Dissertations / Theses on the topic 'Seedling stands'

Euclea natalensis A.DC. belongs to the Ebenaceae family, and is extensively distributed along the eastern coast of southern Africa. Many Euclea species are widely gathered by indigenous people because of their medicinal properties. Roots of these plant species are frequently used to treat respiratory complications such as chest pains, bronchitis, pleurisy and asthma. Ground root powder is topically applied in cases of leprosy and is used by some ethnic groups to treat toothache and headache. The bioactivity encountered is attributable to naphthoquinones, which are common phenolic compounds in the Ebenaceae family. Naphthoquinones isolated from E. natalensis (shinanolone, 7-methyljuglone, diospyrin, isodiospyrin and neodiospyrin) have exhibited a broad spectrum of antimicrobial activity. The demand for these products will escalate due the amount of plant material required to further research. We need to explore techniques that can maximize their productivity. The present study was conducted on E. natalensis, in an attempt to establish if there exists any correlation between the accumulation of naphthoquinones and stages of seedling growth, seasonal fluctuations and application of fertilizers. A possible correlation between seedling growth stages and the accumulation of naphthoquinones (shinanolone, 7-methyljuglone and diospyrin) was investigated in seeds and seedlings of Euclea natalensis. In this study, the seeds represented the first stage, whereas the second seedling stage was defined as the stage when the radicles were about 6 cm long. The lengths of the seedlings at the third, fourth and fifth seedling stages were 9 cm, 12 cm and 16 cm respectively. Plant materials collected from the five seedling stages were separately extracted using chloroform and the naphthoquinones were then quantified by means of High Performance Liquid Chromatography (HPLC). Mobile phase of MeCN: H2O: AcOH (62.5: 32.5: 5) was used as an eluent in an isocratic mode and at a flow rate of 0.8 ml/min. Standard curves of each of the four compounds were obtained by making a series of dilutions in the concentration range of 22.5 µg/ml to 2.25 µg/ml. Ten microlitres of each dilution was injected three times into the HPLC, and the run time for each injection was 20 minutes. Calibration curves were then generated and used for the quantification of each compound. Shinanolone, which was the only naphthoquinone detectible in seeds, accumulated at variable rates (P<0.01) and no trend could be established between its synthesis and seedling growth. The content of shinanolone ranged from 87.5 mg/kg dry weight (dw) in seeds to a high mean value of 1047 mg/kg (dw) during the fourth seedling stage. A significant correlation (P<0.01) was found between the mean concentrations of 7-methyljuglone and seedling growth. 7-Methyljuglone was quantified at a high mean level of 5003 mg/kg during the third seedling stage and was not detected in the seed samples. A positive correlation (P<0.01) was established between the concentration of diospyrin and seedling stages. Diospyrin was detected at an elevated mean concentration of 6182 mg/kg during the fifth seedling stage, which was higher than the other quantified naphthoquinones. Seasonal variation of naphthoquinones (shinanolone, 7-methyljuglone, diospyrin, isodiospyrin and neodiospyrin) was investigated from eleven plants of E. natalensis subsp. natalensis growing in natural populations, over a period of four seasons. The roots were harvested, dried, extracted and analysed as in the previous study. The mean levels of shinanolone and 7-methyljuglone were found to be uniform in all the seasons and no statistically significant variation could be found between seasonal changes and their mean concentrations. Accumulation of isodiospyrin and neodiospyrin varied significantly with seasonal changes (P<0.05). These two bioactive naphthoquinones were detected only in summer and autumn respectively, and not in winter. A statistically significant variation (P<0.05) was established between the levels of diospyrin and seasonal fluctuations. Diospyrin was detected at a mean concentration of 3190 mg/kg (dw) during spring, which was higher than the other naphthoquinones quantified in all four seasons. The effect of NPK fertilizers on growth performance and accumulation of naphthoquinones (shinanolone, 7-methyljuglone, diospyrin, isodiospyrin and neodiospyrin) in seedlings of E. natalensis grown in shade and under field conditions was investigated. Each group was subdivided into four subgroups, which were then subjected to four respective treatments of water-soluble foliar feed (2:1:2 (44) NPK) at three different concentrations. Treatments tested were as follows: Treatment 1 at 40 g/l, Treatment 2 and Treatment 3 at 20 g/l and 10 g/l respectively. The control group received only supplemental water. The first harvest was conducted after 6 months of application of fertilizers and the second one was done after 12 months of treatment. Roots and shoots were harvested and analysed separately. The naphthoquinones were quantified as previously described. The bioactivity of root extracts from seedlings was tested against Mycobacterium smegmatis and extracts with lower MIC were further tested on M. tuberculosis. Growth parameters differed between the two groups, with seedlings from the shadehouse showing more plant vigour than the field grown plants. No significant interaction could be established between the measured growth factors and treatment. A significant interaction (P<0.001) was found between Treatment 2 and shadehouse seedlings. Treatment 2 enhanced vegetative performance with the mean values of fresh weight of shoots and roots being twice as much as their respective control mean values. A significantly positive correlation was established between the concentration of shinanolone (P<0.01), isodiospyrin (P<0.05) and neodiospyrin (P<0.05) with fertilization from field-grown seedlings. Application of NPK fertilizers significantly (P<0.05) increased the accumulation of neodiospyrin in seedlings subjected to shadehouse conditions. The most potent naphthoquinone, 7-methyljuglone, was found to be abundant in all the extracts and was quantified at a high mean concentration of 10200 mg/kg from shadehouse seedlings. Root extracts of E. natalensis seedlings grown under field conditions were generally more active against the bacterial strain of M. smegmatis as compared to extracts acquired from roots of seedlings maintained under a shadehouse setting. A lowest minimum inhibitory concentration (MIC) of 0.78mg/ml against M. smegmatis was observed from the second harvest of field-cultivated seedlings of the control and Treatment 1 subgroups. The MIC values for shadehouse seedlings ranged from 1.6 to 6.3 mg/ml. Minimum bactericidal concentration (MBC) values from all the extracts tested were relatively higher than their respective MIC’s. Root extracts of E. natalensis were more active against M. tuberculosis and their MIC values were lower than the tested concentrations. Extracts acquired from field-grown seedlings were more active against M. smegmatis with a lowest MIC value of 0.78 mg/ml. Extracts from the control group and Treatment 1, which had less application of fertilizers were more active against strains of M. tuberculosis with MIC value of 10 µg/ml. This shows the selectivity of E. natalensis against the mycobacterial strain of M. tuberculosis. Based on the findings, synthesis and accumulation of naphthoquinones in E. natalensis is highly variable within individuals of the species investigated. Naphthoquinones accumulate in relatively higher amounts in roots of E. natalensis than in the aboveground structures, which validate their harvest by indigenous people. The concentration of shinanolone varied slightly and its production increased with seedling growth. The synthesis of 7-methyljuglone is independent of fertilisation as its accumulation was enhanced in seedlings subjected to control treatment. Neodiospyrin and isodiospyrin were always present in every sample obtained from the seedlings but they were not detectible in every profile of samples from mature plants. Diospyrin is the only naphthoquinone that was detected in every sample analysed and also quantified in high concentrations from mature plants harvested in spring. The study showed that depending on the requirement of a particular naphthoquinone for research, one could target the seasons and seedling stages recommended from this study. This study also showed that field-cultivated seedlings produced more potent naphthoquinones than the ones subjected to controlled environments.<br>Dissertation (MSc (Plant Science))--University of Pretoria, 2008.<br>Plant Production and Soil Science<br>unrestricted

