No description available.

To date, there has been little research into the role of microbial community structure in the functioning of the soil ecosystem and on the links between microbial biomass size, microbial activity and key soil processes that drive nutrient availability. The maintenance of structural and functional diversity of the soil microbial community is essential to ensure the sustainability of agricultural production systems. Soils of the same type with similar fertility that had been under long-term organic and conventional crop management in Canterbury, New Zealand, were selected to investigate relationships between microbial community composition, function and potential environmental impacts. The effects of different fertilisation strategies on soil biology and nitrogen (N) dynamics were investigated under field (farm site comparison), semi-controlled (lysimeter study) and controlled (incubation experiments) conditions by determining soil microbial biomass carbon (C) and N, enzyme activities (dehydrogenase, arginine deaminase, fluorescein diacetate hydrolysis), microbial community structure (denaturing gradient gel electrophoresis following PCR amplification of 16S and 18S rDNA fragments using selected primer sets) and N dynamics (mineralisation and leaching). The farm site comparison revealed distinct differences between the soils in microbial community structure, microbial biomass C (conventional>organic) and arginine deaminase activity (organic>conventional). In the lysimeter study, the soils were subjected to the same crop rotation (barley (Hordeum vulgare L.), maize (Zea mais L.), rape (Brassica napus L. ssp. oleifera (Moench)) plus a lupin green manure (Lupinus angustifolius L.) and two fertiliser regimes (following common organic and conventional practice). Soil biological properties, microbial community structure and mineral N leaching losses were determined over 2½ years. Differences in mineral leaching losses were not significant between treatments (total organic management: 24.2 kg N ha⁻¹; conventional management: 28.6 kg N ha⁻¹). Crop rotation and plant type had a larger influence on the microbial biomass, activity and community structure than fertilisation. Initial differences between soils decreased over time for most biological soil properties, while they persisted for the enzyme activities (e.g. dehydrogenase activity: 4.0 and 2.9 µg g⁻¹ h⁻¹ for organic and conventional management history, respectively). A lack of consistent positive links between enzyme activities and microbial biomass size indicated that similarly sized and structured microbial communities can express varying rates of activity. In two successive incubation experiments, the soils were amended with different rates of a lupin green manure (4 or 8t dry matter ha⁻¹), and different forms of N at 100 kg ha⁻¹ (urea and lupin) and incubated for 3 months. Samples were taken periodically, and in addition to soil biological properties and community structure, gross N mineralisation was determined. The form of N had a strong effect on microbial soil properties. Organic amendment resulted in a 2 to 5-fold increase in microbial biomass and enzyme activities, while microbial community structure was influenced by the addition or lack of C or N substrate. Correlation analyses suggested treatment-related differences in nutrient availability, microbial structural diversity (species richness or evenness) and physiological properties of the microbial community. The findings of this thesis showed that using green manures and crop rotations improved soil biology in both production systems, that no relationships existed between microbial structure, enzyme activities and N mineralisation, and that enzyme activities and microbial community structure are more closely associated with inherent soil and environmental factors, which makes them less useful as early indicators of changes in soil quality.

