Au Burkina Faso comme ailleurs en Afrique et dans le monde, des enfants, des femmes et des hommes ont faim parce qu’ils n’arrivent pas à se procurer quotidiennement de la nourriture pour satisfaire leurs besoins énergétiques; ceci, en raison de la rareté et de la cherté des produits alimentaires de base dans ces pays. Et pourtant, face à la prédominance de l’agriculture de subsistance, une bonne politique agricole et éducative avec des conditions de réalisation capables d’attirer les jeunes sortants vers la production principale des céréales, aliment de base de la plupart de ces pays, permettrait d’aboutir à l’autosuffisance et la sécurité alimentaires. À travers l’analyse de l’efficacité externe du centre de promotion rurale (CPR) de Goundi au Burkina Faso, la présente recherche s’est appuyée sur les dimensions sociologique, sociopsychologique et psychoprofessionnelle pour identifier les déterminants contextuels et individuels dont la prise en compte dans les politiques agricoles et dans les formations professionnelles des jeunes agriculteurs pourrait aider les sortants à s’insérer mieux dans le domaine céréalier en tant qu’emploi principal. Les principaux résultats indiquent : l’âge de sortie situé entre 21 et 34 ans, la situation matrimoniale, le genre, les rituels d’installation, les céréales en tant qu’aliment de base, l’accès à la terre et à l’équipement à la sortie du centre, le père, le promotionnaire, les épouses et les enfants comme facteurs significativement liés à l’insertion en emploi principal céréalier au plan sociologique et sociopsychologique. Au plan psychoprofessionnel, ce sont : l’autonomie, l’initiative, l’intimité, le courage, la volonté, l’industrie, la passion, la logique non marchande, la vision de continuité et le moi-idéal qui sont les principaux résultats. Le difficile accès à la terre, à l’équipement et aux intrants et les difficultés d’insertion en groupe et en famille constituent les obstacles de cette insertion. / In Burkina Faso and elsewhere in Africa and in the world, children, women and men are hungry because they can not get food daily to meet their energy needs; this, because of the scarcity and high cost of basic food products in these countries. And yet, given the predominance of subsistence agriculture, agricultural policy and a good education with performance conditions that attract young people leaving to the main production of cereals, the staple food of most of these countries would to achieve self-sufficiency and food security. Through the analysis of the external efficiency of rural promotion center (CPR) Goundi Burkina Faso, the present research was based on the sociological dimensions, counseling and psychoprofessionnelle to identify contextual and individual determinants whose management account in agricultural policies and vocational training for young farmers could help outgoing fit best in that employment as principal grain. The main results show: the exit age between 21 and 34 years of age, marital status, gender, installation rituals, grains as a staple food, access to land and the equipment outside the center, father, promotionnaire, wives and children as factors significantly related to the main job insertion grain the sociological and socio-psychological level. In psychoprofessionnel plan, autonomy, initiative, intimacy, courage, determination, industry, passion, non-market logic, the vision of continuity and ideal ego are the main results. The difficult access to land, equipment and inputs and integration problems in group and family are the obstacles of this insertion. / L'étude combine les méthodes qualitative et qualitative à travers l’utilisation du questionnaire et du canevas d’entrevue. Elle s’appuie sur un cadre conceptuel élaboré à partir de revue de littérature et de concepts clefs tels que : le capital social, le capital humain, l’identité personnelle, l’identité professionnelle et la socialisation, Les résultats déterminent le profil d’un céréalier indiquant son attachement aux valeurs professionnelles liées au transfert de ses connaissances, à la modernisation de l’exploitation, à la recherche de l’amélioration du rendement et à l’utilisation d’outils modernes.

The current South African tax system offers livestock farmers a variety of forms of relief. There are also certain aspects that do not make it so advantageous to be regarded as a farmer by the tax collector. A large number of farmers emigrate to other countries without knowing how the tax systems of those countries function or how much tax they will have to pay. With these factors in mind the question arises concerning how other countries tax their livestock farmers and what relief is provided to them. The objective of this research is to examine and compare the theoretical tax legislation of South Africa, Australia and New Zealand, where after it will be applied in a case study. Finally conclusions and recommendations will be made based on the results of the research. It was found that, although the relief provided to South African livestock farmers regarding some aspects exceeds the relief provided in Australia and New Zealand, there are certain aspects that could be adjusted in order to make it more advantageous for livestock farmers to stay in South Africa. These proposed adjustments can indirectly stimulate the national economy. / Thesis (M.Com. (Tax))--North-West University, Potchefstroom Campus, 2011.

