaves, flowers, branches and soil were identified by paper chromatography and a high performance liquid chromatography (HPLC). They are phenolic acids, namely, gallic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzaldehyde, chlorogenic acid, 4-hydroxybenzioc acid, 3,5-dinitrobenzoic acid, 3,4-dihydroxycinnamic acid, and some unidentified flavonoids and others as well. The findings of the present study concluded that the inhibition pattern beneath the trees of D. regia is due primarily to the allelopathic substances in D. regia. The responsible allelopathic substances are mostly phenolic acids, but could be flavonoids and others as well. These metabolites could possobly be degraded by soil microorganisms, such as Candida guilliermondii and Enterobacter agglomerans, Klebsiella spp. and Rhodotorula spp.