Les Taillis à Très Courte Rotation sont une culture destinée à produire des plaquettes de bois énergie. L'objectif de la thèse était d'étudier l'impact des TTCR sur le fonctionnement des sols et de proposer des indicateurs de qualité. Cinq prélèvements ont été effectués chaque printemps et automne entre 2010 et 2012 sur les sols de quatre couples de TTCR et bandes enherbées, d'une forêt alluviale et d'un agrosystème, localisés dans la vallée de l'Aisne. Les paramètres suivants ont été mesurés: matières organiques, carbone total, capacité d'échange cationique et éléments échangeables, phosphore disponible, minéralisation du carbone et de l'azote, biomasse, abondance et diversité des communautés lombriciennes, abondance relative et diversité des communautés fongiques et bactériennes, activités enzymatiques, caractérisations physiques et chimiques des matières organiques. 6 années après la mise en place des TTCR, les densités fongiques et lombriciennes, la respiration basale, l'activité laccase étaient plus élevées dans les TTCR par rapport à l'agrosystème. Ces modifications peuvent être reliées aux changements quantitatifs et qualitatifs des matières organiques (augmentation du C/N, diminution de l'indice hydrogène). L'azote et le phosphore semblent être limitant mais les retours importants et le turn over rapide de la MO viennent tamponner les fortes exportations. Ces mesures ont conduit à la définition d'indicateurs et aboutissent à la proposition de trois indices : fertilité, activité biologique, abondance et diversité des communautés biologiques. L'utilisation des courbes de réponses principales confirme l'effet positif des TTCR sur la qualité du sol, observée avec le calcul d'indices synthétiques / Short Rotation Coppices (SRC) are a crop system intended to produce energy wood chips. This thesis aimed at assessing the impact of SRC on soil functioning and proposing quality indicators. Five samplings were performed in spring and autumn between 2010 and 2012 on plots including four couples of SRC and grassland, an alluvial forest and an agrosystem, in the Aisne valley. The following parameters were monitored: organic matter, total carbon, cation capacity exchange, available phosphorus, carbon and nitrogen basal respiration, earthworm biomass, density and diversity, fungal and bacterial density and diversity, enzymatic activity, physical and chemical organic matter characterisations. 6 years after conversion to SRC, earthworm and fungal density, basal respiration and laccase activity were higher in SRC soil compared to conventional agrosystem. These changes can be linked to qualitative and quantitative organic matter evolutions (increase of the C/N ratio and decrease of hydrogen index). Nitrogen and phosphorus seemed to be limiting factors for SRC crop yields. However, soil nutrient return and the good turnover of organic matter can buffer strong exportations. The measured parameters led to indicator definition and proposition of three indices: fertility, biological activity, density and diversity of biological communities. Principal response curves confirmed the positive effect of SRC on soil quality as observed with synthetic indices calculation

O estudo de indicadores biológicos da qualidade do solo em áreas com araucária é muito importante para entender os processos ecológicos que ocorrem nestes sistemas, já que a fauna edáfica atua na decomposição e mineralização da matéria orgânica e, também, nas propriedades e processos físicos, químicos e biológicos do solo. O objetivo deste estudo foi verificar a possibilidade de utilizar alguns grupos da fauna edáfica e das variáveis ambientais como indicadores da qualidade do solo em áreas com araucária natural e reflorestada, impactadas ou não pela queima acidental, por meio de técnicas de análise multivariada. As áreas estudadas incluem: 1. floresta nativa com araucária (NF); 2. reflorestamento de araucária (R); 3. reflorestamento de araucária submetido a incêndio acidental (RF); e 4. pastagem natural com araucárias nativas e ocorrência de incêndio (NPF). Em cada área, amostras de solo para avaliação da comunidade da fauna edáfica e das variáveis ambientais foram coletadas em 0,3 ha, perto de dez árvores de araucária selecionadas ao acaso, em três épocas contrastantes, usando diferentes métodos de coleta (monólitos e armadilhas). As análises de componentes principais (ACP), canônica discriminante (ACD) e de correlação canônica (ACC) foram aplicadas às variáveis ambientais [carbono da biomassa microbiana (CBM), respiração basal (C-CO2) e quociente metabólico (qCO2), estoques de serapilheira, umidade do solo, pH (CaCl2), matéria orgânica (MO) e teores de P, K, Ca, Mg, H+Al] e atributos da fauna edáfica. Foram encontradas cinco espécies de minhocas (2 famílias), 20 famílias de aranhas e oito famílias de colêmbolos nestas áreas. A diversidade da fauna, CBM, C-CO2, estoques de serapilheira e MO foram sempre superiores na área NF e inferiores na NPF. A comunidade de fauna do solo e as variáveis ambientais apresentaram potencial para serem usadas como indicadores da qualidade do solo. Houve alta correlação canônica entre as variáveis ambientais e a fauna edáfica. Os grupos