藿香薊種子發芽生態生理學及其田間建立之研究

Abstract

本論文目的在於探討紫、白花藿香薊種子發芽生態生理，包括環境因子與種子發芽能力關係、種子發芽能力之周年變遷，以瞭解紫、白花藿香薊影響種子發芽的因素，並藉以建構兩種植物作為休耕地田間覆蓋植物之方法。結果如下: 恆溫下兩種植物種子發芽率均不高；30/25、35/300C、23/130C等變溫環境下則容易發芽。紫花與白花藿香薊種子基礎發芽溫度(Tb)分別為6.40C與6.60C，發芽所需要之積溫紫花藿香薊為700Cd、白花藿香薊為720Cd。高水勢會影響種子發芽，溫度為25/200C時紫花藿香薊在-0.8MPa下尚有部分種子可發芽；白花藿香薊最高忍受之缺水逆境達-1.0MPa，較紫花藿香薊更耐。紫花藿香薊種子發芽較白花藿香薊需要接收更高的光量；光照無氧下紫花藿香薊種子發芽率較高，白花藿香薊的發芽率低。土壤酸鹼度對兩種植物種子發芽的影響一致，以pH7下發芽率最高。埋土深度2公分以上藿香薊種子即不能發芽，能忍受埋土深度為1.5公分；溫度愈低愈不能忍受深埋。 紫花藿香薊種子發芽之基礎溫度為7.00C，基礎水勢Ψb(50) 為-0.436 MPa，水溫積蘊值θHT為250C Mpa-day、基礎水勢變方σΨb為0.316 Mpa，種子發芽模式為Probit(G)=【Ψ-25/(T-7.0)Tg-(-0.436)】/0.316。 就種子發芽能力週年變遷而言，紫白花藿香薊種子採收後初期在黑暗下有制約休眠，紫花藿香薊制約休眠較白花藿香薊為強；不同季節之埋土試驗種子在黑暗下制約休眠差異極大。冬天進行旱田埋土試驗之種子於埋土半年後兩種藿香薊種子約有35%種子消失，試驗2年結束後約有70%之種子消失，埋土1-4 個月發芽率尚達70%以上，試驗結束各發芽率不到10%。夏天進行旱田埋土試驗之種子於埋土3個月後紫花藿香薊種子約有10%消失，白花藿香薊則達15%種子消失，紫花試驗半年、白花試驗3個月發芽率則低於20%。夏天進行水田埋土試驗種子於埋土3個月後紫花藿香薊種子約有5%消失，白花藿香薊則達8%種子消失，紫、白花試驗8個月發芽率則低於30%，水、旱田試驗顯示：水田埋土種子消失較慢，發芽率較高。兩種植物萌芽高峰期在每年10月。 田間犁田顯示一年12個月紫花與白花藿香薊皆可由田間自發。播種種子田間自然萌芽前3個月累計萌芽率達80%以上。除12月播種生長較慢外，其餘播種於3月、6月、9月者植株生長良好，播種後60天田間覆蓋率可達77%。但12月份播種者生長較遲緩。不同月份播種下，紫花藿香薊單株所產生種子數差異極大介於3000-7000粒之間；而白花藿香薊單株種子數則介於2000-22000 粒之間；湛水水田撒播每平方公尺0.2 g(約1300-1600粒種子)之紫、白花藿香薊種子， 4個月水田收割後每平方公尺約長出80-100株之藿香薊。二期作水田收割後自行長出之紫白花藿香薊全開花期為45天、一期作之水田收割後紫、白花藿香薊全開花期則達80天。 於種植玉米、落花生、田菁與休耕地等旱田中撒播藿香薊種子，每平方公尺0.05 g(約300粒種子)在秋作者有89-124粒之種子出土，可達到完整之植被景觀覆蓋，且全開花期達60天以上，在春作者有57-93粒之種子出土，可達到完整之植被景觀覆蓋，且全開花期達80天以上。前述旱田於作物收穫後翻耕後，藿香薊田間出現率在秋作者每平方公尺在58-116株間，全開花期45天；春作者每平方公尺在66-90株之間，且全開花期約72天。 稻田收穫後施以淺耕或覆蓋，藿香薊植株出土的數量較焚燒稻草者多；秋作落花生收穫後與春作玉米收穫後的焚燒，亦會降低藿香薊植株之出現；藿香薊與田菁混植，當田菁發生嚴重蟲害時，藿香薊可發揮補償作用快速覆蓋農田。

