Nitrogen (N) is an essential element to plants for growth, maintenance and reproduction, however most N does not exist in a form that is biologically available to plants. In order to maximise the acquisition and retention of N, plants have evolved a variety of morphological and physiological adaptations and life history strategies, as well as the ability to respond plastically to changes in resource availability in ecological time. Determining the ecophysiological responses of plants to changes in root N availability is crucial to further understanding of the mechanisms underlying competitive interactions between plants, and between plants and other organisms, that ultimately contribute to community structure and ecosystem functioning. Carnivorous plants are ideal systems for investigating ecophysiological responses to N availability as:- (i) they share a unique adaptation for obtaining supplemental N from captured prey, therefore ecological stoichiometry and energetic cost/benefit models may be explored; (ii) the trait of botanical carnivory is widely considered to have independently co-evolved as a response to N-deficient, sunny and wet environments, therefore resource allocation trade-offs between plant investment in N and carbon (C) acquisition may be observed, and (iii) they are extremely sensitive to changes in root N availability in ecological time. In this research, the carnivorous plant Drosera rotundifolia (round-leaved sundew) was used to address several unanswered ecophysiological and evolutionary questions relating to patterns and processes of prey capture and the N nutrition of carnivorous plants. Furthermore, the potential for reducing uncertainty in the calculation of plant reliance on carnivory using a δ15N natural abundance multi-level linear mixing model was explored. A combined approach of in-situ and ex-situ studies was employed, using co-occurring non-carnivorous plants or carnivorous plant species with differing evolutionary lineages or prey capture mechanisms respectively to provide context. Results show that the adaptations of carnivory, high reproductive investment and a relatively short life span enable Drosera rotundifolia to survive and thrive in an extreme, N deficient environment. Phenotypically plastic responses by the plant to light and root N availability provide evidence of resource allocation trade-offs between investment in carnivory for N acquisition and in photosynthesis for C acquisition. Plants invested less heavily in prey capture (measured as the stickiness of leaf mucilage) as N availability increased or light availability decreased. These results show that the energetic costs associated with carnivory are avoided by the plant when less costly sources of N are available for uptake and that the production of carbon-rich mucilage is only made under nutrient-limited and well-lit conditions. Results obtained from the comparison of captured insect prey with background invertebrates of potential prey indicate that Drosera rotundifolia is a dietary generalist, where the quantity of prey captured per plant is positively correlated with leaf stickiness and total leaf area. Plant reliance on prey-derived N decreased with increasing root N availability, providing evidence that carnivory is only of net benefit to the plant in N-deficient and well-lit environments, as the photosynthetic costs of investment in the trait are not exceeded by the energetic gain from prey N uptake in shady or dry habitats. A more accurate and precise method for calculating plant reliance on botanical carnivory is presented which incorporates the insect diet of the plant. This method has wider significance for reducing uncertainty in the calculation of relative source contributions to a mixture for most natural abundance applications using a multi-level linear mixing model. To conclude, results from this research further understanding of the ecophysiological mechanisms underlying plant responses to changes in resource availability and the selective pressures driving the evolution of plant adaptations. These results therefore assist with predicting how plants and plant communities may respond to sustained N deposition inputs and future environmental scenarios.

Chenopodium album is considered one of the most important weeds adversely affecting agricultural production due to its highly competitive influence on field crops. Chemical herbicides have increased the efficiency of farming, but recently problems of herbicideresistant weed populations and herbicide residues in soil, water, food products and effects on non-target organisms have increased, consequently, other methods of control of weeds by using specific fungi as herbicides have been suggested. The purpose of this research was to evaluate the biological control of the weed Chenopodium album by the fungus Ascochyta caulina. Some of the factors which control dormancy and germination of Chenopodium album seeds have been investigated to understand better the weed population dynamics. The results showed that seeds from two populations (UK and Libya) differ in their response to factors such as light, chilling, and burying in soil. This could have implications for effective control of the weed in different regions. Two formulations of mycoherbicides (Tween 80 and Gelatine based applications) were tested in the laboratory, and showed promise in reducing growth of the weed, especially the formula of Tween 80. There was extensive shoot fresh and dry weight reduction of inoculated Chenopodium album, as well as reduced root growth. Highest disease severity rates were observed on plants in the first three week of life. A field trial revealed similar results but less disease severity was observed, possibly because of dry weather. However, it was concluded that the fungus Ascochyta caulina is a potentially useful biological control agent but many factors still can be modified in relation to application of the mycoherbicide to increase its efficacy.