The current South African tax system offers livestock farmers a variety of forms of relief. There are also certain aspects that do not make it so advantageous to be regarded as a farmer by the tax collector. A large number of farmers emigrate to other countries without knowing how the tax systems of those countries function or how much tax they will have to pay. With these factors in mind the question arises concerning how other countries tax their livestock farmers and what relief is provided to them. The objective of this research is to examine and compare the theoretical tax legislation of South Africa, Australia and New Zealand, where after it will be applied in a case study. Finally conclusions and recommendations will be made based on the results of the research. It was found that, although the relief provided to South African livestock farmers regarding some aspects exceeds the relief provided in Australia and New Zealand, there are certain aspects that could be adjusted in order to make it more advantageous for livestock farmers to stay in South Africa. These proposed adjustments can indirectly stimulate the national economy. / Thesis (M.Com. (Tax))--North-West University, Potchefstroom Campus, 2011.

Annotation This thesis is part of Project of the Grant Agency of the Czech Republic No. P504/11/1151 (Role of plants in the greenhouse gas budget of a sedge fen) aims at estimating the turnover of aboveground biomass of Carex acuta L. in a flooded part of the Wet Meadows near Třeboň. The biomass turnover was estimated using both destructive and non-destructive types of measurement and was assessed separately for generative and vegetative tillers, which markedly differ in their life cycles. Vegetative tillers last throughout the vegetation season. Generative tillers have a fast development at the beginning of the vegetatin season but die out soon after seed development. They disapper from the stand in mid-July. Vegetative shoots reached their maximum aboveground biomass at the end of June. The average dry weight of all leaves produced so far was 1,51 g per tiller and the average dry weight of all aboveground biomass produced per tiller was 2,28 g. The turnover coefficient was 1,39 year-1 and 1,01 year-1 for leaves and whole tillers, respectively. Also generative shoots reached their maximum aboveground biomass at the end of June. The average dry weight of aboveground biomass produced so far was 1,95 g per tiller. The turnover coefficient was 1, 38 year-1and 1,10 year-1.

Made available in DSpace on 2016-06-02T19:29:34Z (GMT). No. of bitstreams: 1 3657.pdf: 23563912 bytes, checksum: ceff0481d51dd5b9b20c1cb8cfdfe91f (MD5) Previous issue date: 2011-02-28 / Universidade Federal de Minas Gerais / The human activities are continually altering the ecosystems constituting an important environmental modifier agent, promoting changes in balance and dynamics of the landscape pattern and process. There are several examples of this interference, however the understanding of dimension and effects of human activities and the measures to aid in decision make are still incipient. In that sense, the watershed basin has been used as a physical-temporal component for natural resources planning, being supported by the use of landscape indicators, that has been proposed for better understanding the human activity influence in the ecosystems dynamics. This work analyzed the physical, socioeconomic and biotic factors interaction, in the integrity of the landscape, in the context of the watershed basin through indicators, between 1989 and 2009. The study area was the Medium-Superior Mogi-Guacu river watershed basin, inserted in the northeast area of the State of Sao Paulo, Brazil. This area was sub-divided in three geomorphological units (Cuestas Basalticas, Depressao Periferica and Planalto Ocidental) and in 12 geopolitical units, referring the municipal districts of its inclusion. It was proceeded the landscape environmental characterization and the use of the following indicators: topographical characteristics; landscape pattern; landscape structure (Landscape richness, Landscape diversity; Landscape naturalness (Urbanity and Hemeroby); landscape fragmentation, and the Index of Human Appropriation of the Liquid Primary Productivity (HANPP), considering the total area of the watershed basin (UGB), the geopolitical units (UGP) and thegeomorphological units (UGM). The data acquisition happened for field risings, bibliographical and of official documental sources. It was used LANDSAT TM-5 1989, 1999 and 2009 satellite images for land-use mapping, that subsidized the analysis of the landscape indicators, following specific literature. The correlation among the indicators was tested