溪頭鳯凰山闊葉樹葉部生長動態及不同發育階段之葉片特性

Abstract

一、葉部生長動態及葉部化學特性對於植物適應環境有很重要的影響，本研究藉由溪頭鳯凰山天然闊葉林不同光環境生長之林木的物候調查及葉部化學特性的分析，希望能了解植物演化及適應環境的重要特徵。 二、調查對象為較陰暗之林下區域11種林木及光線充足之稜線區域10種林木，其中有5種為林下及稜線之共同樹種，在2007年12月到2009年4月間，持續調查芽之開裂、發葉、落葉，並觀察芽的型式及嫩葉延綠(delayed greening)與否，之後以葉部生長及掉落數據用來估算葉片壽命。並另外選取非長期調查的林木(林下12種及稜線10種，其中有6種為共同樹種)測定不同發育階段葉片(L25：葉子小於25%的完全開展葉片的大小，且已開展；LFE：剛開展為成熟葉的大小；LM：完全開展且較硬的成熟葉)的氮、磷、總酚類濃度及葉綠素計讀值。 三、中型或大型喬木中具有鱗芽的比例較高，而小喬木或灌木的樹種中則是具有葉狀苞芽的比例較高。大部份樹種的芽於3月至5月開裂，但是台灣山香圓(Turpinia formosana)及柃木(Eurya loquaiana)除外。 四、林下烏心石(Michelia compressa var. formosana)、長尾柯(Castanopsis cuspidata var. carlesii)稚樹芽開裂的時間較稜線的成熟林木早1~2個月，林下柃木芽開裂的時間也較早於稜線植株。 五、發葉型式為持續型的樹種4種，抽芽型7種，中間型5種，抽芽型的樹種芽的形態大部份為鱗芽，發葉型式不因生長的環境(林下及稜線)而有所差異。 六、大部份稜線林木與鳯凰山同種之冠層林木的落葉時間一致，大部份林下林木落葉時間較鳯凰山同種之冠層林木晚且不一致。且利用2種方式計算葉片壽命，一致發現林下林木葉片壽命較稜線林木為長。 七、大部份林木葉片之氮、磷及總酚類濃度是L25＞LFE＞LM，而葉綠素計讀值則是LM＞LFE＞L25；延綠型樹種L25之氮、磷及葉綠素計讀值顯著低於正常型，但總酚類濃度則顯著較高，顯示防禦上的投資較多，而生長的投資較少；隨著葉片越趨成熟，葉片防禦與生長調節的機制越不明顯。 八、本研究於不同光環境下之葉部生長動態(芽的開裂、落葉、葉片壽命)及葉片磷濃度確實有差異。但是由於影響各樹種的物候及葉部化學性質的因子相當複雜，還需要更多長期的觀察及調查，才能對台灣原生林木環境的適應機制有更精確的了解。

I. Leaf growth dynamic and leaf chemical properties have important implications of plant acclimation. This study was aimed to investigate the major phenological events of leaf growth and shedding and leaf chemical properties at two sites with contrasting light conditions in a natural hardwood forest of Feng Huang mountain, Chitou. II. Sixteen tree species were selected at two sites: understory (11 species) and ridge species (10 species), with 5 species common to two sites. From December of 2007 till April of 2008, the leaf numbers were censused at least once a month on the marked twigs and the bud types and delayed greening of young leaves were noted. The data of leaf growth and shedding were then used to calculate leaf life span. In addition, trees without any marked twigs (11 understory species and 10 ridge species, with 5 species found in both sites) were sampled to analyze leaf nitrogen, phosphorus, total phenols and the chlorophyll meter value in different developmental stages of leaves (L25: ≦25% of the fully expanded size and unfolded; LFE: Fully expanded with tender texture; LM: Fully expanded with tougher texture). III. Most medium and large trees have scaled buds, and most small trees and shrubs have hypsophyllary buds. The budbreak occurred from March to May for most species, with two exceptions in Turpinia formosana and Eurya loquaiana. IV. The buds on small trees of Michelia compressa var. formosana and Castanopsis cuspidata var. carlesii in understory opened 1-2 months earlier than the mature trees in ridge. The buds of Eurya loquaiana in understory also opened earlier than the individual in ridge. V. Based on the categories of leaf emergence, there are 4 species in succeeding type, 7 species in flush type, and 5 species in intermediate type. Most species in flush type have scaled buds. In addition, the leaf emergence types cannot differentiate between understory and ridge sites. VI. The leaf fall of most ridge species peaked at the similar time with canopy species; but most understory trees peaked at later time with greater variation than canopy species. Based on two calculations of leaf life span, leaf life span was longer for understory species than those growing in ridge. VII. The foliar concentrations of nitrogen, phosphorus and total phenols mostly followed the order of L25＞LFE＞LM, while the leaf chlorophyll meter value LM＞LFE＞L25. Trees of delayed greening contain significantly lower foliar nitrogen, phosphorus and chlorophyll meter value, but higher total phenols than those of normal greening. It suggests that trees of delayed greening invest relatively more in defense and less in growth. This trade-off between defense and growth became less evident in mature leaves. VIII. Indeed, we found certain differences between different light regimes in leaf growth dynamic (budbreak, leaf fall and leaf life span) and foliar phosphorus. Because the factors influencing phenological events and leaf chemical properties are numerous and complicated, more long-term studies on leaf dynamics and leaf traits are required to understand the ecological and evolutionary characteristics of major tree species in the natural forests of Taiwan.