亞熱帶森林生態系附生植物營養限制之研究

Abstract

限制生態系初級生力的因子相當多，除了降雨和溫度之外，營養元素也是常見影響森林生態系生產力的重要因子，溫帶及熱帶地區已有相當多營養限制相關的研究，這些研究指出溫帶森林初級生產力主要受到氮的限制，而熱帶森林則是受到磷的限制；然而亞熱帶地區森林之營養限制卻鮮少有實驗研究，使我們對於全球生態系之營養循環尚未有全面的了解。此外亞熱帶、熱帶地區森林富含多樣的附生植物，其所含的營養占森林總營養相當大的一部分，為森林營養循環中重要的一環，然而附生植物是否與一般地生植物有著相同的營養限制，而可作為森林生態系營養限制之指標物種，我們無從得知。本研究於亞熱帶氣候的台灣福山試驗林，採集台灣巢蕨及巢蕨，及地生與附生之腎蕨，共三種植物種植於溫室內，並透過施肥實驗，添加氮、磷、及加氮又加磷及未施肥之控制組，共四種處理，觀察附生植物地上部生物量的增益，以檢驗附生植物受哪項營養元素所影響；同時觀察不同生長方式腎蕨地上部生物量是否有差異，以評估附生植物之營養限制是否和地生植物一樣，進而做為亞熱帶森林營養限制之指標。實驗結果顯示，施肥處理對兩巢蕨之地上部生物量變化皆有顯著的影響，以巢蕨而言，加氮加磷組的地上部生物量變化顯著高於加氮組、控制組，以加磷組的地上部生物量變化增加最少；而台灣巢蕨同樣以加氮加磷處理組的地上部生物量變化高於加氮組，並高於其他兩處理組。附生型腎蕨的檢測結果顯示三種肥料添加方式之間沒有顯著的差異，但均顯著的高於控制組的地上部生物量變化；地生型腎蕨地上部生物量變化則是以加磷處理組顯著的高於加氮加磷組並高於加氮與控制組。由上述結果可見，台灣亞熱帶地區森林內附生植物的營養限制在不同物種間並不一致，且並非受到單一元素所限制，可能同時受到氮、磷兩元素限制其生長。而本次的實驗結果也顯示，地生與附生生長類型之植被有著相同之營養限制。There are several mechanisms to affect forest ecosystem, these mechanisms change forest ecosystem’s structure, microenvironment, nutrient cycling in different ways. Nutrient limitation is one of the famous mechanism that have been well-studied through fertilization experiment in last twenty years, and studies have shown that temperate forest limit by nitrogen and tropical forest limit by phosphorus, but there are few researches in subtropical area. And it’s critical to know nutrient limitation in subtropical forest in order to understanding global nutrient cycling. Epiphytes play an important role in forest ecosystem, especially for tropical and subtropical forest. They take big part of nutrient capital in forest ecosystem even though their biomass is low. In general, studies show that epiphyte’s limiting factor is water, but study in Hawaii shows different result, they said epiphyte share the same limiting nutrient with plant which grow on ground, and it also display epiphytes have faster reaction after fertilization because their short life cycle. So we don’t really know about epiphyte’s limiting factor, especially in subtropical forest. Our studies try to figure out nutrient limitation in subtropical forest through fertilization experiment in the greenhouse. We chose two common epiphytes and another epiphyte which can grow on tree and ground, fertilize these plants with nitrogen and phosphorus in four treatments in the greenhouse to test the nutrient limitation in subtropical forest ecosystem. We use last data build a regression model, then estimate the real aboveground biomass with leaf dry weight, average leaf length, total leaf number each month. The Asplenium antiquum analysis shows aboveground biomass in fertilization with nitrogen and phosphorus are significant higher than other treatment; and aboveground biomass of Asplenium nidus L. in nitrogen and phosphorus treatment are also higher than nitrogen treatment and the others. Nephrolepidaceae’s analysis in epiphyte form show there are no differences between treatments with fertilization, but their aboveground biomass are all significant higher than control; the aboveground biomass of Nephrolepidaceae which grow on ground in phosphorus treatment is higher than the nitrogen and phosphorus treatment and the others. Our results show epiphytes in subtropical forest in Taiwan are not limited by single element but co-limited by several elements like nitrogen and phosphorus. Our results also show epiphytes share the same nutrient limitation with plant which grow on ground.