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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The phytosociology of a tropical seasonal forest in southeastern Mexico

Shepherd, John Dorsey, January 1975 (has links)
Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 114-120).
2

The role of pathogens in determining plant recruitment and distribution patterns in a western Amazonian floodplain

Alvarez-Loayza, Patricia C. January 2009 (has links)
Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Ecology and Evolution." Includes bibliographical references.
3

Der maniok, ein beitrag zur Wirtschaftsgeographie der warmen länder ...

Kiok, Walter. January 1934 (has links)
Inaugural-Dissertation zur Erlangung der Doktorwürde der Philosophischen Fakultät der Ernst-Moritz-Arndt-Universität zu Greifswald, 1933.
4

The impact of vesicular-arbuscular (VA) mycorrhizal mycelium upon VA-incompatible species

Marques, Maria Isabel Batista January 1997 (has links)
No description available.
5

Distribution and functional significance of Al in tropical forest plants

Mahmud, Khairil January 2017 (has links)
The general aim of this thesis was to investigate the mechanisms that determine variation in Al accumulation among tropical woody plants. The focus of the study variation among populations of the well-studied Al accumulator Melastoma malabathricum, but this was coupled with sampling 50 tree species growing on the 50 ha forest dynamics plot at Pasoh Forest Reserve in Peninsular Malaysia in order to gain a perspective on Al accumulation at a community scale. I sampled mature leaves and seeds of M. malabathricum from 20 populations growing in six habitats across Peninsular Malaysia. Concentrations of Al, N, P, K, Ca and Mg were determined in air-dried leaves and the soil from each site. The seeds were used to generate cohorts of seedlings that were grown in hydroponic solutions amended with Al in the form of 1.0 mM AlCl3. Foliar Al concentrations varied significantly among populations, but were not consistently different among plants growing in different habitats and showed no relationship to total or exchangeable Al concentrations in soils collected at the 20 sites. Similarly, foliar Al concentrations in seedlings grown in the presence of Al differed significantly among source populations, but values did not correlate with foliar Al concentrations in wild plants from parent populations. Mean foliar Al concentration in wild plants was positively correlated with foliar Ca concentration, and with total soil Ca and Mg concentrations, across the 20 populations. Furthermore, total dry mass and relative growth rates were significantly greater for seedlings that had received Al in the growth medium than for seedlings that had received no Al. The growth response to Al addition varied among populations of M. malabathricum, and relative growth rate in response to Al addition was greater for populations that accumulated higher foliar Al concentrations. In a further experiment, increasing Al concentrations from In a further experiment, increasing Al concentrations from 0 to 2.0 mM in the nutrient solution increased rates of growth, but growth declined at 5.0 mM Al. The responses to Al addition varied among populations for growth, photosynthesis, respiration, carbon allocation, and foliar P, Ca, and Mg concentrations. The rates of photosynthesis and respiration, and total nonstructural carbohydrate concentrations, were higher for seedlings grown in the presence of 2.0 mM Al in the nutrient solution than in the absence of Al, while lignin concentration in roots decreased. These results suggest that Al addition stimulate growth stimulation by increasing rates of photosynthesis and respiration, resulting in higher non-structural carbohydrate concentrations. Increased allocation of photosynthate to root systems coupled with their lower lignification results in enhanced nutrient uptake (particularly P, Ca and Mg), which contributes to enhanced whole-plant growth. To test the prevalence of Al accumulation at the community scale I sampled 50 tree species growing on the 50 ha Forest Dynamics Plot at Pasoh Forest Reserve in Peninsular Malaysia. Twenty two species possessed foliar Al concentrations that exceeded a value of 2.3 mg g-1 Al dry mass, which is a suitable threshold for detecting Al accumulators in Southeast Asian forests. A phylogenetic signal was detected for foliar concentrations of Al and other elements, suggesting that more closely related species have more similar values of these traits. A canonical correspondence analysis (CCA) revealed that soil Al concentrations have limited influence on the fine-scale distribution of the tree species sampled at Pasoh. I conclude that the distribution of differences in the expression of Al accumulation among populations of M. malabathricum and the distribution of Al accumulator species within a tree community growing at one site are uncoupled from soil Al concentrations, but may be linked to other soil properties such as Ca and Mg concentrations. When supplied in nutrient solutions, Al promotes the growth of the Al accumulator M. malabathricum through a physiological mechanism that includes up-regulation of photosynthetic and respiration rates. The functional significance of this growth response for plants growing under natural conditions in the field requires further investigation.
6

Colonizing abilities of six alien weeds in the coastal farmlands of Guyana, S.A.

