A recuperação de funções e processos ecossistêmicos, entre outros atributos, é um dos indicadores mais importantes no processo de retorno de um ecossistema à sua trajetória histórica. A ciclagem de nutrientes é um atributo fundamental do ecossistema, e relaciona-se diretamente à regulação do funcionamento e do desenvolvimento dos ecossistemas e inclui, em um modelo geral, as entradas de nutrientes, as transferências internas entre plantas e solo e as saídas do sistema. A compreensão das mudanças nos processos biogeoquímicos durante a sucessão secundária em áreas em restauração ecológica ainda é incipiente, principalmente em áreas de florestas tropicais. Esse estudo tem por objetivo elucidar a dinâmica do nitrogênio ao longo do processo de restauração ecológica em áreas reflorestadas com espécies nativas da Mata Atlântica. A questão norteadora deste estudo é a seguinte: A restauração florestal com alta diversidade de espécies e predominância de espécies arbóreas nativas regionais restaura a dinâmica original do nitrogênio? Esse estudo visa investigar o funcionamento da ciclagem de nutrientes, com foco no nitrogênio, que é um elemento limitante à sucessão secundária, especialmente em florestas tropicais. Para tal, alguns indicadores da ciclagem do nitrogênio foram mensurados em uma cronosequência florestal formada por uma floresta natural preservada e florestas restauradas de diferentes idades (21 e 52 anos) reflorestadas com alta diversidade de espécies e predominância de nativas regionais. Os indicadores utilizados foram: 15N e teor de N da vegetação, serrapilheira e solo; razão N:P da vegetação e da serrapilheira; taxas líquidas de mineralização e nitrificação; teor de amônio, nitrato, N mineral e razão nitrato:amônio. As florestas foram amostradas entre agosto de 2008 e abril de 2009, nas seguintes estações: seca, transição entre seca e chuvosa, chuvosa, e transição entre chuvosa e seca. Foram encontrados padrões claros de mudanças na ciclagem do N ao longo da cronosequência estudada, incluindo diferenças nos valores de 15N foliar, teor de N, razão N:P, N mineral e taxas líquidas de mineralização e nitrificação, caracterizadas por um aumento de valores médios dessas variáveis ao longo da cronosequência. Os resultados encontrados sugerem que as florestas em processo de restauração, mesmo a de 52 anos, ainda não possuem uma ciclagem de N característica de uma floresta madura e, portanto, a recuperação da ciclagem de N ainda não foi completamente atingida. Entretanto, é possível afirmar que as florestas em processo de restauração estudadas estão seguindo uma trajetória de desenvolvimento caracterizada por uma ciclagem de N cada vez mais parecida com a de uma floresta natural madura, como a da floresta natural madura utilizada como referência. Através dos modelos de restauração utilizados para as florestas da cronosequência estudada, os processos da ciclagem do N são recuperados à medida que a floresta desenvolve-se, com uma clara tendência de mudança na economia de N para economia de P típica de florestas tropicais maduras. / The recuperation of ecosystem processes and functions, among other attributes, is one of the most important indicators in the process of return of an ecosystem to its historic trajectory. Nutrient cycling is a fundamental ecosystem attribute, and relates directly to regulation of functioning and development of ecosystems and includes, in a general model, nutrients entering, being transferred internally between plants and soil, end leaving the system. The comprehension of changes in biogeochemical processes during secondary succession in areas in ecological restoration is still incipient, mainly in tropical forests. This study aims to elucidate nitrogen dynamics along the process of ecological restoration in areas reforested with Atlantic Forest native species. The question driving this study is: Does ecological restoration with high diversity of species and predominance of regional native tree species restore nitrogen original dynamics? This research investigated nutrients cycling functioning, focusing on nitrogen, which is a limiting nutrient in secondary succession, particularly in tropical forests. In order to do so, some indicators of nutrient cycling were assessed in a forest chronosequence formed by a preserved natural forest and restored forests of different ages (21 and 52 years) reforested using high species diversity and predominance of regional native species. The indicators used were: 15N and N content in green foliage, litter and soil; N:P ratio of green foliage and litter; net mineralization and net nitrification rates; content of ammonium, nitrate, inorganic N, and nitrate:ammonium ratio. The forests were sampled between August 2008 and April 2009, in the following seasons: dry, dry-rainy transition, rainy, rainy-dry transition. Clear patterns of change in the N cycling along the studied chronosequence were found, including differences in green foliage 15N values, N content, N:P ratio, inorganic N and net mineralization and nitrification rates, characterized by an increase in the mean values of these variables along the chronosequence. The results found suggest that the forests in restoration process, even the 52 years old one, still do not present a N cycling characteristic of a mature forest and, therefore, the recuperation of the N cycling was not completely reached yet. However, it is possible to state that the forests in restoration process studied here are following a development trajectory characterized by a N cycling progressively more similar to what is common to a mature native forest, as the one used as the reference ecosystem in this study. Through the restoration models used for the forests studied, the N cycle processes are recovered as the forests develop, as they present a clear tendency of changing from N economy to P economy, typical to mature tropical forests.

