Resumo: O sequestro de carbono nos ambientes terrestres, sendo feito de forma natural pelos vegetais através da fotossíntese, cujo processo permite fixar o carbono nos solos e, em forma de matéria lenhosa nas plantas, vem sendo apontado como uma alternativa mitigadora das mudanças climáticas, segundo acordos internacionais como o Protocolo de Kyoto. A retirada da floresta nativa provoca a diminuição significativa da biomassa microbiana e da fertilidade do solo. A reserva de carbono na matéria orgânica do solo é uma importante estratégia para atenuar a concentração de CO2 na atmosfera. Com o reflorestamento dessas áreas ocorre uma recuperação lenta e contínua da quantidade e qualidade da matéria orgânica. O eucalipto é a essência florestal mais plantada no Brasil e essas plantações florestais com eucalipto poderão cumprir o papel de aumentar as concentrações de carbono orgânico no solo, recuperando estruturas perdidas quando da exportação da madeira através da colheita, bem como, provocando mudanças ambientais associadas. Este trabalho objetivou quantificar a fixação de carbono no compartimento do solo de 0 a 60 cm de uma floresta nativa em comparação com plantios de eucalipto com 3 diferentes idades: 0 a 1 ano (área recém implantada); 3 a 4 anos (metade do ciclo) e 6 a 7 anos (época de corte). Foram escolhidos quatro diferentes sítios de amostragem com uma área amostral de 1 ha cada. Foram coletadas amostras de solo no inverno e no verão a diferentes profundidades para que se pudesse conhecer a quantidade de carbono orgânico fixado ao longo do perfil do solo considerando o fator da sazonalidade. Os resultados indicam que o manejo nas áreas interferiu no acúmulo de carbono no solo dos quatro sítios estudados, mostrando também que o fragmento de Cerrado estoca menos carbono que os plantios de eucalipto. Quanto à sazonalidade, houve diferença significativa... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The carbon sequestration in terrestrial environments, by plants through photosynthesis, allows carbon fixing as a woody matter in plants. This process has been identified as an alternative to mitigate climate change, according to Kyoto Protocol, an international environmental agreement. The removal of the native forest causes a significant decrease of microbial biomass and soil fertility. The storage of carbon in soil organic matter is an important strategy to reduce the concentration of CO2 in the atmosphere. With the reforestation of these areas, occurs a slow and continuous recovery of the quantity and quality of organic matter. The eucalyptus is the most planted species in Brazil for industrial supply. These eucalyptus reforestations may fulfill the role of increasing soil organic carbon concentration, recovering some structures lost by wood harvesting and causing associated environmental changes. This study aimed to quantify the carbon fixation within the soil compartment from 0 to 60 cm depth of a native forest formation in comparison with eucalyptus plantations with 3 different ages: 0 to 1 year (newly planted area); 3 to 4 years (half the harvesting cycle) and 6 to 7 years (harvesting time). Four different sites were chosen for sampling, with a sampling area of 1 ha each. Soil samples were collected in winter and summer time, at different depths, to quantify the organic carbon fixed throughout the soil profile, considering the seasonality factor. The results indicate that management in each area interfered in the accumulation of carbon in the soil in the four sites studied. The savanna fragment stored less carbon than the eucalyptus plantations. Regarding seasonality, a significant difference was found between the accumulation of carbon in winter and summer... (Complete abstract click electronic access below) / Orientador: Iraê Amaral Guerrini / Coorientador: Vera Lex Engel / Banca: Dirceu Maximino Fernandes / Banca: Jacob Siva Souto / Mestre

Solos com horizonte A escurecido, com presença de artefatos humanos como cerâmicas, ossos e/ou conchas, alta saturação por bases, carbono orgânico e carvões são denominados comumente de Terras Pretas de Índio (TPI), de ampla ocorrência na região Amazônica. Tais características tornam estes solos muito favoráveis para o cultivo agrícola, sobretudo pelo elevado conteúdo de matéria orgânica do solo (MOS). No entanto, dentre as questões ainda não desvendadas quanto à gênese destes solos, está a natureza e mecanismos de retenção desta matéria orgânica nas TPI. Nesse sentido, o objetivo deste trabalho foi elucidar a natureza química da MOS em solos com horizonte A antrópico e em solos de referência (sem horizonte A antrópico). Para isso, dois perfis de TPI e um perfil de referência foram selecionados