Orientador: Massanori Takaki<br>Banca: João Domingos Rodrigues<br>Banca: Silvio Moure Cícero<br>Banca: José Marcos Barbosa<br>Banca: Márcia Balistiero Figliolia<br>Resumo: Este estudo teve como objetivo avaliar a relação entre a massa e características morfométricas de frutos e sementes de Tecoma stans, bem como relacionar a massa das sementes a suas características morfológicas, utilizando paquímetro e imagens de raios X, e fisiológicas, através da germinação, emergência e desenvolvimento inicial de suas plântulas, sob duas condições de luminosidade . a pleno sol e sombra. Além disso, também foram avaliados os efeitos de diferentes condições de temperatura e luz constantes, em laboratório, e em ambiente natural no sol e na sombra na germinação e emergência das plântulas. A massa dos frutos apresentou relações lineares significativas e positivas com suas características morfológicas e de produção de sementes. As relações entre a massa das sementes e suas características morfológicas foram positivas e significativas, porém na forma de uma função potência, sendo esta relação mais evidente com a largura do embrião. A massa das sementes também esteve relacionada a determinadas anomalias do desenvolvimento embrionário, observadas nas imagens de raios X. A germinação, a emergência e o desenvolvimento inicial das plântulas foram significativamente afetados pela massa das sementes, porém somente durante os três primeiros meses de desenvolvimento no ambiente de sol. A temperatura apresentou efeito na germinação e suas sementes germinaram tanto na luz quanto no escuro, contudo a emergência e sobrevivência das plântulas no ambiente de sol foi superior em relação ao observado na sombra.<br>Abstract: This study had the objective to evaluate the relationship between the mass and the morphometric characteristics of Tecoma stans fruits and seeds, as well as to relate the seed mass with its morphometric characteristics, utilizing caliper and X-ray images, and physiological characteristics, thought germination, emergency and seedlings initial development, under two conditions of light - at the sun and shade. More than, also were evaluated the effects of different conditions of constant temperature and light, under laboratory, and natural environment under sun and shade in the germination and emergency of the seedlings. The fruit mass presented positive, significative linear relationship with his morphological characteristics and with its seed production characteristics. The relationship between seed mass and its morphological characteristics were positive and significative, nevertheless with the model (shape) of power function, being the relationship more clear with the embryo width. The seed mass also was related to determinate anomalies of the embryo development that could be observed in the X-ray images. The germination, the seedling emergence and the initial seedling development were significative affected by seed mass, but only in the firth three months of development at the sun environment. The temperature affected Tecoma stans seed germination in both light and darkness environment, however the seedlings emergency and survival was greater at the sun environment than shade.<br>Doutor

In wheat, stem rust is known to rapidly evolve new virulence to resistance genes. While more than 50 stem rust resistance (Sr) loci have been identified in wheat, only a few remain effective, particularly against the highly virulent race Ug99 (TTKSK race) and a mixture of durum-specific races. An association mapping (AM) study based on 183 durum wheat accessions was utilized to identify resistance loci for stem rust response in Ethiopia over four seasons and artificial inoculation with Ug99 (TTKSK race) and a mixture of durum-specific races under field conditions as well as in greenhouse test at seedling stage under controlled conditions for resistance to four highly virulent stem rust races: TRTTF, TTTTF, (TTKSK (Ug99) and JRCQC. The panel was profiled with 1,253 SSR and DArT markers. Twelve QTL-tagging markers were significant (P < 0.05) across three to four seasons. The role of Sr13, Sr9, Sr14, Sr17, and Sr28 was confirmed. Thirteen significant markers were in regions with no Sr genes/QTLs. The results under controlled conditions showed that 15, 20, 19 and 19 chromosome regions harbored markers that showed significant effects for races TRTTF, TTTTF, TTKSK and JRCQC, respectively. These genomic regions showed marker R2 values ranging from 1.13 to 8.34, 1.92 to 17.64, 1.75 to 23.12 and 1.51 to 15.33% for races TRTTF, TTTTF, TTKSK and JRCQC, respectively. The study demonstrates that stem rust resistance in durum wheat is governed in part by shared loci and in part by race-specific ones. The QTLs identified in this study through AM will be useful in the marker-assisted development of durum wheat cultivars with durable stem rust resistance.

In wheat, stem rust is known to rapidly evolve new virulence to resistance genes. While more than 50 stem rust resistance (Sr) loci have been identified in wheat, only a few remain effective, particularly against the highly virulent race Ug99 (TTKSK race) and a mixture of durum-specific races. An association mapping (AM) study based on 183 durum wheat accessions was utilized to identify resistance loci for stem rust response in Ethiopia over four seasons and artificial inoculation with Ug99 (TTKSK race) and a mixture of durum-specific races under field conditions as well as in greenhouse test at seedling stage under controlled conditions for resistance to four highly virulent stem rust races: TRTTF, TTTTF, (TTKSK (Ug99) and JRCQC. The panel was profiled with 1,253 SSR and DArT markers. Twelve QTL-tagging markers were significant (P < 0.05) across three to four seasons. The role of Sr13, Sr9, Sr14, Sr17, and Sr28 was confirmed. Thirteen significant markers were in regions with no Sr genes/QTLs. The results under controlled conditions showed that 15, 20, 19 and 19 chromosome regions harbored markers that showed significant effects for races TRTTF, TTTTF, TTKSK and JRCQC, respectively. These genomic regions showed marker R2 values ranging from 1.13 to 8.34, 1.92 to 17.64, 1.75 to 23.12 and 1.51 to 15.33% for races TRTTF, TTTTF, TTKSK and JRCQC, respectively. The study demonstrates that stem rust resistance in durum wheat is governed in part by shared loci and in part by race-specific ones. The QTLs identified in this study through AM will be useful in the marker-assisted development of durum wheat cultivars with durable stem rust resistance.

Made available in DSpace on 2014-06-11T19:30:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-06-20Bitstream added on 2014-06-13T20:01:15Z : No. of bitstreams: 1 socolowski_f_dr_rcla.pdf: 774673 bytes, checksum: 524e3b5dcb3693c8da59453eb583ea90 (MD5)<br>Este estudo teve como objetivo avaliar a relação entre a massa e características morfométricas de frutos e sementes de Tecoma stans, bem como relacionar a massa das sementes a suas características morfológicas, utilizando paquímetro e imagens de raios X, e fisiológicas, através da germinação, emergência e desenvolvimento inicial de suas plântulas, sob duas condições de luminosidade . a pleno sol e sombra. Além disso, também foram avaliados os efeitos de diferentes condições de temperatura e luz constantes, em laboratório, e em ambiente natural no sol e na sombra na germinação e emergência das plântulas. A massa dos frutos apresentou relações lineares significativas e positivas com suas características morfológicas e de produção de sementes. As relações entre a massa das sementes e suas características morfológicas foram positivas e significativas, porém na forma de uma função potência, sendo esta relação mais evidente com a largura do embrião. A massa das sementes também esteve relacionada a determinadas anomalias do desenvolvimento embrionário, observadas nas imagens de raios X. A germinação, a emergência e o desenvolvimento inicial das plântulas foram significativamente afetados pela massa das sementes, porém somente durante os três primeiros meses de desenvolvimento no ambiente de sol. A temperatura apresentou efeito na germinação e suas sementes germinaram tanto na luz quanto no escuro, contudo a emergência e sobrevivência das plântulas no ambiente de sol foi superior em relação ao observado na sombra.<br>This study had the objective to evaluate the relationship between the mass and the morphometric characteristics of Tecoma stans fruits and seeds, as well as to relate the seed mass with its morphometric characteristics, utilizing caliper and X-ray images, and physiological characteristics, thought germination, emergency and seedlings initial development, under two conditions of light - at the sun and shade. More than, also were evaluated the effects of different conditions of constant temperature and light, under laboratory, and natural environment under sun and shade in the germination and emergency of the seedlings. The fruit mass presented positive, significative linear relationship with his morphological characteristics and with its seed production characteristics. The relationship between seed mass and its morphological characteristics were positive and significative, nevertheless with the model (shape) of power function, being the relationship more clear with the embryo width. The seed mass also was related to determinate anomalies of the embryo development that could be observed in the X-ray images. The germination, the seedling emergence and the initial seedling development were significative affected by seed mass, but only in the firth three months of development at the sun environment. The temperature affected Tecoma stans seed germination in both light and darkness environment, however the seedlings emergency and survival was greater at the sun environment than shade.