O conhecimento da dinâmica de crescimento das raízes da cana-de-açúcar, bem como da arquitetura de seu sistema radicular, permite melhor compreensão das relações entre a planta e o seu ambiente de produção, possibilitando o manejo a partir de práticas agrícolas mais eficientes e sustentáveis que resultem em aumento de produtividade e longevidade da cultura. O presente estudo teve por objetivo desenvolver um método para determinação da distribuição e do desenvolvimento de raízes metabolicamente ativas de cana-de-açúcar no solo, por meio da técnica da diluição do isótopo 15N, associado aos métodos de amostragem com monólito e sonda amostradora de raízes. O experimento foi realizado em área comercial de cana-de-açúcar na região canavieira de Piracicaba, Estado de São Paulo, em LATOSSOLO VERMELHO distrófico arenoso, com uma segunda rebrota do cultivar RB85 5156. O delineamento experimental foi em blocos subdivididos no tempo, com as amostragens de raízes realizadas a cada 50 a 60 dias de janeiro a junho de 2004. A uréia foi o veículo de fornecimento do marcador isotópico 15N, por meio de solução aplicada às folhas das plantas. Após colheita da parte aérea, realizada 96 horas após a aplicação da solução de uréia, foram abertas trincheiras, transversalmente à linha da cultura, com dimensões de 1 m de comprimento e 1,4 m de largura. Amostras foram colhidas por meio de monólito nas profundidades de 0 a 20, 20 a 40, 40 a 60 e 60 a 80 cm, na projeção da linha da cultura e lateralmente nas distâncias de 14 a 42 cm e de 42 a 70 cm da linha da cultura. Outras amostras foram colhidas com sonda amostradora de raízes, paralelamente à parede interna das trincheiras, a 10 cm de distância do local onde foram retirados os monólitos, nas mesmas profundidades e nas distâncias de 28 e 56 cm da linha. Em cada profundidade de amostragem, e na projeção da linha da cultura, foram separadas amostras de raízes visualmente ativas. Estas amostras forma consideradas padrão para a determinação por diluição isotópica de raízes com metabolismo ativo. As determinações do teor de N e de abundância de 15N em amostras de planta e de solo foram realizadas em um espectrômetro de massas modelo ANCA-SL da Eurapa Scientific Ltda. Os resultados mostraram que o método da diluição isotópica com 15N possibilitou avaliar a massa de raízes com metabolismo ativo e sua distribuição no solo, e o método de amostragem de raízes com a sonda foi viável em comparação com a amostragem do monólito, nas seguintes condições: na quantificação de raízes nas profundidades de 0 a 20, 20 a 40 e 60 a 80 cm do perfil do solo para raízes totais, e nos 20 cm superficiais do solo, profundidade na qual a massa de raízes foi maior, para raízes metabolicamente ativas. / Knowledge about of sugarcane root growth dynamic, as well as the root system architecture of sugarcane crop allows understanding better the relationships between the plant and its environment. This knowledge is important to define the crop management with most efficiency and using sustainable practices, to increasing both sugarcane crop yield and longevity. The aim of this study was to evaluate a method in order to determine sugarcane roots with active metabolism and its distribution and growth in the soil profile, by using isotopic dilution technique with 15N associated with sampling by monolite and probe. The experiment was conducted in the sugarcane field, on the region of Piracicaba, State of São Paulo, Brazil, by using the second rattoon of the variety RB 85 5156, grown in a Rhodic Hapludox. The experimental design was in randomized blocks, with four replications. The split plot was considered in relation to the time. The 15N tracer was applied in the plants as urea solution. The above ground part of sugarcane plants were harvested 96 hours after urea solution applications, and trenches with one meter of length and 1.4 meter width were opened transversely to sugarcane rows. Samples were taken by monolite in 0-20, 20-40, 40-60 and 60-80 cm of depth in the soil profile in the row projection and horizontally in the distances of 14 to 42 and 42 to 70 cm from the cane row. Samples were taken by probe in a parallel plan with the internal trench wall at 10 cm of distance from the spot where monolites were collected, in the same depths and at 28 and 56 cm from the row. Roots visually assumed as metabolisms active were separated to each sampling depth and to row lateral projection and were considered standards to determine active roots. Determinations of N contents and 15N abundance in both plant and soil were carried on a mass spectrometer model ANCA-SL (Europa Scientific Ltda.). The results showed the isotopic dilution method with 15N allowed the evaluation of active roots mass and the root distribution in the soil. The root sampling method with probe was adequate comparing with root sampling by monolite in trench to quantify roots, in the following conditions: in the soil depths of 0 to 20, 20 to 40 and 60 to 80 cm to total roots; and in the first 20 cm of depth, where the root mass was higher to active roots.