Collembola, Diplopoda, Chilopoda, Isoptera, Araneae, Oligochaeta, biomassa da macrofauna, índice de diversidade de Shannon (H), estoques de serapilheira, P, CBM e C-CO2 foram responsáveis por praticamente toda a separação entre as áreas, sendo bons indicadores das modificações que ocorrem nos ecossistemas com araucária. A ACD demonstrou que a contribuição de cada atributo para separar as áreas sofreu efeito de sazonalidade. As técnicas de análise multivariada (especialmente ACC e ACD) são importantes ferramentas no estudo de indicadores biológicos de qualidade do solo. / The study of biological soil quality indicators in areas with Araucaria is very important to understand ecological processes in these systems, since groups of the soil fauna are major factors in the decomposition and mineralization of organic matter, as well as modifiers of soil physical, chemical and biological properties and processes. The objective of this study was to evaluate the use of soil fauna and environmental variables as quality indicators in natural and reforested Araucaria areas, impacted or not by fire, by means of multivariate analysis techniques. Four study areas included: native forest with Araucaria (NF); Araucaria reforestation (R); Araucaria reforestation submitted to an accidental fire (RF); and native grass pasture with native Araucaria , submitted to an intense accidental fire (NPF). Soil samples containing the soil fauna community and environmental variables were taken in a 0.3 ha area in each area, close to ten Araucaria trees selected at random, in three contrasting seasons, using different collection methods (soil monolith, Pitfall traps). Canonical discriminant analysis (CDA) and canonical correlation analysis (CCA) were applied to the environmental variables [(carbon of the microbial biomass (CMB), basal respiration (C-CO2) and metabolic quotient (qCO2), litter stocks, soil humidity, pH (CaCl2), organic matter (OM), P, K, Ca, Mg, H+Al] and soil fauna attributes. Five earthworm species (two families), 20 spider families and eight springtail families were found in these areas. Soil fauna diversity, CMB, C-CO2, litter stocks and OM were always higher for the NF area and lower for the NPF. The canonical correlation between environmental variables and soil fauna was highly significant. Soil fauna and environmental variables have a great potential as indicators of soil quality. The groups Collembola, Diplopoda, Chilopoda, Isoptera, Araneae, Oligochaeta, biomass of macrofauna, Shannon's diversity index (H), litter stocks, P, CMB and C-CO2 were mostly responsible for the separation between areas, and are therefore good indicators of the changes that occur in the Araucaria ecosystems. CDA identified that the contribution of each attribute for the separation of the areas varied according to the seasonal variation. Multivariate analyses (such as CDA and CCA) are important auxiliary tools in the study of soil quality indicators.

O estudo de indicadores biológicos da qualidade do solo em áreas com araucária é muito importante para entender os processos ecológicos que ocorrem nestes sistemas, já que a fauna edáfica atua na decomposição e mineralização da matéria orgânica e, também, nas propriedades e processos físicos, químicos e biológicos do solo. O objetivo deste estudo foi verificar a possibilidade de utilizar alguns grupos da fauna edáfica e das variáveis ambientais como indicadores da qualidade do solo em áreas com araucária natural e reflorestada, impactadas ou não pela queima acidental, por meio de técnicas de análise multivariada. As áreas estudadas incluem: 1. floresta nativa com araucária (NF); 2. reflorestamento de araucária (R); 3. reflorestamento de araucária submetido a incêndio acidental (RF); e 4. pastagem natural com araucárias nativas e ocorrência de incêndio (NPF). Em cada área, amostras de solo para avaliação da comunidade da fauna edáfica e das variáveis ambientais foram coletadas em 0,3 ha, perto de dez árvores de araucária selecionadas ao acaso, em três épocas contrastantes, usando diferentes métodos de coleta (monólitos e armadilhas). As análises de componentes principais (ACP), canônica discriminante (ACD) e de correlação canônica (ACC) foram aplicadas às variáveis ambientais [carbono da biomassa microbiana (CBM), respiração basal (C-CO2) e quociente metabólico (qCO2), estoques de serapilheira, umidade do solo, pH (CaCl2), matéria orgânica (MO) e teores de P, K, Ca, Mg, H+Al] e atributos da fauna edáfica. Foram encontradas cinco espécies de minhocas (2 famílias), 20 famílias de aranhas e oito famílias de colêmbolos nestas áreas. A diversidade da fauna, CBM, C-CO2, estoques de serapilheira e MO foram sempre superiores na área NF e inferiores na NPF. A comunidade de fauna do solo e as variáveis ambientais apresentaram potencial para serem usadas como indicadores da qualidade do solo. Houve alta correlação canônica entre as variáveis ambientais e a fauna edáfica. Os grupos Collembola, Diplopoda, Chilopoda, Isoptera, Araneae, Oligochaeta, biomassa da macrofauna, índice de diversidade de Shannon (H), estoques de serapilheira, P, CBM e C-CO2 foram responsáveis por praticamente toda a separação entre as áreas, sendo bons indicadores das modificações que ocorrem nos ecossistemas