by models of linear regression and validated by Bootstrap method. It was observed a positive relation between HANPP and hemeroby; a weak positive relation between HANPP and urbanity and HANPP and steepness; a tiny positive relation between HANPP and slope orientation; a weak negative relation between HANPP and net road influence, and between HANPP and distance from highways; and tiny positive relation between HANPP and distance of urban settlements. The smallest values of HANPP were obtained in 1999 for all the landscape units. The landscape metric didn't show a significant correlation with HANPP, however, flotation of the values is verified among the years and between the units. For 1999 and for UGP-7 (municipal district of Luis Antonio) and UGP-11 (Santa Rita do Passa Quatro) registered the metric values that allow to infer better. / Padrão espacial e temporal das mudanças de uso da terra e sua relação com indicadores da paisagem. Estudo de Caso: Bacia Hidrográfica do Médio rio Mogi-Guaçu Superior (SP). O ser humano esta continuamente alterando os ecossistemas, constituindo de um relevante agente modificador do meio, promovendo mudancas no equilibrio e dinamica dos processos naturais. Diversos sao os exemplos desta interferencia, entretanto a compreensao da dimensao e dos efeitos das atividades humanas e as medidas para auxiliar na tomada de decisao ainda sao incipientes. Nesse sentido, a bacia hidrografica tem sido utilizada como um componente fisico-temporal para o planejamento e o gerenciamento dos recursos naturais, sendo auxiliada pelo uso de indicadores, que tem sido proposto para melhor compreensao da influencia antropica na dinamica dos ecossistemas. O presente trabalho analisou a interacao dos fatores fisico, socio-economicos e bioticos na integridade da paisagem, no contexto de bacia hidrografica por meio de indicadores, entre 1989 e 2009. A area de estudo compreende a Bacia Hidrografica do Medio Rio Mogi-Guacu Superior, inserida na regiao nordeste do Estado de Sao Paulo, Brasil e foi sub-dividida em tres unidades geomorfologicas (Cuestas Basalticas, Depressao Periferica e Planalto Ocidental) e em 12 unidades geopoliticas, referentes aos municipios de sua abrangencia. Procedeu-se a caracterizacao da paisagem e a geracao dos indicadores: de caracteristicas topograficas (Altimetria, Declividade, Orientacao de Vertentes), do padrao da paisagem (Numero de Fragmentos, Indice de Similaridade, Indice de Forma, Circulo Circunscrito Relacionado, Distancia Euclidiana do Vizinho mais Proximo, Indice de Area de Interior, Indice de Contraste de Borda), da estrutura da paisagem (Riqueza da Paisagem, Diversidade da Paisagem e Indice de Urbanidade), da fragmentacao (Influencia da Malha viaria, Proximidade de Rodovias, Proximidade de Estradas, Distancia de Areas Urbanas) e Indice de Apropriacao Humana da Produtividade Primaria Liquida (HANPP), considerando a area total da bacia hidrografica (UGB), as unidades geopoliticas (UGP) e as unidades geomorfologicas (UGM). A aquisicao de dados ocorreu por levantamentos de campo, bibliograficos e de fontes documentais oficiais. Utilizaram-se as imagens de satelite LANDSAT TM-5 de 1989, 1999 e 2009 para o mapeamento de uso e ocupacao da terra, que subsidiaram a analise dos indicadores, seguindo literatura especifica. A correlacao entre os indicadores foi testada por modelos de regressao linear e validados pelo metodo de reamostragem Bootstrap.Verificou-se que correlacao moderada positiva entre HANPP e hemerobia, fraca positiva entre HANPP e urbanidade e HANPP e declividade; infima positiva entre HANPP e orientacao de vertentes; fraca negativa entre HANPP e influencia da malha viaria e entre HANPP e distancia de estradas e de rodovias; e infima positiva entre HANPP e distancia de manchas urbanas. Os menores valores de HANPP foram obtidos em 1999 para todas as unidades de gerenciamento. As metricas da paisagem nao apresentaram correlacao significativa com HANPP, entretanto, verifica-se flutuacao dos valores entre os anos e entre as unidades, sendo que 1999 e as UGP- 7 (municipio de Luis Antonio) e UGP-11 (Santa Rita do Passa Quatro) registraram as metricas com valores que permitem inferir melhores condicoes para a conservacao da biodiversidade. Nessas unidades estao as duas unidades de conservacao de protecao integral da bacia hidrografica do Medio Rio Mogi-Guacu Superior. Como os indicadores utilizados neste trabalho mensuram principalmente a condicao das manchas e como estao espacializadas e a HANPP e eficaz na quantificacao da intervencao na paisagem como um todo, este estudo pode auxiliar na definicao dos fatores que podem interferir ou priorizar a ocupacao da terra, principalmente quando se destina a praticas agricolas.

