蘇鐵蕨之物候、孢子繁殖與溫度及養液濃度對生長之影響

Abstract

觀察埔里石坑地區(23°59’ N, 121°00’E；Alt. 790 m)蘇鐵蕨之物候現象，包括萌芽期、展葉期、孢子成熟期、孢子發散期及生長停滯期。結果顯示，4月為主要萌芽期；5月為主要展葉期、孢子成熟期及孢子發散期；6至11月則生長減緩，而12到3月為主要生長停滯期。蘇鐵蕨莖徑寬大於7 cm時，已具形成孢子的能力，但需莖徑大於10 cm以上時才會有較多的孢子葉形成，而莖徑大小與萌發葉片數亦有顯著正相關，莖徑越大萌發的葉片數越多且結孢葉片數也會較多。 蘇鐵蕨孢子撒播於直徑12 cm之塑膠盒，每盒分別滴入70滴孢子懸浮液，每滴約300粒孢子，以不同溫度(20、25或30℃)栽培和栽培介質浸泡不同養液處理。結果顯示以25℃最適合配子體發育及形成孢子體，孢子撒播後一週內即發芽並形成二次元原葉體，3週後原葉體形成頂端分生組織，5週後分化藏精器及藏卵器，10週後長出第一片幼孢子葉， 14週後每盒平均已有178孢子體。養液濃度方面，將撒播孢子之無土混合介質以25%、50%及100%不同強生氏營養液浸泡一次和對照組只給予一次蒸餾水處理11週，只有以100%強生氏營養液處理者，平均每盒有1.1棵幼孢子體產生，其餘處理則在孢子發芽形成配子體後，陸續死亡並未形成孢子體。 將具3至4片葉之蘇鐵蕨幼孢子體置於15/13、20/15、25/20、30/25或35/30 ℃等五種日/夜溫處理。處理198天後，以 15/13及20/15℃處理者生長緩慢，葉片呈紅褐色並未結孢子。以 30/25及25/20 ℃處理者生長快速，植株平均有22葉片並已開始結孢子，其中以25/20 ℃下有較多之結孢植株，而在35/30 ℃處理者，則生長不良，四個月後植株全部死亡。另外蘇鐵蕨以每週施用一次25%、50%或100%強生氏完全營養液及自來水處理10週後，自來水處理者葉片黃化，而以50%強生氏營養液處理者生長最佳，植株總葉數較多、莖徑較大，且有較多的結孢植株。因此將蘇鐵蕨的孢子體置於日/夜溫25/20 ℃下並每週施用一次50%強生氏完全營養液，蘇鐵蕨的孢子體生長即有良好的表現。 不同氮濃度(0、4、8、12或16 mM)處理蘇鐵蕨幼孢子體，以12 mM氮處理者表現最佳，有最大的葉長，葉寬及莖徑，植株地上部和地下部乾重亦最重，且並有較多的葉片形成孢子。而以16 mM氮處理者其生長下降， 4 mM氮處理者並未有植株產生孢子，而8 mM氮處理只有12.5%的植株結孢。施用12 mM氮處理者在8週後就開始有孢子葉展開，試驗結束後以12或16 mM氮處理者有較多的結孢植株，可達50%，但以12 mM氮處理者有較多的羽片形成孢子囊群，且16 mM氮處理者之孢子葉呈皺縮，似乎有生長不正常之現象。

Phenology of Brainea insignis was investigated at Puli, Nantou Shihkung area in Taiwan (23°59’ N, 121°00’E；Alt. 790 m). Phenology of Brainea insignis could be classified into the following phases: 1) main frond emergence in April, 2) frond expansion, spore maturation, and spore release in May, 3) slow growth from June to November, and 4) standstill growth from December to March, when the plants exhibit no obvious growth. In the wild, plants of Brainea insignis could form trophosporophyll when stem diameter reached 7 cm. More trophosporophylls were observed in plants with stem diameter wider than 10 cm. New frond number and trophosporophyll number increased with increasing stem diameter. Spore solution of Brainea insignis were dripped in plastic boxes with soilless mix, each drop contains about 300 spores. The effects of temperature (20, 25, and 30 ℃) and nutrient solution concentration on gametophyte development and sporophyte formation were studied. A temperature of 25 ℃ was found to be the optimum temperature for growth of gametophyte and sporophyte formation. After sowing for one week under 25 ℃ conditions, spores germinated and developed to two dimensional prothalli. After sowing for three weeks, apical meristem formed in the gametophyte. Antheridia and archegonia were observed in gametophytes after sowing for five weeks. First young sporophyte was recorded after sowing for ten weeks. A total of 178 sporophytes per box were recorded after sowing for 14 weeks. Different concentrations of Johnson’s solution (0%, 25%, 50%, and 100%) were incorporated to the sowing mix before sowing, only treatment with 100% Johnson’s solution formed sporophytes after sowing for 11 weeks. Spores germinated and formed gametophytes but did not form sporophyte in other treatments and were dead after sowing for 11 weeks. Young sporophytes of Brainea insignis with 3 to 4 unfolded fronds were grown under various day/night temperature regimes (15/13, 20/15, 25/20, 30/25, and 35/30 ℃) for 198 days. Sporophytes grew faster under 30/25 and 25/20 ℃, and started to form trophosporophylls with 22 fronds. In contrast, growth of sporophytes was slow under 20/15 and 15/13 ℃, where the fronds turned red and no trophosporophyll formed. No sporophyte was survived under 35/30 ℃ after 120 days. Plants under 25/20 ℃ produced the most trophosporophylls. Moreover, after weekly fertigation of distilled water or 25%, 50%, or 100% Johnson’s solution for ten weeks, sporophytes fertigated with 50% Johnson’s solution resulted in most frond number, stem diameter and trophosporophylls, but sporophytes given distilled water turned yellow. Thereby, young sporophytes of Brainea insignis should be grown under day/night temperature 25/20 ℃, and fertigated with 50% Johnson’s solution weekly, which resulted in better growth. Young sporophytes of Brainea insignis were fertigated with Johnson’s solution containing various nitrogen (N) concentrations. Plants at 12 mM N produced the maximum frond length and width, stem diameter, shoot and root dry weights, and trophosporophylls. Reduced growth was recorded in plants at 16 mM N concentrations. No trophosporophyll was seen in plants at 0 or 4 mM N treatments, while 12.5 % of plants formed sori at 8 mM N. Plants at 12 mM N had highest frond appearance rate and started to expand trophosporophylls after eight weeks of treatment. Half plants formed trophosporophyll at 12 or 16 mM N treatments. The 12 mM N treated plants had more pinnule with sori, while the 16 mM N treated plants exhibited wrinkled trophosporophylls.