Natural abundance of 15N varies greatly and unpredictably within and between environments. The unpredictable nature of 15N limits the use of N isotope natural abundance (d15N) in tracing the flow and fate of N in environments. Recent investigations have, however, revealed consistent and repeatable patterns of 15N in some ecosystem components. These patterns suggest that d15N may yet provide a tool to investigate and illuminate ecosystem N cycling processes. Identifying and quantifying the sources of isotopic variation must precede any significant advance in the application of this technique, and to this end an assessment of isotopic variation associated with major ecosystem components has been carried out in this thesis. d15N patterns have been established, hypotheses proposed and tested, and conclusions about the application of the technique are presented. 15N patterns in surface and groundwater were measured in a variety of different land-use catchments in an attempt to identify distinct isotopic 'fingerprints'. High levels of 15N variation were measured in both stream and groundwaters, resulting in strongly overlapping land-use 'fingerprints'. Environmental 15N variation in streams and groundwaters was found to be too great to differentiate between land-uses based on d15N alone. In contrast, the artificially 15N enriched signature of effluent N was used to trace its flow and fate, following irrigation, in a forested catchment. The effluent d15N signature allowed it to be traced into the major ecosystem components, permitting a first order N budget to be determined for effluent N storage and loss. N sources with significantly different 15N signatures to that of 'background ecosystem N' can therefore be used to trace the flow and fate of N in ecosystems. During the course of this work a number of higher and lower order plants were observed to have highly depleted (lt; -8 ) d15N signatures. Epiphytes and lithophytes, strongly reliant on atmospheric N sources, were consistently depleted in 15N, with signatures as low as -24 , measured in a range of environments. A similar level of depletion was measured in a wide range of plants growing in early primary succession sites (as low as -22.3 ), which could not be accounted for by any abiotic or biotic factor or significantly depleted N source. The absence of any measurable driver of depletion suggested a universal fractionating mechanism which acts in a wide range of environments and vegetation types. Diffusive uptake of atmospheric NH3(g) and the proportional uptake of a supplied N source were two proposed mechanisms that could theoretically account for the level and universal nature of depletion. Diffusive uptake of atmospheric NH3(g) was tested as a primary fractionating mechanism in plants. Strongly N deficient plants were capable of utilising NH3(g) as a nutritional source, but the level of 15N depletion measured in these plants closely approximated that of the inherent NH3(g) d15N signature. No significant additional fractionation is associated with NH3(g) diffusive uptake. Diffusive uptake of atmospheric NH3(g) by plants cannot alone account for the level of depletion measured in early primary succession plant communities. Proportional uptake of a N source as a primary fractionating mechanism was tested by growing plants in various concentrations and rates of applied N. Fractionation attributed to the proportional uptake of a supplied N source, as a consequence of P limitation or rapid flow over roots, resulted in a significant level of 15N depletion in plants. The level of depletion attributed to this mechanism was, however, not sufficient to account for the level measured in early primary succession plant communities. Individual 15N fractionating mechanisms cannot alone explain the level of depletion observed in early primary succession plants, however a combination of fractionating mechanisms can. Fractionation attributed to the proportional uptake of an already depleted N source, i.e., wet deposited N, largely accounts for the level of depletion measured in early succession plant communities. This two-step fractionation model can act on both higher and lower plants, independent of ecosystem biotic and abiotic factors. Additional, and less dramatic fractionations attributed to atmospheric NH3(g) uptake, mycorrhizal associations, internal remobilisation, and taxon-specific N acquisition strategies, will contribute to the level of d15N depletion. This thesis presents the first extensive survey of highly depleted d15N signatures in terrestrial vegetation. Furthermore, thorough testing of theoretically plausible mechanisms has resulted in a full account of the highly depleted d15N signatures measured in a wide range of vegetation types and environments.