na área do Campo Experimental do Caldeirão no município de Iranduba - AM. Amostras de todos os horizontes foram coletadas e submetidas ao fracionamento físico e químico da matéria orgânica, gerando as frações: i) (FLL); ii) Leve oclusa (FLO); iii) extraível com NaOH (EX) iv) Resíduo (RES). Todas elas foram caracterizadas por meio da pirólise CG/EM. A FLL e EX estão presentes em quantidades maiores nas TPI, devido, respectivamente, ao maior imput de mateiral fresco promovido intencionalmente pelo homem nestas áreas e à maior humificação deste material. Por outro lado a FLO foi maior no perfil de referência. A FLL possui alta expressão da liteira, sendo constituída, sobretudo por materiais vegetais e carvões. A FLO teve alta variabilidade composicional, no entanto de modo geral possui semelhança com a FLL, mas é menos enriquecida em derviados do BC (compostos poliaromáticos) e maior quantidade de material vegetal fresco (ligninas). No entanto, esta fração contribui muito pouco para o carbono total do solo. Entre os diferentes perfis, a principal diferenciação ocorreu na FLL, que possuiu menos levoglucosan e mais poliaromáticos nos perfis antrópicos, o que mostra, portanto, condições mais avançadas de mineralização e enriquecimento relativo em BC. No entanto, no geral há maior abundância de compostos aromáticos nos perfis de TPI, demonstrando maior contribuição de BC. A fração do resíduo mostrou, grande contribuição de compostos alifáticos. No entanto quando compara-se os diferentes perfis, as TPI são enriquecidas com compostos poliaromáticos, reforçando novamente a contribuição do BC. Não foi possível, com os métodos de extração e fracionamento utilizados, afirmar se os produtos derivados do BC nesta fração estão realmente ligados a fração mineral ou estão presentes no RES por serem insolúveis em alcalino. Nesse sentido, conclui-se que há uma grande contribuição do BC para a estabilização (pelo mecanismo da recalcitrância química) da MO nos perfis de TPI nas diferentes frações e, além disso, verificou-se também nestes perfis estágios mais avançados de decomposição, concordando com o fato de que nas TPI há um maior grau de humificação da MO. / The Anthrosols known as Amazon Dark Earths (ADE) are peculiar soils found in Amazonian Forest, presenting dark coloured A horizons that combine the following features: presence of human artefacts, bones and shells; high levels of organic carbon and coal; and a high base saturation index. Such characteristics are an advantage for agriculture practices, even in the current days. However, their genesis mechanisms are still poorly understood, especially the processes related to organic matter fixation. This contribution aims to elucidate the chemical nature of soil organic matter (SOM) in some Anthrosols and reference soils (without Anthropic A horizons), comparing two pedons with the referred characteristics in the county of Iranduba (Amazon State, Brazil). Soil samples were physically and chemically fractioned, into the following groups: i) FLL, ii) light occluded (FLO), iii) NaOH extractable (EX); iv) residual (RES). SOM samples were chemically characterized using the CG/EM pyrolysis technique. The FLL and EX fractions are more common in IDA soil samples due to the high inputs of fresh plant materials intentionally introduced by human groups in the past, and to the high degree of humification. The FLO fraction was higher in the reference soil samples (without Anthropic A horizons). The FLL fraction was more expressive in the litter samples, consisting of plant materials and coal. The FLO fraction presented a high compositional variability but similar to FLL fraction, less enriched in polyaromatic compounds (BC) and fresh plant materials (lignin). Nevertheless, this fraction represents a minor contribution to total organic carbon of soils. Within the different pedons, the main difference was observed in the FLL fraction, less enriched in levoglucosan and polyaromatic compounds in the Anthrosols. It suggests a rapid mineralization of organic matter and high contribution of BC compounds in these soils. In general, the BC compounds are a major control in Anthrosols. The residual fraction shows high levels of aliphatic compounds. However, in the Anthrosols the BC compounds maintain a high level. It was not possible to determine whether the BC bearing compounds are bound to the mineral fraction or belong to RES fraction (low solubility in high pH values). The BC compounds must contribute significantly to SOM stabilization in the different fractions of Anthrosols pedons (chemical recalcitrance mechanism). Moreover, decomposition degree of SOM is higher in the Anthrosols, in agreement to the high degree of humification.

