南仁山區亞熱帶雨林植物葉片水份狀態在不同生育地反應的研究

Abstract

本研究目的是為了探討植物在不同生育地分佈情形和水份利用的關係。利用樹種的各季節蒸散速率變化和葉片水勢的測量來觀察環境因數對植物水份利用狀態的影響，進而觀察不同生育地的植物水份利用狀態差異。 位於屏東縣滿州鄉欖仁溪上源的南仁山亞熱帶雨林三公頃的永久樣區內，由於東北季風和地形影響，所有樹種在樣區內分化出迎風坡面及背風坡面兩截然不同植物形相社會。迎風坡面的植物受風侵襲常呈植株低矮生長緩慢現象；背風坡較不受風影響，植株均可生長成大徑級樹。因迎風坡面常發生短暫乾旱使土壤水份較背風坡少，本研究即試圖由葉片水份生理角度來探討不同生育地之取樣樹種，如何適應環境的水份利用方式。 採樣上於典型的迎風坡面及背風坡面共選取八種植物，包括廣泛分佈於兩坡面的虎皮楠及紅花八角、迎風坡局限分佈種嶺南椆、恆春石斑木、臺灣柯、武威山新木薑子以及背風坡局限分佈種鵝掌柴和南仁山新木薑子。來觀察植物水分狀態在不同生育地的表現。 測量的主要變量是環境因數（光照、風速、氣溫、濕度）於不同季節的天氣狀況對植物水勢、蒸散速率、葉溫和水蒸氣擴散阻抗產生的影響，以及植物相對應的適應反應。 經由環境因數日變化RDA（Redundancy Analysis）判別因數分析的研究結果，迎風坡面的植物日蒸散量的變化顯著相關於光及濕度，葉片水勢亦有相關。而背風坡各因數則變化較不顯著。在季節的變化上，迎風坡面植物受到季風來臨時短暫乾旱的影響，而呈現水分吸收量不足的現象。背風坡面植物受季風的影響較小，但不論如何，兩坡面樹種氣孔反應明顯地與氣溫相關。比較樹種的水分利用狀態發現，廣泛分佈樹種不管在風季和非風季時，葉片的水勢變化皆較穩定，水勢維持在水分充足的數值。而新木薑子屬的兩取樣樹種，則相反的在面臨乾旱時有嚴重的失水現象。就取樣的廣泛分佈種而言，紅花八角的水分利用與氣孔對缺水的反應也比虎皮楠佳，這或許是紅花八角能廣泛分佈於本樣區且優勢度居冠的原因。 從葉子水分生理反應來看，南仁山永久樣區的植物常年在高溫多濕的環境下生長，當面臨季風來臨的短暫乾旱時，並未發展出特化的抗旱機制。這和熱帶山地雨林的其他研究結果相仿，認為耐迎風乾旱植物葉片水分反應為一種適應的結果，並無形成耐旱機制。

The major subject in this study is to investigate the responses of 8 selected plant species to different niches with distinct wind effects. The 3-ha study area locates in subtropical monsoon forest in Nanjenshan. The environmental factors studied include light intensity, wind velosity, air temperature and moisture during climate changes in different seasons. The effects in leaves explored about water potential, transpiration rate, temperature and diffusive resistance. Suppose that plants have adaptive mechanism, the results by RDA (Redundancy Analysis) show that the diurnal transpiration rate changes of winward species in different seasons reduce a lot due to drought in monsoon season. While the diurnal transpiration rate of leeward species reduced little, but related to air temperature change. Comparing water use status of all selected species with drought happened, the dorminant winward and leeward species have little change in leaf water potential reduced, but the two selected tree genus Neolistea have significat leaf water potential reduced in drought condition. Furthmore, in the two dorminant windward and leeward species, the water use efficiency and stomatal responce to environmental change of Illicium arborescens was better than Daphniphyllum glaucescens The above result might suggest that Illicium arborescens is the most dominant species in this area. In the view of water ecophysiological response of leaves, species growing in this area with high temperature and moisure all year round have not yet developed drought resistance mechanism when meeting short period drought. The water status of leaves to drought in this site is similar to other tropical mountain forests. It shows that the response is just an adaptive result, not due to a drought - resistance mechanism.