Thompson, Sheila R. January 1984 (has links)
Weeds severely limit agricultural production in many Third World tropical countries where productivity is already marginal due to unfavourable environmental, biological, economic and social factors. Lack of both ecological and distributional information at the scale of the weed assemblage, and lack of detailed data on the life histories and responses of the constituent weedy species hinders development of cheap and effective weed management strategies not contingent on intensive use of herbicides. / Plant geographers can contribute to the solution of tropical weed problems by investigating factors which mediate the dynamics of species: regional and local ranges. The research in this thesis departs from other plant geographic studies on tropical week assemblages (e.g. Kellman, 1973) by undertaking experimental field studies which are designed to uncover aspects of the differential abilities of species to make the transition from localized immigrant population to widespread and abundant weed. / The research focusses on six alien species invading agricultural and non-agricultural land in a lowland tropical region: coastal Guyana. Experiments are directed towards propositions concerning the basis for differential colonizing success of two common (Echinochloa colonum (L) Link, Macroptilium lathyroides L.) and four uncommon (Asclepias curassavica L., Emilia fosbergii D. H. Nicholson, Malachra alceifolia Jacq., Paspalum virgatum L.) species of cultivated fields in an area of prime agricultural land. Experimental colonizing trials, which equalize the opportunities of each species to colonize, provide a reference point against which to assess inter- and intra-species differences. / Results of colonizing trials suggest that the species represent four ecological groups. These are Macroptilium and Emilia (Group 1), Echinochloa (Group 2), Malachra and Asclepias (Group 3), and Paspalum (Group 4). / Species of Group 1 have the highest potential for establishment in cultivated fields within a single growing season. Emilia, though currently not a prominent species in the study area, should be controlled early. Heavy insect predation and consequent slow maturity of Asclepias reduce the likelihood of its rapid establishment in the area. Malachra and Paspalum, though not predated, have slow generation times, and hence are also unlikely to rapidly invade frequently cultivated fields. However, the high incidence of interruption of cultivation in the coastal farmlands is likely to promote their range expansion.
7

Colonizing abilities of six alien weeds in the coastal farmlands of Guyana, S.A.

Thompson, Sheila R. January 1984 (has links)
No description available.
8

Vegetation von Inselbergen in Zimbabwe : Struktur, Diversität und ökogeographische Differenzierung einer tropischen Lebensgemeinschaft /

Seine, Rüdiger. January 1996 (has links)
Thesis--Rheinische Friedrich-Wilhelms-Universität Bonn, 1996. / Includes bibliographical references (p. 317-327).
9

Regeneration and growth of several canopy tree species in the Maya Forest of Quintana Roo, Mexico : the role of competition and microhabitat conditions /

Sorensen, NaDene S. January 1900 (has links)
Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 204-236). Also available on the World Wide Web.
10

Estudo fitoquímico guiado por bioensaios em algumas espécies da Mata Atlântica e Floresta Amazônica / Phytochemical study guided by bioassays in some species of the Atlantic Forest and Amazonian Forest

Benevides, Paulo José Coelho 26 October 2001 (has links)
Neste trabalho o estudo fitoquímico foi guiado por dois bioensaios visando o fracionamento e o isolamento de substâncias com atividades antitumoral e antifúngica potenciais. Os bioensaios utilizados são específicos e foram realizados com três cepas modificadas da levedura Saccharomyces cerevisiae e com duas espécies de fungos: Cladosporium cladosporioides e Cladosporium sphaerospermum. O fracionamento guiado por estes bioensaios foi desenvolvido com duas espécies da Mata Atlântica: Petiveria alliacea L. e Bathysa meridionalis L.; e uma espécie da Floresta Amazônica: Psichotria spectabillis S. Este trabalho resultou no isolamento de vinte e duas substâncias. Da espécie P. alliacea foram isolados dois sulfetos, dois dissulfetos, três polissulfetos e um esteróide. A espécie P. spectabillis forneceu três cumarinas, dois diterpenos e dois flavonóides. Da espécie B. meridionalis foram isolados sete triterpenos. Além do estudo químico guiado por bioensaios, os óleos essenciais obtidos das espécies estudadas foram analisados por cromatografia gasosa e trinta substâncias foram identificadas como polissulfetos, mono, sesqui e diterpenos. As substâncias 1, 3, 4, 5, 13 e 22 apresentaram forte atividade antifúngica. As substâncias 1, 4, 6, 9, 13, 22 e a mistura 20-21 foram capazes de inibir seletivamente o crescimento dos mutantes de S. cerevisiae indicando que a atividade citotóxica destas substâncias está relacionada com as vias de reparo do DNA celular. O sulfeto 3, o dissulfeto 4 e os polissulfetos 6 e 8 até então não haviam sido descritos na literatura como substâncias de origem natural. / In this work the phytochemical guided-fractionation, using two bioassays was performed aiming the fractionation and the isolation of potential antifungal and antitumoral compounds. The bioassays used are specific and were performed with three mutants strains of the yeast Saccharomyces cerevisiae, and with two species of fungi: Cladosporium cladosporioides and Cladosporium sphaerospermum. The bioassays guided-fractionation were clone using two plant species: Petiveria alliacea L. and Bathysa meridionalis L. from Atlantic forest: and Psychotria spectabillis S. from Amazon forest: This study resulted in the isolation of 22 substances. From P. alliacea were isolated 2 sulfydes, 2 disulfydes, 3 polissulfydes and 1 steroid. From P. spectabillis supplied 3 cumarins, 2 diterpens and 2 flavonoids. From B. meridionallis were isolated 7 triterpens. Besides the chemical guided-fractionation study, the essential oils obtained of these species were also analyzed by gaseous chromatography and 30 compounds were identified as polisulfydes, mono, sesqui and diterpens. The substances 1, 3, 4, 5, 13 and 22, showed strong antifungal activity. The substances 1, 4, 6, 9, 13, 22 and the mixture 20-21 showed DNA-damaging activity, which was evidenced by selective inhibition of the growth of the mutants of S. cerevisiae. The sulfyde 3, the disulfyde 4 and the polisulfydes 6 and 8 have been described as natural derivatives for the time in this work.

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