Zur Sicherung der Fischbestände muss die Aquakultur ihren Beitrag zur Weltfischversorgung weiter steigern. Solange jedoch die Fischfutter Produktion stark von der Gewinnung von Fischmehl abhängig ist, bestehen für die Aquakultur natürliche Begrenzungen und die Gefahr der Überfischung der Fischbestände bleibt erhalten. Wenn das Wachstumspotenzial der Aquakultur ausgeschöpft werden soll, müssen beträchtliche Mengen von Nährstoffeinträgen in Form von vollständigen Aquakultur-Mischfuttermitteln auf einer nachhaltigen Basis verfügbar sein. Aufgrund des gestiegenen Preises von kommerziellem Fischfutter sind Kleinproduzenten nicht in der Lage dieses zu erwerben. Daher ist es notwendig, ihnen alternatives Fischfutter zur Verfügung zu stellen. Wasserpflanzen können eine bedeutende Nahrungsquelle für herbivore- und omnivore Fische sein. Dennoch ist die Nutzung dieser Pflanzen als Zusatz für Fischfutter durch eine Reihe antinutritiver Substanzen, welche das normale Fischwachstum negativ beeinträchtigen, begrenzt. Unterschiedliche Behandlungen der Pflanzen können den Anteil an antinutritiven Substanzen reduzieren. Das Ziel dieser Dissertation war es, das nutritive Potential von Wasserpflanzen zu bestimmen. Die Wirkung der Behandlungen wie Sonnentrocknung oder Fermentierung zu bewerten und den Effekt ihrer Nutzung als Fischfutter auf das Wachstum von kultivierten Fischen zu erfassen. Dazu wurden Rationen mit einem geringen Gehalt an Fischmehl (3%) und bis zu 25% der Wasserpflanzen an die Fischspezies P. brachypomus und O. niloticus verfüttert. Die Ergebnisse der Untersuchung zeigen dass, eine ausschließlich auf aquatischen Makrophyten basierende Fütterung nicht empfehlenswert ist. Indem sie jedoch mit anderen lokal verfügbaren Agrar-Nebenerzeugnissen oder sogar mit kommerziellen Futtermitteln kombiniert werden, könnten die Futterkosten erheblich reduziert werden und bäuerlichen Kleinbetrieben eine Möglichkeit zum Wettbewerb auf den lokalen Märkten eröffnen. / It is commonly known that aquaculture needs to increase further its net contribution to the total world fish supplies. However, at present almost all farming operations, based on the use of fish feed, are highly dependent on available fishery resources for the production of fish meal, becoming a reducing activity rather than an activity suppling fishery resources. If the aquaculture growth potential is to be maintained, then considerable quantities of nutrient inputs in the form of aquafeeds will have to be available on a sustainable basis. On a long-term the small producers will be unable to depend on commercial aquafeeds based traditionally on fish meal, due to its increased price. Small-scale farmers need an alternative fish feed wherever possible based on the use of non-food grade locally feed resources, which is available in rural areas, is low-cost and is suitable for the proper growth and maintenance of native fish. Aquatic plants are considered important nutritional sources for herbivorous-omnivorous fish. However, the use of plant-derived materials as fish feed ingredient is limited by the presence of wide variety of antinutrients that affect the normal fish growth negatively; so that plants should be processed to reduce the effects of these compounds. Considering these aspects, this study assessed the nutritional potential of aquatic plants available in rural Colombia treated by sun drying and by fermentation and the effect of their use as fish feed on the growth performance of common cultured tropical fish (Piaractus brachypomus and Oreochromis niloticus) fed low fishmeal diets (3%) and until 25% of aquatic plants. The results of this study showed that a feeding exclusively based on aquatic plants is not recommendable; but to combine them with other locally available by-products of agriculture or even with commercial diets might considerably reduce feeding cost and provide to the small-scale farmers the opportunity to compete in local markets.

In this thesis I investigate several aspects of local quantum criticality, a concept of key importance in a number of physical contexts ranging from critical heavy fermion compounds to quantum dot systems. Quantum critical points are associated with second order phase transitions at zero temperature. In contrast to their finite-temperature counterparts, the zero-point motion cannot be neglected near a quantum critical point. As a result, the incorporation of quantum dynamics leads to an effective dimension larger than the spatial dimension of the system for the order parameter fluctuations within the Ginzburg-Landau-Wilson treatment of criticality. This so-called quantum-to-classical mapping works well for the critical properties in insulating systems but apparently fails in systems containing gapless fermions. This has been experimentally most clearly been demonstrated within a particular class of intermetallic compounds called heavy fermions. A particular way in which the Ginzburg-Landau-Wilson paradigm fails is for critical Kondo destruction that seems to underlie the unconventional quantum criticality seen in the heavy fermions. I focus on studying the properties of critical Kondo destruction and the emergence of energy-over-temperature-scaling in systems without spatial degrees of freedom, i.e., so-called quantum impurity systems. In particular, I employ large-N techniques to address critical properties of this class of quantum phase transitions in and out of equilibrium. As quantum critical systems are characterized by a scale-invariant spectrum with many low-lying excitations, it may appear that any perturbation can lead to a response beyond the linear response regime. Understanding what governs the non-linear response regime near quantum criticality is an interesting area. Here, I first present a path integral version of the Schrieffer-Wolff transformation which relates the functional integral form of the partition function of the Anderson model to that of its effective low-energy model. The equivalence between the low-energy sector of the Anderson model in the Kondo regime and the spin-isotropic Kondo model is usually established via a canonical transformation performed on the Hamiltonian, followed by a projection. The resulting functional integral assumes the form of a spin path integral and includes a geometric phase factor, i.e. a Berry phase. The approach stresses the underlying symmetries of the model and allows for a straightforward generalization of the transformation to more involved models. As an example of the efficiency of the approach I apply it to a single electron transistor attached to ferromagnetic leads and derive the effective low-energy model of such a magnetic transistor. As Kondo screening is a local phenomenon, it and its criticality can be studied using the appropriate impurity model. A general impurity model to study critical Kondo destruction is the pseudogap Bose-Fermi Kondo model. Here, I concentrate on the multi-channel version of the model using the dynamical large-N study. This model allows to study the non-trivial interplay between two different mechanisms of critical Kondo destruction. The interplay of two processes that can each by itself lead to critical Kondo destruction. The zero-temperature residual entropy at various fixed points for the model is also discussed. The two channel Anderson model exhibits several continuous quantum phase transitions between weak- and strong-coupling phases. The non-crossing approximation (NCA) is believed to give reliable results for the standard two-channel Anderson model of a magnetic impurity in a metal. I revisit the reliability of the NCA for the standard two channel Anderson model (constant conduction electron density of states) and investigate its reliability for the two-channel pseudogap Anderson model. This is done by comparing finite-temperature, finite-frequency solutions of the NCA equations and asymptotically exact zero-temperature NCA solutions with numerical renormalization-group calculations. The phase diagram of this model is well established. The focus here will be on the dynamical scaling properties obtained within the NCA. Finally, I study the thermal and non-thermal steady state scaling functions and the steady-state dynamics of the pseudogap Kondo model. This model allows us to study the concept of effective temperatures near fully interacting as well as weak-coupling fixed points and compare the out-of-equilibrium scaling properties of critical Kondo destruction to those of the traditional spin-density wave (SDW) scenario. The differences I identify can be experimentally probed. This may be helpful in identifying the nature of the quantum critical points observed in certain heavy fermion compounds.

