臺灣兩種滿江紅的鑑定、生理特徵及生長探討

Abstract

滿江紅是多年生、漂浮型水生蕨類，植株會與固氮藍綠菌共生，逆境下葉片會由綠轉紅。根據台灣植物誌記載，台灣只有一種原生種滿江紅 (Azolla pinnata R. Br.)，但近幾年野外較常見的是另一分類地位不明的歸化種滿江紅，且其族群有增加趨勢，本研究目的為：一、比較台灣兩種滿江紅的外部形態並以分子工具鑑定；二、分析與兩種滿江紅共生的固氮藍綠菌菌株；三、探討歸化種滿江紅逐漸佔優勢的原因。 原生種滿江紅與歸化種滿江紅植株分別近似三角形與樹枝狀的多邊形，掃描式電子顯微鏡觀察浮水葉表面的結果顯示原生種滿江紅有較大的氣孔孔隙和較高的毛茸密度，據此推測：原生種也許有較高的氣孔導度以及能反射較多的光線，可能影響其光合作用速率與其受光抑制情形。 抽取生長在不同地區的兩種滿江紅葉綠體DNA之四個基因片段，定序後與NCBI下載的參考序列比對分析，結果顯示同一種滿江紅的序列不因來源而有差異，原生種滿江紅為A. pinnata，歸化種滿江紅屬於A. mexicana 與A. microphylla複合群 (MIC-MEX complex)。 將滿江紅葉片壓碎後取得共生的藍綠菌懸浮液，分析其16S rRNA基因，再與NCBI下載的參考序列比對，發現兩種滿江紅與不同的共生藍綠菌共生，分布在不同地區的同種滿江紅族群具相同的共生藍綠菌菌株，顯示其共生具有專一性。 在不同季節將滿江紅種植於台大農場水池，並進行全光照及70 % 遮陰處理，測量發現在相同光環境下，兩者具有相似的光合作用氣體交換特徵，但歸化種比原生種更容易受到光抑制。在2015年冬季與秋季期間歸化種比原生種有較快的相對生長速率 (RGR)，而於此兩季的歸化種分別比原生種有較高的比葉面積 (SLA) 及光合作用氮使用效率 (PNUE)；根據結果推論，資源使用效率是影響兩種滿江紅生長速率不同的重要原因。

Azolla, a perennial and floating aquatic fern, often forms symbiosis with nitrogen-fixing cyanobacteria and turns red under stress. One native Azolla species (A. pinnata R. Br.) was recorded in Flora of Taiwan. Recently, a naturalized Azolla species is commonly found in field and becomes more dominant than the native species. The identity of the naturalized species is unknown. The aims of this study are: (I) to compare the morphological traits and to identify the two Azolla species in Taiwan by molecular tool, (II) to compare their cyanobacterial symbionts, and (III) to figure out what make the naturalized species becomes more dominant than the native species. The plant shape of the native and naturalized species are triangular and polygonal, respectively. The SEM observation of the upper lobe of leaves revealed that the native species had larger stomatal pore length and higher trichome density than the naturalized species. These imply that the native species might have higher stomatal conductance and reflect more light than the naturalized species, therefore may impact on the photosynthetic rate and the level of photoinhibition. The DNA sequence data of four plastid loci of the two Azolla species sampled from different populations revealed that the native and naturalized species belong to A. pinnata and MIC-MEX complex, respectively. Results of the analysis of 16S rRNA genes suggest that two species harbored different species of cyanobionts, but different populations of the same Azolla species formed symbiosis with same cyanobionts. Thus, host-symbiont specificity in Azolla and cyanobionts was found. Growth of the two Azolla spp. in NTU paddy field in different seasons under two light treatments (full sun and 70 % reduction of light) were measured. Under the same light treatment, two species had similar photosynthetic gas exchange traits, but the naturalized species was more photoinhibited than the native species (A. pinnata). In comparision to A. pinnata, the naturalized species had higher relative growth rate (RGR) in winter and fall of 2015. Besides, the naturalized species had higher specific leaf area (SLA) and higher photosynthetic nitrogen use efficiency (PNUE) than A. pinnata respectively in winter and and fall of 2015. Accordingly, resource use efficiency might contribute to the differences in RGR of both species.