臺灣西半部金毛杜鵑開花韻律分析與族群分布之研究

Abstract

植物繁殖研究方面可藉由開花物候調查及開花類型分析發現更細緻多樣的開花模式，在世界上廣泛分布的杜鵑花屬植物，其花期會隨著緯度及氣候的變化而改變，其中熱帶山區的杜鵑花期歧異度有增高的現象。廣泛分布的臺灣特有種金毛杜鵑，已發現在嘉義楠梓仙溪林道的金毛杜鵑花期分散，且有樣株一年開花兩次的現象，不同於一般杜鵑花屬植物在春或初夏集中開花的花期。 本研究為了釐清金毛杜鵑的開花時間及韻律，自2007年1月開始每月中旬進行花期調查，在臺灣西半部12個監測區紀錄開花植株的開花數量，其中也進行樣條的生長繁殖紀錄。調查結果指出監測區1634棵植株年開花期範圍從1~11個月，開花次數為1~4次；年花季的變化是在2月及6月有明顯的低峰，屬集中春季與分散夏秋季一短一長的花期。 根據金毛杜鵑多樣的開花現象，進一步依花期季數與季節進行單株開花類群分型，可分成4大類22型，利用各類型的開花重要值指數=（開花株數百分比＋開花量百分比），展現花期或地理分布的差異，以單季春天開花、兩季夏秋、三季夏秋冬與全年開花為前四高的開花類型。分布於大安溪以北的植株以春季開花為主，中南部中低海拔植株由多樣的開花類型組成全年開花，在冬季有明顯的花期低峰，高海拔監測區的植株則集中在春或夏開花。 依分布位置的距離及受東北季風影響可細分成58個樣區，依各開花類型在樣區中的重要值，以TWINSPAN分析各類型樣區的分群，結果可分成春及非春兩群，分別以單季春及兩季夏秋為指標類型。進一步以CCA探討不同開花類型的樣區對環境因子的關係，結果表示樣區與海拔、緯度及5、6、8、11月雨量具有相關性，顯示金毛杜鵑的開花韻律與梅雨季、西南氣流、東北季風有密切關係。 分析花芽形成到開花的韻律，依花芽度冬性及花芽形成次數共分成三類，一為花芽在秋季一次形成後度冬，一致在春季開花；二為花芽在夏季一次形成，隨後月份開花不需度冬；第三類花芽在夏初形成，隨後開花，接著又長出新枝條且形成花芽，在隨後月份開花，一年內共形成花芽兩次。 透過開花的物候調查了解臺灣西半部金毛杜鵑的全年開花現象是由不同開花時間及少數全年開花的植株所構成，且在地域上有不同的開花類型組合，另外深入研究花芽形成及開花韻律上也有發現形成時間及次數的多樣性，本研究首次清楚剖析廣泛分布杜鵑花的花芽-開花韻律，提供物候研究和繁殖演化相關的新資訊，未來可進一步探討形成不同開花韻律的機制與在適應演化上的意義。

In studies of plant reproductive biology, flowering phenology and the classification of flowering types could discover further delicate and diversified flowering patterns. The genus Rhododendron is widely distributed throughout the world. Its flowering periods changed through the latitude and climate variation. The heterogeneity of flowering period of Rhododendron increased in tropical mountains. R. oldhamii Maxim. is an endemic species, and it spreads widely from low to high altitude in Taiwan. The previous study of investigation of R. oldhamii in Nantzuhsienhsi trail, Chiayi County, suggested where flowering time throughout the year and some individuals blooming twice in the year. Its flowering time differs from mass flowering in spring of most other Rhododendron species. This study was to clarify this special flowering rhythm of R. oldhamii for other than Nantzuhsienhsi trail. The 12 study sites were selected from north to south in western Taiwan since January 2007. Results showed that annual flowering period among 1634 individuals varied from 1 to 11 months, and the annual flowering frequency was 1~4 times. The obviously low flowering amounts were in February and June, and the flowering period was divided into two parts flowering in spring and flowering in summer-fall. The individuals of different flowering time were classified as 4 classes based on the number of flowering seasons in a year. These classes can differentiate into 22 types by the flowering seasons and sustainability. The important value index (IVI) of each flowering type was summed up the proportion of flowering individuals and the proportion of flowering amount. The top 4 IVI indicated the most important flowering types which were flowering in spring, in summer-fall, summer-fall-winter, and 4 seasons. The flowering periods were composed of the different individuals of flowering types in 12 sites. The individuals to the north of Dana River were flowering in spring. The individuals in southern Taiwan were flowering throughout the year, but there were low flowering amount in winter. Those at sites of high latitude were flowering in spring and summer. According to the distribution distance and the effect of the northeast monsoon, 12 sites were subdivided into 58 plots. The TWINSPAN resulted in two groups, flowering in spring and other seasons, and the indicators were flowering in spring and flowering in summer-fall. The CCA correlation among plots and environmental factors suggested that the latitude, altitude and the rainfall in May, June, August, and November were highly correlated in plots. This result showed the flowering rhythms were related to plum-rain, the southwest front and the northeast monsoon. The rhythms from floral bud initiation to flowering were classified to 3 types based on the floral bud riding out the winter and the frequency of floral bud formation. Type I was the floral bud initiation once in fall, riding out the winter, and flowering in next spring. Type II was the floral bud initiation once in summer, and flowering in later months. Type III was the floral bud initiation in summer, and flowering in later months, then new shoots sprout and floral bud initiation twice in a year. Results for flowering phenology showed that the phenomenon of flowering throughout the year in western Taiwan consisted of the individuals of flowering in different time and flowering throughout the year. There were constituted different flowering types in study sites. On the other hand, further study of flowering rhythm indicates that the diversity of the period and frequency of floral bud initiation. This study at first clearifies the floral bud to flowering rhythm of the widespread R. oldhamii, and provides the new information of phenology and reproductive evolution. The future perspective is worth discovering the mechanism of diverse flowering rhythm and the meaning for adaptation.