The different period of growth and reproduction in the life cycle of organisms implied that the limited resources within their bodies have to be allocated between different processes as a 'trade-off'. Therefore, it would be important to understand how they adapt to the environment by understanding their life history, how they allocate their resources in different life stages and the strategies they adopt when there are changes in their living condition. / Sargassum siliquastrum is a dominant alga in Hong Kong. How it allocates its resources to growth and reproduction was examined in this thesis research. Its phenology in Lung Lok Shiu of Tung Ping Chau Marine Park, Hong Kong was studied by general monthly quadrat survey from September 2004 to May 2006. The four typical developmental stages of regeneration (slow growth), active growth, reproductive and senescence (die back) stage were observed. Maxima in length (90.28 士 45.13 cm in January 2005; 70.18 土 18.65 cm in February 2006), number of main axes (2.21 士 0.81 main axes in January 2005; 2.29 士 0.47 main axes in December 2005), number of size class 1 (l-3cm) new shoots (6.71 士 3.05 new shoots in February 2005; 5.18 士 1.39 new shoots in January 2006), number of size class 2 / (>3-5cm) new shoots (2.53 士 1.23 new shoots in February 2005), fertility (70.59 士 33.08% in January 2005; 77.74 士 17.94% in February 2006) and reproductive effort (21.13 土 7.59% in December 2004; 10.80 士 7.24% in February 2006) of the population were recorded in winter, and their minima were obtained in summer. In contrast, density of the population was highest during the slow growth stage in summer (90.50 士 62.78 individuals / m2 in July 2005), and lowest during its reproductive months (35 士 41.33 individuals / m2 in January 2005; 23.50 士 11.00 individuals / m2 in December 2005). Among the physical parameters evaluated, cooler temperature and decreasing day-length from summer to winter was found to favor the growth in length of the population whereas production of receptacles was favored by low water temperature and short day-length. / The seasonal and individual variations (between holdfast, basal, middle, top blade regions and receptacles) of the reserve sugar alcohol, mannitol, in Sargassum siliquastrum collected monthly from December 2003 to May 2006 were investigated using the HPLC technique. Seasonal variation of its mannitol content ranged from about 1% to 17% of its dry weight. Mannitol content increased as growth proceeded and peaked during the active growing stage (10.81 士 4.87 g mannitol/ lOOg dry seaweed in September 2004; 13.17 士 5.60 g mannitol/ lOOg dry seaweed in October / 2005). A drop in mannitol content was recorded only at the start of the reproductive period in December and remained stable thereafter. Dramatic decrease in mannitol concentration occurred after the reproductive period and a small increase in mannitol content was identified in the middle of the slow growth stage in April (5.69 士 2.11 g mannitol/ lOOg dry seaweed in 2004; 5.91 士 3.71 g mannitol/ lOOg dry seaweed in 2005; 17.87 ± 7.46 g mannitol/ lOOg dry seaweed in 2006), suggesting that the surplus produced during the slow growth period