com araucária. A ACD demonstrou que a contribuição de cada atributo para separar as áreas sofreu efeito de sazonalidade. As técnicas de análise multivariada (especialmente ACC e ACD) são importantes ferramentas no estudo de indicadores biológicos de qualidade do solo. / The study of biological soil quality indicators in areas with Araucaria is very important to understand ecological processes in these systems, since groups of the soil fauna are major factors in the decomposition and mineralization of organic matter, as well as modifiers of soil physical, chemical and biological properties and processes. The objective of this study was to evaluate the use of soil fauna and environmental variables as quality indicators in natural and reforested Araucaria areas, impacted or not by fire, by means of multivariate analysis techniques. Four study areas included: native forest with Araucaria (NF); Araucaria reforestation (R); Araucaria reforestation submitted to an accidental fire (RF); and native grass pasture with native Araucaria , submitted to an intense accidental fire (NPF). Soil samples containing the soil fauna community and environmental variables were taken in a 0.3 ha area in each area, close to ten Araucaria trees selected at random, in three contrasting seasons, using different collection methods (soil monolith, Pitfall traps). Canonical discriminant analysis (CDA) and canonical correlation analysis (CCA) were applied to the environmental variables [(carbon of the microbial biomass (CMB), basal respiration (C-CO2) and metabolic quotient (qCO2), litter stocks, soil humidity, pH (CaCl2), organic matter (OM), P, K, Ca, Mg, H+Al] and soil fauna attributes. Five earthworm species (two families), 20 spider families and eight springtail families were found in these areas. Soil fauna diversity, CMB, C-CO2, litter stocks and OM were always higher for the NF area and lower for the NPF. The canonical correlation between environmental variables and soil fauna was highly significant. Soil fauna and environmental variables have a great potential as indicators of soil quality. The groups Collembola, Diplopoda, Chilopoda, Isoptera, Araneae, Oligochaeta, biomass of macrofauna, Shannon's diversity index (H), litter stocks, P, CMB and C-CO2 were mostly responsible for the separation between areas, and are therefore good indicators of the changes that occur in the Araucaria ecosystems. CDA identified that the contribution of each attribute for the separation of the areas varied according to the seasonal variation. Multivariate analyses (such as CDA and CCA) are important auxiliary tools in the study of soil quality indicators.

Made available in DSpace on 2017-07-10T17:37:33Z (GMT). No. of bitstreams: 1 Luciana_Cleci_de_Oliveira.pdf: 753219 bytes, checksum: cc1a5575b73ca9b97e749c6fa03d3cd3 (MD5) Previous issue date: 2009-06-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Due the lack of informatios about fertilization on lettuce (Lactuca sativa L.) in organic growth, this work aimed to study the effect of organic fertilizers on chemical and biological character of soil and on lettuce productivity. The green manure velvet bean (Mucuna aterrima) received two types of management: incorporation into the soil or not incorporation. These both areas received the solid organic fertilizer bovine manure, commercial organic fertilizer and organic compound and a control treatment without fertilization. The samples were obtained at the time of management of velvet bean, and at 15, 55 and 105 days after this process, representing the moments of the distribution of fertilizes, plant and harvest of lettuce, respectively. Were evaluated chemical and biological characteristics of soil, and agronomic characteristics of the lettuce cultivar Vanda. The results showed that the commercial organic fertilizer followed by the organic compound, provided that highest amorents of organic matter, P, K, Ca, Mg, CTC, pH and V, and the two types of management of velvet bean, incorporated or not has similar results. For microbial biomass, better results were fownd with velvet bean not incorporated into soil plus treatment with organic compound. The population of bacteria was increased in the area where velvet bean was incorporated, except for the treatment with organic compound. For fungi, not incorporated velvet bean associated with commercial organic fertilizer provided the higher rate of population. The incorporation of velvet bean associated with organic compound increased the population of mycorrhizal fungi. The bovine manure associated with the incorporation of velvet bean and treatment with organic compound without incorporation of velvet bean increased the population of saprophytic nematodes. The area of aerial part, number of leaves and total fresh and dry weights of aerial part of lettuce, higher values were observed without the incorporation of velvet bean associated with the use of commercial organic fertilizer or bovine manure treatmentes / Em função da carência de informações técnicas sobre adubação da cultura da alface (Lactuca sativa L.), em sistema de cultivo orgânico, este trabalho teve o objetivo de estudar práticas mais convenientes de adubação que auxiliem na manutenção da