There are two transport systems used by agricultural businesses engaged in primary production. These are transport systems involving tractors and motorized vehicles. Transport systems involving tractors are made up of motorized vehicles and vehicles that are Toled Grand Super , or more specifically, a motor vehicle plus one or more vehicles that are towed along. A motorized vehicle refers to an agricultural traktor John Deere 6620. Motorized transport systems are comprised of Lorries Tatra 815 Agro. A lorry can only have one additional vehicle connected to itself. The transport systems mentioned above can be used in agricultural businesses engaged in primary production along with similar or identical productions. Motorized transport systems used in agricultural primary production are in the majority of cases applied to additional productions. This is the given transport system framework, which can be setup with adaptations for various uses. It therefore follows that the possibilities of comparing transport systems using universal undercarriages are increased. Expenditure associated with these transport systems, are easily compared. It is also possible to easily compare transport systems involving tractors with motorized transport systems as long as there is no need for more vehicles connected to them. It is obvious that the use of motorized transport systems for longer distances is preferable to transport systems involving tractors. Expenses for every driven kilometre with the comparable transport systems show a significant difference in cost. This difference is 36,85 Kč. On the other hand, it is preferable to use tractors for shorter distances involving a larger amount of material. he cost of one tonne of material transported is different about 11,55 Kč.

Cette étude effectuée sur le lac Taabo ⁄ (Sud-Est de la Côte d’Ivoire), porte sur l’évaluation des paramètres de la qualité de l’eau, le peuplement phytoplanctonique, et le suivi de la production primaire. Ce lac de 69 km² se caractérise par une profondeur moyenne de 8 m, avec un temps de résidence moyen de 49,2 jours, une température moyenne de 29,5°C, absence de stratification; il concerne une population environnante de 140 000 habitants. Les entrées d’eaux dans le lac sont influencées par le barrage de Kossou situé en amont, la gestion hydroélectrique de Taabo, et le régime du fleuve Bandama qui est affecté par l’alternance saison des pluies, saison sèche. L’analyse des paramètres physico-chimiques a montré une homogénéité spatiale des eaux du lac de Taabo tandis qu’au niveau temporel une saisonnalité marquée est observée entre les périodes des pluies et celle de saison sèche. Cette saisonnalité est principalement imputable aux importantes variations de paramètres tels que la conductivité, la turbidité, la transparence et les éléments nutritifs (valeurs moyennes en nitrate et orthophosphate, respectivement de 1,62 et 10 mg.l-1). Le lac de barrage hydroélectrique est gouverné par la combinaison de deux gradients, celui de l’enrichissement en nutriments et celui de la minéralisation. L’aval du lac présente toutefois quelques particularités : minéralisation et oxygénation plus élevées qu’en amont, au niveau temporel. La chlorophylle a varie de 4,8 à 16,5 μg/l. Au niveau de la composition spécifique algale, 118 taxons repartis en 5 grands groupes et 45 genres ont été identifiés. Le peuplement algal est dominé par les chlorophycées (30,5 %) suivi par des cyanobactéries (27,1 %). La productivité