O Projeto Samambaia-preta (PSP) vem sendo desenvolvido desde o ano 2000, nas áreas de encosta da Floresta Ombrófila Densa, no município de Maquiné, Litoral Norte do Rio Grande do Sul. Nesta região, estão localizadas as zonas núcleo da Reserva da Biosfera da Mata Atlântica (MAB/UNESCO), recebendo várias restrições quanto ao manejo das propriedades. O PSP visava avaliar a sustentabilidade do extrativismo da samambaia-preta, sob o ponto de vista ambiental, social e econômico. A comprovação científica da sustentabilidade ecológica dos sistemas de manejo tradicionalmente utilizados pelos agricultores embasou a construção de uma nova regulamentação, baseada no conhecimento dos agricultores. Apesar deste fato, está sendo registrada pelos agricultores e pesquisadores a diminuição da samambaia, como conseqüência da regeneração dos estádios sucessionais iniciais e médios (capoeira) da Mata Atlântica. Este processo é decorrente da coibição das práticas de manejo tradicionais pela legislação ambiental. Neste contexto, o presente trabalho tem como objetivo: compreender a atividade extrativista da samambaia-preta na área de Encosta da Mata Atlântica, município de Maquiné, e a sua relação com as demais atividades desenvolvidas pelos diferentes tipos de agricultores, correlacionando com uma análise espacial e de produção das áreas de extrativismo. O enfoque metodológico baseia-se em “estudo de caso”, o qual permite ter uma percepção mais completa do objeto de estudo, a partir de um enfoque sistêmico. A partir de uma tipologia prévia dos sistemas de produção dos agricultores familiares extrativistas da samambaia em Maquiné, foram selecionados quatro estudos de caso representativos. As técnicas utilizadas na pesquisa foram: a) observação simples e participante; b) aplicação de entrevistas semi-estruturadas; c) pesquisa em documentação direta e indireta; d) análise espacial através de cartografia e georefenciamento. O extrativismo é praticado por famílias que têm como atividade principal o plantio agrícola e a produção pecuária, sendo a samambaia uma complementação da renda dos tipos II, III e IV, e atividade de renda principal para o tipo I. Do ponto de vista espacial, as distâncias percorridas pelos agricultores para realizar a coleta da samambaia estão aumentado paulatinamente devido à diminuição dos estoques perto das moradias. Além disso, as áreas estão diminuindo devido ao abandono das práticas culturais dos agricultores, que incluem a realização da agricultura de corte e queima e, durante as fases de pousio, a coleta da samambaia. Verificou-se a falta de acesso dos agricultores à informação referente: a) às potencialidades do mercado da samambaia-preta, b) à legislação atual que rege a atividade extrativista e os seus territórios. Além disso, verificaram-se ausência de organização comunitária, deficiência no gerenciamento da produção e comercialização, beneficiamento e meios de transporte para a circulação da samambaia-preta e os baixos preços pagos pela samambaia, os quais ficam restritos aos valores estabelecidos pelo atravessador. A realização deste estudo permitiu uma caracterização mais aprofundada de uma tipologia anteriormente proposta para a região, evidenciando que os agricultores familiares mais empobrecidos estão se desfazendo de suas terras para tentar outras condições de reprodução social, diferentes da agricultura, tendo na coleta regular da samambaia um emprego. Enquanto que agricultores familiares com maiores extensões de terra fazem de o extrativismo uma forma complementar de renda. / The Samambaia-preta Project (PSP) has been developed since 2000, at the slope areas of the Atlantic Forest in Maquiné, in the North Coast of Rio Grande do Sul. The nucleus zones of the Atlantic Forest’s Biosphere Reserve (MAB/UNESCO) are placed in this region, suffering several restrictions concerning the management of the properties. The PSP aimed to assess the sustainability of the harvest of ‘samambaia-preta’, under the environmental social and economical standpoint. The scientifical proof of the environmental sustainability of the management systems traditionally used by farmers substantiated the construction of a new regulation, based upon the farmers’ knowledge. Despite the fact, the reduction of the fern as consequence of the regeneration of the initial and middle successive phases (capoeira) of the Atlantic Forest has been noticed by both farmers and researchers. This process results from the restraint of the traditional management practices by the environmental enactment. In such context, the current paper has as objective: to understand the harvest activity of black-fern at the slope area of the Atlantic Forest, Maquiné and its relationship with the other activities carried on by the different types of farmers, correlating them with a spatial and harvest areas production analyses. The methodological focus is based on “case study”, which allows having a major perception of the study object, from a systemic approach. Four representative case studies were selected from a previous typology of the familiar farmers production system harvesters of the black-fern in Maquiné. The techniques used in the research were: a) simple and participative observation; b) semi-structures interviews application; c) research on direct and indirect documentation; d) spatial analysis through cartography and georeference. Harvest is practiced by families which have as main activity the agricultural planting and the cattleraising production, being the fern an income complement to the types II, III and IV, and a main income activity to the type I. From the spatial point of view, the distances reached by farmers to harvest the fern are increasing gradually, due to the reduction of the stocks near the dwellings. Furthermore, the areas are diminishing due to the abandonment of farmers’ cultural practices. The farmers’ lack of access to information was noticed referring to: a) the blackfern market potentialities; b) current legislation which regulates the harvest activity and its territories. Moreover, a community organization absence, production and trade management deficiencies, manufacturing and transporting for the circulation of the black-fern and the low prices paid for the fern which are restricted to values established by the dealer were observed. The making of this study permitted a deeper characterization of a typology previously posed for the region, highlighting that poorer familiar farmers are selling their lands to attempt conditions of social reproduction other than the agriculture, having in the regular fern harvest a job while familiar farmers owning bigger portions of land have the harvest as a complementary form of income. / El Proyecto Samamabia-preta (PSP) está desarrollándose desde el año 2000, en las áreas de ladera del Bosque Ombrófilo Denso, en el municipio de Maquiné, en la costa norte del Rio Grande do Sul. En esta región, están ubicadas las zonas núcleo de la Reserva de la Biosfera del Bosque Tropical Atlántico (MAB/UNESCO), que tienen varias restricciones en el manejo de las propiedades. El PSP pretendía evaluar la sostenibilidad de la extracción del helecho negro, desde un punto de vista ambiental, social y económico. La evidencia científica de la sostenibilidad ecológica de los sistemas de manejo tradicionalmente usados por los agricultores, originó la construcción de una nueva reglamentación, basada en el conocimiento de estos. A pesar de este hecho, se está registrando por parte de los agricultores y los investigadores la disminución de los helechos, como una consecuencia de la regeneración de los estados sucesionales iniciales y del sotobosque en el Bosque Tropical Atlántico. Este fenómeno está relacionado con la prohibición por parte de la legislación ambiental de las prácticas culturales tradicionales en la agricultura. Dentro de este contexto, el presente trabajo tiene como objetivo: comprender la actividad extractiva del helecho negro en el área de ladera del Bosque Tropical Atlántico, municipio de Maquiné, y su relación con las otras actividades practicadas por los diversos tipos de agricultores, correlacionándolo con un análisis espacial y de producción de las áreas de extracción. El enfoque metodológico es el estudio de caso, que permite tener una percepción mas completa del objeto de estudio, desde un enfoque sistémico. A partir de una caracterización anterior de los sistemas de producción de los agricultores familiares extractores de helecho negro en Maquiné, fueron seleccionados cuatro estudios de caso que representaban cada tipo de agricultor. Las técnicas de investigación utilizadas fueron: a) observación simple y participativa; b) aplicación de entrevistas semiestructuradas; a) análisis documental directo e indirecto; d) análisis espacial a través de cartografía y georreferenciación. La extracción es practicada por familias que tienen como principal actividad la producción agropecuaria, siendo la extracción de helecho negro un ingreso complementario para las familias de los tipos II, III y IV, y una actividad principal en las del tipo I. Desde el punto de vista espacial, las distancias recorridas por los agricultores para la recolección de helechos son cada vez mayores, debido a la disminución del producto en las áreas cercanas a sus viviendas. Igualmente, las áreas productoras de helechos están disminuyendo debido al abandono de las prácticas culturales de los agricultores, que practican la agricultura de corte y quema y, durante las épocas de baldío, la recolección de helechos. Se comprobó la falta de acceso de los agricultores a cierto tipo de información como: a) las potencialidades del mercado de helechos negros; b) la legislación actual que rige la extracción y los lugares donde ésta se practica. De la misma forma, se evidenció la ausencia de organización comunitaria, la deficiencia en la gerencia de la producción y la comercialización, el beneficio y los medios de transporte para la circulación del helecho negro; igualmente, los bajos precios de venta del producto, los cuales son fijados por los mayoristas. La realización de este estudio permitió una caracterización mas profunda de una topología anteriormente propuesta para la región, comprobándose que los agricultores familiares más pobres están vendiendo sus tierras para desarrollar otras formas de reproducción socioeconómica diferentes a la agricultura, encontrando normalmente en la recolección de helechos una alternativa de empleo. Mientras que otros agricultores familiares con mayores extensiones de tierra hacen de la extracción una forma complementaria de ingresos.