abstract: Rangelands are an extensive land cover type that cover about 40% of earth’s ice-free surface, expanding into many biomes. Moreover, managing rangelands is crucial for long-term sustainability of the vital ecosystem services they provide including carbon (C) storage via soil organic carbon (SOC) and animal agriculture. Arid rangelands are particularly susceptible to dramatic shifts in vegetation cover, physical and chemical soil properties, and erosion due to grazing pressure. Many studies have documented these effects, but studies focusing on grazing impacts on soil properties, namely SOC, are less common. Furthermore, studies testing effects of different levels of grazing intensities on SOC pools and distribution yield mixed results with little alignment. The primary objective of this thesis was to have a better understanding of the role of grazing intensity on arid rangeland soil C storage. I conducted research in long established pastures in Jornada Experimental Range (JER). I established a 1500m transect in three pastures originating at water points and analyzed vegetation cover and SOC on points along these transects to see the effect of grazing on C storage on a grazing gradient. I used the line-point intercept method to measure and categorize vegetation into grass, bare, and shrub. Since soil adjacent to each of these three cover types will likely contain differing SOC content, I then used this vegetation cover data to calculate the contribution of each cover type to SOC. I found shrub cover and total vegetation cover to decrease, while grass and bare cover increased with decreasing proximity to the water source. I found areal (g/m2) and percent (go SOC to be highest in the first 200m of the transects when accounting for the contribution of the three vegetation cover types. I concluded that SOC is being redistributed toward the water source via foraging and defecation and foraging, due to a negative trend of both total vegetation cover and percent SOC (g/g). With the decreasing trends of vegetation cover and SOC further from pasture water sources, my thesis research contributes to the understanding of storage and distribution of SOC stocks in arid rangelands. / Dissertation/Thesis / Masters Thesis Biology 2018

A agricultura pode ser uma aliada importante para a mitigação da concentração de gás carbônico (CO2) na atmosfera. Pela fotossíntese pode-se converter o CO2 da atmosfera em massa vegetal, e, além disso, por meio de um manejo adequado desta massa pode-se reter parte do carbono (C) no solo, caracterizando um \"seqüestro de C\" da atmosfera pelo solo. Pesquisas têm se voltado para entender o papel da produção agrícola, como os sistemas conservacionistas de manejo, ou seja, o plantio direto (PD), e das pastagens de Brachiaria sobre a dinâmica do C no solo. Estudos sobre a dinâmica e a estabilidade da matéria orgânica do solo (MOS) são necessários, já que variáveis como estoques de carbono (EC) e graus de humificação podem ser avaliados, e sendo assim, obter parâmetros fundamentais para a mitigação de CO2 na atmosfera, tema que se insere num dos enfoques das Mudanças Climáticas Globais. Nesse contexto, espectroscopias, como por exemplo, a Ressonância Paramagnética Eletrônica (RPE), a Fluorescência de luz no ultravioleta-visível (UV-vis) e a Fluorescência Induzida por Laser (FIL) podem ser fundamentais na avaliação da estabilidade da MOS. Este trabalho teve como objetivo verificar o comportamento da MOS em áreas com potencial para seqüestro de C, por meio da avaliação dos estoques deste no solo, em diferentes sistemas de manejo e posterior caracterização por Espectroscopia. Além disso, e em função das dificuldades encontradas na seleção da melhor metodologia para a quantificação de C, foi também possível avaliar métodos de determinação de C, comparando-os entre si pelos coeficientes de variação e análise multivariada, e assim propondo uma melhor metodologia. Em área tropical de pastagens de Brachiaria decumbens, no Brasil, os resultados mostraram que a determinação dos EC foram maiores nesses