溫度與養液氮濃度對蘇鐵蕨生長與孢子葉形成之影響

Effects of Temperature and Nutrient Solution Nitrogen Concentration on Growth and Sporophyll Production of Brainea insignis

蘇鐵蕨原生於臺灣與東南亞國家，觀賞性高但瀕臨絕滅，亟待建立孢子繁殖與栽培資訊。本研究探討溫度與養液氮(nitrogen, N)濃度對蘇鐵蕨生長，以利保育與復育此原生蕨類。將蘇鐵蕨孢子撒播於無土混合介質，在20、25或30℃環境，每天以24 μmol·m-2·s-1照光12 h，結果以25℃最適合配子體發育及孢子體形成。將具3至4片葉之蘇鐵蕨置於自然光照人工氣候室五種日/夜溫處理198天，結果顯示以15/13及20/15℃處理者生長緩慢且未形成孢子葉；以25/20或30/25℃處理者生長快速，分別有50%與38%植株在具14-16片葉、莖徑約2 cm大小時即可產生孢子葉；於35/30℃處理者生長不良，四個月後植株全部死亡。另取具8-13片葉之蘇鐵蕨，以不同養液N濃度處理2個月後，結果顯示隨N濃度由0增加至12 mM使莖徑、葉數、葉綠素計SPAD-502讀值與地上部乾重等各項生長指標上升，再增加N濃度至16 mM會降低地上部乾重。缺N與4 mM N處理者生長緩慢、葉片之Fv/Fm與光量子產量較低、且未有植株產生孢子葉。以12 mM N處理者有50%的植株於具16片葉大小時產生4-5片孢子葉。

Brainea insignis (Hook.) J. Sm. is an endangered fern native to Taiwan and Southeast Asia areas, with high ornamental values. It is therefore urgent to establish the related spore propagation and cultural practices. Effects of temperature and nutrient solution nitrogen (N) concentration on gametophyte development and sporophyte growth were studied to facilitate conservation and restoration. Fresh spores were collected and sown on soilless mix at 20, 25, and 30℃ with a 12-h photoperiod under 24 μmol·m-2·s-1 photosynthetic photon flux density. The earliest and most sporophytes were seen at 25℃ treatment. Young sporophytes with 3-4 fronds were placed in natural phytotrons with five day/night temperature treatments for 198 days. Results showed that plants at 15/13 and 20/15℃ grew slowly and did not produce any sporophylls. In contrast, plants at 25/20 and 30/25℃ grew faster, with 50% and 38% plants produced sporophylls when they had 14-16 visible fronds, with 2-cm stem diameter. Plants at 35/30℃ died after treatment for 4 months. Sporophytes with 8-13 fronds were fertigated once per week with Johnson’s solution containing various N concentrations for two months. Results showed that increased N concentration up to 12 mM increased stem diameter, frond number, frond SPAD-502 value, and shoot dry weight. Further increased N to 16 mM reduced shoot dry weight. Plants at 0 or 4 mM N grew slowly, with reduced Fv/Fm and quantum yield values, and did not produce any sporophylls. Half plants at 12 mM N produced 4-5 sporophylls when they had 16 fronds.