柳杉人工林下栽植闊葉樹苗木之葉片壽命與相關特性

Abstract

植物的葉片壽命長度會與其光合作用能力、光環境及植食行為等因素有關，故可用來作為植物適應環境的一個指標。本研究地點位於溪頭台大實驗林，藉由調查生長在柳杉人工林下的6種闊葉樹苗(青剛櫟、狹葉櫟、三斗石櫟、栓皮櫟、瓊楠與大葉釣樟)之葉片動態與各種葉片生理特性，希望能了解光環境、葉片壽命、葉片化學特性與植食行為彼此之間的關係，並從而探討苗木適應環境的機制。本研究的重要發現如下： 根據Kikuzawa (1983)對植物展葉型式的定義，本研究中6種樹種的展葉型式均屬於抽芽型，但落葉型態則較不一致，可區分為間歇性、持續性與L型落葉3種型態。 葉片壽命、葉片氮濃度與葉片總酚類濃度在不同冠層開闊度的4條樣帶間無顯著差異，部分樹種在樣帶間的植食程度(葉面積損失率)則具顯著差異，但趨勢並不一致。 在同抽芽群中，6種苗木抽芽群的葉片壽命在樹種間具顯著差異，但僅有青剛櫟的葉片壽命在不同抽芽群間具顯著差異，最早展葉的第1個抽芽群的葉片壽命顯著較第2、3個抽芽群長。樹種間的葉片壽命則會隨著氮濃度與植食程度的增加而有縮短的趨勢，雖然這樣的相關性並不顯著，而在不考慮具有明顯偏高葉片總酚類濃度之栓皮櫟的情況下，樹種間的葉片壽命與葉片總酚類濃度兩者大致呈正相關，在第1個抽芽群中，5種樹種的葉片壽命與葉片總酚類濃度呈顯著正相關。 在同抽芽群中，6種苗木種間的葉片氮濃度具顯著差異，而在同一樹種內，青剛櫟的葉片氮濃度在抽芽群間具顯著差異，以第1個抽芽群的葉片氮濃度顯著高。6種苗木種間的葉片總酚類濃度具顯著差異，栓皮櫟的葉片總酚類濃度顯著比其他5種樹種高；而在同一樹種內，抽芽群間的葉片總酚類濃度具顯著差異，但葉片總酚類濃度在各樹種抽芽群間差異的趨勢並不一致。 6種苗木種間的植食程度具顯著差異，而在同一樹種中，瓊楠以外的5種樹種之植食程度在抽芽群間皆具有顯著差異，以第2個抽芽群具有顯著較高的植食程度。此外，樹種間植食程度與葉片氮濃度、葉片總酚類濃度及葉硬度皆無顯著的關係，但葉片總酚類濃度與氮濃度兩者具顯著負相關。 本研究的結果顯示葉片壽命與光度、葉片氮濃度、葉片總酚類濃度及植食程度有關，而除了上述因子外，還有許多生物和非生物因子會影響葉片壽命，因此未來可能需要更進一步的研究，才能對葉片壽命的變異有更為精確的解釋。

Leaf life-span (LLS) could be affected by the photosynthetic ability of a plant, light availability and herbivory, and thus regarded as an indicator of a plant’s adaptation to the environment. In this study, I investigated the leaf dynamics and the related physiological traits of 6 hardwood species (Cyclobalanopsis glauca, Cyclobalanopsis stenophylloides, Pasania hancei, Quercus variabilis, Beilschmiedia erythrophloia and Lindera megaphylla) in a Cryptomeria japonica plantation in Chitou district, the Experimental Forest, National Taiwan University, central Taiwan to understand the relationships of leaf life-span with light availability, leaf chemical traits and herbivory. The main results were as follows: According to Kikuzawa (1983), 6 species have a common leaf emergence type --Flush type. However, the patterns of leaf fall were more diverse in these species, belonging to three types--Intermittent, Continuous and L-shaped. LLS, leaf nitrogen concentrations and leaf total phenols concentrations did not differ significantly among 4 sampling lines with different canopy openness. By contrast, herbivory (percentage of leaf area loss) of some species differed significantly between sampling lines, but the patterns were inconsistent. Leaf life-spans differed significantly among species within the same cohorts. By contrast, LLS differed significantly among cohorts only in C. glauca, with significantly longer LLS in the 1st cohort than in the 2nd and 3rd. LLS was somewhat negatively correlated with leaf nitrogen concentrations, but the relationship was insignificant. With Q. variabilis excluded, LLS was positively correlated with leaf total phenols concentrations. Within the 1st cohort of 5 species (except Q. variabilis), there was a significantly positive correlation between LLS and leaf total phenols concentrations. Leaf nitrogen concentrations differed significantly among species. In addition, leaf nitrogen concentrations differed significantly among cohorts in C. glauca, with the concentration higher in the 1st cohort than in the 2nd and 3rd. Leaf total phenols concentrations differed significantly among species, with significantly higher concentration in Q. variabilis than in the other 5 species. Leaf total phenols significantly differed among cohorts in some species, but the patterns were inconsistent. Herbivory differed significantly among species. With B. erythrophloia excluded, herbivory differed significantly among cohorts. Within the 5 species (except B. erythrophloia), the herbivory was significantly higher in the 2nd cohort. There was no significant correlations between herbivory and leaf nitrogen concentrations, leaf total phenols concentrations and leaf toughness. By contrast, leaf nitrogen concentration was in significantly negative correlation with total phenols concentration. The results of this study suggest that LLS could be associated with light availability, leaf nitrogen concentrations, leaf total phenols concentrations and herbivory. Beyond the scope of this study, there are many more biotic and abiotic factors which can have influenced LLS. The complexity of LLS demands further studies to help elucidate the mechanisms affecting LLS.