O Projeto Samambaia-preta (PSP) vem sendo desenvolvido desde o ano 2000, nas áreas de encosta da Floresta Ombrófila Densa, no município de Maquiné, Litoral Norte do Rio Grande do Sul. Nesta região, estão localizadas as zonas núcleo da Reserva da Biosfera da Mata Atlântica (MAB/UNESCO), recebendo várias restrições quanto ao manejo das propriedades. O PSP visava avaliar a sustentabilidade do extrativismo da samambaia-preta, sob o ponto de vista ambiental, social e econômico. A comprovação científica da sustentabilidade ecológica dos sistemas de manejo tradicionalmente utilizados pelos agricultores embasou a construção de uma nova regulamentação, baseada no conhecimento dos agricultores. Apesar deste fato, está sendo registrada pelos agricultores e pesquisadores a diminuição da samambaia, como conseqüência da regeneração dos estádios sucessionais iniciais e médios (capoeira) da Mata Atlântica. Este processo é decorrente da coibição das práticas de manejo tradicionais pela legislação ambiental. Neste contexto, o presente trabalho tem como objetivo: compreender a atividade extrativista da samambaia-preta na área de Encosta da Mata Atlântica, município de Maquiné, e a sua relação com as demais atividades desenvolvidas pelos diferentes tipos de agricultores, correlacionando com uma análise espacial e de produção das áreas de extrativismo. O enfoque metodológico baseia-se em “estudo de caso”, o qual permite ter uma percepção mais completa do objeto de estudo, a partir de um enfoque sistêmico. A partir de uma tipologia prévia dos sistemas de produção dos agricultores familiares extrativistas da samambaia em Maquiné, foram selecionados quatro estudos de caso representativos. As técnicas utilizadas na pesquisa foram: a) observação simples e participante; b) aplicação de entrevistas semi-estruturadas; c) pesquisa em documentação direta e indireta; d) análise espacial através de cartografia e georefenciamento. O extrativismo é praticado por famílias que têm como atividade principal o plantio agrícola e a produção pecuária, sendo a samambaia uma complementação da renda dos tipos II, III e IV, e atividade de renda principal para o tipo I. Do ponto de vista espacial, as distâncias percorridas pelos agricultores para realizar a coleta da samambaia estão aumentado paulatinamente devido à diminuição dos estoques perto das moradias. Além disso, as áreas estão diminuindo devido ao abandono das práticas culturais dos agricultores, que incluem a realização da agricultura de corte e queima e, durante as fases de pousio, a coleta da samambaia. Verificou-se a falta de acesso dos agricultores à informação referente: a) às potencialidades do mercado da samambaia-preta, b) à legislação atual que rege a atividade extrativista e os seus territórios. Além disso, verificaram-se ausência de organização comunitária, deficiência no gerenciamento da produção e comercialização, beneficiamento e meios de transporte para a circulação da samambaia-preta e os baixos preços pagos pela samambaia, os quais ficam restritos aos valores estabelecidos pelo atravessador. A realização deste estudo permitiu uma caracterização mais aprofundada de uma tipologia anteriormente proposta para a região, evidenciando que os agricultores familiares mais empobrecidos estão se desfazendo de suas terras para tentar outras condições de reprodução social, diferentes da agricultura, tendo na coleta regular da samambaia um emprego. Enquanto que agricultores familiares com maiores extensões de terra fazem de o extrativismo uma forma complementar de renda. / The Samambaia-preta Project (PSP) has been developed since 2000, at the slope areas of the Atlantic Forest in Maquiné, in the North Coast of Rio Grande do Sul. The nucleus zones of the Atlantic Forest’s Biosphere Reserve (MAB/UNESCO) are placed in this region, suffering several restrictions concerning the management of the properties. The PSP aimed to assess the sustainability of the harvest of ‘samambaia-preta’, under the environmental social and economical standpoint. The scientifical proof of the environmental sustainability of the management systems traditionally used by farmers substantiated the construction of a new regulation, based upon the farmers’ knowledge. Despite the fact, the reduction of the fern as consequence of the regeneration of the initial and middle successive phases (capoeira) of the Atlantic Forest has been noticed by both farmers and researchers. This process results from the restraint of the traditional management practices by the environmental enactment. In such context, the current paper has as objective: to understand the harvest activity of black-fern at the slope area of the Atlantic Forest, Maquiné and its relationship with the other activities carried on by the different types of farmers, correlating them with a spatial and harvest areas production analyses. The methodological focus is based on “case study”, which allows having a major perception of the study object, from a systemic approach. Four representative case studies were selected from a previous typology of the familiar farmers production system harvesters of the black-fern in Maquiné. The techniques used in the research were: a) simple and participative observation; b) semi-structures interviews application; c) research on direct and indirect documentation; d) spatial analysis through cartography and georeference. Harvest is practiced by families which have as main activity the agricultural planting and the cattleraising production, being the fern an income complement to the types II, III and IV, and a main income activity to the type I. From the spatial point of view, the distances reached by farmers to harvest the fern are increasing gradually, due to the reduction of the stocks near the dwellings. Furthermore, the areas are diminishing due to the abandonment of farmers’ cultural practices. The farmers’ lack of access to information was noticed referring to: a) the blackfern market potentialities; b) current legislation which regulates the harvest activity and its territories. Moreover, a community organization absence, production and trade management deficiencies, manufacturing and transporting for the circulation of the black-fern and the low prices paid for the fern which are restricted to values established by the dealer were observed. The making of this study permitted a deeper characterization of a typology previously posed for the region, highlighting that poorer familiar farmers are selling their lands to attempt conditions of social reproduction other than the agriculture, having in the regular fern harvest a job while familiar farmers owning bigger portions of land have the harvest as a complementary form of income. / El Proyecto Samamabia-preta (PSP) está desarrollándose desde el año 2000, en las áreas de ladera del Bosque Ombrófilo Denso, en el municipio de Maquiné, en la costa norte del Rio Grande do Sul. En esta región, están ubicadas las zonas núcleo de la Reserva de la Biosfera del Bosque Tropical Atlántico (MAB/UNESCO), que tienen varias restricciones en el manejo de las propiedades. El PSP pretendía evaluar la sostenibilidad de la extracción del helecho negro, desde un punto de vista ambiental, social y económico. La evidencia científica de la sostenibilidad ecológica de los sistemas de manejo tradicionalmente usados por los agricultores, originó la construcción de una nueva reglamentación, basada en el conocimiento de estos. A pesar de este hecho, se está registrando por parte de los agricultores y los investigadores la disminución de los helechos, como una consecuencia de la regeneración de los estados sucesionales iniciales y del sotobosque en el Bosque Tropical Atlántico. Este fenómeno está relacionado con la prohibición por parte de la legislación ambiental de las prácticas culturales tradicionales en la agricultura. Dentro de este contexto, el presente trabajo tiene como objetivo: comprender la