Pythium diseases are common in the greenhouse production of tobacco transplants and can cause up to 70% seedling loss in hydroponic (float-bed) greenhouses. However, the symptoms and consequences of Pythium diseases are often variable among these greenhouses. A tobacco transplant greenhouse survey was conducted in 2017 in order to investigate the sources of this variability, especially the composition and distribution of Pythium communities within greenhouses. The survey revealed twelve Pythium species. Approximately 80% of the surveyed greenhouses harbored Pythium in at least one of four sites within the greenhouse, including the center walkway, weeds, but especially bay water and tobacco seedlings. Pythium dissotocum, followed by P. myriotylum, were the most common species. Pythium myriotylum, P. coloratum, and P. dissotocum were aggressive pathogens that suppressed seed germination and caused root rot, stunting, foliar chlorosis, and death of tobacco seedlings. Pythium aristosporum, P. porphyrae, P. torulosum, P. inflatum, P. irregulare, P. catenulatum, and a different isolate of P. dissotocum, were weak pathogens, causing root symptoms without affecting the upper part of tobacco seedlings. Pythium adhaerens, P. attrantheridium, and P. pectinolyticum did not affect tobacco seeds or seedlings. The consequences of Pythium infection were more likely to be severe when they occurred during seed germination than at seedling emergence, or after plant stem elongation when seedling roots had started to grow into underlying nutrient solutions, depending on the species of Pythium. High and low variation was observed among isolates of P. dissotocum and P. myriotylum, respectively. Pythium myriotylum co-existed with multiple other Pythium or oomycete species in the same environments within tobacco greenhouses, and significant in vitro and/or in vivo interactions between P. myriotylum and some naturally co-existing species were revealed. Pythium porphyrae may have the potential to protect tobacco seeds and seedlings from P. myriotylum infection. Greenhouse Pythium control trials identified ethaboxam, mefenoxam, and copper ionization as potentially promising alternatives to etridiazole for Pythium disease management in tobacco transplant production. The outcomes of this project provide useful new information to better understand the composition, distribution, and diversity of Pythium communities in tobacco transplant greenhouses and to improve Pythium disease management for tobacco transplant production.<br>Doctor of Philosophy<br>Pythium diseases are common in tobacco transplant production and can cause up to 70% seedling losses in hydroponic (float-bed) tobacco transplant greenhouses. However, little is known about the composition and distribution of Pythium communities in tobacco transplant greenhouses. This project began with a tobacco transplant greenhouse survey, in which 12 Pythium species were recovered from center walkways, weeds, greenhouse bay water, and tobacco seedlings. Pythium dissotocum and P. myriotylum were the two types (species) of Pythium most commonly found in the survey. Pythium myriotylum, P. coloratum, and P. dissotocum were aggressive pathogens that suppressed seed germination and caused root rot, stunting, foliar chlorosis, and death of tobacco seedlings. Pythium aristosporum, P. porphyrae, P. torulosum, P. inflatum, P. irregulare, P. catenulatum, and an isolate of P. dissotocum, were weak pathogens causing root symptoms without affecting the upper part of tobacco seedlings. Pythium adhaerens, P. attrantheridium, and P. pectinolyticum did not affect tobacco seeds or seedlings. The symptoms caused by infection by Pythium species differed among host (tobacco) growth stages, except for the most aggressive species, P. myriotylum. High levels of variation were observed among isolates of P. dissotocum, in terms of vegetative growth rate (on V8 agar media) and aggressiveness on tobacco seed and seedlings. Pythium myriotylum was found to co-exist with multiple other Pythium or oomycete species (neighbor isolates) in the same environments within tobacco greenhouses. Significant interactions between P. myriotylum and some neighbor isolates were revealed, and these interactions significantly affect the consequences of P. myriotylum infection of tobacco seeds. Greenhouse Pythium control trials identified two chemical water treatments (ethaboxam and mefenoxam), and a non-chemical water treatment (copper ionization) as potentially promising alternatives to the current standard Pythium control (etridiazole) for Pythium disease management in tobacco transplant production. The outcomes of this project provide useful new information to both better understand the composition, distribution, and diversity of Pythium communities in tobacco transplant greenhouses and to improve Pythium disease management for tobacco transplant production.

Made available in DSpace on 2014-08-20T13:44:34Z (GMT). No. of bitstreams: 1 tese_caroline_borges_bevilacqua.pdf: 1981019 bytes, checksum: 797e667e01edbc569a7b08d3268c701b (MD5) Previous issue date: 2013-10-30<br>Cold stress adversely modifies their physiology, metabolism plant growth and development, as well as, it limits crop productivity. The responses of rice (Oryza sativa L.) subjected to low temperatures are still poorly understood. A better understanding of stress tolerance mechanism in rice plants will help to develop rice germplasm with improved field level tolerance under variable temperature and sowing depth conditions. To characterize rice genotypes with variation in sensitivity to cold, these are the following objectives: to evaluate the applicability of different Stress Indices using seedling lengthas parameter; classify accessions cultivated rice and red rice as Indica or Japonica; compare response to rice cultivars cold-tolerant and cold-sensitive to cold stress according to the dry matter accumulation and possible changes in chlorophyll content; categorize different genotypes with regard to sensitivity to cold and to sowing depth stresses and, analyze the expression of cold-responsive genes, and also genes submergence-responsive. The seeds after seven days at 25°C were exposed at 4°C for 24h and after that, photosynthesis was measured later, the plants were 72h at 25°C (recovery period) to assess the dry mass and chlorophyll. For the other experiments, the seedlings were collected 7 and/or 14 days maintained at 25°C or 18/13°C day/night and different sowing depths (1.5cm, 5cm, 10cm and 15cm), differential gene expression were performed with those seedlings using different genes induced by cold. To evaluated gene expression using different genes induced by cold and anoxia, samples were collected after exposure to 10 ° C for 6, 24 and 96 h at 1.5 cm and 10 cm deep sowing. The results showed that is possible to identify superior genotypes for tolerance to these abiotic stresses based on the Tolerance Index (STI) and Media Geometric (GM) to select genotypes tolerant to cold or sowing depth, using as a parameter the seedling shoot length measurement. Japonica and Indica subspecies respond differently to abiotic stresses, however for some of these stress-responsive genes, these subspecies responded similarly. Furthermore, the analysis at the molecular level of cold tolerance and sowing depth indicated the importance of ABA- dependent and ABA-independent signal transduction pathways in plants under abiotic stress.<br>O estresse causado pelo frio interfere negativamente na fisiologia, metabolismo, crescimento e desenvolvimento das plantas e, portanto, limita a produtividade em lavouras de arroz. As respostas em nível de crescimento em arroz (Oryza sativa L.) submetido a baixas temperaturas ainda são pouco compreendidas. Um melhor entendimento do mecanismo de tolerância ao estresse em plantas de arroz pode ajudar na identificação, no germoplasma de arroz, de plantas com tolerância submetidas à temperatura variável, além de ser útil para outros estresses abióticos, como diferentes profundidades de semeadura. Para caracterizar genótipos de arroz, com variação na sensibilidade ao frio, tiveram-se como objetivos:avaliar a aplicabilidade de diferentes índices de estresse utilizando-se como parâmetro o comprimento de plântula; classificar acessos de arroz cultivado e vermelho como Japonica ou Indica; comparar a resposta ao frio de cultivares de arroz tolerante e sensível a esse estresse, com relação ao acúmulo de massa seca e possíveis alterações no teor de clorofila;categorizá-los com relação à sensibilidade ao frio e à profundidade de semeadura; e analisar a expressão de genes que respondem a frio, assim como genes responsivos a submersão, sob condições de frio e/ou tratamento constituídos por diferentes profundidades de semeadura. Para avaliar o acúmulo de massa seca e o teor de clorofila, as sementes, após sete dias a 25°C, foram expostas a 4°C durante 24 h e logo após, foi medida a fotossíntese e,posteriormente, as plantas ficaram 72 h a 25°C para sua recuperação. Já para os demais experimentos,as plântulas foram coletadas 7 e/ou 14 dias mantidas a 25°C ou 18/13°C dia/noite e diferentes profundidades de semeadura (1.5cm, 5cm, 10cm e 15cm); as avaliações da expressão gênica diferencial foram realizadas com essas amostras coletadas, para 4 diferentes genes induzidos pelo frio e também em amostras coletadas após exposição a 10°C durante 6, 24 e 96 h a 1.5 cm e 10 cm de profundidade de semeadura.Os resultados indicaram que é possível a identificação de genótipos superiores para a tolerância a esses estresses abióticos com base em seus índices de estresse, utilizando como parâmetro o comprimento da parte aérea, devido a habilidade das plantas tolerar estresses abióticos afetar a morfologia assim como a fisiologia da planta de arroz. Assim como é possível a utilização do Índice de Tolerância (STI) e da Média Geométrica (GM) para selecionar genótipos tolerantes ao frio ou profundidade de semeadura, baseado no comprimento de parte aérea de plântula. As subespécies Japonica e Indica respondem diferentemente aos estresses abióticos, no entanto, para alguns genes responsivos a esses estresses, essas subespécies apresentam o mesmo respondem semelhantemente. Além disso, as análises a nível molecular da tolerância ao frio e a profundidade de semeadura indicaram a importância das vias ABA-dependente e ABA-independente como vias de transdução do sinal em plantas sob estresse abiótico.

Central to the issue of harvest feasibility on the outer BC coast (CWHvh) is the question of whether sites, once harvested, can be regenerated, and whether the time period for replacement and subsequent growth is economically and environmentally acceptable. Since low productivity sites have not been harvested in the past, there is a lack of data to answer this question. We tried to provide an answer by assessing regeneration following natural disturbances. Small scale gap disturbances are the norm within old-growth stands. If regeneration is not a problem in gaps, then we have some evidence that regeneration should not be a problem upon implementation of our management practices. The objectives of this study were: (1) to develop baseline information on the mechanisms and the patterns of regeneration across a sequence of forest types; (2) to assess regeneration success with respect to productivity; and (3) to estimate future growth and productivity.