sistemas, comparado com a vegetação nativa de cerradão, após 27 anos de experimento. Os maiores EC obtidos pelas pastagens foram favorecidos pela constante entrada de material vegetal na superfície do solo, também influenciado pela entrada do nitrogênio (N), além do sistema radicular da gramínea, considerando o tratamento de pastagem com adição anual de N e aplicação de 2 t ha-1 de calcário (com reforço de 1 t ha-1 anual), o melhor tratamento em função do acúmulo da MOS. Os resultados mostraram que essas pastagens bem manejadas podem possibilitar um seqüestro de 6,1 a 12,8 Mg CO2 ha-1 ano-1 da atmosfera. Com a avaliação qualitativa da MOS, também foi possível obter resultados promissores na determinação da estabilidade da MOS. A detecção do aumento do conteúdo de C no solo foi acompanhada pela redução do grau de humificação, por meio da FIL. Esta redução na humificação foi devido à entrada de material orgânico mais lábil, ou seja, menos transformado. Na Fluorescência convencional e RPE, com amostras de AH em solução, os maiores graus de humificação foram obtidos para os AH dos tratamentos de pastagem, principalmente os que tiveram adição de calagem. O Ca2+, além de aumentar a atividade microbiana, pode complexar com os AH, associado ao aumento da estabilidade da MO. No sistema de PD de soja com renovação de cana-de-açúcar, os maiores teores de C foram obtidos nas amostras referentes aos sistemas sob PD após 7 anos sob esse manejo, em comparação com áreas sob manejo convencional. O acúmulo de MOS foi devido principalmente à preservação da cobertura vegetal associada com o não revolvimento do solo, rotação de culturas e a não queimada da cana-de-açúcar. Nessa área experimental, foi possível constatar um seqüestro de 0,15 a 5,29 Mg CO2 ha-1 ano-1 da atmosfera. Com relação à estabilidade da MO avaliada por Espectroscopia de FIL, verificou-se que o sistema de PD apresentou menor grau de humificação, devido à maior entrada de material orgânico lábil. Os resultados obtidos em área experimental de PD com grãos, com até 22 anos de duração, estão provavelmente associados com o tipo de solo analisado. Nos Latossolos com alto conteúdo de argila pode haver proteção física da MO, provavelmente impedindo alterações estruturais desse material, mesmo após longo período sem o revolvimento do solo. Outro fato importante é que o estudo de seqüestro de C depende muito da área avaliada, ou seja, delineamento do experimento, histórico do local, duração, condições climáticas, taxas de decomposição do C, produção de massa vegetal e aporte de resíduos. / Agriculture can play an important role in mitigating carbon dioxide (CO2) concentration in the atmosphere. Through photosynthesis, it is possible to convert CO2 from atmosphere to plant biomass, and moreover, through an adequate agricultural system CO3 can be stored in soil, characterizing \"carbon sequestration\". Nowadays, many researches want to understand the role of agriculture production, as no-tillage, and Brachiaria pastures, in carbon dynamics in soil. Studies about organic matter dynamics and stability are necessary, since variables such as carbon stocks and degree of humification can be evaluated, and as a result, to obtain essential parameters to CO2 mitigation to the atmosphere. This topic is inserted in some Global Climate Change interests. In this context, spectroscopic methods, for example, Electron Paramagnetic Resonance (EPR), UV-Vis light fluorescence and Laser Induced Fluorescence (LIF) can be fundamental in the stability of soil organic matter (SOM) evaluation. The present study aims to examine the SOM behavior in areas with carbon sequestration potential, through evaluation of carbon stocks in soils, in different tillage systems followed by characterization by spectroscopy. Therefore, the knowledge of the organic matter (OM) quantity is important in soil management regarding to a sustainable agriculture. However, little consistent information is found to compare and recommend the most adequate method to obtain satisfactory results for each study. Consequently, it was possible