陳美亞. / "2004年6月". / 論文(哲學碩士)--香港中文大學, 2004. / 附參考文獻. / 附中英文摘要. / "2004 nian 6 yue". / Chen Meiya. / Lun wen (zhe xue shuo shi)--Xianggang Zhong wen da xue, 2004. / Fu can kao wen xian. / Fu Zhong Ying wen zhai yao. / Chapter 第一章 --- 緒論 --- p.1 / Chapter 第一節 --- 引言 --- p.1 / Chapter 第二節 --- 「徐庾體」硏究槪況 --- p.2 / Chapter 第三節 --- 硏究旨趣 --- p.10 / Chapter 一 --- 硏究動機和方法 --- p.10 / Chapter 二 --- 徐、庾父子詩文的流傳狀況和選用版本 --- p.12 / Chapter 第二章 --- 「徐庾體」的產生背景及定名 --- p.17 / Chapter 第一節 --- 「徐庾體」的產生背景 --- p.17 / Chapter 一 --- 梁代好文的風氣 --- p.17 / Chapter 二 --- 追求新變的文壇風¯‘ة --- p.22 / Chapter 三 --- 對文學創作臨界點的探索 --- p.26 / Chapter 四 --- 對聲律辭采的追求 --- p.27 / Chapter 第二節 --- 「徐庾體」的得名及其所涵蓋的範圍 --- p.35 / Chapter 一 --- 「徐庾體」所指涉的人物 --- p.35 / Chapter 二 --- 「徐庾體」所包括的文類 --- p.38 / Chapter 三 --- 「徐庾體」所代表的作品 --- p.46 / Chapter 章節附錄 --- 庾信集中的前期作品 --- p.52 / Chapter 第三章 --- 「徐庾體」詩歌的特色 --- p.57 / Chapter 第一節 --- 題材多樣化 --- p.57 / Chapter 一 --- 宴飲歌舞 --- p.59 / Chapter 二 --- 詠物寫景 --- p.61 / Chapter 三 --- 羈旅送別 --- p.62 / Chapter 四 --- 閨怨行旅 --- p.63 / Chapter 第二節 --- 隸事 --- p.65 / Chapter 第三節 --- 對仗 --- p.67 / Chapter 第四節 --- 聲律 --- p.72 / Chapter 一 --- 「徐庾體」中平仄的特殊形式 --- p.78 / Chapter 二 --- 「徐庾體」詩歌的黏對狀況 --- p.88 / Chapter 三 --- 平頭、上尾、蜂腰、鶴膝的病犯 --- p.90 / Chapter 四 --- 用韻 --- p.92 / Chapter 五 --- 各種詩體的形成 --- p.98 / Chapter 第五節 --- 風格多樣，以綺艷爲主 --- p.109 / Chapter 一 --- 綺艷 --- p.109 / Chapter 二 --- 纖穠 --- p.114 / Chapter 三 --- 淸新 --- p.119 / Chapter 章節附錄一 --- 「徐庾體」詩歌內容題材分類 --- p.127 / Chapter 附錄二 --- 「徐庾體」五言八句及五言四句詩律化程度 --- p.130 / Chapter 第四章 --- 「徐庾體」與「宮體」比較硏究 --- p.134 / Chapter 第一節 --- 「宮體」的定名和發展 --- p.134 / Chapter 一 --- 「宮體」與「徐庾體」出現的時間、地點和人物 --- p.134 / Chapter 二 --- 徐搞的「宮體」與蕭綱的「宮體」 --- p.135 / Chapter 三 --- 「宮體」廣、狹兩義 --- p.141 / Chapter 第二節 --- 「宮體」詩風的特色 --- p.142 / Chapter 一 --- 以女性爲描寫刻劃的對象 --- p.142 / Chapter 二 --- 詩風輕艷 --- p.148 / Chapter 三 --- 聲律諧協 --- p.155 / Chapter 第三節 --- 「徐庾體」與「宮體」的同異 --- p.158 / Chapter 第五章 --- 「徐庾體」詩歌對後世的影響 --- p.166 / Chapter 第一節 --- 初唐對「徐庾體」的承革 --- p.167 / Chapter 一 --- 文學觀念的反撥 --- p.167 / Chapter 二 --- 文學創作 --- p.175 / Chapter 第二節 --- 初唐以後的「徐庾體」 --- p.182 / Chapter 第三節 --- 五律定體 --- p.184 / Chapter 第六章 --- 結語 --- p.187 / 參考書目 --- p.188 / 論文附錄 / 附錄一 「徐庾體」五言八句及四句平仄聲韻詩的平仄、黏對、病犯和用韻 --- p.1 / 附錄二蕭綱五言八句及四句平聲韻詩的平仄、黏對、病犯和用韻 --- p.48 / 附錄三歷代詩話論徐庾 --- p.68

The allocation of resources to male or female progeny, or to male or female reproductive function more generally, is one of the most important life history decisions a sexually reproducing individual must ever make. Sex determination is thus a fundamental process, yet the mechanisms which control it are surprisingly diverse. In this thesis, I examine sex determination in the plant species Mercurialis annua L. (Euphorbiaceae). I assess the mechanism of sex determination operating in dioecious and androdioecious populations of M. annua and also investigate the conservation and evolution of sex-determining mechanisms across the annual mercury clade, the lineages of which display exceptional variation in sexual system. First, using crosses, I establish that sex in dioecious M. annua is controlled by a single-locus genetic mechanism, consistent with recent work that identified a single male-linked DNA marker in the species. My search for new sex-linked genes revealed none, however, suggesting that M. annua possesses at most a small non-recombining region around