In der vorliegenden Arbeit wird die Darstellung neuer organischer Polyazide dokumentiert, die durch einfache nucleophile Substitution mittels NaN3 dargestellt werden können. Organische Azide mit der Formel RN3 können sich unter Stickstoff-Abspaltung in exothermen, teilweise explosionsartigen Reaktionen zersetzen. Sie sind daher prinzipiell als energiereiche Materialien (HEDM) für entsprechende Anwendungen geeignet. Die als Treibladungsmaterialien potentiell geeignetsten, handhabungssicheren, dendritischen Polyazide werden unter anderem mittels Thermogravimetrie und Differenzkalorimetrie analysiert. In einer neuen Synthesemethode können die wenig bekannten Heteroazidomethane aus Tris(azidomethyl)amin erzeugt werden. Von besonderem Interesse ist dabei die Synthese neuartiger Azidohalogenmethane. Diese können durch analytische Gas-Chromatographie charakterisiert und mittels präparativer Gas-Chromatographie isoliert werden. Durch die 1,3-dipolare Cycloaddition mit Cyclooctin konnten einige Heteroazidomethane zu Triazolen abgefangen und so einer Einkristall-Röntgen-Strukturanalyse zugeführt werden. Als letztes in der homologen Reihe der Azidomethane noch fehlendes Azid konnte Tetraazidomethan synthetisiert werden. Das Perazidomethan besitzt mit 93.3% den für organische Azide höchstmöglichen Stickstoffgehalt. Seine Existenz wurde bislang lediglich durch molekültheoretische Berechnungen nahegelegt. Die Synthese dieses homoleptischen Kohlenstoffazides gelang durch die Behandlung von Trichloracetonitril mit Natriumazid. Es ließ sich durch präparative GC als extrem explosive, farblose Flüssigkeit isolieren. Mit Hilfe der analytischen GC konnten sowohl der Siedepunkt als auch die Polarität von C(N3)4 abgeschätzt werden. C(N3)4 wird desweiteren durch IR, MS, 13C-NMR und 15N-NMR-Spektroskopie sowie durch Einkristall-Röntgen-Strukturanalysen seiner Abfangprodukte mit Cyclooctin charakterisiert. Mit Wasser zeigt C(N3)4 eine quantitative Hydrolyse unter Bildung von Carbonyldiazid. Durch Austauschprozesse mit Na15N3 konnte die mögliche Dissoziation von C(N3)4 nachgewiesen werden. Reaktionen von C(N3)4 mit Phosphinen führen zu Cyanamidderivaten, mit Norbornen sowie Norbornadien wurden über vielstufige Reaktionsmechanismen Aminotetraazole erhalten.