to evaluate the OM quantity in Oxisols by different methods and compare them, using coefficient of variation and principal component analysis, to propose the best methodology. In the tropical regions of Brazil, in Brachiaria decumbens pastureland, the results showed that the greatest SOM content occurred under pastureland, against the native dense Cerrado vegetation, after 27 years of experiment. The highest carbon stocks obtained by pasture samples were favored by accumulations of plant biomass on the soil surface, nitrogen input, besides Brachiaria root systems. According to the results obtained, the annual input of adequate amounts of limestone (2 t ha-1 addition and 1 t ha-1 year-1 reinforcement) and N seemed to be the best treatment regarding different pastureland treatments, mainly due to its higher C accumulation. The results also showed that non-degraded pastures can enable an annual sequestration rate ranging from 6.1 to 12.8 Mg CO2 ha-1 year-1. Qualitative evaluation of SOM also obtained satisfactory results on the soil surface. Results showed that higher C amount was followed by lower degree of humification, obtained by LIF. This lower humification was due to labile organic material, or greater fresh input of crop residues. In conventional fluorescence and EPR, with humic acids, the greatest degree of humification was obtained in pastures treatments, especially in treatments with lime input. Ca2+, in addition to increasing the biological activity, can combine with humic acids, increasing OM stability. In the no-tillage system of soya and sugar cane renovation, higher C amounts were obtained in no-tillage samples, after 7 years of experiment. The maintenance of a permanent vegetal cover, without soil disturbing and without sugar cane burning was essential to SOM accumulation against conventional management. In the no-tillage system, in a period of 7 years, it was possible to verify a sequestration rate ranging from 0.15 to 5.29 Mg CO2 ha-1 year-1. In relation to SOM stability by LIF, no-tillage presented lower degree of humification, due to input labile OM. The results obtained under no-tillage cropping system after 22 years are probably associated with the kind of soil analyzed. In Latossols, with high amount of clay, there may be a physical protection of OM, probably preventing structural changes in this material, even after a long period without soil disturbing. Another important factor is that C sequestration studies depend on the evaluated area, such as experiment outline, historical area, time, climate conditions, C decomposition rates, vegetal biomass production and residue input.

Solos com horizonte A escurecido, com presença de artefatos humanos como cerâmicas, ossos e/ou conchas, alta saturação por bases, carbono orgânico e carvões são denominados comumente de Terras Pretas de Índio (TPI), de ampla ocorrência na região Amazônica. Tais características tornam estes solos muito favoráveis para o cultivo agrícola, sobretudo pelo elevado conteúdo de matéria orgânica do solo (MOS). No entanto, dentre as questões ainda não desvendadas quanto à gênese destes solos, está a natureza e mecanismos de retenção desta matéria orgânica nas TPI. Nesse sentido, o objetivo deste trabalho foi elucidar a natureza química da MOS em solos com horizonte A antrópico e em solos de referência (sem horizonte A antrópico). Para isso, dois perfis de TPI e um perfil de referência foram selecionados na área do Campo Experimental do Caldeirão no município de Iranduba - AM. Amostras de todos os horizontes foram coletadas e submetidas ao fracionamento físico e químico da matéria orgânica, gerando as frações: i) (FLL); ii) Leve oclusa (FLO); iii) extraível com NaOH (EX) iv) Resíduo (RES). Todas elas foram caracterizadas por meio da pirólise CG/EM. A FLL e EX estão presentes em quantidades maiores nas TPI, devido, respectivamente, ao maior imput de mateiral fresco promovido intencionalmente pelo homem nestas áreas e à maior humificação deste material. Por outro lado a FLO foi maior no perfil de referência. A FLL possui alta expressão