|Abstract: ||摘 要 本論文於1999年7月至2003年9月, 在台灣東北沿岸海域之副熱帶生態系, 對於細菌, 藍綠細菌及微細鞭毛蟲進行日週數量的季節性變動研究。 發現細菌, 藍綠細菌及微細鞭毛蟲豐度會有明顯的季節性變化, 呈現暖季高 (6至10月) 冷季低 (11至5月)的現象。 另一方面藍綠細菌與微細鞭毛蟲的數量在表水溫超過25℃時 (6月) 開始會有日夜變化產生, 藍綠細菌的高值在晚上會出現,而微細鞭毛蟲相反的則在白天會有高值出現, 但細菌則沒有明顯日夜的數量差異產生。 再者,為進一步瞭解上述細菌與藍綠細菌其日夜數量變化差異的原因,本研究另於2002年8月至2003年7月間, 使用分割過濾法來量測細菌與藍綠細菌成長及被捕食率來探討。 由培養結果發現, 細菌的成長與被攝食速率年間會有10倍左右的變動, 而藍綠細菌變動較小約有2-5倍的年間差異。 經分析之後清楚看出, 在暖季期間, 細菌與藍綠細菌的成長與攝食會有明顯的日夜變化, 細菌兩者速率都呈現白天大於晚上,同時兩者平衡, 因此細菌數量不會產生明顯日夜變化。 而藍綠細菌則與細菌的趨勢相反顯現出白天成長大於攝食, 而晚上則攝食超過成長, 因此造成在暖季時藍綠細菌數量會有日週變動產生。 而冷季期間, 細菌及藍綠細菌之成長與被攝食的速率並沒有呈現明顯的日夜差異。 另外以上述實驗結果可推估微細鞭毛蟲白天攝食餌料的主要來源為細菌 (佔總碳量85%), 而晚上則相反, 82% 的食物是藍綠細菌所供給。 季節間餌料生物重要性也有明顯差異, 暖季期間, 細菌與藍綠細菌佔微細鞭毛蟲餌料生物之比例大略相同, 但在冷季時, 微細鞭毛蟲主要的餌料來源為細菌，佔了所有能量來源的81%, 因此在冷季時, 細菌的角色比藍綠細菌來的重要。 另外為進一步瞭解控制藍綠細菌在暖季期間產生日夜變動的因子, 特別設計添加不同濃度藍綠細菌的培養實驗及使用細胞分裂頻度（Frequency of Dividing Cell）的方法來推估攝食與成長的變動情形,據此建立一個模式與現場藍綠細菌相比較。由此模式的推測結果可知,微細鞭毛蟲的攝食速率與藍綠細菌的密度有關, 表示著藍綠細菌的密度越高其攝食速率也越快。而溫度會改變藍綠細菌的成長, 溫度越高成長越快。 所以可看出在暖季時, 藍綠細菌在白天期間數量增加較快。而當藍綠細菌在晚上達到高值後, 由於藍綠細菌密度的增加致使微細鞭毛蟲的攝食能力增加, 而迅速移除在水體中藍綠細菌的數量。|
Abstract We analyzed seasonal and diel fluctuation patterns of heterotophic bacteria, Synechococcus spp., and nanoflagellates at a coastal station in the northeast of Taiwan between July 1999 and September 2003. All of these organic exhibited a clear seasonal cycle, with high values during the warm seasons (June to October) and lower values during the cold seasons (November to May). Synechococcus spp. and nanoflagellates exhibited diel fluctuation at water temperatures above 25°C. Cell concentrations of Synechococcus spp. were significantly higher during the evening, whereas those of nanoflagellates were higher during the day. The day and night amounts of heterotrophic bacteria did not differ significantly, and we did not observe diel rhythms of these organisms below 25°C. The fractionation experiments we performed between between August 2002 and July 2003. In the subtropical coastal ecosystem, a two-phased (warm>25℃, cold <25℃) seasonal cycle with a 10-fold variation was found in the picoplankton growth and grazing rate. The only exception was the grazing rate of Synechococcus (2-5 fold). A significant diel cycle of picoplankton growth and grazing rates existed during the warm season with both rates in bacteria being day>night while, in contrast, Synechococcus was night>day. During the warm season, our study clearly indicate that nanoflagellates largely depend on bacteria as an energy source in the daytime, but about Synechococcus contributed about 82% of the nanoflagellate diet at night. Another, in the warm season, naoflagellates consumed equal proportions of bacteria and Synechococcus spp. production; therefore, both consumption processes have an equal significance in warm season. However, during the cold season, bacteria contributed about 81% of the nanoflagellate diet, making it a more important food source than Synechococcus. For studying the control factors of diel variations in Synechococcus abundance during the warm season, to use culture experiment with different density of Synechococcus and Frequency of Dividing Cell method to measure the variations of grazing and growth, and build the model by this method. For the results of model, the grazing rates of nanoflagellates are positively correlated with Synechococcus abundance, it mean that nanoflagellate grazing rates were likely to increase with Synechococcus abundance. Another, temperature could control the growth of Synechococcus, by this reason, we know that nanoflagellates grazing rates were likely to increase at night after Synechococcus had peak, and removed the Synechococcus abundance quickly.