actividad extractiva del helecho negro en el área de ladera del Bosque Tropical Atlántico, municipio de Maquiné, y su relación con las otras actividades practicadas por los diversos tipos de agricultores, correlacionándolo con un análisis espacial y de producción de las áreas de extracción. El enfoque metodológico es el estudio de caso, que permite tener una percepción mas completa del objeto de estudio, desde un enfoque sistémico. A partir de una caracterización anterior de los sistemas de producción de los agricultores familiares extractores de helecho negro en Maquiné, fueron seleccionados cuatro estudios de caso que representaban cada tipo de agricultor. Las técnicas de investigación utilizadas fueron: a) observación simple y participativa; b) aplicación de entrevistas semiestructuradas; a) análisis documental directo e indirecto; d) análisis espacial a través de cartografía y georreferenciación. La extracción es practicada por familias que tienen como principal actividad la producción agropecuaria, siendo la extracción de helecho negro un ingreso complementario para las familias de los tipos II, III y IV, y una actividad principal en las del tipo I. Desde el punto de vista espacial, las distancias recorridas por los agricultores para la recolección de helechos son cada vez mayores, debido a la disminución del producto en las áreas cercanas a sus viviendas. Igualmente, las áreas productoras de helechos están disminuyendo debido al abandono de las prácticas culturales de los agricultores, que practican la agricultura de corte y quema y, durante las épocas de baldío, la recolección de helechos. Se comprobó la falta de acceso de los agricultores a cierto tipo de información como: a) las potencialidades del mercado de helechos negros; b) la legislación actual que rige la extracción y los lugares donde ésta se practica. De la misma forma, se evidenció la ausencia de organización comunitaria, la deficiencia en la gerencia de la producción y la comercialización, el beneficio y los medios de transporte para la circulación del helecho negro; igualmente, los bajos precios de venta del producto, los cuales son fijados por los mayoristas. La realización de este estudio permitió una caracterización mas profunda de una topología anteriormente propuesta para la región, comprobándose que los agricultores familiares más pobres están vendiendo sus tierras para desarrollar otras formas de reproducción socioeconómica diferentes a la agricultura, encontrando normalmente en la recolección de helechos una alternativa de empleo. Mientras que otros agricultores familiares con mayores extensiones de tierra hacen de la extracción una forma complementaria de ingresos.

O Projeto Samambaia-preta (PSP) vem sendo desenvolvido desde o ano 2000, nas áreas de encosta da Floresta Ombrófila Densa, no município de Maquiné, Litoral Norte do Rio Grande do Sul. Nesta região, estão localizadas as zonas núcleo da Reserva da Biosfera da Mata Atlântica (MAB/UNESCO), recebendo várias restrições quanto ao manejo das propriedades. O PSP visava avaliar a sustentabilidade do extrativismo da samambaia-preta, sob o ponto de vista ambiental, social e econômico. A comprovação científica da sustentabilidade ecológica dos sistemas de manejo tradicionalmente utilizados pelos agricultores embasou a construção de uma nova regulamentação, baseada no conhecimento dos agricultores. Apesar deste fato, está sendo registrada pelos agricultores e pesquisadores a diminuição da samambaia, como conseqüência da regeneração dos estádios sucessionais iniciais e médios (capoeira) da Mata Atlântica. Este processo é decorrente da coibição das práticas de manejo tradicionais pela legislação ambiental. Neste contexto, o presente trabalho tem como objetivo: compreender a atividade extrativista da samambaia-preta na área de Encosta da Mata Atlântica, município de Maquiné, e a sua relação com as demais atividades desenvolvidas pelos diferentes tipos de agricultores, correlacionando com uma análise espacial e de produção das áreas de extrativismo. O enfoque metodológico baseia-se em “estudo de caso”, o qual permite ter uma percepção mais completa do objeto de estudo, a partir de um enfoque sistêmico. A partir de uma tipologia prévia dos sistemas de produção dos agricultores familiares extrativistas da samambaia em Maquiné, foram selecionados quatro estudos de caso representativos. As técnicas utilizadas na pesquisa foram: a) observação simples e participante; b) aplicação de entrevistas semi-estruturadas; c) pesquisa em documentação direta e indireta; d) análise espacial através de cartografia e georefenciamento. O extrativismo é praticado por famílias que têm como atividade principal o plantio agrícola e a produção pecuária, sendo a samambaia uma complementação da renda dos tipos II, III e IV, e atividade de renda principal para o tipo I. Do ponto de vista espacial, as distâncias percorridas pelos agricultores para realizar a coleta da samambaia estão aumentado paulatinamente devido à diminuição dos estoques perto das moradias. Além disso, as áreas estão diminuindo devido ao abandono das práticas culturais dos agricultores, que incluem a realização da agricultura de corte e queima e, durante as fases de pousio, a coleta da samambaia. Verificou-se a falta de acesso dos agricultores à informação referente: a) às potencialidades do mercado da samambaia-preta, b) à legislação atual que rege a atividade extrativista e os seus territórios. Além disso, verificaram-se ausência de organização comunitária, deficiência no gerenciamento da produção e comercialização, beneficiamento e meios de transporte para a circulação da samambaia-preta e os baixos preços pagos pela samambaia, os quais ficam restritos aos valores estabelecidos pelo atravessador. A realização deste estudo permitiu uma caracterização mais aprofundada de uma tipologia anteriormente proposta para a região, evidenciando que os agricultores familiares mais empobrecidos estão se desfazendo de suas terras para tentar outras condições de reprodução social, diferentes da agricultura, tendo na coleta regular da samambaia um emprego. Enquanto que agricultores familiares com maiores extensões de terra fazem de o extrativismo uma forma complementar de renda. / The Samambaia-preta Project (PSP) has been developed since 2000, at the slope areas of the Atlantic Forest in Maquiné, in the North Coast of Rio Grande do Sul. The nucleus zones of the Atlantic Forest’s Biosphere Reserve (MAB/UNESCO) are placed in this region, suffering several restrictions concerning the management of the properties. The PSP aimed to assess the sustainability of the harvest of ‘samambaia-preta’, under the environmental social and economical standpoint. The scientifical proof of the environmental sustainability of the management systems traditionally used by farmers substantiated the construction of a new regulation, based upon the farmers’ knowledge. Despite the fact, the reduction of the fern as consequence of the regeneration of the initial and middle successive phases (capoeira) of the Atlantic Forest has been noticed by both farmers and researchers. This process results from the restraint of the traditional management practices by the environmental enactment. In such context, the current paper has as objective: to understand the harvest activity of black-fern at the slope area of the Atlantic Forest, Maquiné and its relationship with the other activities carried on by the different types of farmers, correlating them with a spatial and harvest areas production analyses. The methodological focus is based on “case study”, which allows having a major perception of the study object, from a systemic approach. Four representative case studies were selected from a previous typology of the familiar farmers production system harvesters of the black-fern in Maquiné. The techniques used in the research were: a) simple and participative observation; b) semi-structures