da liteira, sendo constituída, sobretudo por materiais vegetais e carvões. A FLO teve alta variabilidade composicional, no entanto de modo geral possui semelhança com a FLL, mas é menos enriquecida em derviados do BC (compostos poliaromáticos) e maior quantidade de material vegetal fresco (ligninas). No entanto, esta fração contribui muito pouco para o carbono total do solo. Entre os diferentes perfis, a principal diferenciação ocorreu na FLL, que possuiu menos levoglucosan e mais poliaromáticos nos perfis antrópicos, o que mostra, portanto, condições mais avançadas de mineralização e enriquecimento relativo em BC. No entanto, no geral há maior abundância de compostos aromáticos nos perfis de TPI, demonstrando maior contribuição de BC. A fração do resíduo mostrou, grande contribuição de compostos alifáticos. No entanto quando compara-se os diferentes perfis, as TPI são enriquecidas com compostos poliaromáticos, reforçando novamente a contribuição do BC. Não foi possível, com os métodos de extração e fracionamento utilizados, afirmar se os produtos derivados do BC nesta fração estão realmente ligados a fração mineral ou estão presentes no RES por serem insolúveis em alcalino. Nesse sentido, conclui-se que há uma grande contribuição do BC para a estabilização (pelo mecanismo da recalcitrância química) da MO nos perfis de TPI nas diferentes frações e, além disso, verificou-se também nestes perfis estágios mais avançados de decomposição, concordando com o fato de que nas TPI há um maior grau de humificação da MO. / The Anthrosols known as Amazon Dark Earths (ADE) are peculiar soils found in Amazonian Forest, presenting dark coloured A horizons that combine the following features: presence of human artefacts, bones and shells; high levels of organic carbon and coal; and a high base saturation index. Such characteristics are an advantage for agriculture practices, even in the current days. However, their genesis mechanisms are still poorly understood, especially the processes related to organic matter fixation. This contribution aims to elucidate the chemical nature of soil organic matter (SOM) in some Anthrosols and reference soils (without Anthropic A horizons), comparing two pedons with the referred characteristics in the county of Iranduba (Amazon State, Brazil). Soil samples were physically and chemically fractioned, into the following groups: i) FLL, ii) light occluded (FLO), iii) NaOH extractable (EX); iv) residual (RES). SOM samples were chemically characterized using the CG/EM pyrolysis technique. The FLL and EX fractions are more common in IDA soil samples due to the high inputs of fresh plant materials intentionally introduced by human groups in the past, and to the high degree of humification. The FLO fraction was higher in the reference soil samples (without Anthropic A horizons). The FLL fraction was more expressive in the litter samples, consisting of plant materials and coal. The FLO fraction presented a high compositional variability but similar to FLL fraction, less enriched in polyaromatic compounds (BC) and fresh plant materials (lignin). Nevertheless, this fraction represents a minor contribution to total organic carbon of soils. Within the different pedons, the main difference was observed in the FLL fraction, less enriched in levoglucosan and polyaromatic compounds in the Anthrosols. It suggests a rapid mineralization of organic matter and high contribution of BC compounds in these soils. In general, the BC compounds are a major control in Anthrosols. The residual fraction shows high levels of aliphatic compounds. However, in the Anthrosols the BC compounds maintain a high level. It was not possible to determine whether the BC bearing compounds are bound to the mineral fraction or belong to RES fraction (low solubility in high pH values). The BC compounds must contribute significantly to SOM stabilization in the different fractions of Anthrosols pedons (chemical recalcitrance mechanism). Moreover, decomposition degree of SOM is higher in the Anthrosols, in agreement to the high degree of humification.