varie de 0,4 à 0,8 mg Oxygène produit par mg Chl a-1 heure -1 (soit ± 2,31 à 4,6 mg C. mg Chl a-1. heure -1). Extrapolées à l’échelle annuelle, nos estimations de production primaire phytoplanctonique journalière se situent entre 1,5 à 2,66 g C m-2, avec une valeur annuelle de 167 à 306 g C m-2. Une étude théorique de la production des macrophytes implantés dans la zone amont et centrale, montre que ceux-ci représentent 77 % de la production primaire du lac. Ceux-ci affectent aussi les activités socio-économiques. Le lac Taabo est remarquable par les nombreux conflits d’usages liés à l’eau engendrées par la gestion hydraulique et les diverses activités humaines, aux quels se rajoutent des risques sanitaires (comme vecteurs de maladies humaines et des conflits d’usages, etc.). / This study of the Taabo Lake (South-East Coast Ivory) focuses on the evaluation of parameters of water quality, phytoplankton communities, and estimation of primary production. his lake of 69 km² is characterized by an average depth of 8 m, a mean residence time of 49.2 days, a mean temperature of 29.5 ° C, no stratification; it concerns a population of about 140 000 inhabitants. The inputs of water in the lake are influenced by the dam upstream Kossou, the hydroelectric activity of Taabo plant, and the regime of the river Bandama which is affected by alternating rainy season, dry season. The analysis of physicochemical parameters showed a spatial homogeneity of the waters of Lake Taabo but a marked seasonality was observed between periods of rainfall and the dry season. This is mainly due to seasonal variations of parameters such as conductivity, turbidity, transparency and nutrients (average values in nitrate and orthophosphate, respectively 1.62 and 10 mg.l-1). The lake is governed by a combination of two gradients; a nutrient enrichment and the mineralization. The dowstream part of the lake has some peculiarities as mineralization and higher dissolved oxygen content, depending on season. Chlorophyll a varied from 4.8 to 16.5 μg.l-1. In terms of algal species composition, 118 taxa divided into five major groups and 45 genera were identified. The algal population is dominated by Chlorophyceae (30.5%) followed by Cyanobacteria (27.1%). The productivity varies from 0.4 to 0.8 mg oxygen per mg Chl a producted hour -1 (or ± 2.31 to 4.6 mg C mg Chl a. Hour -1). Extrapolated on an annual cycle, our estimates of daily phytoplankton primary production ranged from 1.5 to 2.66 g C m-2, with an annual value of 167 to 306 g C m-2. A theoretical study of the production of macrophytes located in the upstream and central zone indicates that they represent 77% of primary production of the lake. They also affect the socio-economic activities. Taabo Lake is remarkable by the numerous conflicting uses related to water caused by the water management and the various human activities, which are in addition to health risks (such as vectors of human diseases and use conflicts, etc.. ).