- Ziele der Arbeit - Das primäre Ziel der vorliegenden Arbeit bestand in einer möglichst umfassenden Be-schreibung einzelner Entwicklungsstadien im Verjüngungszyklus von Betula pendula Roth. Dabei waren die lokalen Bestandes- und Standortsbedingungen im Untersuchungsgebiet in besonderer Weise zu berücksichtigen. Des Weiteren sollten Optionen zur waldbaulichen Integration der Sand-Birkenverjüngung in bestehende Behandlungskonzepte für in Auflösung befindliche Fichtenaltbestände aufgezeigt werden. - Untersuchungsgebiet - Der Tharandter Wald liegt im Freistaat Sachsen (50° 55’-50° 00’n. Br., 13° 25’-13° 35’ ö. L.) und umfasst eine Fläche von etwa 6.000 ha. Das von der Baumart Fichte dominierte Gebiet kolliner bis submontaner Höhenstufe (350 - 420 m ü. NN) wird der „Unteren Nordostab-dachung des Erzgebirges“ zugeordnet. Als Untersuchungsflächen wurden wechselfeuchte (wechselfrische) Standorte mittlerer Trophie gewählt, die von einschichtigen Fichtenbe-ständen in einem Alter von ≥ 80 Jahren bestockt waren. Einzeln bis truppweise eingemischte Samenbäume der Sand-Birke (B. pendula) bildeten eine Grundvoraussetzung für die Flächen-auswahl. - Methodisches Vorgehen - Das methodische Vorgehen konzentrierte sich auf die verjüngungsökologisch relevanten Entwicklungsstadien (fruktifizierender Samenbaum, Diaspore, Keimling, Sämling und eta-blierte Verjüngungspflanze) der Sand-Birke. Die Wachstumsparameter der vorhandenen Samenbäume wurden durch Untersuchungen zum Fruchtbehang unterlegt. Der mehrstufige Versuchsansatz zur Erfassung einzelner Verjüngungsstadien stützte sich auf Bestandesauf-nahmen, Gefäß- und Laborversuche. Erhebungen auf Bestandesebene erfassten die Diaspo-renausbreitung mithilfe von Samenfallen und dokumentierten die Keimlings- und Ver-jüngungsstadien von B. pendula auf entsprechend etablierten Aufnahmeplots (1 m x 1 m). Darüber hinaus umfassten die Aufnahmen Strahlungs- und Feuchtemessungen und die Charakterisierung der Bodenvegetation. Für die Einschätzung des mikrostandörtlichen Um-feldes wurden exemplarisch Bodendeckungsvarianten (Mineralboden, Nadelstreuauflage, Calamagrostis villosa CHAIX (GMEL.) und Deschampsia flexuosa L. (TRIN.)) ausgewählt, die als besonders repräsentativ für reine Fichtenbestände des Erzgebirges gelten. Für die räumliche Modellierung der Diasporen und Keimlinge auf Bestandesebene stand das Pro-gramm WALDSTAT (NÄTHER &amp; WÄLDER 2003) zur Verfügung. Im Rahmen des Mitscherlich-Gefäßversuchs wurden gleichermaßen quantitative und qualitative Entwicklungen von Sand-Birkenkeimlingen und -sämlingen erhoben. Der Einfluss ausgewählter Bodendeckungs-varianten wurde in diesen Betrachtungen berücksichtigt. Neben zahlreichen Pflanzenpara-metern (Spross-, Blatt- und Wurzelentwicklung, Allokationen, Allometrien) war die kleinstandörtliche räumliche Verteilung dieser Verjüngungspflanzen von vorrangiger Be-deutung. Als Verteilungs- und Konkurrenzmaße auf Ebene des Mikrostandortes dienten Tessellationsmodelle, der Aggregationsindex nach CLARK &amp; EVANS, der Gini-Koeffizient und das “Constant Yield Law“. - Ergebnisse - - Die Erfassung der Samenbaumparameter von B. pendula führte zu flächenspezifischen und signifikanten Unterschieden in der Dimension, Höhe und soziologischen Stellung. Für die Darstellung der Durchmesser-Höhenverteilungen erwiesen sich logarithmische und quadra-tische Funktionen gleichermaßen geeignet. Das Kronenprozent ereichte im Mittel Werte zwi-schen 37 % und 49 %. Die einzelnen Kronenparameter (Kronendurchmesser, Kronenlänge und Kronenmantelfläche) zeigten straffe lineare Zusammenhänge. Innerhalb der Kronen-strukturen (z. B. Blatt- und Zweigtrockenmasse) ließen sich zum Teil allometrische Be-ziehungen nachweisen. Im Rahmen der Vollbaumbeerntung war ein durchmesserabhängiger Fruchtbehang nachweisbar, der für den Einzelbaum eine Anzahl zwischen 2,3 und 4,2 Millionen Diasporen erreichte. - Mit den Erhebungen zur zeitlichen Ausbreitungsdynamik der Diasporen waren durch mehrjährige Untersuchungszeiträume, auch für eine Pionierbaumart wie B. pendula, stärkere Samenjahre nachzuweisen. Die räumliche Modellierung der anemochoren Diasporenaus-breitung belegte erwartungsgemäß bessere Modellanpassungen für den anisotropen (richtungsgebundenen) Modellansatz. Dennoch zeichneten sich sowohl jahres- als auch flächenspezifisch deutliche Unterschiede in der Modellgüte ab. Als maximale Diasporen-dichte pro m² wurde ein Wert von 20.700 Diasporen ermittelt. Die mittleren Ausbreitungs-distanzen (MDD - “Mean Dispersal Distances“) lagen nach Modellschätzung für die ge-samten Beprobungszeiträume und unter Berücksichtigung aller Versuchsflächen zwischen 37 m und 90 m. Die durchschnittliche Diasporenproduktion eines Einzelbaumes lag nach Anga-ben des Modells in einem Bereich von 180.000 bis 7.400.000. Die Qualitätsansprache an den Diasporen ergab einen Anteil von etwa 5 % bis 8 % äußerlich Schadhaften. Der unmittelbare Windeinfluss auf Hauptausbreitungsrichtung und -entfernung konnte ebenfalls nachgewiesen werden. - Untersuchungen zum Keimlingsstadium zeigten deutliche Abhängigkeiten zwischen den ausgewählten Bodendeckungsvarianten, der Keimlingsdichte und dem Keimlingswachstum. Sand-Birkenkeimlinge waren sowohl unter Bestandesbedingungen als auch unter den freif-lächenähnlichen Bedingungen des Mitscherlich-Gefäßversuchs auf der Variante mit Mine-ralboden besonders dicht aufgelaufen, blieben jedoch stark in ihrer weiteren Entwicklung zurück. Als besonders wüchsig erwiesen sich Keimlinge auf den Bodendeckungsvarianten mit Nadelstreuauflage und in D. flexuosa. Sand-Birkenkeimlinge der Bodendeckungsvarianten ohne Konkurrenz durch Bodenvegetation (Mb, Nd) besaßen eine längere Hauptwurzel und eine höhere Wurzelmasse (56 % - 60 % der Gesamtmasse). Die oberirdische Allokation (Blatt- und Sprossmasse) fiel hingegen für Sand-Birkenkeimlinge in den Bodendeckungs-varianten mit C. villosa und D. flexuosa höher aus. Verteilungs- und Konkurrenzerhebungen in den Gefäßversuchen erbrachten signifikante Zusammenhänge zwischen Keimlingsdichte, Standraum und Wachstum der Einzelpflanze. - Das Sämlingsstadium und die älteren Verjüngungspflanzen wiesen einen deutlichen Rückgang in der Mortalität auf. Die Erhebungen im Bestand ergaben ein unterschiedliches Durchschnittsalter für Sand-Birken auf den einzelnen Bodendeckungsvarianten (C. villosa 7,6 Jahre, D. flexuosa 6,2 Jahre und Nadelstreu 4,7 Jahre). Die wachstumsrelevanten Umweltbe-dingungen wie Strahlungsverfügbarkeit, Feuchteregime und Entfernung zum nächsten Alt-baum unterschieden sich außerdem in Abhängigkeit von den als repräsentativ eingestuften Bodendeckungsvarianten unter Bestandesbedingungen. Das bestandesbezogene Wachstum der Sand-Birken in einem Alter von 2 bis 6 Jahren ließ sich durch eine exponentielle Funktion mit hoher Anpassungsgüte (p ≤ 0,000) abbilden. Innerhalb des Mitscherlich-Gefäßversuchs haben sich ebenfalls Unterschiede in der Individuendichte, den Mortalitäts- und Wachstums-raten in Abhängigkeit von den Bodendeckungsvarianten ausgebildet. Höchste Verjüngungs-dichten wurden nach einem 2,5jährigen Entwicklungszeitraum auf der Bodendeckungs-variante Nadelstreuauflage erreicht. Die Allokationen in der Trockenmasse näherten sich hingegen in den unterschiedlichen Varianten stärker an. Ein dichteabhängiges Wachstum konnte in der letzten Aufnahme nicht mehr nachgewiesen werden. Abschließend bleibt festzuhalten, dass die ermittelten Untersuchungsergebnisse in Abhängig-keit vom jeweiligen Verjüngungsstadium die zeitliche und räumliche Präsenz, Konkurrenz- und Entwicklungsfähigkeit der Sand-Birke in Fichtenaltbeständen des Tharandter Waldes charakterisieren. Sie belegen eine kleinstandörtliche Heterogenität in den untersuchten Beständen, die sich nachhaltig auf die Etablierung der hier untersuchten Pionierbaumart auswirkt. Anhand der räumlichen Modellierung lässt sich die zu erwartende Verteilung von Diasporen und Keimlingen in Abhängigkeit von den Positionen der Samenbäume prognostizieren. Insgesamt ergibt sich aus den vorliegenden Ergebnissen ein vergleichsweise hohes Verjüngungspotenzial für B. pendula, das sich durch waldbauliche Maßnahmen effizient nutzen ließe. Ein detailliertes Wissen über die einzelnen Verjüngungsstadien bietet zudem die Möglichkeit einer gezielten waldbaulichen Steuerung der Baumart und zur Risikoabschätzung des Verjüngungserfolgs unter den gegebenen Rahmenbedingungen. Bei einer wachsenden waldbaulichen Unsicherheit im Umgang mit unterschiedlichsten Klima-prognosen, die sich in ihrer Wirkung regionalspezifisch erheblich unterscheiden können, sollte die Sand-Birke als Misch- und Vorwaldbaumart unbedingt berücksichtigt werden. Um dem viel zitierten Anspruch an die Nachhaltigkeit waldbaulichen Handelns gerecht zu werden, muss die Option zur Integration von B. pendula gewährleistet bleiben, auch für künftige Generationen und bei sich wandelnden Ansprüchen an den Wald<br>- Objectives - The main goal of this study was to describe comprehensively the particular stages of the regeneration cycle of Betula pendula Roth. Investigations were carried out in local stand and site conditions of a research area in South-East Germany (Tharandter Forest) are considered. In this context options for integrating Silver birch regeneration into silvicultural management concepts of old Spruce stands (Picea abies L.) with lacking vitality are pointed out. - Research area - The Tharandter Forest is located (50°00’N, 13°35’E.) in Saxony (South-East Germany) with an area of around 6.000 ha. It is dominated by Norway spruce stands, and ranges from colline to submontane altitudinal belt (350 to 420 m a.s.l.). These sites are part of the northern declivity of the Ore Mountains. Mono-layered Norway spruce stands with soils of medium trophy and well drained, but featured highly variable soil moisture levels during the growing season were selected for this study. The stand age was ≥ 80 years. Seed trees of Silver birch were mixed as single trees or small groups. - Methodical aspects - The methodical work was concentrated on relevant regeneration aspects like fructification of seed trees, seeds, seedlings, saplings and established regeneration of Silver birch. Growth parameters of seed