may be used to maintain the perennial holdfast or to develop new shoots for the next season. On an individual level, more mature basal part of the plant (i.e. holdfast and basal blade region) contained higher levels of mannitol when compared with the younger middle and top blade regions. Receptacles of S. siliquastrum displayed the lowest mannitol content, which appeared to match its low photosynthetic activity. The disproportionally high level of mannitol in the photosynthetically less active holdfast suggested that mannitol may be diffused from the basal blades down to the holdfast. The positive correlation between the two months antecedent mannitol content in the basal parts of S. siliquastrum plant with its various population growth parameters (e.g. plant mean length, number of main axes and new shoots) implied that storage compounds in the holdfast and basal blade regions were utilized for the development and elongation of / new shoots. / Manipulative experiments were performed to test the hypotheses that reduced resources would lead to reduced growth and reproduction in Sargassum siliquastrum and that holdfast plays an important role for nutrient storage. Both hypotheses were supported by experimental data in this study. Vegetative shoots of tagged individuals were either trimmed to 15cm in length or removed down to the holdfast before the active growing period (in August 2004 and 2005) and the reproductive period (in November 2004 and 2005). Various growth, reproductive parameters and mannitol content of the control and treatment plants were monitored thereafter. Individuals trimmed to 15 cm before the active growing period in August showed reduced growth (maximum mean lengths = 72.76 士 44.11 cm for 2004 treatment; 51.65 士 20.46 cm for 2005 treatment) and delayed reproduction when compared with tagged controls (maximum mean lengths = 178.00 士 48.26 cm for 2004 treatment; 95.57 土 21.01 cm for 2005 treatment). Only about 70% of the plants trimmed in August 2004 and 60% of those trimmed in August 2005 became reproductive in February 2005 and 2006 respectively, compared with 100% of the tagged controls that became reproductive in December 2004 and January 2006. Plants trimmed to 15 cm before the reproductive period in November 2004 and 2005 remained at around 25 cm in length throughout the reproductive period. However, around 45% (2004 treatment) and 50% (2005 / treatment) of them still became reproductive in February 2005 and 2006 respectively / although their sizes were smaller than the minimum reproductive size of 40 cm recorded earlier. Treatment plants displayed lower mannitol content in various parts and they also produced fewer receptacles when compared with the control plants. For plants trimmed down to holdfast, more new shoots emerged from those trimmed in November 2004 and 2005 than from those trimmed in August, suggesting that more reserved resources were available in the holdfast in November, after the plants had gone through rapid growth in autumn. None of these plants however, ever became reproductive. These responses suggested that in the existence of a trade-off between growth and reproduction, differential allocation of