臺灣雲杉葉部碳氮之分布與動態

Abstract

碳、氮為植物體內含量極豐的兩種元素。前者可概分為結構性碳(如木質素、纖維素、半纖維素)及非結構性碳(如醣類、脂質、二次代謝物)，後者則大致可區分為有機氮(如蛋白質、胺基酸)及無機氮(如硝酸根離子)。本研究以南投塔塔加鞍部的臺灣雲杉(Picea morrisonicola)為對象，分冠層為六個不同部位，並區分針葉年齡，探討葉部全氮、全碳及非結構性碳水化合物(即醣類，以下簡稱TNC)的濃度與分布。其中TNC定義為可溶性醣類及澱粉兩種物質的加總。 在季節變化方面，全氮濃度在生長季初始、芽苞初脫鱗(bud-break)而生長時濃度特別高。隨著針葉完全開展(flush)，其濃度則受到增加之生物量(biomass)稀釋。可溶性醣類和TNC濃度呈現相同趨勢，芽苞初脫鱗時濃度最少，展葉後逐漸累積直至隔年3月(葉齡10個月)，在新芽苞於生長季脫鱗展葉時再度下降。推論TNC會由其他年齡的針葉轉移至新生針葉，提供初展葉時的碳水化合物來源。澱粉的濃度則上下震盪，大約維持10%濃度；由於光合作用旺盛時，產生過多之葡萄糖會以蔗糖或澱粉形式暫存，故推論澱粉濃度的多寡可能和枝條、針葉的生長相關。 在冠層位置方面，全氮、全碳及澱粉的濃度基本上不受影響；可溶性醣類及TNC則傾向分布於冠層上部及外側的區域。推論這些部位因受光量強，光合作用較為旺盛。 隨著葉齡增長，針葉內的全氮濃度顯著減少，可溶性醣類及TNC濃度顯著增加，全碳及澱粉濃度則不受影響。推論氮元素傾向分布於新生針葉，而醣類及TNC則會隨葉齡不斷累積。 整體而言，本研究中探討的物質有明顯的季節性動態，並分別受到葉齡及冠層位置的影響。

Carbon and nitrogen both are very important elements in plants. Carbon can be divided into structural carbon (like lignin, cellulose and hemicellulose) and nonstructural carbon (like carbohydrate, lipid and metabolite). Nitrogen can be divided into organic nitrogen (like protein and amino acid) and inorganic nitrogen (like nitrate). In this study, Taiwan spruce (Picea morrisonicola) was used to discuss the distribution and dynamics of total nitrogen, total carbon and carbohydrates in green needles, with different canopy positions and needle ages. The carbohydrates here are defined as soluble sugars plus starch. Total nitrogen concentration after bud-breaking in early growth season is particularly high. With the needle flushing, it was diluted by increasing biomass. Soluble sugars and non-structural carbohydrates showed the same trend that accumulated until the following March (needle ages was ten months) after bud-breaking, and decreased in May when next bud-breaking. It showed that carbohydrates in older needles would be transferred into new ones, providing the nutrient sources for beginning of growth. Starch concentration up and down repeated and maintain about 10 %. If forming too much glucose through photosynthesis, it will be a temporary storage by converting to sucrose or starch, so that starch contents may be associated with needle growth and branch elongation. Besides to be the energy sources of respiration and physiological reactions, carbohydrates could convert to structural materials, lipids, and metabolites through kinds of biosynthetic pathway. Soluble sugars and carbohydrates tended to distribute to upper and outer in crown, showing that these parts of crown might receive more irradiation and could product more photosynthetic materials. Total carbon and starch in needles only had the seasonal trends, and no differences no matter which canopy position or needle ages. With needle age increasing, total nitrogen in green needles was deceasing obviously, soluble sugars and carbohydrates were increasing instead. It showed that nitrogen tended to distribute to younger needles, but soluble sugars and carbohydrates tended to be accumulated in older ones. As a whole, the substances in this study had significantly seasonal trends, and affected by canopy position and needle age separately.