trees and the amount of fructification were used to quantify allometric relationships. The multi-level research design was based on measurements under stand conditions, pot and laboratory experiments. Seed traps and plots (1m x 1m) were located in spruce stands with regard to different stages of Silver birch development. Therefore micro-environmental growth conditions like soil humidity and photosynthetic active radiation were measured, and plants of ground cover characterized. As examples of ground cover variants with highest presence in homogeneous spruce stands mineral soil, needle litter, Calamagrostis villosa CHAIX (GMEL.) und Deschampsia flexuosa L. (TRIN.) were chosen. Using the program WALDSTAT (NÄTHER &amp; WÄLDER 2003) spatial distribution of dispersed seeds (diaspores) and seedlings could be modelled. Additionally pot experiments were done to compare quantitative and qualitative development of birch seedlings between stand and open site conditions. Regeneration density, number of leaves, shoot and root growth and allocations were measured as important growth parameters to evaluate single plant development under different environmental conditions. Finally, spatial distribution of seedlings in microsites and intraspecific competition were calculated by tessellation models, aggregation indices after CLARK &amp; EVANS, Gini-coefficient and ‘constant yield law’. - Main results - - Measurements on seed trees of B. pendula indicate stand specific differences significantly in dimension, height and biosocial position of trees within the birch population (crown classes). For specific height-dbh curves logarithmic and quadratic equations were adapted. The relative crown length for seed trees was located between 37 % and 49 %. Allometric relationships between crown parameters (e.g. crown diameter, crown length and crown surface) were strongly correlated. In specific cases crown structures (e.g. dry mass of leaves and twigs) were also correlated, certainly with different grades. Direct seed counting of felled seed trees provided the relationships between dbh and number of seeds. Counted seeds for single Silver birch trees ranged between 2.300.000 - 4.200.000. - As one result of seed trapping huge varieties in seed production of Silver birch were detectable between years with different seed potential. Spatial modeling of seed dispersal supported strong influences caused by wind (direction and speed). Hence, best fitted model estimations were found for anisotropic scenarios. The maximum in seed density was recorded with 20.700 seeds per m². As data for ‘Mean Dispersal Distances’ (MDD) the program WALDSTAT calculated between 37 m and 90 m. Furthermore the amount of seeds produced by a single tree was estimated with 180.000 - 7.400.000 depending on dbh. Physical quality evaluations for seeds have shown a mean proportion of damaged and not germinable seeds between 5 % and 8 %. - Direct effects of ground cover variants have been identified for seedling density and growth. Seedling density was highest on mineral soil for both, stand conditions and pot experiment, but these birch seedlings developed slowly compared with individuals in the other ground cover variants. The best growth was realized by birch seedlings in needle litter and D. flexuosa. Regarding to root length and mass, birches in ground cover variants without grass competition (mineral soil and needle litter) have shown a significant better development of underground parts. Root dry mass of these birch seedlings reached proportions between 56 % and 60 % of whole plant dry mass. By contrast the aboveground dry mass (leaves and shoot) was higher for birches competing with grasses. Overall results of birch seedling distribution and competition were significant correlations between densities, space, and growth per single plant. - For saplings and established birch regeneration a notable decrease in mortality rates were found. According to regeneration analyses under stand conditions age distributions in Silver birch regeneration have been controlled by ground cover variants and their environment conditions. The average age of Silver birch seedlings was high in areas with C. villosa (7.6 years) and low in needle litter (4.7 years). Furthermore growth influencing environmental conditions like light, humidity, and distance of old spruce trees have shown differences between variants in ground cover. The growth of regenerated Silver birches at the age of 2 to 6 years under those stand conditions can be described by an exponential function with high degree of adaptation (p ≤ 0,000). There were also differences in sapling densities, mortality and growth rates caused by ground cover variants in the pot experiments. After 2.5 years maximum regeneration densities in pots were registered on ground covers with needle litter. Allocations in regeneration dry mass were less influenced by ground cover variants than in previous stages. Density dependent growth rates could not be proved during last measurements. Finally, the presented results provide the opportunity to characterize temporal and spatial presence of different regeneration stages of Silver birch, its potential of competition and further development in old Norway spruce stands of the Tharandter Forest. They document heterogeneous structures of micro-environmental conditions in these spruce stands, which have sustainable effects on regeneration establishment of this studied pioneer tree species. On the basis of spatial modeling it is possible to estimate spatial distribution of seeds and seedlings depending on seed tree positions. Overall the results involve a high potential of successful regeneration in Silver birch, which opens up promising vistas for silvicultural management. More detailed knowledge in particular regeneration stages induces possibilities for selective control in silviculture with Silver birch. Additionally, estimating the regeneration risks and the success under given surrounding conditions will be more precisely. Considering uncertainty in giving prognoses for climate change Silver birch should be integrated in silvicultural strategies because of its role as admixed tree species and pioneer crop combined with comparably high resilience against warming

Student Number : 0115350V - MSc dissertation - School of Plant, Animal and Environmental Science - Faculty of Science<br>The effect of between-tree competition in separate even aged stands of a Eucalyptus grandis seedling and a single Eucalyptus grandis x Eucalyptus urophylla hybrid clone was assessed. This was done by comparing treatments within an experiment, that was designed to test the effect planting density and genotype had on timber production and stand dynamics through time. This experiment is located on an escarpment in the Summer rainfall region of South Africa, approximately 7 km North West of Albert Falls dam in the Kwa-Zulu Natal Midlands. The terrain is flat with deep apedal soils, and the site has an estimated mean annual precipitation of 1143 mm. The simplest method of evaluating competition effects in plantation stands is through the use of spacing trials. Spacing trials create stands/plots in which all silvicultural and climatic variables are constant. Differences between treatments can then be attributed to competition alone. The planting densities tested were 6667 stems.ha-1, 3333 stems.ha-1, 2222 stems.ha-1, 1587 stems.ha-1 and 1111 stems.ha-1 respectively. Competition was measured at three levels, namely; (i)individual tree, (ii)size-class and (iii)stand level. Vigour and its distribution within the population were used to explain competition processes. Basal area was chosen as the size variable for which vigour would be analysed. Relative Growth Rate (RGR) and Relative Production Rate (RPR) were chosen as the measures of vigour for analysis. Morphological changes in the trees as a result of competition were also used to understand the competitive mechanisms. It was found that resources are not shared amongst individuals in proportion to their size, but rather the larger individuals use disproportionately more of the resources than the smaller individuals, and therefore competition is asymmetrical. The dominant form of competition was found to be resource pre-emption where larger individuals passively prevent solar resources from reaching smaller competitors. Using RPR as the measure of vigour, competition was found to be one-sided, meaning that smaller individuals do not reduce the vigour of larger ones. If RGR is accepted as the measure of vigour then competition is two-sided meaning that the smaller individuals do reduce the vigour of the larger ones to a certain extent. There was no difference in the degree to which the smaller competitors in the clonal and seedling treatments reduced the growth of the larger individuals. The self-thinning rate in the seedling treatments was significantly higher than in the clonal treatments. Increases in mean tree size and production per hectare were accompanied by increases in mortality in the seedling treatments. In the clonal treatments it was found that even once the mean tree size approached the self thinning line, very few or no trees died, however there was also very little or no increase in mean tree size. When the relationship between number of live trees and production per hectare was analysed it was found that the clone could increase production per hectare without any change in survivorship, which is contrary to popular theory. As time progressed the skewness of the population progressed from negative to positive. This increase was the most pronounced in the higher planting density treatments, and the clonal treatments. The size variability in the population first decreased, then steadily increased. This increase was more pronounced in the high planting density treatments, and the clonal treatments. Clones and seedlings react in very different ways to competition. The large differences in population dynamics observed, indicate that we cannot just apply knowledge built up over the years regarding the management of Eucalyptus grandis and other plantation species to Eucalyptus hybrid clones.