resources was adopted by Sargassum siliquastrum, with the ultimate effect of propagating itself through sexual reproduction or vegetative growth. / The results of this study revealed the phenology of Sargassum siliquastrum, its seasonal variation of mannitol content and the strategy for growth and reproduction it adopted when resources were reduced. The ability and flexibility of algae to grow and reproduce under reduced resources or change in environmental conditions using different strategies, with S. siliquastrum as an example, suggested the reasons for their success in the marine environment. All these data and observation provide significant baseline information on how algae, the ecologically important primary producer in the / coastal area would be able to cope, especially in a rapidly changing marine environment like that of Hong Kong or elsewhere in other parts of the world where changes could be taking place at a global scale. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / 生物在它們的生活週期中有著不同時期的生長和繁殖期，從這點可以看出生物將 有限的資源分配到不同的生長過程時，要面對一定程度的取捨。因此在了解生物 如何面對及適應環境轉變的時候，一些有關它們的生活週期、體內資源在不同時 期的分佈情況，以及運用資源的策略的資料亦變得尤其重要。 / 在2004年9月至2006年5月期間，我們進行了每月樣方測量，以紀錄位於東平 洲海岸公園龍落水內裂葉馬尾藻(Sargassum siliquastrum (Turn.) Ag.)的物候 性。我們發現這個物種有四個典型的生長階段：新生期（緩慢生長期）、活躍生 長期、繁殖期及老化期（回枯期）。而這個族群最高的長度（2005年1月的90.28 ±45.13cm; 2006 年 2 月的 70.18 士 18.65cm)、主莖的數量（2005 年 1 月的 2.21 士 0.81條；2005年12月的2.29 土 0.47條）、第一類(l-3cm)新生枝條數量(2005 年 2 月的 6/71 ± 3.05 條；2006 年 1 月的 5.18士 1.39 條）、第二類（>3-5cm)新 生枝條數量（2005年2月的2.53 ± 1.23條）、繁殖比率（2005年的70.59 士 33.08% ； 2006 年的 77.74 士 17.94%)、及繁殖力(2004 年 12 月的 21.13 士 7.59% ； 2006年2月的10.80 ± 7.24%)均出現在冬季，而這些相應參數的最低點則在夏 季出現。相反，對比這個族群在繁殖時期的密度（2005年1月的5 ± 41.33個體 /平方米；2005年12月的23.50 ± 11.00個體/平方米），最高的族群密度則紀錄在 生長較緩慢的夏季（2005年7月的90.50 ± 62.78個體/平方米）。在被鑑定的物理 參數中，由夏季轉到冬季時的低溫及短日照均有助於族群內個體長度及其繁殖器 的生長。 / 在2003年12月到2006年5月期間，我們利用了高效能液相色譜法（High Performance Liquid Chromatography)，來硏究裂葉馬尾藻體內的儲備物質甘露醇 / (Mannitol)的季節性及其在個體內不同部分（包括固著器、植物的底部、中部、 頂部以及繁殖器)的差異。結果顯示，裂葉馬尾藻的甘露醇季節性的含量介乎於 它們乾水重量的1%到17%。當它們進入活躍生長期，甘露醇的含量便會提升， 而最高含量則紀錄在2004年9月的10.81 ± 4.87克甘露醇/100克乾海藻及2005 年10月的13.17 ±5.60克甘露醇/100克乾海藻。當它們在12月間進入繁殖期時， 體內的甘露醇含量便開始下降，在繁殖期間則維持不變。直到繁殖期完結後，此 物種體內的甘露醇含量便大幅度下降。在4月這個緩慢生長期間，我們紀錄到一 個小幅度的甘露醇增長(2004年的5.69 ± 2.11克甘露醇/100克乾海藻；2005年 的5.91 ± 3.71克甘露醇/100克乾海藻；2006年的17.87 ± 7.46克甘露醇/100克乾 海藻）。由此可以看出在緩慢生長期間生產的過剩資源均用在維持多年生的固著 器的生命，或用作發展下一個季節所需的新生枝條。從個體的層面來看，相對植 物上較年青的中部及頂部，較成熟的部分（即固著器及植物的底部）含有較多的 甘露醇。此物種繁殖器的甘露醇含量是最低的，這亦與其較低的光合作用效率吻 合。相反，裂葉馬尾藻的固著器內有很高的甘露醇含量，這與其低光合作用效率 不成比例，相信是因爲甘露醇從植物的底部滲到固著器內。另外，此物種底部所 含的甘露醇與其兩個月後的一些生長參數（例如長度、主莖及新生枝條的數量） 成顯著的正向關聯，這暗示裂葉馬尾藻體在固著器及植物底部內的儲備物質均用 在新生枝條的發展及延長。 / 我們亦利用切除實驗來硏究不同程度的資源減少對裂葉馬尾藻的生長及繁殖的 影響。在此物種的活躍生長期前（2004年及2005年8月）及繁殖期前（2004年 及2005年11月），個別標記樣本上的無性枝條被切除至固著器上方15cm處或被 切除至留下固著器，而各組別內所有標記樣本的長度、生殖狀態及甘露醇含量則 被每月記錄。實驗結果顯示，在八月（活躍生長期前）的實驗中，與對照組別相 比（最高長度爲 2004 年 178.00 士 48.26cm ； 2005 年的 95.57 ± 21.01cm) , 無性枝 / 條被切除至固著器上方15cm處的個體顯示了較緩慢的生長（最高長度爲2004 / 年的72.76 ± 44.11cm ； 2005年的51.65 ± 20.46cm)及延緩的繁殖期。在2004及 2005年8月的實驗中，所有在對照組別內的個體均在2004年12月及2006年1 月進入繁殖期，但無性枝條被切除至固著器上方15cm處的個體中，分別只有70% 和60%的個體在翌年的2月進入繁殖期。相比無性枝條在繁殖期前（2004年及 2005年11月）被切除至固著器上方15cm處的個體的長度，它們在整個繁殖期 中均維持在25cm左右。儘管這些個體的長度遠低於該品種的40cm之最低繁殖 長度，可是當中仍有45% (2004年）及50% (2005年）的個體分別在2005及2006 年的2月進入繁殖期。