fertilidade do solo e produtividade da cultura. O delineamento experimental foi o de blocos ao acaso em parcelas subdivididas onde o adubo verde mucuna preta (Mucuna aterrima) recebeu dois tipos de manejo: incorporação ao solo seguida do levantamento de canteiros, e não incorporação. As subparcelas receberam os adubos orgânicos sólidos: esterco bovino, adubo orgânico comercial e composto além da testemunha sem adubação, com cinco repetiçiões, sendo utilizada a alface cultivar Vanda. As épocas de avaliação ocorreram no momento do manejo da mucuna, e aos 15, 55 e 105 dias após esse manejo, representando momentos da distribuição dos adubos, plantio e colheita da alface, respectivamente. Foram avaliadas características químicas e biológicas do solo, e características fitométricas da planta. Pelos resultados observou-se que o adubo orgânico comercial seguido do composto, foram os que proporcionaram índices superiores de matéria orgânica, P, K, Ca, Mg, CTC, V e pH, e o manejo diferenciado do adubo verde, com ou sem incorporação possibilitou resultados semelhantes. Para a biomassa microbiana, resultados superiores foram observados com a mucuna sem incorporação e o tratamento com composto. A população de bactérias foi aumentada para o manejo da mucuna com incorporação, exceto para o tratamento composto. Para fungos, o manejo sem incorporação associado ao adubo orgânico comercial proporcionou maiores índices populacionais. O manejo com incorporação associado ao composto se mostraram favoráveis para aumento da população de fungos micorrízicos. O esterco bovino associado a incorporação da mucuna e o tratamento com composto sem incorporação da mucuna aumentaram a população de nematóides saprófitas. Para a área de projeção de saia, número de folhas e massa fresca e seca totais da parte aérea, foram observados valores superiores sem a incorporação da mucuna preta e para os tratamentos adubo orgânico comercial e esterco bovino

Recent declines in returns from primary forest products in New Zealand and projected increases in world food prices have led to the land-use conversion from plantation forest to pastoral farming in many lowland areas. After decades of forest cover the soils are in many cases less than adequate for pastoral farming, as they are acidic, with toxic levels of exchangeable aluminum, and contain low levels of available nitrogen (N), very high carbon (C):N ratio, and are devoid of earthworms and structural integrity. Overcoming the major site limitations of low soil pH and available N was a major priority and a field experiment was established in April 2005 to determine the impact of various rates of lime and N in relation to pasture establishment and production. Concerns about the short and long-term effects of these inputs on biological soil quality gave rise to the present study. The effects of land-use change and establishment inputs were assessed by comparison of selected treatment plots with two adjacent reference sites (long-term pasture and a 60–year Pinus radiata forest) on the same soil type. The effects of lime and N on soil biological quality were investigated under field and controlled environment conditions by determination of: microbial community structure (phospholipid fatty acids - PLFA), microbial biomass (total PLFA), and microbial activity (dehydrogenase activity). Soil physical (percentage water-stable aggregates) and chemical (pH, and total C and N) properties were also determined. Similarly, the effects of earthworm addition on soil biological properties were explored in a short-term glasshouse pot experiment. The role of earthworms as indicators of soil biological quality in the field was assumed by nematodes and these were assessed in field trial plots and the reference sites mentioned above. Land-use change and applications of lime and N contributed to changing the microbial community structure determined by principal component analysis of transformed PLFA data. However, the effect of lime was more pronounced in the field, while N contributed most to changing microbial community structure in the glasshouse. Mean microbial activity in the field increased from 4 µg dwt/hr without lime to 16 and 21 µg dwt/hr where lime was applied at 5 and 10 tons/hectare (t/ha), respectively. Mean microbial activity in the field was markedly higher (7-fold) than in the glasshouse at similar rates of lime. Lime application also increased soil moisture retention in the field, mean gravimetric soil moisture increased from 0.33 in control plots to 0.38 and 0.39 in plots treated with 5 and 10 t/ha lime, respectively. Lime application was associated with greater soil aggregate stability. Soils from test plots treated with 5 and 10 tons/ha lime had 45-50% water-stable aggregates compared to 34% in treatments without lime. After 16 weeks in pots, earthworm treatments increased mean plant dry matter (DM)/pot by at least 19% above the control. The increase was attributed primarily to greater N mineralization in the presence of earthworms. For the duration of the trial the earthworm species tested (Apporectodea caliginosa and Lumbricus rubellus, individually or combined) did not affect any of the measured soil microbial properties. However, the survival