The thesis aims to study the seed eco-phsiology of Ageratum houstonianum Mill. and Ageratum conyzoides L., including how the germination was affected by various environment factors. The second propose of the thesis is to explore the possibility and method establishing these two weeds as cover plants for fallow land field. Both the seeds of A. houstonianum and A. conyzoides were low in germination percentage under constant temperature; the percentage was higher under alternate temperatures such as 30/25, 35/30 and 23/130C. The base temperature (Tb) for the germination of A. houstonianum and A. conyzoides seeds were 6.40C and 6.60C respectively. The thermal time for seed germination of A. houstonianum was 700Cd; for A. conyzoides it was 720Cd. High water potential affected seed germination. Part of seed of A. houstonianum still germinated under -0.8MPa and 25/200C regimes. Seeds of A. conyzoides were more tolerate to low water potential; some seeds germinated at as low as -1.0MPa. The seeds of A. houstonianum required more light photons to germinate than those of A. conyzoides. Under light and anoxia condition the germination percentage of A. houstonianum was higher than that of A. conyzoides. Soil pH showed the same effect on seed germination of both two species, the germination percentage was highest at pH7. The seeds of both species were not able to germinate at burial condition deeper than 2 cm. The lower the temperature, the less depth the seeds might tolerate in terms of germination. The base temperature, base water potential (Ψb(50)), hydrothermal time (θHT), and base water potential variance (σΨb) for seed germination of A. houstonianum were 7.0°C, -0.436MPa, 250CMpa-day, and 0.316Mpa respectively. The seed germination model for this species was: Probit(G) = [Ψ-25/(T-7.0)Tg-(-0.436)]/0.316. Under dark germination condition, the exhumed seed of both species showed conditional dormancy at the beginning of burial experiment; the dormancy was higher in seeds of A. houstonianum. Dormancy profile were different between burial experiments initiated at different season. Burial experiment initiated in winter upland showed a loss of about 35% in seeds after 6 months burial, and 70% after two years. More than 70% of the buried seeds remained germinable after 4 months burial; however, there were less than 10% at the end of the two-year experiment. Burial experiment initiated in summer upland showed a loss of 10 and 15% in seeds of A. houstonianum and A. conyzoides respectively after 3 months burial. Less than 20% seeds remained germinable after 6 and 3 months burial for A. houstonianum and A. conyzoides respectively. Burial experiment initiated in summer paddy field showed a loss of 5 and 8% in seeds of A. houstonianum and A. conyzoides respectively after 3 months burial. Less than 30% seeds remained germinable after 8 months burial for both Ageratum species. The disappearances of seeds were slower and the germinability higher in those seeds buried in paddy field than those in upland field. Both species showed a peak emergence in October each year. Monthly plowing treatment showed that the seeds of both species could emerge all year round. In the field the emergence percentage of the sowed seeds of both species reached 80% after 3 months. The plants of both species grew well when sowed in March, June, and September. Field covering rate reached 77% at 60th days after sowing. The growth appeared slower when sowed in December. Seed number produced by a single plant varied from 3000 to 7000 and from 2000 to 22000 for A. houstonianum and A. conyzoides respectively, dependent on the sowing month. In a flooding rice field, a sowing rate of approximately 1300-1600 seeds (0.2g/m2) of Ageratum could grow 80-100 plants after 4 months at rice harvest. Volunteer Ageratum appeared after the harvest of the 2nd rice crop had a flowering period of 45 days, and 80 days for those appeared after the harvest of the 1st rice crop. In autumn crops of corn, peanut, sesbania fields or let fallow, sowing approximately 300 seeds of Ageratum (0.05g/m2) resulted in 89-124 plants and could reach full covering with a flowering period of 60 days. While in spring crops, the same treatment resulted in 57-93 plants and could reach full covering with a flowering period of 80 days. About 58-116 volunteer Ageratum per meter square appeared after the harvest and plowing of the autumn crops, with a full flowering period of 45 days; while for those of the spring season, 66-90 plants appeared with 72 days of full flowering period. After rice harvest, more Ageratum appeared in the fields that were managed with shallow plowing or straw-mulching than that managed with straw-burning. In spring crop of corn and fall crop of peanut, burning the straw after harvesting also reduced the appearance of Ageratum. In a stand mixed sowing with sesbania and Ageratum, Ageratum could be able to grow quickly to cover the farmland if the sesbania be damaged by pests, according to the result of sesbania cutting experiment.