這些實驗個體的繁殖力及各部分的甘露醇含量均較對照組 別的個體爲低。此外，對比8月及11月時無性枝條被切除至固著器的實驗個體， 後者在固著器所重新長出的葉片均較前者爲低，反映裂葉馬尾藻的固著器在剛過 度了秋季活躍生長期的11月時，內部所集存的資源較8月時爲高。可是，所有 這些重新長出葉片的個體均沒有進入繁殖期。所有實驗個體以上的反應顯示出， 裂葉馬尾藻在生長及繁殖兩者間要面對一定的取捨，因此此物種需要作出有效的 資源分配，以達致其利用有性或無性的繁殖方法來延續後代的最終目標。 / 是次硏究紀錄了裂葉馬尾藻的物候學、其季節性的甘露醇含量，以及此物種在資 源減少的情況下作出的最佳分配策略。這顯示出爲適應環境變化，此物種能有彈 性地改變其生長週期及資源分配策略，這一切均可進一步證明此物種在海洋環境 中佔優的原因。是次硏究所得的數據，均是發展香港藻類保育及管理計劃時所需 的重要基本資料。 / Wong, Suet Ying. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 270-299). / Abstracts in English and Chinese. / Acknowledgements --- p.i / Abstract (English) --- p.iii / Abstract (Chinese) --- p.ix / Contents --- p.xii / List of Tables --- p.xvii / List of Figures --- p.xxi / Chapter Chapter 1 --- General Introduction / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.1.1 --- Life History and Resource Allocation --- p.1 / Chapter 1.1.2 --- Resource Allocation in Plants --- p.3 / Chapter 1.1.3 --- Resource Allocation in Algae --- p.4 / Chapter 1.2 --- Importance of Sargassum Communities --- p.8 / Chapter 1.3 --- Marine Environment and Sargassum Communities in Hong Kong --- p.11 / Chapter 1.4 --- Study Organism --- p.13 / Chapter 1.5 --- General Objectives --- p.15 / Chapter 1.6 --- Study Site --- p.16 / Chapter 1.7 --- Organization of the Thesis --- p.18 / Chapter Chapter 2 --- Phenology of Sargassum siliquastrum / Chapter 2.1 --- Introduction --- p.23 / Chapter 2.2 --- Materials and Methods --- p.29 / Chapter 2.2.1 --- "Seasonal Change in Size, Number of Main Axes, Number of New Shoots, Density and Population Structure" --- p.29 / Chapter 2.2.2 --- Percentage of Reproductive Individuals --- p.30 / Chapter 2.2.3 --- Seasonal Change in Biomass and Reproductive Effort (RE) of Sampled Individuals --- p.31 / Chapter 2.2.4 --- Seasonal Change in Physical Parameters --- p.32 / Chapter 2.2.5 --- Statistical Analysis --- p.33 / Chapter 2.3 --- Results --- p.34 / Chapter 2.3.1 --- "Seasonal Trend in Size, Number of Main Axes and Number of New Shoots in the Population" --- p.34 / Chapter 2.3.2 --- Seasonal Trend in Mean Density and Population Structure --- p.37 / Chapter 2.3.3 --- Seasonal Change in Dry Weight of Sampled Individuals --- p.39 / Chapter 2.3.4 --- Reproductive Phenology --- p.41 / Chapter 2.3.5 --- Seasonal Trends of Physical Parameters and Their Correlation with Growth and Reproduction of the Populations --- p.43 / Chapter 2.4 --- Discussion --- p.45 / Chapter 2.4.1 --- The Global Trend of Seasonality of Sargassum --- p.45 / Chapter 2.4.2 --- Annual Growth Cycle of Sargassum siliquastrum Population --- p.47 / Chapter 2.4.3 --- Growth Seasonality of Sargassum siliquastrum --- p.49 / Chapter 2.4.4 --- Reproductive Seasonality of Sargassum siliquastrum --- p.53 / Chapter 2.4.5 --- Population Decline of Sargassum siliquastrum in Lung Lok Shui --- p.55 / Chapter 2.5 --- Summary --- p.58 / Chapter Chapter 3 --- Mannitol Content in Sargassum siliquastrum / Chapter 3.1 --- Introduction --- p.76 / Chapter 3.2 --- Materials and Methods --- p.85 / Chapter 3.2.1 --- Sample Collection and Preparation --- p.85 / Chapter 3.2.2 --- Extraction of Mannitol from Sargassum siliquastrum --- p.87 / Chapter 3.2.3 --- Determination of Mannitol extracted from