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The turbulent fluxes of carbon dioxide (CO2 ) were investigated in two sites of irrigated rice in southern Brazil, using the eddy covariance technique over 385 days of analysis at the site of Paraiso do Sul and 683 days in site Cachoeira do Sul also used the model of filling the gaps in order to estimate the net ecosystem exchange CO2 -C (NEE). Throughout the growing season, rice fields, both for the site of Paraiso do Sul to the site of Cachoeira do Sul, acted as carbon sinks (C). During fallow periods, these fields were the source of C. The NEE accumulated at the site of Cachoeira do Sul was similar in both cycles and practically equal to the estimated site of Paraiso do Sul. The GPP accumulated during the crop cycle 2010-2011, the rice field of Cachoeira do Sul, was less than 12% of the 2011-2012 cycle and higher than 15% of the site of Paraiso do Sul. The Re accumulated was similar at the site of Paraíso do Sul in the 2010-2011 cycle Cachoeira do Sul, but less than the 2011- 2012 cycle. The values of NEE, GPP and R e for the site of Paraíso do Sul were - 270.53 gCm2 , -821.19gCm2 and 527.59gCm2 , respectively. To the site of Cachoeira do Sul, were -282,53 gCm2 , -933,40gCm2 and 597,05gCm2 for NEE, GPP and Re , respectively, in the 2010-2011 cycle. For the 2011-2012 cycle in the rice field of Cachoeira do Sul, the values of NEE, GPP and Re were -279,69gCm2 , - 1062,64gCm2 and 716,58gCm2 , respectively. The total C accumulated over the period analyzed for the site of Paraíso do Sul was -45,90gCm2 , considering this area of rice cultivation, as a sink for C. While the growing area of Cachoeira do Sul was considered a source of C (19,94 gCm2 ). Showing by this that long periods of fallow contribute significantly to the accumulated fluxes due to constant presence of vegetation. The contribution of this work will assist in the investigation of CO2 in these ecosystems. / Os fluxos turbulentos de dióxido de carbono (CO2 ) foram investigados em dois sítios de cultura de arroz irrigado no Sul do Brasil, utilizando a técnica de covariância de vórtices ao longo de 385 dias de análise no sítio de Paraíso do Sul e de 683 dias, no sítio de Cachoeira do Sul. Além disso, utilizou-se o modelo de preenchimento das lacunas com o objetivo de estimar a troca líquida de C-CO2 no ecossistema (NEE). Ao longo do período de cultivo, os campos de arroz, tanto para o sítio de Paraíso do Sul quanto para o sítio de Cachoeira do Sul, atuaram como sumidouros de carbono (C). Durante os períodos de pousio, esses campos foram fontes de C. O NEE acumulado, no sítio de Cachoeira do Sul foi semelhante em ambos os ciclos e praticamente igual ao estimado no sítio de Paraíso do Sul. A GPP acumulada durante o ciclo de cultivo de 2010-2011, no campo de arroz de Cachoeira do Sul, foi inferior a 12% do ciclo de 2011-2012 e superior em 15% a do sítio de Paraíso do Sul. A Re acumulada foi semelhante no sítio de Paraíso do Sul e no ciclo de 2010- 2011 de Cachoeira do Sul, mas inferior a do ciclo de 2011-2012. Os valores de NEE, GPP e Re para o sítio de Paraíso do Sul foram de -270,53 gCm2 , -821,19gCm2 e 527,59gCm2 , respectivamente. Para o sítio de Cachoeira do Sul, foram de - 282,53gCm2 , -933,40gCm2 e 597,05gCm2 para NEE, GPP e Re , respectivamente, no ciclo de 2010-2011. Para o ciclo de 2011-2012, no campo de arroz de Cachoeira do Sul, os valores de NEE, GPP e Re foram de -279,69gCm2 , - 1062,640gCm2 e 716,58gCm2 , respectivamente. O total de C acumulado ao longo do período analisado para o sítio de Paraíso do Sul foi de -45,90gCm2 , considerando esta área de cultivo de arroz, como um sumidouro de C. Enquanto que a área de cultivo de Cachoeira do Sul foi considerada fonte de C (19,94 gCm2 ). Mostrando com isso, que períodos longos de pousio contribuem consideravelmente para os fluxos acumulados devido a permanência constante de vegetação. A contribuição deste trabalho auxiliará na investigação das emissões de CO2 nesses ecossistemas.