sex-determining loci. Why many dioecious plants lack heteromorphic sex chromosomes is still poorly understood and I consider explanations for this. I extend my investigation by comparing genetic diversity between loci that differ in their linkage to the sex-determining locus. I find a single male-linked marker to possess significantly lower diversity than autosomal loci, but no difference in the diversity of partially sex-linked and non-sex-linked genes. I also assess the conservation of a sex-linked marker among annual mercury lineages and conduct crosses between lineages to examine the conservation of sex determination. My findings indicate a conserved mechanism of single-locus genetic sex determination and I consider the role polyploidisation and hybridisation have played in sexual system evolution and the modification of sex-determining mechanisms in the clade. Finally, I assess the presence of environmental sex determination in androdioecious M. annua, concluding that although male frequency is not influenced by growing density, a degree of sexual lability exists in the lineage.

The genetic diversity and genetic structure of populations, and the processes shaping gene flow within and between populations, are influenced by the landscapes they occur within. Within terrestrial landscapes, rivers and their riparian habitat are among the most dynamic, diverse and complex of landscapes and their linear structure appears as an interlinking feature across large landscapes. This thesis took a landscape genetics approach to examine the influence of river landscape features on Alnus glutinosa populations, a widespread keystone tree species of European riparian ecosystems. By accounting for the differing dispersal mechanisms of A. glutinosa (wind and water), landscape effects on seed- and pollen-mediated gene flow, genetic diversity, demographic and genetic structure were identified at different spatial scales of a large UK river catchment. Widespread gene flow within and between A. glutinosa populations was identified with no apparent limitation of wind-mediated pollen dispersal. Hydrochorous dispersal of seed between populations was evident, and found to increase genetic connectivity between riparian populations; however an isolation by distance effect was identified between populations located further apart from each other. No pattern of genetic diversity was found, with high levels of genetic diversity identified at all spatial and temporal scales. At the river-catchment scale no genetic clustering was observed, either within or between the six rivers studied. Demographic structuring within A. glutinosa populations was evident, and correlated with distance from the main river channel. Interactions between seed dispersal, hydrological disturbance, colonisation, and historical influences are discussed in relation to fine-scale spatial genetic structure between A. glutinosa sapling and adult generations. Central to the landscape genetics approach taken in this thesis was the incorporation of key A. glutinosa life history attributes. By incorporating gene flow analyses, species ecology and landscape features, the research presented here furthers our understanding of riverine landscape influences on their riparian populations at different spatial scales and can be used to inform management principles.