Made available in DSpace on 2014-06-11T19:30:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-09-21Bitstream added on 2014-06-13T19:40:03Z : No. of bitstreams: 1 borghi_e_dr_botfca.pdf: 848383 bytes, checksum: 44d5e9fbafc7f7b8fefd5bb90ee2d35a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O trabalho de pesquisa teve por objetivo: 1) avaliar a produtividade de grãos da cultura de milho em épocas de consorciação com Brachiaria brizantha cv. Marandu e Panicum maximum cv. Mombaça em SPD; 2) avaliar o desempenho das plantas forrageiras consorciadas em épocas e a resposta à adubação nitrogenada aplicada após a colheita do milho, quanto à produtividade e valor nutritivo; 3) verificar, na B. brizantha, o acúmulo de nitrogênio total e proveniente do fertilizante nitrato de amônio (NPPF) com doses de nitrato de amônio (15NH4NO3) aplicado em cobertura nas plantas forrageiras após a colheita da cultura do milho; 4) avaliar o residual da adubação nitrogenada nas plantas forrageiras na cultura do milho cultivado em sucessão; 5)avaliar o aproveitamento do nitrogênio (15N), aplicado em cobertura na B. brizantha, pela cultura sucedânea do milho. Para atingir tais propósitos, foram conduzidos três estudos simultaneamente, conduzidos em condições de campo durante os anos agrícolas de 2003/04, 2004/05 e 2005/06 na Fazenda Experimental Lageado, da Faculdade de Ciências Agronômicas – Campus de Botucatu, em NITOSSOLO VERMELHO Estruturado, cultivado em SPD. O delineamento experimental utilizado foi o de blocos casualizados, com quatro repetições. No estudo I, os tratamentos foram: 1) cultivo do milho solteiro; 2) milho com Brachiaria brizantha cv. Marandu consorciada na semeadura; 3) milho com Brachiaria brizantha cv. Marandu consorciada na adubação de cobertura; 4) milho com Panicum maximum cv. Mombaça consorciado na semeadura; 5) milho com Panicum maximum cv. Mombaça consorciado na adubação de cobertura. No segundo e terceiro anos de condução do experimento (anos agrícolas 2004/05 e 2005/06), após a colheita da cultura do milho, foi aplicado nitrato de amônio em cobertura nas quantidades equivalentes a 0, 30, 60 e 120 kg ha-1 de N... / The present work aimed to: 1) evaluate corn grain yield under different intercropping epochs with Brachiaria brizantha cv. Marandu and Panicum maximum cv. Mombaça under no-tillage system; 2) evaluate the performance of the forages intercropped and the answer of these crops to nitrogen rates applied after corn harvest, considering the productivity and nutritional value; 3) verify, in B. brizantha, the total nitrogen accumulation and the nitrogen accumulated from the fertilizer ammonium nitrate (NPPF) under different ammonium nitrate rates (15NH4NO3) applied in the forages as cover crop after corn harvest; 4) evaluate the nitrogen profit (15N), applied as cover crop in B. brizantha, by corn cultivated in succession. To reach the proposed objectives, it was carried on three simultaneous studies, carriers on at field conditions, during the cropping years of 2003/04, 2004/05 and 2005/06 at Lageado Experimental Farm, College of Agricultural Sciences, in Botucatu, State of São Paulo, Brazil, in a structured Oxisol cultivated under no-tillage system. The experimental design was in blocks completely randomized, with four replicates. In the experiment I, the treatments were: 1) corn cultivated alone; 2) corn with Brachiaria brizantha cv. Marandu as consortium seeded at corn seeding; 3) corn with B. brizantha cv. Marandu as consortium seeded at corn cover fertilization; 4) corn with Panicum maximum cv. Mombaça as consortium seeded at corn seeding; 5) corn with P. maximum cv. Mombaça as consortium seeded at corn cover fertilization. In the second and third experimental years (2004/05 and 2005/06), after corn grain harvest, it was applied cover rates of ammonium nitrate, equivalent to 0, 30, 60 and 120 kg ha-1 of N. Only under B. brizantha were allocated micro parcels in which it was applied enriched ammonium nitrate (15NH4NO3), to evaluate the N recovery by Brachiaria ...(Complete abstract click electronic access below)