Les activités anthropiques affectent les cycles biogéochimiques globaux, principalement par l'ajout de nutriments dans les écosystèmes. Il est donc crucial de déterminer dans quelle mesure les cycles biogéochimiques globaux peuvent être régulés. Les autotrophes peuvent réguler les réservoirs de nutriments par la consommation des ressources, mais la majorité des ressources leur sont inaccessibles à l'échelle globale. Par des modèles théoriques, nous avons cherché à évaluer la manière dont les autotrophes répondent à la fertilisation à l'échelle globale et leur capacité à réguler les concentrations des nutriments quand leur accessibilité est limitée. Nous avons également étudié les mécanismes qui déterminent la régulation des rapports de Redfield dans l'océan, ainsi que les effets de l'ajout de nutriments sur la production primaire océanique totale. Nous avons montré que les organismes ne régulent pas efficacement les réservoirs de nutriments. Le couplage des cycles biogéochimiques et la compétition entre groupes fonctionnels peuvent altérer, négativement ou positivement, la régulation des cycles biogéochimiques globaux par les organismes. Une régulation inefficace des concentrations de nutriments n'exclut par contre pas une forte régulation des rapports entre ces nutriments, comme dans le cas des rapports de Redfield. La fertilisation des écosystèmes terrestres et océaniques risque donc de fortement impacter la production primaire et les cycles biogéochimiques globaux, à de courtes comme à de grandes échelles de temps. / Anthropogenic activities heavily impact global biogeochemical cycles, mainly through nutrient fertilisation of ecosystems; thus it is crucial to assess the extent to which global biogeochemical cycles are regulated. Autotrophs can regulate nutrient pools locally through resource consumption, but most resources are inaccessible to them at global scales. We used theoretical models to assess how organisms respond nutrient fertilisation at global scales and how they can regulate the concentration of these nutrients when their accessibility of is limited. We further investigated the mechanisms driving the regulation of Redfield ratios in oceans, and the effects of nutrient fertilisation on total oceanic primary production. We showed that organisms cannot efficiently regulate nutrient pools. Mechanisms such as coupling of nutrient cycles and competition between functional groups can alter the strength of biotic regulation of global biogeochemical cycles, either positively or negatively. An inefficient regulation of inaccessible nutrient concentration, however, does not exclude a strong biotic regulation of nutrient ratios, as is the case with Redfield ratios in oceans. Nutrient fertilization of oceanic and terrestrial ecosystems is thus likely to have a strong impact on primary production and global nutrient cycles at both small and long timescales.

Ziel der Arbeit war es, die Hypothese von CARNEY & ELSER (1990), dass unter mesotrophen Bedingungen die trophische Transfereffizienz vom Phytoplankton zum Crustaceenplankton maximal ist, in einem Ganz-Seen-Experiment zu überprüfen. Die Untersuchungen erfolgten im Rahmen des Projektes "Top-Down-Steuerung planktischer Biozönosen" am mesotrophen Großen Vätersee (Brandenburg). Die Fragen, welchen Einfluß das Crustaceenplankton auf die Primärproduzenten ausübt, wie die Primärproduzenten auf den Grazingdruck reagieren, und welche Verhaltensweisen der Crustaceen die Kopplungsstärke zu den Primärproduzenten oder den Prädatoren kausal beeinflussen, standen im Mittelpunkt. Primärproduktion (PPR) und Crustaceengrazing wurden in situ gemessen, Crustaceen-biomassen, -produktion und -verteilung bestimmt und mit den Daten der angrenzenden Teilprojekte in Beziehung gesetzt. Der prozentuale Anteil des Nanoplanktons an der absoluten PPR erreichte im Durchschnitt 52 %. Die Chl a spezifische PPR dieser Fraktion war signifikant positiv korreliert mit den effektiven Filtrierraten der Daphnien. Die spezifische PPR von Pico- und Netzphytoplankton blieb von den effektiven Filtrierraten unbeeinflusst. Die Blaualgen, Hauptbestandteil des Picoplanktons, stellten eine schlechte Nahrungsquelle für Daphnien dar. Dies zeigten Laborversuche zur Nahrungsqualität. Durch den hohen Beitrag des Nanoplanktons an der PPR bestand zwischen den Primärproduzenten und den Crustaceen eine starke Kopplung. 1998 betrug die Konsumtions-Transfereffizienz von den Primärproduzenten zu den Crustaceen 25 %. Im Vergleich dazu war der Anteil der Planktivorenkonsumtion an der Produktion der Crustaceen mit 14 % deutlich geringer. Die Konsumtion erklärte im Frühsommer während der hohen Verluste der Daphnien maximal 20 % der Mortalität. Kam es im Hochsommer zu höheren Abundanzen invertebrater Räuber, war deren Prädationsdruck hoch genug, die Daphnienpopulation auf niedrigem Niveau zu halten. Somit war der Top-down-Druck der Planktivoren auf die Daphnien sehr gering. Eine Nahrungskettensteuerung durch Besatz mit Piscivoren würde keine Verminderung der Mortalität der Crustaceen zur Folge haben, sondern eher den Fraßdruck auf Cladoceren durch erhöhte Abundanzen der invertebraten Räuber verstärken.