碩士<br>國立中興大學<br>生命科學院碩士在職專班<br>95<br>Rice (Oryza sativa L. ), one of the most important cereal crops in the world. There are three major cereal crops in the world, namely rice, wheat, and maize and totally offer 50% of the calorie sources to the world population. Soil salinity is a complex and harmful threat faced by plants. High concertrations of salts will suppress crops growth and interfer physiological metabolisms. Rice is a salt-sensitive crop and the soil salinity decreases the yield. This thesis is aimed at the characterizations of physiological responses to salt stress in rice. Mutants of Tainung 67 ( TNG 67 ) rice variety were screened for salt tolerance at seedling stage. Two mutant strains were successfully identified with ST-099, a salt-tolerant strain, and ST-300, a salt-sensitive strain. Their agricultural characteristics showed no difference in growth. The tolerance to salt of ST-099 (salt-tolerant strain) was the same at germination stage and seedling stage. ST-099 has higher relative water content (RWC) and relative growth rate (RGR) than salt-sensitive strain ST-300 under salt stress. On the other hand, ST-099 is more sensitive to water-deficit stress at seedling stage than at germination stage. The results suggest that the adaptation mechanisms to salt and water-deficit stress are not identical. Elemental Analyses showed salt-sensitive strain ST-300 had a lower potassium content, a higher sodium content, a higher chlorine content, and a higher Na+/K+ ratio. There was no significant difference in the amount of calcium at initial stage of salt stress suggesting that delay of Ca2+-mediated signaling was a factor contributing to its salt sensitivity. As for salt-tolerant ST-099 strain, it had the lowest sodium content and Na+/K+ ratio. A rapid increase in calcium concentration at initial stage of salt stress was very prominent in this salt-tolerant strain. Furthermore, other evidences leaded us to hypothesize that this strain might be able to use excess Na+ for osmoregulation, and as the result, the rate of decrease in relative water content was much slower in ST-099. Under the same NaCl concentration, the salt-sensitive strain had a higher proline concent, and the salt-tolerant strain accumulated much lower level of proline suggesting proline accumulation is a result of injury caused by salt stress.

碩士<br>國立彰化師範大學<br>地理學系<br>95<br>We set up three plots at Tamshui mangrove forest, and investigated the stand structure including measuring stem density, tree height, the diameter at the breast height, and seedlings density and height. We also measure leaf area index (LAI) for each transect within the three plots five times using Plant Canopy Analyzer to examine the temporal and spatial pattern of leaf area index. We also measured understory light environment using hemispherical photography. The result show that tree density was 1.18 trees/m2, mean tree height was 500 cm, mean diameter at the breast height was 6.3 cm, and seedling density was 38.3 seedlings/m2. There seemed to be a trend of higher densities toward upstream plot. Seedling density decrease 59% throughout the study period. LAI was higher in summer (3.06) and fall (3.06) and lower in winter (3.01) and spring (2.59). The seasonal difference was rather minor. Both direct and indirect site factors (DSF and ISF) were highest in fall, and lowest in summer. Light availability in the winter and spring cloud be adversely affected by the growth and therefore shielding of propagules causing the understory light to be similar to that in the summer. There was no obvious spatial and temporal difference in light availability suggesting that understory light was homogeneous at Tamshui mangrove forest. The relationship between the seedling density and understory light was not significant. The Tamshui mangrove forest is located in relatively high latitude near the northern boundary of mangrove distribution. This probably contributed to the low stature of the forest. Furthermore, the mangrove canopy at Tamshui had only one canopy layer. This should also contributed to the high the understory light environment which likely exceeded the requirement of seedling establishment.