interviews application; c) research on direct and indirect documentation; d) spatial analysis through cartography and georeference. Harvest is practiced by families which have as main activity the agricultural planting and the cattleraising production, being the fern an income complement to the types II, III and IV, and a main income activity to the type I. From the spatial point of view, the distances reached by farmers to harvest the fern are increasing gradually, due to the reduction of the stocks near the dwellings. Furthermore, the areas are diminishing due to the abandonment of farmers’ cultural practices. The farmers’ lack of access to information was noticed referring to: a) the blackfern market potentialities; b) current legislation which regulates the harvest activity and its territories. Moreover, a community organization absence, production and trade management deficiencies, manufacturing and transporting for the circulation of the black-fern and the low prices paid for the fern which are restricted to values established by the dealer were observed. The making of this study permitted a deeper characterization of a typology previously posed for the region, highlighting that poorer familiar farmers are selling their lands to attempt conditions of social reproduction other than the agriculture, having in the regular fern harvest a job while familiar farmers owning bigger portions of land have the harvest as a complementary form of income. / El Proyecto Samamabia-preta (PSP) está desarrollándose desde el año 2000, en las áreas de ladera del Bosque Ombrófilo Denso, en el municipio de Maquiné, en la costa norte del Rio Grande do Sul. En esta región, están ubicadas las zonas núcleo de la Reserva de la Biosfera del Bosque Tropical Atlántico (MAB/UNESCO), que tienen varias restricciones en el manejo de las propiedades. El PSP pretendía evaluar la sostenibilidad de la extracción del helecho negro, desde un punto de vista ambiental, social y económico. La evidencia científica de la sostenibilidad ecológica de los sistemas de manejo tradicionalmente usados por los agricultores, originó la construcción de una nueva reglamentación, basada en el conocimiento de estos. A pesar de este hecho, se está registrando por parte de los agricultores y los investigadores la disminución de los helechos, como una consecuencia de la regeneración de los estados sucesionales iniciales y del sotobosque en el Bosque Tropical Atlántico. Este fenómeno está relacionado con la prohibición por parte de la legislación ambiental de las prácticas culturales tradicionales en la agricultura. Dentro de este contexto, el presente trabajo tiene como objetivo: comprender la actividad extractiva del helecho negro en el área de ladera del Bosque Tropical Atlántico, municipio de Maquiné, y su relación con las otras actividades practicadas por los diversos tipos de agricultores, correlacionándolo con un análisis espacial y de producción de las áreas de extracción. El enfoque metodológico es el estudio de caso, que permite tener una percepción mas completa del objeto de estudio, desde un enfoque sistémico. A partir de una caracterización anterior de los sistemas de producción de los agricultores familiares extractores de helecho negro en Maquiné, fueron seleccionados cuatro estudios de caso que representaban cada tipo de agricultor. Las técnicas de investigación utilizadas fueron: a) observación simple y participativa; b) aplicación de entrevistas semiestructuradas; a) análisis documental directo e indirecto; d) análisis espacial a través de cartografía y georreferenciación. La extracción es practicada por familias que tienen como principal actividad la producción agropecuaria, siendo la extracción de helecho negro un ingreso complementario para las familias de los tipos II, III y IV, y una actividad principal en las del tipo I. Desde el punto de vista espacial, las distancias recorridas por los agricultores para la recolección de helechos son cada vez mayores, debido a la disminución del producto en las áreas cercanas a sus viviendas. Igualmente, las áreas productoras de helechos están disminuyendo debido al abandono de las prácticas culturales de los agricultores, que practican la agricultura de corte y quema y, durante las épocas de baldío, la recolección de helechos. Se comprobó la falta de acceso de los agricultores a cierto tipo de información como: a) las potencialidades del mercado de helechos negros; b) la legislación actual que rige la extracción y los lugares donde ésta se practica. De la misma forma, se evidenció la ausencia de organización comunitaria, la deficiencia en la gerencia de la producción y la comercialización, el beneficio y los medios de transporte para la circulación del helecho negro; igualmente, los bajos precios de venta del producto, los cuales son fijados por los mayoristas. La realización de este estudio permitió una caracterización mas profunda de una topología anteriormente propuesta para la región, comprobándose que los agricultores familiares más pobres están vendiendo sus tierras para desarrollar otras formas de reproducción socioeconómica diferentes a la agricultura, encontrando normalmente en la recolección de helechos una alternativa de empleo. Mientras que otros agricultores familiares con mayores extensiones de tierra hacen de la extracción una forma complementaria de ingresos.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The epidemiology, pathogenesis, clinical and pathological aspects of the spontaneous and experimental poisoning of cattle by bracken fern (Pteridium aquilinum) were studied. Two scientific papers that stemmed from these studies are presented and discussed here. Initially, 6,256 necropsy reports from cattle necropsied during a de 43-year-period (1964-2006) were reviewed. Of those, 15 cases were consistent with acute poisoning caused by the ingestion of P. aquilinum and they occurred in cattle from small farms in the Central region of the State of Rio Grande do Sul, Brazil. In 40% of the farms the disease occurred in small outbreaks affecting several cattle per farm and in 60% only one bovine was affected in each farm. Morbidity and mortality were 17.9% and lethality was virtually 100%. The poisoning was experimentally produced in four calves; it was concluded that exclusively the events of the primary hemostasis due to thrombocytopenia are responsible for the hemorrhages. Blood culture from three affected calves yield the growth of Klebsiella oxytoca, Staphylococcus hyicus and S. aureus, indicating that septicemia, facilitated by neutropenia could have a role in the death of cattle acutely poisoned due to the ingestion of P. aquilinum. / Foram estudados a epidemiologia, a patogênese, os aspectos clínicos e patológicos da intoxicação aguda, espontânea e experimental, por samambaia (Pteridium aquilinum) em bovinos. Dois trabalhos científicos que resultaram desse estudo são aqui apresentados e discutidos. Inicialmente, foram revisados 6.256 laudos de necropsia de bovinos num período de 43 anos (1964-2006). Desses, 15 casos corresponderam a quadros de intoxicação aguda causada pela ingestão de P. aquilinum e os casos ocorreram em bovinos de pequenas propriedades rurais da Região Central do Rio Grande do Sul. Em 40% das propriedades a doença ocorreu em pequenos surtos e em 60% delas apenas um bovino era afetado por propriedade. As taxas médias de morbidade e mortalidade foram de 17,9% e a letalidade foi virtualmente 100%. A intoxicação foi produzida experimentalmente em quatro bovinos e foi demonstrado que apenas eventos da hemostasia primária devidos a trombocitopenia são responsáveis pelas hemorragias. A hemocultura de três dos bovinos intoxicados produziu crescimentos de Klebsiella oxytoca, Staphylococcus hyicus e S. aureus, indicando que a septicemia, facilitada pela neutropenia, pode ter participação na causa da morte de bovinos na intoxicação aguda pela ingestão de P. aquilinum.

