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Mudanças no uso e cobertura do solo na Amazônia e suas implicações no ciclo de nitrogênio; Land-use and land-cover changes in the Amazon and their implications for the nitrogen cycle

Figueira, Adelaine Michela e Silva
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 20/10/2006 PT
Relevância na Pesquisa
46.48%
O estudo da dinâmica de áreas alteradas na Amazônia pode contribuir para a elucidação dos possíveis impactos dos atuais modelos de uso do solo sobre o sistema florestal bem como sua capacidade de recuperação ao longo do tempo, permitindo assim, que sejam feitas previsões quanto ao futuro ambiental da região. O objetivo deste trabalho foi investigar a dinâmica de nitrogênio ao longo de florestas secundárias formadas pela agricultura de corte e queima no município de São Francisco do Pará, e ao longo de clareiras formadas pela exploração seletiva de madeira na Floresta Nacional do Tapajós, ambas no Estado do Pará. Foram selecionadas florestas secundárias de diferentes idades (6, 20 e 40 anos) e clareiras de diferentes idades de formação (1, 3 e 5 anos) bem como áreas de florestas de terra-firme não perturbadas. Nestas áreas, foram avaliadas a abundância natural de 15N e concentrações de N e C em solo, serapilheira e vegetação. Nas clareiras e floresta não perturbada em áreas de exploração seletiva também foram realizados experimentos de mineralização e nitrificação. De um modo geral, todas as áreas investigadas apresentaram um aumento nos valores de &23515N no solo de acordo com a profundidade. Ao longo da cronossequência de florestas secundárias foi observado um aumento no ð15N e na concentração de N foliar...

Efeitos da irrigação com esgoto tratado e fertilização nitrogenada na ciclagem de carbono e nitrogênio e no metabolismo microbiano de um solo cultivado com capim-Bermuda Tifton 85; Effects of irrigation with secondary treated sewage effluent and nitrogen fertilization on carbon and nitrogen cycling and on microbial metabolism on a Tifton 85 bermudagrass pasture

Nogueira, Sandra Furlan
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/06/2008 PT
Relevância na Pesquisa
56.48%
Em muitas partes do mundo o aumento na demanda de água tem estimulado pesquisas relacionadas às práticas de reuso sustentáveis. Dentre as atividades humanas, a irrigação agrícola se revela como uma das práticas de maior consumo de recursos hídricos naturais. Uma alternativa para minimizar este problema é o reuso de efluentes gerados por sistemas biológicos de tratamento de esgotos. O objetivo desta pesquisa foi avaliar os efeitos da irrigação com esgoto tratado na dinâmica do carbono (C) e nitrogênio (N) e na atividade microbiana de um solo sob pastagem. O estudo foi conduzido em uma pastagem de capim-Bermuda Tifton 85 (Lins-SP), onde o delineamento experimental foi o de blocos completos com seis tratamentos: SI (sem irrigação e sem fertilização), A100 (água potável + 520 kg de N ha-1 ano-1); E0, E33, E66 e E100 (irrigação com esgoto tratado + 0, 33, 66 e 100% de 520 kg de N ha-1 ano-1). Os tratamentos receberam entre 420 a 1500 mm de esgoto tratado e água por ano, correspondendo a uma entrada pelo esgoto tratado de 640 a 2300 kg ha-1 ano-1 de C e de 135 a 480 kg ha-1 ano-1 de N. Utilizando como referência os estoques de C e N de SI, o menor decréscimo de C ocorreu em E33 (1,2 Mg ha-1) e o maior em A100 (7...

Dinâmica do nitrogênio no solo e sua implicação na qualidade da água em uma bacia hidrográfica com diferentes tipos de uso de solo com ênfase no papel da floresta ripária; Nitrogen dynamic in the soil and its implication on the water quality of a watershed where different land uses are present with emphasis on the role of riparian forest