Stable carbon isotope analyses of the humin fraction of the soil organic matter were conducted on more than 160 soil profiles from Tikal, Guatemala. The profiles were collected from near areas associated with the earthworks of Tikal; an ancient ditch and parapet construction hypothesized to have formed ancient boundaries of the polity. In addition to the isotope analyses, the physical and chemical characteristics of the horizons were determined. Maize, a C4 plant, formed an integral part of the ancient Maya diet and is the only known C4 plant cultivated by the Maya. Prior to and subsequent to the ancient Maya occupation of Tikal, the landscape was dominated by C3 forest vegetation. Over the centuries C4 plant biomass including rhizodeposition decomposed to form soil organic matter that contains a distinct C4 signature reflecting the vegetation history of the area. Forested areas anciently cleared for agriculture were identified through interpretation of significant isotopic shifts that signaled past vegetation changes. Buried horizons were encountered in the upland depressions and bajo wetlands. The aggraded soil deposits were likely the result of increased human activity related to settlement and agriculture. The buried horizons and the overlying sediments exhibited stable carbon isotope shifts associated with forest clearance and maize agriculture. Geospatial analysis of the stable carbon isotope ratios indicated that ancient Maya agriculture was focused on deeper footslope and toeslope soils in both bajos and upland depressions. Some evidence of infield agriculture or food processing was also encountered in connection with ancient settlement at upland locations. The soil data provide insight into ancient land use and sustainability that could potentially contribute to subsistence and population reconstruction models.

Carbon isotope studies are commonly used to provide a proxy for past vegetation communities and for evaluating environmental change. Original studies suggested carbon isotope ratios of soil organic matter (SOM) faithfully preserved the isotopic composition of standing vegetation with little or no modification in the pedogenic and shallow burial environment. Recent studies of modern soils and laboratory experiments suggest that this may not necessarily be the case and that degradation of SOM in the burial environment may alter the original C-isotope ratio of bulk SOM. A first step in addressing the issue is to begin to understand the transformations of SOM in the burial environment; of particular interest in this study are transformations involving microbial residues. Sedimentary sequences with stacked buried soils afford the opportunity to study the changes that may occur through time and are especially useful if numerical ages and other environmental proxies are present. The objective of this study is to thoroughly investigate the composition and quantity of organic matter that has been preserved in the surface and buried soils at the Claussen site, using Fourier Transform Infrared Spectroscopy (FTIR), which provides an estimate for the abundance of organic matter components preserved in each paleosol's SOM. We can trace the fate of bioavailable OM and determine the magnitude of preferential decay of SOM with time by first comparing the composition of bulk SOM to the composition of physically protected carbon, located in soil microaggregates (Christensen, 1992) of the stacked buried soils. The results of this project suggest differences in the composition of paleosol and surface soil SOM that could impact paleovegetation interpretations derived from δ13C values.

The primary objective of this research was to develop a landscape-oriented, process-based approach that can enhance understanding and prediction of SOC fluxes in IMLs by incorporating the key mechanisms impacting soil carbon dynamics when moving from the soilscape to the landscape. The mechanisms that are considered to be the focus of this study are redistribution of SOC due to erosion and deposition without neglecting the importance of litter incorporation into the soil column, decomposition due to microbial activity, and physical and chemical stabilization of carbon. To accomplish this objective, field experiments were performed to examine how selective entrainment of different soil size fractions, quantified through the enrichment ratio (ER), varies with management and hillslope position. Differential modes in soil mobilization between rill and interrill areas were either elevated or dampened depending on the prevalent management practice, the gradient of the site and landscape position. Sites where sediment and runoff fluxes were highest were found to have lower ER values (around unity) due to the mobilization of all size classes making static and dynamic samples almost identical. The size fractions analyzed in these experiments were found to have varying levels of carbon associated with them, especially the larger aggregates, which encapsulate organic material. Neglecting them in transport estimates could lead to large errors in predicted fluxes of SOC. For this reason, a careful attention was placed on identifying how aggregate stability varies with respect to management and hillslope position, through controlled experiments looking size distributions to reflect tillage disturbance and aggregate stability to assess resistance to rainsplash. Lastly, a landscape-oriented modeling framework was developed that captures not only the SOC spatial heterogeneity in IMLs but also determines the impacts that redistribution has on this heterogeneity and ultimately on SOC dynamics. The integrative modeling framework considers the collective effects of both rainsplash/rainfall- and tillage-induced erosion on SOC redistribution in IMLs through an ER-module developed and woven within this framework to connect an upland erosion model with a soil biogeochemical model. It provides not only size fraction updates to the active layer and ER values, but also explicitly considers the effects of splash-driven interrill erosion on those ER estimates. The model was applied to twentieth-century changes in SOC across a representative agricultural hillslope in the study watershed and compared to recent SOC data. The chronosequence in SOC storage within the erosional zone revealed that soils were continually depleted of the rich organic matter long after the 1930’s “Dust bowl” due to enhanced erosion that accompanied agricultural practices. However, conservation tillage and enhanced crop production that began in the late 1980’s reversed the downward trend in SOC losses, causing nearly 26% of the lost SOC to be regained. Results from this study can be used to aid policy and decision makers in developing a food-system that accounts for the co-evolution of human and natural activity, to develop sustainable agro-ecosystems through the use of data supported recommended best management practices.