In this thesis I investigate several aspects of local quantum criticality, a concept of key importance in a number of physical contexts ranging from critical heavy fermion compounds to quantum dot systems. Quantum critical points are associated with second order phase transitions at zero temperature. In contrast to their finite-temperature counterparts, the zero-point motion cannot be neglected near a quantum critical point. As a result, the incorporation of quantum dynamics leads to an effective dimension larger than the spatial dimension of the system for the order parameter fluctuations within the Ginzburg-Landau-Wilson treatment of criticality. This so-called quantum-to-classical mapping works well for the critical properties in insulating systems but apparently fails in systems containing gapless fermions. This has been experimentally most clearly been demonstrated within a particular class of intermetallic compounds called heavy fermions. A particular way in which the Ginzburg-Landau-Wilson paradigm fails is for critical Kondo destruction that seems to underlie the unconventional quantum criticality seen in the heavy fermions. I focus on studying the properties of critical Kondo destruction and the emergence of energy-over-temperature-scaling in systems without spatial degrees of freedom, i.e., so-called quantum impurity systems. In particular, I employ large-N techniques to address critical properties of this class of quantum phase transitions in and out of equilibrium. As quantum critical systems are characterized by a scale-invariant spectrum with many low-lying excitations, it may appear that any perturbation can lead to a response beyond the linear response regime. Understanding what governs the non-linear response regime near quantum criticality is an interesting area. Here, I first present a path integral version of the Schrieffer-Wolff transformation which relates the functional integral form of the partition function of the Anderson model to that of its effective low-energy model. The equivalence between the low-energy sector of the Anderson model in the Kondo regime and the spin-isotropic Kondo model is usually established via a canonical transformation performed on the Hamiltonian, followed by a projection. The resulting functional integral assumes the form of a spin path integral and includes a geometric phase factor, i.e. a Berry phase. The approach stresses the underlying symmetries of the model and allows for a straightforward generalization of the transformation to more involved models. As an example of the efficiency of the approach I apply it to a single electron transistor attached to ferromagnetic leads and derive the effective low-energy model of such a magnetic transistor. As Kondo screening is a local phenomenon, it and its criticality can be studied using the appropriate impurity model. A general impurity model to study critical Kondo destruction is the pseudogap Bose-Fermi Kondo model. Here, I concentrate on the multi-channel version of the model using the dynamical large-N study. This model allows to study the non-trivial interplay between two different mechanisms of critical Kondo destruction. The interplay of two processes that can each by itself lead to critical Kondo destruction. The zero-temperature residual entropy at various fixed points for the model is also discussed. The two channel Anderson model exhibits several continuous quantum phase transitions between weak- and strong-coupling phases. The non-crossing approximation (NCA) is believed to give reliable results for the standard two-channel Anderson model of a magnetic impurity in a metal. I revisit the reliability of the NCA for the standard two channel Anderson model (constant conduction electron density of states) and investigate its reliability for the two-channel pseudogap Anderson model. This is done by comparing finite-temperature, finite-frequency solutions of the NCA equations and asymptotically exact zero-temperature NCA solutions with numerical renormalization-group calculations. The phase diagram of this model is well established. The focus here will be on the dynamical scaling properties obtained within the NCA. Finally, I study the thermal and non-thermal steady state scaling functions and the steady-state dynamics of the pseudogap Kondo model. This model allows us to study the concept of effective temperatures near fully interacting as well as weak-coupling fixed points and compare the out-of-equilibrium scaling properties of critical Kondo destruction to those of the traditional spin-density wave (SDW) scenario. The differences I identify can be experimentally probed. This may be helpful in identifying the nature of the quantum critical points observed in certain heavy fermion compounds.

No description available.

In the present thesis, implications of pasture establishment, fertilization and abandonment on soil C and nutrient dynamics were investigated for the mountain rainforest region of southern Ecuador. Over the past decades the natural forest of the study area has been threatened by conversion to cattle pastures. However, the soil fertility of these extensively grazed pastures (active pastures) declines continuously during pasture use. The invasion of bracken fern (Pteridium arachnoideum) leads to pasture abandonment when bracken becomes dominant. In order to reveal the mechanisms behind the deterioration of soil fertility, biotic and abiotic soil properties and their interaction were analyzed along a land‐use gradient (natural forest – active pasture – abandoned pasture). The ecosystem disturbance of the mountain rainforest through pasture use changed the microbial function and structure, and affected soil CO2‐C fluxes. Annually, 2 Mg soil CO2‐C ha‐1 were additionally emitted from the pasture land. This acceleration in soil respiration rates was related to accelerated rates of microbial C mineralization and fine‐root respiration. The high‐quality, N‐rich above‐ and belowground residues of the pasture grass (S. sphacelata, C4‐plant), especially the huge fine‐root biomass, provided a high C and N availability for soil microbes. Compared to the forest, increased soil pH and accelerated base saturation were further factors beneficial for soil microbial growth and metabolism of the upper mineral soil at active pastures. Three times higher amounts of microbial biomass C and a significant shift in the microbial community structure towards a higher relative abundance of Gram(‐)‐ bacteria and fungi were observed. Long‐term pasture use and the invasion of bracken (C3‐plant) diminished beneficial effects for microbes, causing a significant decrease in the C, net, and gross N mineralization rates as well as a two‐third reduction in the microbial biomass. A preferential substrate utilization of grass‐derived C4 by the soil microbes resulted in a rapid decline of the C4‐pool. As a consequence, the less available C3‐pool from bracken and former forest increased its dominance in the SOC‐pool, further decreasing pasture productivity and finally causing pasture abandonment. The lower quality and quantity of above‐ and belowground residues of the bracken (high lignin content, C/N) resulted in resource‐limited conditions that influenced the microbial function to greater extent than their structure. The microbial structure seemed to be sensitive mainly to soil pH along the land‐use gradient. Thus, a disconnection between microbial structure and function was identified. Fertilization experiments were conducted both in the lab and in the field to evaluate the impact of urea and/or rock phosphate amendment on SOM dynamics and on pasture productivity of active pastures. After combined fertilization the pasture yield was most efficiently increased by 2 Mg ha−1 a−1, indicating a NP‐limitation of grass growth. Furthermore, the fodder quality was improved by a higher content of P and Ca in the grass biomass. The microorganisms of the active pasture soil responded with an adaptation of their structure to the increased substrate availability in the short term, but did not change their initial functions in the long term. After urea/ rock phosphate addition a significant increase in the relative fungal abundance was detected, but neither a microbial limitation of energy nor of N or P was observed. However, urea addition accelerated gaseous losses of soil CO2‐C in the short term. In the study area, pronounced alterations in ecosystem functioning