Bezerra, Maíra Ometto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 13/10/2009 PT
Relevância na Pesquisa
46.45%
Embora o nitrogênio seja um nutriente limitado, em excesso, ele pode causar a degradação de sistemas aquáticos. Apesar de, no âmbito nacional, o Brasil não apresentar problemas de escassez hídrica, regiões altamente populosas já tem enfrentado problemas de déficit hídrico, inclusive em função da poluição difusa de nitrogênio. Zonas ripárias têm sido apontadas como um dos atributos da bacia hidrográfica que pode ajudar na melhoria e manutenção da qualidade hídrica devido a sua capacidade de retirar nitrogênio do sistema terrestre oriundo de fontes difusas. Essa característica lhe é conferida por serem ambientes favoráveis ao processo de desnitrificação. A desnitrificação é um dos processos, se não o primeiro, responsável por converter o nitrato para formas gasosas N2O e N2. Considerando que os estudos sobre a função desempenhada por vegetações ripárias como sumidouro de nitrogênio se concentraram em países de clima temperado e que paisagens alteradas são o uso da terra majoritário no Estado de São Paulo, onde o problema de déficit hídrico já é uma realidade. Entender o papel que zonas ripárias desempenham sobre a dinâmica do nitrogênio torna-se fundamental para o desenvolvimento de estratégias de manejo do uso da terra voltadas para a manutenção da qualidade de sistemas aquáticos em regiões tropicais. O objetivo do trabalho é investigar se existe mudança dos processos que regulam a dinâmica do nitrogênio no solo em paisagens alteradas...

Ciclagem do nitrogênio em uma cronosequência formada por florestas restauradas e floresta natural; Nitrogen cycling in a chronosequence formed by restored forests and a natural forest

Amazonas, Nino Tavares
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/03/2010 PT
Relevância na Pesquisa
46.61%
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...

The role of multiple partners in a digestive mutualism with a protocarnivorous plant

Nishi, Aline Hiroko; Vasconcellos-Neto, João; Romero, Gustavo Quevedo
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 143-150
ENG
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Background and aimsThe protocarnivorous plant Paepalanthus bromelioides (Eriocaulaceae) is similar to bromeliads in that this plant has a rosette-like structure that allows rainwater to accumulate in leaf axils (i.e. phytotelmata). Although the rosettes of P. bromelioides are commonly inhabited by predators (e.g. spiders), their roots are wrapped by a cylindrical termite mound that grows beneath the rosette. In this study it is predicted that these plants can derive nutrients from recycling processes carried out by termites and from predation events that take place inside the rosette. It is also predicted that bacteria living in phytotelmata can accelerate nutrient cycling derived from predators.MethodsThe predictions were tested by surveying plants and animals, and also by performing field experiments in rocky fields from Serra do Cipó, Brazil, using natural abundance and enriched isotopes of 15N. Laboratory bioassays were also conducted to test proteolytic activities of bacteria from P. bromelioides rosettes.Key ResultsAnalyses of 15N in natural nitrogen abundances showed that the isotopic signature of P. bromelioides is similar to that of carnivorous plants and higher than that of non-carnivorous plants in the study area. Linear mixing models showed that predatory activities on the rosettes (i.e. spider faeces and prey carcass) resulted in overall nitrogen contributions of 26·5 % (a top-down flux). Although nitrogen flux was not detected from termites to plants via decomposition of labelled cardboard...

Spatial distribution of feces and estimates of nitrogen return by dairy cows on mombasa grass pastures

Silva,Rodrigo Gregório da; Neiva,José Neuman Miranda; Santos,Antonio Clementino dos; Cândido,Magno José Duarte; Sousa,Antonio Luiz Dias; Lopes,Marcos Neves; Silva,Rafael de Oliveira da; Carneiro,Leovegildo Caldas
Fonte: Sociedade Brasileira de Zootecnia Publicador: Sociedade Brasileira de Zootecnia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2013 EN
Relevância na Pesquisa
46.35%
The objective of this study was to identify the pattern of deposition of feces by supplemented crossbred dairy cows after the lactation peak on cultivated areas under levels of intensification of the system and its effects on nitrogen cycling, with the aid of geostatistics, in the rainy period. Treatments were composed of two levels of nitrogen fertilization (equivalent to 400 and 800 kg N/ha/year) and two types of animals, according to the daily milk production. Geostatistical and descriptive analyses of the data were conducted. The data presented positive coefficients of skewness and platykurtic kurtosis. For the coefficient of variation, there was elevated alteration, with rest areas showing higher values and paddocks with a higher level of fertilization showing lower values.The climate factors radiation, temperature and relative humidity significantly influenced the dispersion and location of feces. As to the degree of spatial dependence, the classification varied from moderated to strong. The range was from 14.0 to 12.7 m for the rest areas and paddocks, respectively. Fertilization and concentrate supply affected the deposition and loss of nitrogen via feces, elevating its values as the nutritional uptake is elevated. Fecal deposition showed heterogeneity...

