天然群落中微型浮游植物的元素含量及組成變化

Abstract

水環境中浮游植物對於物質在生物地球化學循環中，扮演極為重要角色。本研究利用超微過濾方式 (Ultrafiltration) 分離族群並配合多種技術 (計數器、高壓液相層析儀、元素分析儀、石墨爐式原子吸光儀及顯微鏡)，探討在自然環境中，微型浮游植物 (0.2~10μm) 基本元素組成、微量金屬含量與莫耳比變化。 本實驗結果顯示，季節轉變會造成淡水湖及海洋微型浮游植物族群及個體元素組成改變。綠藻、藍綠藻、矽藻、金黃藻等族群元素組成皆不相同。個體元素組成平均而言，碳、氮、硫及磷含量分別為20.56 ± 8.78 %、4.11 ± 1.82 %、1.06 ± 0.75 %，以及4.32 ± 3.39 %，各元素組成各異，非為定值。此外，各微量金屬 (鐵、鋅、銅、鎳、鎘) 含量及濃度莫耳比值與前人研究亦不相同。本研究醉月湖微型浮游植物平均元素含量為 (C105.6N16.6P1S0.8)1000Fe141Zn3.2Cu0.20Ni0.31Cd0.006，而台灣邊緣海浮游植物則為 (C90.9N16.7P1S1.6)1000Fe27Zn2.0Cu0.19Ni0.16Cd0.001。水中浮游植物隨著季節轉變，族群組成及其個體元素含量差異性明顯。此外，本研究亦發現鐵與銅及鎳與鎘有良好線性關係，各受到光合作用與代謝作用互相影響導致。不同物種之微型浮游植物其碳、氮、硫含量 (及各微量金屬)，並非遵循固定之等比吸收代謝比值 (i.e., Redfield ratio)，由實驗室馴化培養微型浮游植物所得之莫耳吸收比或反應比率，並不適用於自然環境。

In natural water, phytoplankton plays an extremely important role in biogeochemical cycle of elements. In this study, nanoplankton populations and elemental composition were investigated. The planktons were first isolated and concentrated with the used of ultra-clean cross-flow filtration technique, and then, cell numbers were counted by Coulter Counter, phytoplankton photopigments were analyzed by High Pressure Liquid Chromatography, carbon and nitrogen were measured by Elemental Analyzer, trace metals were measured by Graphite Furnace-Atomic Absorption Spectrometry. The results showed that the phytoplankton populations (green algae, blue-green algae, diatoms, golden algae) and elemental composition are significantly different among each month, and between freshwater and marine environments. On the average, the concentrations of C, N, S, and P in collected nanoplankton were 20.56 ± 8.78 %, 4.11 ± 1.82 %, 1.06 ± 0.75 %, and, 4.32 ± 3.39 % respectively. Trace metal (Fe, Zn, Cu, Cd, Ni) contents, and the elemental (C, N, S, P) to trace metal mole ratio were found different then previous studies. On average, a mole stoichiometry ratio of (C105.6N16.6P1S0.8)1000Fe141Zn3.2Cu0.20Ni0.31Cd0.006 is found for freshwater nanoplankton, and (C90.9N16.7P1S1.6)1000Fe27Zn2.0Cu0.19Ni0.16Cd0.001 for marine nanoplankton. In addition, strong correlations were found between Fe and Cu, and that of Ni and Cd, due to corresponding roles in photosynthese and metabolic reactions. It is concluded that molar absorption ratio and reaction rate obtained from lab-cultured experiments and domesticated nanophytoplankton are significant different than the ones collected from natural environment.