due to land‐use changes were detected, especially in soil C and N cycling rates. For a sustainable land‐use in this region it is crucial to prevent pasture degradation and to rehabilitate degraded pastures in order to protect the prevailing mountain rainforest ecosystem. It is of crucial importance for active pasture soils to maintain or even increase resource availability, being one indicator of soil fertility. In this context, the soil organic matter has to be retained in the long‐term to maintain high microbial activity and biomass, and thus pasture productivity. A moderate fertilization with urea and rock phosphate can be a first step to provide continuous nutrient supply for grass growth and to strengthen livestock health through increased fodder quality. However, the risk of further additional emissions of soil CO2‐C due to increased loads of urea fertilizer application has to be kept in mind. Overall, for the establishment of a sustainable land‐use management the control of bracken invasion and an adjusted nutrient management are needed. Further investigations on the reduction of soil nutrient losses and increased nutrient use efficiencies of plants, such as combined planting with legumes or the usage of cultivars with special nutrient acquisition strategies, should be in the focus of future work. / In der vorliegenden Dissertation werden die Auswirkungen der Weideetablierung, ‐düngung sowie des Verlassens von Weiden auf Bodenkohlenstoff‐ und Nährstoffdynamik in einer tropischen Bergregenwaldregion Ecuadors zusammenfassend dargestellt und diskutiert. Der Naturwald des Untersuchungsgebietes ist seit Jahrzehnten durch Brandrodung und die Umwandlung in extensiv genutztes Weideland (aktive Weide) in seinem flächenhaften Bestand bedroht. Als Problem hat sich der Verlust an Fruchtbarkeit der Weideböden während ihrer Bewirtschaftung herausgestellt. Des Weiteren führt die Einwanderung des Tropischen Adlerfarns (Pteridium arachnoideum, C3‐Pflanze) zu einer Reduktion der oberirdischen Grasbiomasse. Nimmt diese Entwicklung überhand, werden die betroffenen Flächen von den Bauern nicht mehr aktiv genutzt, verlassen und neuer Regenwald gerodet. Um mehr über die Mechanismen der Verringerung der Bodenfruchtbarkeit zu erfahren, wurden biotische und abiotische Bodeneigenschaften und deren Interaktion entlang eines Landnutzungsgradienten (Naturwald – aktive Weide – verlassene Weide) untersucht. Die Zerstörung des Bergregenwaldökosystems und die Überführung der gerodeten Flächen zur Weidebewirtschaftung verändert die Funktion und Struktur der Bodenmikroorganismen und beeinflusst den CO2‐C Fluss aus dem Boden. Jährlich werden 2 t CO2‐C ha‐1 zusätzlich vom Weideland emittiert. Diese Erhöhung der Bodenatmungsraten kann mit erhöhten Raten der mikrobiellen C‐Mineralisierung und Feinwurzelatmung in Verbindung gebracht werden. Das Weidegras (S. sphacelata, C4‐Pflanze) liefert C‐ und N‐reiche ober und unterirdische organische Substanz (z.B. durch die Feinwurzelbiomasse) und trägt damit zu einer Erhöhung der C‐ und N‐Verfügbarkeit für die mikroorganismen bei. Darüber hinaus stellen ein höherer pH‐Wert und eine erhöhte Basensättigung im oberen Mineralboden der aktiven Weide günstige Bedingungen für mikrobielles Wachstum und Metabolismus dar. Als Konsequenz sind die Gehalte an mikrobiellem Biomassekohlenstoff um das Dreifache erhöht und die mikrobiellen Gemeinschaftsstrukturen signifikant in Richtung einer höheren relativen Abundanz der Gram(‐)‐Bakterien und Pilze verschoben. Eine längerfristige Weidebewirtschaftung ohne Kompensation von Nährstoffverlusten sowie die Einwanderung des Tropischen Adlerfarnes verschlechterte die Bedingungen für die Mikroorganismen, was zu einem signifikanten Rückgang des SOC, der Netto‐ und Brutto‐N‐Mineralisierungsraten sowie zu einer Halbierung der mikrobiellen Biomasse führt. Eine bevorzugte Substratnutzung von Graskohlenstoff (C4) durch die Mikroorganismen hat einen schnellen Abbau des C4‐Pools zur Folge. Somit dominiert nun der mikrobiell schlechter verfügbare C3‐Pool den Bodenkohlenstoffpool. Dies führt zu einem weiteren Rückgang der Weideproduktivität und schließlich zum Offenlassen der Weide. Die geringere Qualität und Quantität der vom Farn stammenden ober‐ und unterirdischen organischen Substanz (hoher Ligninanteil, weites C/N), führten zu einer Limitierung der Ressourcen für die Mikroorganismen, welche deren Funktionen in größerem Maße beeinflussen als deren Gemeinschaftsstruktur. Im Gegensatz dazu wird entlang des Landnutzungsgradienten die Struktur hauptsächlich durch den pH‐Wert beeinflusst. Daraus folgt, dass Struktur und Funktion der Bodenmikroorganismen voneinander entkoppelt auf Veränderungen reagieren können. Um den Einfluss von Harnstoff‐ und/ oder Rohphosphatdüngung aktiver Weiden auf die Dynamik der organischen Bodensubstanz und auf die Weideproduktivität zu untersuchen, wurden sowohl Labor‐ als auch Feldversuche durchgeführt. Im Feldexperiment wurde gezeigt, dass eine NP‐Limitierung der Grasbiomasseproduktion vorliegt und durch eine geringe NP‐Kombinationsdüngung die oberirdische Phytomasseproduktion um 2 t ha−1 a−1 gesteigert und die Futterqualität durch eine Erhöhung der P‐ und Ca‐ Gehalte verbessert werden kann. Die Mikroorganismen reagierten mit einer Anpassung ihrer Struktur an die kurzzeitig erhöhte Substratverfügbarkeit. Nach Gabe von Harnstoff und/ oder Rohphosphat wurde weder eine N‐ noch eine P‐Limitierung der Bodenmikroorganismen festgestellt, und die mikrobiellen Funktionen wurden langfristig nicht verändert. Dagegen bewirkte die Düngergabe einen erhöhten relativen Anteil der Pilzabundanz. Im Labor sowie im Feld kam es nach Harnstoffdüngung kurzzeitig zu verstärkten gasförmigen Verlusten des Bodenkohlenstoffs. Aufgrund der Landnutzungsänderungen im Untersuchungsgebiet veränderten sich die Ökosystemfunktionen stark, speziell die Boden‐C‐ und Boden‐N‐Umsatzraten. Für eine nachhaltige Landnutzung in der Region, d. h., für den Schutz der noch verbliebenen natürlichen Bergregenwaldflächen, ist es von entscheidender Bedeutung, dass die Weidedegradierung verhindert wird und degradierte Flächen wieder in Nutzung genommen werden. Als entscheidend für die Weideproduktivität hat sich in dieser Studie die Ressourcenverfügbarkeit für Bodenmikroorganismen herausgestellt. Daher ist es sehr wichtig, diese Ressourcenverfügbarkeit in Böden aktiv‐genutzter Weiden zu erhalten oder noch zu erhöhen, denn sie wirkt sich vor allem auf die organische Bodensubstanz und im Wechselspiel damit auf die mikrobielle Biomasse und Aktivität aus. Eine moderate Kombinationsdüngung aus Harnstoff und Rohphosphat ist ein erster Schritt in diese Richtung. Dabei sollte jedoch das Risiko zusätzlicher bodenbürtiger CO2‐C Emissionen in Folge höherer Düngergaben berücksichtigt werden. Für ein nachhaltiges Landnutzungsmanagement sind Maßnahmen gegen die Einwanderung des Adlerfarnes und ein angepasstes Nährstoffmanagement notwendig. Weitere Untersuchungen sollten auf eine Minimierung der Nährstoffverluste und eine erhöhte Nährstoffnutzungseffizienz der Pflanzen fokussiert werden. Weidemischkulturen aus Gräsern mit Leguminosen sowie der Einsatz von Kulturen mit speziellen Nährstoffaneignungsstrategien könnten dabei eine große Rolle spielen und sollten in der Region erprobt werden. / La tesis presentada investiga el impacto del establecimiento de pasto, de su fertilización y de su manejo tradicional (abandono del pastizal) a la dinámica del carbono y de los nutrientes de suelo en la región de los bosques tropicales montañosos en el Sur de Ecuador. Durante las últimas décadas el bosque natural en el área de estudio ha estado amenazada por su conversión a pastizales. Sin embargo, la fertilidad del suelo en pastos de tipo extensivo (pastos activos) decrece frecuentemente durante el uso de los pastos. La invasión de Llashipa (Pteridium arachnoideum) conduce al abandono de los pastos cuando la ésta se vuelve dominante. Con la finalidad de revelar los mecanismos detrás de esta disminución de la fertilidad de suelo, se analizaron las propiedades bióticas y abióticas del suelo y sus interacciones, a lo largo de una gradiente del uso de la tierra (bosque natural —pasto activo — pastos abandonados). La perturbación del ecosistema de bosque tropical montañoso por su cambio de uso, mediante el establecimiento de pastizales, ha alterado la función y la estructura de los microorganismos y ha afectado el flujo de CO2‐C del suelo. Cada año 2 Mg CO2‐C ha‐1 