Impact of trichloroethylene and toluene on nitrogen cycling in soil.

Fuller, M E; Scow, K M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1997 EN
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46.36%
The effects of trichloroethylene (TCE) and toluene on soil nitrogen-cycling activities were examined. Ammonium oxidation potential (AOP) was reduced after incubation with as little as 1 microgram of TCE ml-1, and the effects were generally greater when toluene was present and increased with longer exposure. Arginine ammonification potential and denitrification enzyme activity were constant regardless of TCE concentration or the presence of toluene, while nitrite oxidation potential (NOP) exhibited variable sensitivity. KCl-extractable ammonium levels increased dramatically after exposure to 30 and 60 micrograms of TCE ml-1 in the presence of toluene, whereas gamma-irradiated or sodium azide-treated soil incubated with the same concentrations of TCE and toluene showed no increase. Alfalfa-amended soils showed similar decreases in AOP and increases in extractable ammonium during incubation with 60 micrograms of TCE ml-1 and 20 micrograms of toluene ml-1, although most probable number estimates of the ammonium oxidizer population showed no difference between exposed and unexposed soil. AOP and extractable ammonium returned slowly to control levels after 28 days of incubation in the presence of TCE and toluene. Activity assays to which various TCE and toluene concentrations were added indicated that AOP and NOP were relatively more sensitive to these compounds than was arginine ammonification potential. These results indicate that the soil microbial populations responsible for nitrogen cycling exhibit different sensitivities to TCE and toluene and that they may be more susceptible to adverse effects than previously thought.

Species-driven changes in nitrogen cycling can provide a mechanism for plant invasions

Laungani, Ramesh; Knops, Johannes M. H.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.46%
Traits that permit successful invasions have often seemed idiosyncratic, and the key biological traits identified vary widely among species. This fundamentally limits our ability to determine the invasion potential of a species. However, ultimately, successful invaders must have positive growth rates that longer term result in higher biomass accumulation than competing established species. In many terrestrial ecosystems nitrogen limits plant growth, and is a key factor determining productivity and the outcome of competition among species. Plant nitrogen use may provide a powerful framework to evaluate the invasive potential of a species in nitrogen-limiting ecosystems. Six mechanisms influence plant nitrogen use or acquisition: photosynthetic tissue allocation, photosynthetic nitrogen use efficiency, nitrogen fixation, nitrogen-leaching losses, gross nitrogen mineralization, and plant nitrogen residence time. Here we show that among these alternatives, the key mechanism allowing invasion for Pinus strobus into nitrogen limited grasslands was its higher nitrogen residence time. This higher nitrogen residence time created a positive feedback that redistributed nitrogen from the soil into the plant. This positive feedback allowed P. strobus to accumulate twice as much nitrogen in its tissues and four times as much nitrogen to photosynthetic tissues...

Metagenomic Profiling of a Microbial Assemblage Associated with the California Mussel: A Node in Networks of Carbon and Nitrogen Cycling

Pfister, Catherine A.; Meyer, Folker; Antonopoulos, Dionysios A.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 06/05/2010 EN
Relevância na Pesquisa
46.39%
Mussels are conspicuous and often abundant members of rocky shores and may constitute an important site for the nitrogen cycle due to their feeding and excretion activities. We used shotgun metagenomics of the microbial community associated with the surface of mussels (Mytilus californianus) on Tatoosh Island in Washington state to test whether there is a nitrogen-based microbial assemblage associated with mussels. Analyses of both tidepool mussels and those on emergent benches revealed a diverse community of Bacteria and Archaea with approximately 31 million bp from 6 mussels in each habitat. Using MG-RAST, between 22.5–25.6% were identifiable using the SEED non-redundant database for proteins. Of those fragments that were identifiable through MG-RAST, the composition was dominated by Cyanobacteria and Alpha- and Gamma-proteobacteria. Microbial composition was highly similar between the tidepool and emergent bench mussels, suggesting similar functions across these different microhabitats. One percent of the proteins identified in each sample were related to nitrogen cycling. When normalized to protein discovery rate, the high diversity and abundance of enzymes related to the nitrogen cycle in mussel-associated microbes is as great or greater than that described for other marine metagenomes. In some instances...