<p>This thesis presents results from several studies that have focused on the carbon and nutrient dynamics in soils at the forest – tundra ecotone in Fennoscandia. The main objectives of the study were: (i) to investigate the links between the physical environment, above-ground vegetation communities, soil carbon storage, nutrient status and the chemical composition of the soil organic matter (SOM), and (ii) to quantify trace gas fluxes (methane and carbon dioxide) between mesic soils and the atmosphere. Four main field areas spanning an 8 degree latitudinal gradient were established at the ecotone in 1998 and studied for four years. In addition to the natural gradients we also established a warming treatment. Decomposition rates (i.e. carbon dioxide efflux and litter decomposition) were higher at our forest sites. This was linked principally to the more favourable physical environment at the forest sites, rather than to SOM quality, despite some indications of higher SOM quality at forest sites based upon conventional chemical analysis and ¹³C NMR techniques. Tundra soils stored large amounts of potentially labile carbon that could readily be accessed by microorganisms when transferred to a forest environment. The interrelation between increased soil temperature and reduced soil moisture content is likely to moderate the response of decomposition rates to increased temperatures. Generally, these mesic soils showed net methane uptake from the atmosphere, which was enhanced by the warming treatment. No differences between forest or tundra soils could be detected.</p><p>The major conclusions presented here are that (1) soil carbon storage is likely to be reduced if mountain birch forest replaces tundra heath and (2), methane uptake in mesic soils in the Fennoscandian mountains represents a negative feedback to further environmental change in a warmer climate.</p>

This thesis presents results from several studies that have focused on the carbon and nutrient dynamics in soils at the forest – tundra ecotone in Fennoscandia. The main objectives of the study were: (i) to investigate the links between the physical environment, above-ground vegetation communities, soil carbon storage, nutrient status and the chemical composition of the soil organic matter (SOM), and (ii) to quantify trace gas fluxes (methane and carbon dioxide) between mesic soils and the atmosphere. Four main field areas spanning an 8 degree latitudinal gradient were established at the ecotone in 1998 and studied for four years. In addition to the natural gradients we also established a warming treatment. Decomposition rates (i.e. carbon dioxide efflux and litter decomposition) were higher at our forest sites. This was linked principally to the more favourable physical environment at the forest sites, rather than to SOM quality, despite some indications of higher SOM quality at forest sites based upon conventional chemical analysis and 13C NMR techniques. Tundra soils stored large amounts of potentially labile carbon that could readily be accessed by microorganisms when transferred to a forest environment. The interrelation between increased soil temperature and reduced soil moisture content is likely to moderate the response of decomposition rates to increased temperatures. Generally, these mesic soils showed net methane uptake from the atmosphere, which was enhanced by the warming treatment. No differences between forest or tundra soils could be detected. The major conclusions presented here are that (1) soil carbon storage is likely to be reduced if mountain birch forest replaces tundra heath and (2), methane uptake in mesic soils in the Fennoscandian mountains represents a negative feedback to further environmental change in a warmer climate.