碩士<br>國立屏東科技大學<br>森林系<br>93<br>Leaf is the most important organ for photosynthesis. There will be a trade-off between the length of a living leaf and the capability of its photosynthetic rate. A short-lived leaf often performs higher physiological activity with shorter active period than a long-lived leaf does. Bischofia javanica, Machilus japonica var. kusanoi, and Gordonia axillaris are 3 common tree species in subtropical broad-leaved forest of Taiwan. This study investigates the patterns of physiological activities in various leaf age of these species. The amount of carbon fixed during a leaf’s life-span was investigated also. The physiological activities and leaf life-span of each species were measured for potted young trees in nursery of the National Pingtung University of Science and Technology. The hypothesis of this study was that, with shorter leaf life-span, B. javanica should perform higher photosynthetic rate than M. japonica and G. axillaris which have longer leaf life-span. In addition, the physiologically active duration of B. javanica should be shorter than those of the other 2 species. Result showed that average leaf life-span in potted B. javanica in the nursery was about 7 months which was shorter than that of M. japonica and G. axillaries. In addition, leaf life-span of mature trees of M. japonica and G. axillaris were determined in terms of annual leaf turnover rate and half-life in Nanjenshan Forest. Their leaf life-spans were about 18 and 15 months, respectively. Physiological activities of all these 3 species increased as their leaves start to mature. Physiological activities of B. javanica peaked when the leaves just became fully expend. On the other hand, physiological activities of M. japonica and G. axillaris peaked 20-40 days after their leaves became fully expend. Maximum rate of photosynthesis of B. javanica, M. japonica, and G. axillaris were between 12.7-13.8 μmol CO2 m-2s-1. There was no significant difference in the length of days when the photosynthetic rates of the 3 species maintained over 90% of their peak rates (photosynthetic peak stage). However, the length of the photosynthetic peak stage for B. javanica composed 23.4% of its leaf life-span, which was longer than those for the other 2 species. In addition, both the slopes of linear regressions between potential photosynthetic rates and the leaf age from the first day to the day of peak photosynthesis as well as from the peak day to the end of the leaf in B. javanica were all much steeper than those for the other 2 species. These findings indicated that initiation and senescence in photosynthetic machinery of B. javanica were all faster than the other 2 species. Bischofia javanica had the same patterns in photosynthetic rate, stomatal conductance, transpiration rate, chlorophyll concentration and chlorophyll fluorescence (Fv/Fm) during their leaf life-span. However, both Chlorophyll concentration and chlorophyll fluorescence of M. japonica and G. axillaris still maintained at high values before senescence of their leaves. These patterns were different form those of photosynthesis, stomatal conductance, and transpiration. During the whole life-span, single leaf of G. axillaris fixed only 1.4 g of carbon but B. javanica and M. japonica fixed much higher amount of carbon, 4.3 and 4.4 g, respectively. In conclusion, there were no significant differences in terms of both the length of physiological peak stage and the potential of photosynthesis among the 3 species. Therefore, the hypothesis of this study was not supported. Key words: fixed carbon, chlorophyll concentration, chlorophyll fluorescence, leaf age, leaf life-span

- Ziele der Arbeit - Das primäre Ziel der vorliegenden Arbeit bestand in einer möglichst umfassenden Be-schreibung einzelner Entwicklungsstadien im Verjüngungszyklus von Betula pendula Roth. Dabei waren die lokalen Bestandes- und Standortsbedingungen im Untersuchungsgebiet in besonderer Weise zu berücksichtigen. Des Weiteren sollten Optionen zur waldbaulichen Integration der Sand-Birkenverjüngung in bestehende Behandlungskonzepte für in Auflösung befindliche Fichtenaltbestände aufgezeigt werden. - Untersuchungsgebiet - Der Tharandter Wald liegt im Freistaat Sachsen (50° 55’-50° 00’n. Br., 13° 25’-13° 35’ ö. L.) und umfasst eine Fläche von etwa 6.000 ha. Das von der Baumart Fichte dominierte Gebiet kolliner bis submontaner Höhenstufe (350 - 420 m ü. NN) wird der „Unteren Nordostab-dachung des Erzgebirges“ zugeordnet. Als Untersuchungsflächen wurden wechselfeuchte (wechselfrische) Standorte mittlerer Trophie gewählt, die von einschichtigen Fichtenbe-ständen in einem Alter von ≥ 80 Jahren bestockt waren. Einzeln bis truppweise eingemischte Samenbäume der Sand-Birke (B. pendula) bildeten eine Grundvoraussetzung für die Flächen-auswahl. - Methodisches Vorgehen - Das methodische Vorgehen konzentrierte sich auf die verjüngungsökologisch relevanten Entwicklungsstadien (fruktifizierender Samenbaum, Diaspore, Keimling, Sämling und eta-blierte Verjüngungspflanze) der Sand-Birke. Die Wachstumsparameter der vorhandenen Samenbäume wurden durch Untersuchungen zum Fruchtbehang unterlegt. Der mehrstufige Versuchsansatz zur Erfassung einzelner Verjüngungsstadien stützte sich auf Bestandesauf-nahmen, Gefäß- und Laborversuche. Erhebungen auf Bestandesebene erfassten die Diaspo-renausbreitung mithilfe von Samenfallen und dokumentierten die Keimlings- und Ver-jüngungsstadien von B. pendula auf entsprechend etablierten Aufnahmeplots (1 m x 1 m). Darüber hinaus umfassten die Aufnahmen Strahlungs- und Feuchtemessungen und die Charakterisierung der Bodenvegetation. Für die Einschätzung des mikrostandörtlichen Um-feldes wurden exemplarisch Bodendeckungsvarianten (Mineralboden, Nadelstreuauflage, Calamagrostis villosa CHAIX (GMEL.) und Deschampsia flexuosa L. (TRIN.)) ausgewählt, die als besonders repräsentativ für reine Fichtenbestände des Erzgebirges gelten. Für die räumliche Modellierung der Diasporen und Keimlinge auf Bestandesebene stand das Pro-gramm WALDSTAT (NÄTHER &amp; WÄLDER 2003) zur Verfügung. Im Rahmen des Mitscherlich-Gefäßversuchs wurden gleichermaßen quantitative und qualitative Entwicklungen von Sand-Birkenkeimlingen und -sämlingen erhoben. Der Einfluss ausgewählter Bodendeckungs-varianten wurde in diesen Betrachtungen berücksichtigt. Neben zahlreichen Pflanzenpara-metern (Spross-, Blatt- und Wurzelentwicklung, Allokationen, Allometrien) war die kleinstandörtliche räumliche Verteilung dieser Verjüngungspflanzen von vorrangiger Be-deutung. Als Verteilungs- und Konkurrenzmaße auf Ebene des Mikrostandortes dienten Tessellationsmodelle, der Aggregationsindex nach CLARK &amp; EVANS, der Gini-Koeffizient und das “Constant Yield Law“. - Ergebnisse - - Die Erfassung der Samenbaumparameter von B. pendula führte zu flächenspezifischen und signifikanten Unterschieden in der Dimension, Höhe und soziologischen Stellung. Für die Darstellung der Durchmesser-Höhenverteilungen erwiesen sich logarithmische und quadra-tische Funktionen gleichermaßen geeignet. Das Kronenprozent ereichte im Mittel Werte zwi-schen 37 % und 49 %. Die einzelnen Kronenparameter (Kronendurchmesser, Kronenlänge und Kronenmantelfläche) zeigten straffe lineare Zusammenhänge. Innerhalb der Kronen-strukturen (z. B. Blatt- und Zweigtrockenmasse) ließen sich zum Teil allometrische Be-ziehungen nachweisen. Im Rahmen der Vollbaumbeerntung war ein durchmesserabhängiger Fruchtbehang nachweisbar, der für den Einzelbaum eine Anzahl zwischen 2,3 und 4,2 Millionen Diasporen erreichte. - Mit den Erhebungen zur zeitlichen Ausbreitungsdynamik der Diasporen waren durch mehrjährige Untersuchungszeiträume, auch für eine Pionierbaumart wie B. pendula, stärkere Samenjahre nachzuweisen. Die räumliche Modellierung der anemochoren Diasporenaus-breitung belegte erwartungsgemäß bessere Modellanpassungen für den anisotropen (richtungsgebundenen) Modellansatz. Dennoch zeichneten sich sowohl jahres- als auch flächenspezifisch deutliche Unterschiede in der Modellgüte ab. Als maximale Diasporen-dichte pro m² wurde ein Wert von 20.700 Diasporen ermittelt. Die mittleren Ausbreitungs-distanzen (MDD - “Mean Dispersal Distances“) lagen nach Modellschätzung für die ge-samten Beprobungszeiträume und unter Berücksichtigung aller Versuchsflächen zwischen 37 m und 90 m. Die durchschnittliche Diasporenproduktion eines Einzelbaumes lag nach Anga-ben des Modells in einem Bereich von 180.000 bis 7.400.000. Die Qualitätsansprache an den Diasporen ergab einen Anteil von etwa 5 % bis 8 % äußerlich Schadhaften. Der unmittelbare Windeinfluss auf Hauptausbreitungsrichtung und -entfernung konnte ebenfalls nachgewiesen werden. - Untersuchungen zum Keimlingsstadium zeigten deutliche Abhängigkeiten zwischen den ausgewählten Bodendeckungsvarianten, der Keimlingsdichte und dem Keimlingswachstum. Sand-Birkenkeimlinge waren sowohl unter Bestandesbedingungen als auch unter den freif-lächenähnlichen Bedingungen des Mitscherlich-Gefäßversuchs auf der Variante mit Mine-ralboden besonders dicht aufgelaufen, blieben jedoch stark in ihrer weiteren Entwicklung zurück. Als besonders wüchsig erwiesen sich Keimlinge auf den Bodendeckungsvarianten mit Nadelstreuauflage und in D. flexuosa. Sand-Birkenkeimlinge der Bodendeckungsvarianten ohne Konkurrenz durch Bodenvegetation (Mb, Nd) besaßen eine längere Hauptwurzel und eine höhere Wurzelmasse (56 % - 60 % der Gesamtmasse). Die oberirdische Allokation (Blatt- und Sprossmasse) fiel hingegen für Sand-Birkenkeimlinge in den Bodendeckungs-varianten mit C. villosa und D. flexuosa höher aus. Verteilungs- und Konkurrenzerhebungen in den Gefäßversuchen erbrachten signifikante Zusammenhänge zwischen Keimlingsdichte, Standraum und Wachstum der Einzelpflanze. - Das Sämlingsstadium und die älteren Verjüngungspflanzen wiesen einen deutlichen Rückgang in der Mortalität auf. Die Erhebungen im Bestand ergaben ein unterschiedliches Durchschnittsalter für Sand-Birken auf den einzelnen Bodendeckungsvarianten (C. villosa 7,6 Jahre, D. flexuosa 6,2 Jahre und Nadelstreu 4,7 Jahre). Die