Sargassum siliquastrum --- p.87 / Chapter 3.2.4 --- Statistical Analysis --- p.89 / Chapter 3.3 --- Results --- p.90 / Chapter 3.3.1 --- Seasonal Trend of Mean Mannitol Content and Dry Weight in Different Parts of Sargassum siliquastrum --- p.90 / Chapter 3.3.2 --- "Correlation of Mannitol Content in Various Parts with Length, Number of Main Axes and Number of New Shoots in the Population" --- p.99 / Chapter 3.3.3 --- Mannitol Content in Reproductive and Non-reproductive Individuals --- p.100 / Chapter 3.4 --- Discussion --- p.101 / Chapter 3.4.1 --- Seasonal Variation of Mannitol Content in Sargassum siliquastrum --- p.101 / Chapter 3.4.2 --- Vertical Distribution of Mannitol in Sargassum siliquastrum --- p.105 / Chapter 3.4.3 --- Mannitol for Growth and Reproduction in Sargassum siliquastrum --- p.108 / Chapter 3.5 --- Summary --- p.111 / Chapter Chapter 4 --- Effect of Reduced Resources on Growth or Reproduction of Sargassum siliquastrum / Chapter 4.1 --- Introduction --- p.135 / Chapter 4.2 --- Materials and Methods --- p.141 / Chapter 4.2.1 --- Effect of Reduced Resources on Growth of Sargassum siliquastrum --- p.141 / Chapter 4.2.2 --- Effect of Reduced Resources on Reproduction of Sargassum siliquastrum --- p.142 / Chapter 4.2.3 --- Mannitol Content and Reproductive Effort of Treatment Plants of Sargassum siliquastrum --- p.143 / Chapter 4.2.4 --- Statistical Analysis --- p.145 / Chapter 4.3 --- Results --- p.146 / Chapter 4.3.1 --- Responses of Treatment Plants of Sargassum siliquastrum Trimmed before Active Growth Period --- p.146 / Chapter 4.3.1.1 --- Growth of the Control and Treatment Plants --- p.146 / Chapter 4.3.1.2 --- Reproduction of the Control and Treatment Plants --- p.155 / Chapter 4.3.1.3 --- Survival of the Control and Treatment Plants --- p.157 / Chapter 4.3.1.4 --- Mannitol Content of the Treatment Plants --- p.159 / Chapter 4.3.2 --- Responses of Treatment Plants of Sargassum siliquastrum Trimmed before Reproductive Period --- p.164 / Chapter 4.3.2.1 --- Growth of the Control and Treatment Plants --- p.164 / Chapter 4.3.2.2 --- Reproduction of the Control and Treatment Plants --- p.172 / Chapter 4.3.2.3 --- Survival of the Control and Treatment Plants --- p.174 / Chapter 4.3.2.4 --- Mannitol Content of the Treatment Plants --- p.176 / Chapter 4.4 --- Discussion --- p.179 / Chapter 4.4.1 --- Effect of Trimming on the Growth of Sargassum siliquastrum --- p.179 / Chapter 4.4.2 --- Effect of Trimming on Reproduction of Sargassum siliquastrum --- p.185 / Chapter 4.4.3 --- Resource Allocation Pattern in Sargassum siliquastrum --- p.190 / Chapter 4.5 --- Summary --- p.194 / Chapter Chapter 5 --- Summary and Conclusion --- p.262 / References --- p.270
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_326150 |
| Date | January 2008 |
| Contributors | Wong, Suet Ying., Chinese University of Hong Kong Graduate School. Division of Environmental Science. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography |
| Format | print, xxviii, 299 leaves : ill. ; 30 cm. |
| Coverage | China, Hong Kong, Ping Chau (Hong Kong, China) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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