O conhecimento da dinâmica de crescimento das raízes da cana-de-açúcar, bem como da arquitetura de seu sistema radicular, permite melhor compreensão das relações entre a planta e o seu ambiente de produção, possibilitando o manejo a partir de práticas agrícolas mais eficientes e sustentáveis que resultem em aumento de produtividade e longevidade da cultura. O presente estudo teve por objetivo desenvolver um método para determinação da distribuição e do desenvolvimento de raízes metabolicamente ativas de cana-de-açúcar no solo, por meio da técnica da diluição do isótopo 15N, associado aos métodos de amostragem com monólito e sonda amostradora de raízes. O experimento foi realizado em área comercial de cana-de-açúcar na região canavieira de Piracicaba, Estado de São Paulo, em LATOSSOLO VERMELHO distrófico arenoso, com uma segunda rebrota do cultivar RB85 5156. O delineamento experimental foi em blocos subdivididos no tempo, com as amostragens de raízes realizadas a cada 50 a 60 dias de janeiro a junho de 2004. A uréia foi o veículo de fornecimento do marcador isotópico 15N, por meio de solução aplicada às folhas das plantas. Após colheita da parte aérea, realizada 96 horas após a aplicação da solução de uréia, foram abertas trincheiras, transversalmente à linha da cultura, com dimensões de 1 m de comprimento e 1,4 m de largura. Amostras foram colhidas por meio de monólito nas profundidades de 0 a 20, 20 a 40, 40 a 60 e 60 a 80 cm, na projeção da linha da cultura e lateralmente nas distâncias de 14 a 42 cm e de 42 a 70 cm da linha da cultura. Outras amostras foram colhidas com sonda amostradora de raízes, paralelamente à parede interna das trincheiras, a 10 cm de distância do local onde foram retirados os monólitos, nas mesmas profundidades e nas distâncias de 28 e 56 cm da linha. Em cada profundidade de amostragem, e na projeção da linha da cultura, foram separadas amostras de raízes visualmente ativas. Estas amostras forma consideradas padrão para a determinação por diluição isotópica de raízes com metabolismo ativo. As determinações do teor de N e de abundância de 15N em amostras de planta e de solo foram realizadas em um espectrômetro de massas modelo ANCA-SL da Eurapa Scientific Ltda. Os resultados mostraram que o método da diluição isotópica com 15N possibilitou avaliar a massa de raízes com metabolismo ativo e sua distribuição no solo, e o método de amostragem de raízes com a sonda foi viável em comparação com a amostragem do monólito, nas seguintes condições: na quantificação de raízes nas profundidades de 0 a 20, 20 a 40 e 60 a 80 cm do perfil do solo para raízes totais, e nos 20 cm superficiais do solo, profundidade na qual a massa de raízes foi maior, para raízes metabolicamente ativas. / Knowledge about of sugarcane root growth dynamic, as well as the root system architecture of sugarcane crop allows understanding better the relationships between the plant and its environment. This knowledge is important to define the crop management with most efficiency and using sustainable practices, to increasing both sugarcane crop yield and longevity. The aim of this study was to evaluate a method in order to determine sugarcane roots with active metabolism and its distribution and growth in the soil profile, by using isotopic dilution technique with 15N associated with sampling by monolite and probe. The experiment was conducted in the sugarcane field, on the region of Piracicaba, State of São Paulo, Brazil, by using the second rattoon of the variety RB 85 5156, grown in a Rhodic Hapludox. The experimental design was in randomized blocks, with four replications. The split plot was considered in relation to the time. The 15N tracer was applied in the plants as urea solution. The above ground part of sugarcane plants were harvested 96 hours after urea solution applications, and trenches with one meter of length and 1.4 meter width were opened transversely to sugarcane rows. Samples were taken by monolite in 0-20, 20-40, 40-60 and 60-80 cm of depth in the soil profile in the row projection and horizontally in the distances of 14 to 42 and 42 to 70 cm from the cane row. Samples were taken by probe in a parallel plan with the internal trench wall at 10 cm of distance from the spot where monolites were collected, in the same depths and at 28 and 56 cm from the row. Roots visually assumed as metabolisms active were separated to each sampling depth and to row lateral projection and were considered standards to determine active roots. Determinations of N contents and 15N abundance in both plant and soil were carried on a mass spectrometer model ANCA-SL (Europa Scientific Ltda.). The results showed the isotopic dilution method with 15N allowed the evaluation of active roots mass and the root distribution in the soil. The root sampling method with probe was adequate comparing with root sampling by monolite in trench to quantify roots, in the following conditions: in the soil depths of 0 to 20, 20 to 40 and 60 to 80 cm to total roots; and in the first 20 cm of depth, where the root mass was higher to active roots.