rate of A. caliginosa was 83% compared to 25% for L. rubellus. The control not receiving any lime or N and plots treated with 10t/ha lime and 200 kgN/ha had similar nematodes species composition, comprising 40% each of bacterial and fungal feeding nematodes. They differed markedly from the reference sites as the forest soil was dominated by plant associated species (38%) and the long-term pasture had 44% plant parasitic nematodes. Accordingly, the soil food web condition inferred from nematode faunal analysis characterized all test plots as basal, stressed and depleted, while the forest soil was categorized as highly structured and fungal dominated. The findings of this thesis demonstrated that land-use change from forest to pasture can have significant impacts on soil biological properties, earthworms can contribute to pasture productivity even in the short term, and nematode faunal analysis is a robust and reliable indicator of soil biological quality.

Recent declines in returns from primary forest products in New Zealand and projected increases in world food prices have led to the land-use conversion from plantation forest to pastoral farming in many lowland areas. After decades of forest cover the soils are in many cases less than adequate for pastoral farming, as they are acidic, with toxic levels of exchangeable aluminum, and contain low levels of available nitrogen (N), very high carbon (C):N ratio, and are devoid of earthworms and structural integrity. Overcoming the major site limitations of low soil pH and available N was a major priority and a field experiment was established in April 2005 to determine the impact of various rates of lime and N in relation to pasture establishment and production. Concerns about the short and long-term effects of these inputs on biological soil quality gave rise to the present study. The effects of land-use change and establishment inputs were assessed by comparison of selected treatment plots with two adjacent reference sites (long-term pasture and a 60–year Pinus radiata forest) on the same soil type. The effects of lime and N on soil biological quality were investigated under field and controlled environment conditions by determination of: microbial community structure (phospholipid fatty acids - PLFA), microbial biomass (total PLFA), and microbial activity (dehydrogenase activity). Soil physical (percentage water-stable aggregates) and chemical (pH, and total C and N) properties were also determined. Similarly, the effects of earthworm addition on soil biological properties were explored in a short-term glasshouse pot experiment. The role of earthworms as indicators of soil biological quality in the field was assumed by nematodes and these were assessed in field trial plots and the reference sites mentioned above. Land-use change and applications of lime and N contributed to changing the microbial community structure determined by principal component analysis of transformed PLFA data. However, the effect of lime was more pronounced in the field, while N contributed most to changing microbial community structure in the glasshouse. Mean microbial activity in the field increased from 4 µg dwt/hr without lime to 16 and 21 µg dwt/hr where lime was applied at 5 and 10 tons/hectare (t/ha), respectively. Mean microbial activity in the field was markedly higher (7-fold) than in the glasshouse at similar rates of lime. Lime application also increased soil moisture retention in the field, mean gravimetric soil moisture increased from 0.33 in control plots to 0.38 and 0.39 in plots treated with 5 and 10 t/ha lime, respectively. Lime application was associated with greater soil aggregate stability. Soils from test plots treated with 5 and 10 tons/ha lime had 45-50% water-stable aggregates compared to 34% in treatments without lime. After 16 weeks in pots, earthworm treatments increased mean plant dry matter (DM)/pot by at least 19% above the control. The increase was attributed primarily to greater N mineralization in the presence of earthworms. For the duration of the trial the earthworm species tested (Apporectodea caliginosa and Lumbricus rubellus, individually or combined) did not affect any of the measured soil microbial properties. However, the survival rate of A. caliginosa was 83% compared to 25% for L. rubellus. The control not receiving any lime or N and plots treated with 10t/ha lime and 200 kgN/ha had similar nematodes species composition, comprising 40% each of bacterial and fungal feeding nematodes. They differed markedly from the reference sites as the forest soil was dominated by plant associated species (38%) and the long-term pasture had 44% plant parasitic nematodes. Accordingly, the soil food web condition inferred from nematode faunal analysis characterized all test plots as basal, stressed and depleted, while the forest soil was categorized as highly structured and fungal dominated. The findings of this thesis demonstrated that land-use change from forest to pasture can have significant impacts on soil biological properties, earthworms can contribute to pasture productivity even in the short term, and nematode faunal analysis is a robust and reliable indicator of soil biological quality.