wachstumsrelevanten Umweltbe-dingungen wie Strahlungsverfügbarkeit, Feuchteregime und Entfernung zum nächsten Alt-baum unterschieden sich außerdem in Abhängigkeit von den als repräsentativ eingestuften Bodendeckungsvarianten unter Bestandesbedingungen. Das bestandesbezogene Wachstum der Sand-Birken in einem Alter von 2 bis 6 Jahren ließ sich durch eine exponentielle Funktion mit hoher Anpassungsgüte (p ≤ 0,000) abbilden. Innerhalb des Mitscherlich-Gefäßversuchs haben sich ebenfalls Unterschiede in der Individuendichte, den Mortalitäts- und Wachstums-raten in Abhängigkeit von den Bodendeckungsvarianten ausgebildet. Höchste Verjüngungs-dichten wurden nach einem 2,5jährigen Entwicklungszeitraum auf der Bodendeckungs-variante Nadelstreuauflage erreicht. Die Allokationen in der Trockenmasse näherten sich hingegen in den unterschiedlichen Varianten stärker an. Ein dichteabhängiges Wachstum konnte in der letzten Aufnahme nicht mehr nachgewiesen werden. Abschließend bleibt festzuhalten, dass die ermittelten Untersuchungsergebnisse in Abhängig-keit vom jeweiligen Verjüngungsstadium die zeitliche und räumliche Präsenz, Konkurrenz- und Entwicklungsfähigkeit der Sand-Birke in Fichtenaltbeständen des Tharandter Waldes charakterisieren. Sie belegen eine kleinstandörtliche Heterogenität in den untersuchten Beständen, die sich nachhaltig auf die Etablierung der hier untersuchten Pionierbaumart auswirkt. Anhand der räumlichen Modellierung lässt sich die zu erwartende Verteilung von Diasporen und Keimlingen in Abhängigkeit von den Positionen der Samenbäume prognostizieren. Insgesamt ergibt sich aus den vorliegenden Ergebnissen ein vergleichsweise hohes Verjüngungspotenzial für B. pendula, das sich durch waldbauliche Maßnahmen effizient nutzen ließe. Ein detailliertes Wissen über die einzelnen Verjüngungsstadien bietet zudem die Möglichkeit einer gezielten waldbaulichen Steuerung der Baumart und zur Risikoabschätzung des Verjüngungserfolgs unter den gegebenen Rahmenbedingungen. Bei einer wachsenden waldbaulichen Unsicherheit im Umgang mit unterschiedlichsten Klima-prognosen, die sich in ihrer Wirkung regionalspezifisch erheblich unterscheiden können, sollte die Sand-Birke als Misch- und Vorwaldbaumart unbedingt berücksichtigt werden. Um dem viel zitierten Anspruch an die Nachhaltigkeit waldbaulichen Handelns gerecht zu werden, muss die Option zur Integration von B. pendula gewährleistet bleiben, auch für künftige Generationen und bei sich wandelnden Ansprüchen an den Wald.<br>- Objectives - The main goal of this study was to describe comprehensively the particular stages of the regeneration cycle of Betula pendula Roth. Investigations were carried out in local stand and site conditions of a research area in South-East Germany (Tharandter Forest) are considered. In this context options for integrating Silver birch regeneration into silvicultural management concepts of old Spruce stands (Picea abies L.) with lacking vitality are pointed out. - Research area - The Tharandter Forest is located (50°00’N, 13°35’E.) in Saxony (South-East Germany) with an area of around 6.000 ha. It is dominated by Norway spruce stands, and ranges from colline to submontane altitudinal belt (350 to 420 m a.s.l.). These sites are part of the northern declivity of the Ore Mountains. Mono-layered Norway spruce stands with soils of medium trophy and well drained, but featured highly variable soil moisture levels during the growing season were selected for this study. The stand age was ≥ 80 years. Seed trees of Silver birch were mixed as single trees or small groups. - Methodical aspects - The methodical work was concentrated on relevant regeneration aspects like fructification of seed trees, seeds, seedlings, saplings and established regeneration of Silver birch. Growth parameters of seed trees and the amount of fructification were used to quantify allometric relationships. The multi-level research design was based on measurements under stand conditions, pot and laboratory experiments. Seed traps and plots (1m x 1m) were located in spruce stands with regard to different stages of Silver birch development. Therefore micro-environmental growth conditions like soil humidity and photosynthetic active radiation were measured, and plants of ground cover characterized. As examples of ground cover variants with highest presence in homogeneous spruce stands mineral soil, needle litter, Calamagrostis villosa CHAIX (GMEL.) und Deschampsia flexuosa L. (TRIN.) were chosen. Using the program WALDSTAT (NÄTHER &amp; WÄLDER 2003) spatial distribution of dispersed seeds (diaspores) and seedlings could be modelled. Additionally pot experiments were done to compare quantitative and qualitative development of birch seedlings between stand and open site conditions. Regeneration density, number of leaves, shoot and root growth and allocations were measured as important growth parameters to evaluate single plant development under different environmental conditions. Finally, spatial distribution of seedlings in microsites and intraspecific competition were calculated by tessellation models, aggregation indices after CLARK &amp; EVANS, Gini-coefficient and ‘constant yield law’. - Main results - - Measurements on seed trees of B. pendula indicate stand specific differences significantly in dimension, height and biosocial position of trees within the birch population (crown classes). For specific height-dbh curves logarithmic and quadratic equations were adapted. The relative crown length for seed trees was located between 37 % and 49 %. Allometric relationships between crown parameters (e.g. crown diameter, crown length and crown surface) were strongly correlated. In specific cases crown structures (e.g. dry mass of leaves and twigs) were also correlated, certainly with different grades. Direct seed counting of felled seed trees provided the relationships between dbh and number of seeds. Counted seeds for single Silver birch trees ranged between 2.300.000 - 4.200.000. - As one result of seed trapping huge varieties in seed production of Silver birch were detectable between years with different seed potential. Spatial modeling of seed dispersal supported strong influences caused by wind (direction and speed). Hence, best fitted model estimations were found for anisotropic scenarios. The maximum in seed density was recorded with 20.700 seeds per m². As data for ‘Mean Dispersal Distances’ (MDD) the program WALDSTAT calculated between 37 m and 90 m. Furthermore the amount of seeds produced by a single tree was estimated with 180.000 - 7.400.000 depending on dbh. Physical quality evaluations for seeds have shown a mean proportion of damaged and not germinable seeds between 5 % and 8 %. - Direct effects of ground cover variants have been identified for seedling density and growth. Seedling density was highest on mineral soil for both, stand conditions and pot experiment, but these birch seedlings developed slowly compared with individuals in the other ground cover variants. The best growth was realized by birch seedlings in needle litter and D. flexuosa. Regarding to root length and mass, birches in ground cover variants without grass competition (mineral soil and needle litter) have shown a significant better development of underground parts. Root dry mass of these birch seedlings reached proportions between 56 % and 60 % of whole plant dry mass. By contrast the aboveground dry mass (leaves and shoot) was higher for birches competing with grasses. Overall results of birch seedling distribution and competition were significant correlations between densities, space, and growth per single plant. - For saplings and established birch regeneration a notable decrease in mortality rates were found. According to regeneration analyses under stand conditions age distributions in Silver birch regeneration have been controlled by ground cover variants and their environment conditions. The average age of Silver birch seedlings was high in areas with C. villosa (7.6 years) and low in needle litter (4.7 years). Furthermore growth influencing environmental conditions like light, humidity, and distance of old spruce trees have shown differences between variants in ground cover. The growth of regenerated Silver birches at the age of 2 to 6 years under those stand conditions can be described by an exponential function with high degree of adaptation (p ≤ 0,000). There were also differences in sapling densities, mortality and growth rates caused by ground cover variants in the pot experiments. After 2.5 years maximum regeneration densities in pots were registered on ground covers with needle litter. Allocations in regeneration dry mass were less influenced by ground cover variants than in previous stages. Density dependent growth rates could not be proved during last measurements. Finally, the presented results provide the opportunity to characterize temporal and spatial presence of different regeneration stages of Silver birch, its potential of competition and further development in old Norway spruce stands of the Tharandter Forest. They document heterogeneous structures of micro-environmental conditions in these spruce stands, which have sustainable effects on regeneration establishment of this studied pioneer tree species. On the basis of spatial modeling it is possible to estimate spatial distribution of seeds and seedlings depending on seed tree positions. Overall the results involve a high potential of successful regeneration in Silver birch, which opens up promising vistas for silvicultural management. More detailed knowledge in particular regeneration stages induces possibilities for selective control in silviculture with Silver birch. Additionally, estimating the regeneration risks and the success under given surrounding conditions will be more precisely. Considering uncertainty in giving prognoses for climate change Silver birch should be integrated in silvicultural strategies because of its role as admixed tree species and pioneer crop combined with comparably high resilience against warming.