A recuperação de funções e processos ecossistêmicos, entre outros atributos, é um dos indicadores mais importantes no processo de retorno de um ecossistema à sua trajetória histórica. A ciclagem de nutrientes é um atributo fundamental do ecossistema, e relaciona-se diretamente à regulação do funcionamento e do desenvolvimento dos ecossistemas e inclui, em um modelo geral, as entradas de nutrientes, as transferências internas entre plantas e solo e as saídas do sistema. A compreensão das mudanças nos processos biogeoquímicos durante a sucessão secundária em áreas em restauração ecológica ainda é incipiente, principalmente em áreas de florestas tropicais. Esse estudo tem por objetivo elucidar a dinâmica do nitrogênio ao longo do processo de restauração ecológica em áreas reflorestadas com espécies nativas da Mata Atlântica. A questão norteadora deste estudo é a seguinte: A restauração florestal com alta diversidade de espécies e predominância de espécies arbóreas nativas regionais restaura a dinâmica original do nitrogênio? Esse estudo visa investigar o funcionamento da ciclagem de nutrientes, com foco no nitrogênio, que é um elemento limitante à sucessão secundária, especialmente em florestas tropicais. Para tal, alguns indicadores da ciclagem do nitrogênio foram mensurados em uma cronosequência florestal formada por uma floresta natural preservada e florestas restauradas de diferentes idades (21 e 52 anos) reflorestadas com alta diversidade de espécies e predominância de nativas regionais. Os indicadores utilizados foram: 15N e teor de N da vegetação, serrapilheira e solo; razão N:P da vegetação e da serrapilheira; taxas líquidas de mineralização e nitrificação; teor de amônio, nitrato, N mineral e razão nitrato:amônio. As florestas foram amostradas entre agosto de 2008 e abril de 2009, nas seguintes estações: seca, transição entre seca e chuvosa, chuvosa, e transição entre chuvosa e seca. Foram encontrados padrões claros de mudanças na ciclagem do N ao longo da cronosequência estudada, incluindo diferenças nos valores de 15N foliar, teor de N, razão N:P, N mineral e taxas líquidas de mineralização e nitrificação, caracterizadas por um aumento de valores médios dessas variáveis ao longo da cronosequência. Os resultados encontrados sugerem que as florestas em processo de restauração, mesmo a de 52 anos, ainda não possuem uma ciclagem de N característica de uma floresta madura e, portanto, a recuperação da ciclagem de N ainda não foi completamente atingida. Entretanto, é possível afirmar que as florestas em processo de restauração estudadas estão seguindo uma trajetória de desenvolvimento caracterizada por uma ciclagem de N cada vez mais parecida com a de uma floresta natural madura, como a da floresta natural madura utilizada como referência. Através dos modelos de restauração utilizados para as florestas da cronosequência estudada, os processos da ciclagem do N são recuperados à medida que a floresta desenvolve-se, com uma clara tendência de mudança na economia de N para economia de P típica de florestas tropicais maduras. / The recuperation of ecosystem processes and functions, among other attributes, is one of the most important indicators in the process of return of an ecosystem to its historic trajectory. Nutrient cycling is a fundamental ecosystem attribute, and relates directly to regulation of functioning and development of ecosystems and includes, in a general model, nutrients entering, being transferred internally between plants and soil, end leaving the system. The comprehension of changes in biogeochemical processes during secondary succession in areas in ecological restoration is still incipient, mainly in tropical forests. This study aims to elucidate nitrogen dynamics along the process of ecological restoration in areas reforested with Atlantic Forest native species. The question driving this study is: Does ecological restoration with high diversity of species and predominance of regional native tree species restore nitrogen original dynamics? This research investigated nutrients cycling functioning, focusing on nitrogen, which is a limiting nutrient in secondary succession, particularly in tropical forests. In order to do so, some indicators of nutrient cycling were assessed in a forest chronosequence formed by a preserved natural forest and restored forests of different ages (21 and 52 years) reforested using high species diversity and predominance of regional native species. The indicators used were: 15N and N content in green foliage, litter and soil; N:P ratio of green foliage and litter; net mineralization and net nitrification rates; content of ammonium, nitrate, inorganic N, and nitrate:ammonium ratio. The forests were sampled between August 2008 and April 2009, in the following seasons: dry, dry-rainy transition, rainy, rainy-dry transition. Clear patterns of change in the N cycling along the studied chronosequence were found, including differences in green foliage 15N values, N content, N:P ratio, inorganic N and net mineralization and nitrification rates, characterized by an increase in the mean values of these variables along the chronosequence. The results found suggest that the forests in restoration process, even the 52 years old one, still do not present a N cycling characteristic of a mature forest and, therefore, the recuperation of the N cycling was not completely reached yet. However, it is possible to state that the forests in restoration process studied here are following a development trajectory characterized by a N cycling progressively more similar to what is common to a mature native forest, as the one used as the reference ecosystem in this study. Through the restoration models used for the forests studied, the N cycle processes are recovered as the forests develop, as they present a clear tendency of changing from N economy to P economy, typical to mature tropical forests.

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Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.