Response of the Abundance of Key Soil Microbial Nitrogen-Cycling Genes to Multi-Factorial Global Changes

Zhang, Ximei; Liu, Wei; Schloter, Michael; Zhang, Guangming; Chen, Quansheng; Huang, Jianhui; Li, Linghao; Elser, James J.; Han, Xingguo
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 04/10/2013 EN
Relevância na Pesquisa
46.63%
Multiple co-occurring environmental changes are affecting soil nitrogen cycling processes, which are mainly mediated by microbes. While it is likely that various nitrogen-cycling functional groups will respond differently to such environmental changes, very little is known about their relative responsiveness. Here we conducted four long-term experiments in a steppe ecosystem by removing plant functional groups, mowing, adding nitrogen, adding phosphorus, watering, warming, and manipulating some of their combinations. We quantified the abundance of seven nitrogen-cycling genes, including those for fixation (nifH), mineralization (chiA), nitrification (amoA of ammonia-oxidizing bacteria (AOB) or archaea (AOA)), and denitrification (nirS, nirK and nosZ). First, for each gene, we compared its sensitivities to different environmental changes and found that the abundances of various genes were sensitive to distinct and different factors. Overall, the abundances of nearly all genes were sensitive to nitrogen enrichment. In addition, the abundances of the chiA and nosZ genes were sensitive to plant functional group removal, the AOB-amoA gene abundance to phosphorus enrichment when nitrogen was added simultaneously, and the nirS and nirK gene abundances responded to watering. Second...

Sagebrush carrying out hydraulic lift enhances surface soil nitrogen cycling and nitrogen uptake into inflorescences

Cardon, Zoe G.; Stark, John M.; Herron, Patrick M.; Rasmussen, Jed A.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.52%
Plant roots serve as conduits for water flow not only from soil to leaves but also from wetter to drier soil. This hydraulic redistribution through root systems occurs in soils worldwide and can enhance stomatal opening, transpiration, and plant carbon gain. For decades, upward hydraulic lift (HL) of deep water through roots into dry, litter-rich, surface soil also has been hypothesized to enhance nutrient availability to plants by stimulating microbially controlled nutrient cycling. This link has not been demonstrated in the field. Working in sagebrush-steppe, where water and nitrogen limit plant growth and reproduction and where HL occurs naturally during summer drought, we slightly augmented deep soil water availability to 14 HL+ treatment plants throughout the summer growing season. The HL+ sagebrush lifted greater amounts of water than control plants and had slightly less negative predawn and midday leaf water potentials. Soil respiration was also augmented under HL+ plants. At summer’s end, application of a gas-based 15N isotopic labeling technique revealed increased rates of nitrogen cycling in surface soil layers around HL+ plants and increased uptake of nitrogen into HL+ plants’ inflorescences as sagebrush set seed. These treatment effects persisted even though unexpected monsoon rainstorms arrived during assays and increased surface soil moisture around all plants. Simulation models from ecosystem to global scales have just begun to include effects of hydraulic redistribution on water and surface energy fluxes. Results from this field study indicate that plants carrying out HL can also substantially enhance decomposition and nitrogen cycling in surface soils.

The microbial nitrogen cycling potential is impacted by polyaromatic hydrocarbon pollution of marine sediments

Scott, Nicole M.; Hess, Matthias; Bouskill, Nick J.; Mason, Olivia U.; Jansson, Janet K.; Gilbert, Jack A.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 25/03/2014 EN
Relevância na Pesquisa
46.41%
During hydrocarbon exposure, the composition and functional dynamics of marine microbial communities are altered, favoring bacteria that can utilize this rich carbon source. Initial exposure of high levels of hydrocarbons in aerobic surface sediments can enrich growth of heterotrophic microorganisms having hydrocarbon degradation capacity. As a result, there can be a localized reduction in oxygen potential within the surface layer of marine sediments causing anaerobic zones. We hypothesized that increasing exposure to elevated hydrocarbon concentrations would positively correlate with an increase in denitrification processes and the net accumulation of dinitrogen. This hypothesis was tested by comparing the relative abundance of genes associated with nitrogen metabolism and nitrogen cycling identified in 6 metagenomes from sediments contaminated by polyaromatic hydrocarbons from the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico, and 3 metagenomes from sediments associated with natural oil seeps in the Santa Barbara Channel. An additional 8 metagenomes from uncontaminated sediments from the Gulf of Mexico were analyzed for comparison. We predicted relative changes in metabolite turnover as a function of the differential microbial gene abundances...