No description available.

<p>Methane (CH₄) is the second most powerful greenhouse gas (GHG) behind carbon dioxide (CO₂), and is able to trap a large amount of long-wave radiation, leading to surface warming. Carbon monoxide (CO) plays an important role in controlling the oxidizing capacity of the atmosphere by reacting with OH radicals that affect atmospheric CH₄ dynamics. Terrestrial ecosystems play an important role in determining the amount of these gases into the atmosphere. However, global quantifications of CH₄ emissions from wetlands and its sinks from uplands, and CO exchanges between land and the atmosphere are still fraught with large uncertainties, presenting a big challenge to interpret complex atmospheric CH₄ dynamics in recent decades. In this dissertation, I apply modeling approaches to estimate the global CH₄ and CO exchanges between land ecosystems and the atmosphere and analyze how they respond to contemporary and future climate change.</p> <p>Firstly, I develop a process-based biogeochemistry model embedded in Terrestrial Ecosystem Model (TEM) to quantify the CO exchange between soils and the atmosphere at the global scale (Chapter 2). Parameterizations were conducted by using the CO <i>in situ</i> data for eleven representative ecosystem types. The model is then extrapolated to global terrestrial ecosystems. Globally soils act as a sink of atmospheric CO. Areas near the equator, Eastern US, Europe and eastern Asia will be the largest sink regions due to their optimum soil moisture and high temperature. The annual global soil net flux of atmospheric CO is primarily controlled by air temperature, soil temperature, SOC and atmospheric CO concentrations, while its monthly variation is mainly determined by air temperature, precipitation, soil temperature and soil moisture. </p> <p>Secondly, to better quantify the global CH₄ emissions from wetlands and their uncertainties, I revise, parameterize and verify a process-based biogeochemical model for methane for various wetland ecosystems (Chapter 3). The model is then extrapolated to the global scale to quantify the uncertainty induced from four different types of uncertainty sources including parameterization, wetland type distribution, wetland area distribution and meteorological input. Spatially, the northeast US and Amazon are two hotspots of CH₄ emissions, while consumption hotspots are in the eastern US and eastern China. The relationships between both wetland emissions and upland consumption and El Niño and La Niña events are analyzed. This study highlights the need for more in situ methane flux data, more accurate wetland type and area distribution information to better constrain the model uncertainty.</p> <p>Thirdly, to further constrain the global wetland CH₄ emissions, I develop a predictive model of CH₄ emissions using an artificial neural network (ANN) approach and available field observations of CH₄ fluxes (Chapter 4). Eleven explanatory variables including three transient climate variables (precipitation, air temperature and solar radiation) and eight static soil property variables are considered in developing the ANN models. The models are then extrapolated to the global scale to estimate monthly CH₄ emissions from 1979 to 2099. Significant interannual and seasonal variations of wetland CH₄ emissions exist in the past four decades, and the emissions in this period are most sensitive to variations in solar radiation and air temperature. This study reduced the uncertainty in global CH₄ emissions from wetlands and called for better characterizing variations of wetland areas and water table position and more long-term observations of CH₄ fluxes in tropical regions.</p> <p>Finally, in order to study a new pathway of CH₄ emissions from palm tree stem, I develop a two-dimensional diffusion model. The model is optimized using field data of methane emissions from palm tree stems (Chapter 5). The model is then extrapolated to Pastaza-Marañón foreland basin (PMFB) in Peru by using a process-based biogeochemical model. To our knowledge, this is among the first efforts to quantify regional CH₄ emissions through this pathway. The estimates can be improved by considering the effects of changes in temperature, precipitation and radiation and using long-period continuous flux observations. Regional and global estimates of CH₄ emissions through this pathway can be further constrained using more accurate palm swamp classification and spatial distribution data of palm trees at the global scale.</p>