fueron emitidas adicionalmente por el establecimiento de pastos. Esta aceleración en la tasa de respiración del suelo está relacionada con el aumento de las tasas de mineralización microbiana de carbono y de la respiración de las raíces. La alta calidad y abundancia de N de los residuos orgánicos del suelo con pasto Mequeron (S. sphacelata, C4‐planta), especialmente debido a la gran biomasa de las raíces finas, ofrecen una disponibilidad alta de C y N para los microorganismos. En comparación con el bosque natural, el aumento del pH y la saturación bases acelerada fueron condiciones más favorables para el crecimiento microbiano y para el metabolismo microbiano en el parte superior del suelo mineral en pastos activos. La cantidad de C de la biomasa de los microorganismos fue tres veces mayor que la del bosque y se ha observado un cambio significativo de la estructura de la comunidad microbiana, en donde la abundancia relativa de los hongos y de las bacterias Gram(‐) ha aumentado. El uso de pasto a largo plazo y la invasión de Llashipa (C3‐planta) han reducido los efectos benéficos para los microorganismos, que resultaron en una reducción significativa de las tasas de la mineralización de C y N, y en una reducción en dos tercios de la biomasa microbiana. El uso preferencial de los microorganismos por sustrato de pasto C4 han resultado en una rápida disminución de la reserva de C4. Como consecuencia, la menor disponibilidad de la reserva de C3 de las plantas de Llashipa y de la cobertura anterior de bosque ha incrementado su dominancia en la reserva de materia orgánica del suelo. Eso resulta, en una mayor disminución de la productividad de los pastos, conduciendo finalmente al abandono de los campos de pastos. La menor calidad y cantidad de los residuos acumulados sobre y bajo el suelo provenientes de la Llashipa han dado como resultado un sustrato de limitadas condiciones que están afectando más a las funciones microbiales antes que a su estructura. La estructura microbiana parece ser más sensible al pH del suelo a largo de la gradiente del uso de la tierra; de manera que se ha identificado una desconexión entre la estructura y función microbial. Experimentos de fertilización en laboratorio y en campo han sido realizados para evaluar el impacto de la aplicación de enmiendas (urea y/o roca fosfórica) a la dinámica de la materia orgánica y a la productividad de los pastos activos. El resultado del experimento de campo ha demostrado que la fertilización combinada es más efectiva, mostrando un aumento en la producción de biomasa de 2 Mg ha−1 a−1, lo que indica una limitación de N y P para el crecimiento del pasto. Además, la calidad de forraje se mostró incrementada ya que el contenido de P y de Ca han aumentado significativamente. Los microorganismos del suelo en el pasto activo han respondido a corto plazo con una adaptación de su estructura ante la disponibilidad de sustrato, pero no han mostrado un cambio de sus funciones iniciales a largo plazo. Después de la aplicación de urea y de la roca fosfórica, se detectó un incremento significativo en la abundancia de los hongos, pero tampoco se observó una limitación de energía microbial ni de N o P. Sin embargo, la aplicación de urea ha aumentado la pérdida gaseosa de CO2‐C del suelo a corto plazo. Debido al cambio de uso de la tierra en la área de investigación, se ha detectado una alteración notable de la función del ecosistema, especialmente en el ciclo de C y N de suelo. Para un uso sostenible de la tierra en esta región, es crucial el prevenir la degradación de pastos y rehabilitar aquellos degradados. En el suelo de pastos activos es de gran importancia el mantener o aún mejor el aumentar la disponibilidad del sustrato, que es uno de los indicadores de la fertilidad del suelo. En este contexto, la materia orgánica se debe ser retenida a largo plazo para mantener la actividad y biomasa microbiana alta y por ende la productividad de pasto. Una moderada fertilización con urea y roca fosfórica puede ser un primer paso para proveer un continuo suministro de nutrientes por el crecimiento del pasto y para reforzar la sanidad pecuaria por medio de un forraje de mayor calidad. Sin embargo, el riesgo de emisiones adicionales de CO2‐C del suelo debido a una aplicación más alta de urea debe tenerse en cuenta. Se puede concluir que para un manejo sostenible del uso de la tierra, tanto el control de la invasión de Llashipa y como un suministro adecuado de nutrientes son necesarios. Adicionalmente se podría decir que es necesario profundizar el estudio de la reducción de las pérdidas de los nutrientes de suelo y de la eficiencia del uso de los nutrientes en las plantas, así como las asociaciones de pastos con leguminosas o el uso de cultivos de absorción selectiva de nutrientes, que serían estrategias importantes para el futuro.

Chickpea (Cicer arietinum L.) production on the semi-arid Canadian Prairies is challenging due to a short growing season and low and variable moisture. The current recommended chickpea population density of 44 plants m-2 is based on preliminary studies and a narrow range of 20 to 50 plants m-2. The aims of this study were to i) determine optimum population density of varying chickpea canopy types, i.e., leaf type and growth habit, by investigating seed yield responses at 30 to 85 plants m-2 and ii) identify desirable parental traits for breeding programs by assessing growth and yield parameter responses to varying leaf types and growth habits at a range of population densities. Field experiments were conducted from 2002 to 2005. Canopy measurements and calculated variables included light interception, biomass, growth rate, seed yield, harvest index, ascochyta blight severity and radiation- and water use efficiencies. The plant density which produced the highest seed yield when averaged over years for each location for each treatment revealed that a plant density of at least 55 plants m-2 produced a 23% to 49% seed yield increase above that of the currently recommended plant density. This indicates that a higher seed yield average over the long term in spite of periodic low seed yield episodes will be more profitable to producers. Increasing plant density increased lowest pod height significantly in all except one location-year but did not explicitly increase ascochyta blight severity or decrease individual seed size. This suggests that increasing the recommended chickpea plant density on the Canadian Prairies will increase seed yield but would neither negatively impact individual seed size nor ascochyta blight severity, especially, when combined with good agronomic practices. Fern-leaved cultivars had significantly higher maximum intercepted light (62 to 91%), seed yield (136 to 369 g m-2), harvest index (0.33 to 0.53), yield-based water use efficiency (0.56 to 1.06 g m-2 mm-1) and lower ascochyta blight severity (3 to 27%) than the unifoliate cultivars in all location-years. The fern-leaved cultivars also tended to show significantly higher cumulative intercepted radiation (221 to 419 MJ m-2) and biomass (306 to 824 g m-2) but leaf type showed no consistent effect on radiation use efficiency. Cultivars with bushy growth habit generally performed better regarding maximum intercepted light (62 to 90%), cumulative intercepted radiation (233 to 421 MJ m-2), biomass (314 to 854 MJ m-2), seed yield (120 to 370 g m-2), harvest index (0.37 to 0.50), yield-based water use efficiency (0.56 to 1.06 g m-2 mm-1) and ascochyta blight severity (7 to 36%) than the erect cultivars. The overall performance of the spreading cultivar was generally intermediate between the bushy and erect cultivars except for ascochyta blight severity where the spreading cultivar exhibited significantly lower disease severity (3 to 36%). Radiation use efficiency was generally not influenced by growth habit. Increasing plant population density generally increased intercepted light, biomass and cumulative intercepted radiation on each sampling day after seeding resulting in a general increase in seed yield. Harvest index, however, remained constant and ascochyta blight severity was generally stable but radiation use efficiency decreased with increasing population density. Chickpea cultivars with fern leaves and bushy growth habit at higher than currently recommended population densities would best utilize the limited resources of the short-season Canadian prairie environment to maximize and stabilize seed yield.