Impacts of bioturbation on temporal variation in bacterial and archaeal nitrogen-cycling gene abundance in coastal sediments

Laverock, B; Tait, K; Gilbert, J A; Osborn, A M; Widdicombe, S
Fonte: BlackWell Publishing Ltd Publicador: BlackWell Publishing Ltd
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.46%
In marine environments, macrofauna living in or on the sediment surface may alter the structure, diversity and function of benthic microbial communities. In particular, microbial nitrogen (N)-cycling processes may be enhanced by the activity of large bioturbating organisms. Here, we study the effect of the burrowing mud shrimp Upogebia deltaura upon temporal variation in the abundance of genes representing key N-cycling functional guilds. The abundance of bacterial genes representing different N-cycling guilds displayed different temporal patterns in burrow sediments in comparison with surface sediments, suggesting that the burrow provides a unique environment where bacterial gene abundances are influenced directly by macrofaunal activity. In contrast, the abundances of archaeal ammonia oxidizers varied temporally but were not affected by bioturbation, indicating differential responses between bacterial and archaeal ammonia oxidizers to environmental physicochemical controls. This study highlights the importance of bioturbation as a control over the temporal variation in nitrogen-cycling microbial community dynamics within coastal sediments.

15N in tree rings as a bio-indicator of changing nitrogen cycling in tropical forests: an evaluation at three sites using two sampling methods

van der Sleen, Peter; Vlam, Mart; Groenendijk, Peter; Anten, Niels P. R.; Bongers, Frans; Bunyavejchewin, Sarayudh; Hietz, Peter; Pons, Thijs L.; Zuidema, Pieter A.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 09/04/2015 EN
Relevância na Pesquisa
46.47%
Anthropogenic nitrogen deposition is currently causing a more than twofold increase of reactive nitrogen input over large areas in the tropics. Elevated 15N abundance (δ15N) in the growth rings of some tropical trees has been hypothesized to reflect an increased leaching of 15N-depleted nitrate from the soil, following anthropogenic nitrogen deposition over the last decades. To find further evidence for altered nitrogen cycling in tropical forests, we measured long-term δ15N values in trees from Bolivia, Cameroon, and Thailand. We used two different sampling methods. In the first, wood samples were taken in a conventional way: from the pith to the bark across the stem of 28 large trees (the “radial” method). In the second, δ15N values were compared across a fixed diameter (the “fixed-diameter” method). We sampled 400 trees that differed widely in size, but measured δ15N in the stem around the same diameter (20 cm dbh) in all trees. As a result, the growth rings formed around this diameter differed in age and allowed a comparison of δ15N values over time with an explicit control for potential size-effects on δ15N values. We found a significant increase of tree-ring δ15N across the stem radius of large trees from Bolivia and Cameroon...

Gross and net nitrogen transformation rates and availability in late summer in tall shrub and birch hummock ecosystems of the Canadian low Arctic

Zufelt, Erik
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 3478016 bytes; application/msword
EN
Relevância na Pesquisa
56.73%
Climate change is occurring most rapidly in the Arctic where warming has been twice as fast as the rest of the globe over the last few decades. Arctic soils contain a vast store of carbon and warmer arctic soils may mediate current atmospheric CO2 concentrations and global warming trends. Warmer soils could increase nutrient availability to plants, leading to increased primary production and sequestration of CO2. Presumably because of these effects of warming on shrub ecosystems, shrubs have been expanding across the arctic over the last 50 years, Arctic shrub expansion may track or cause changes in nutrient cycling and availability that favour growth of larger, denser shrubs. This study aimed at measuring gross and net nitrogen cycling rates, major soil nitrogen and carbon pool sizes, and elucidating controls on nutrient cycling and availability between a mesic birch (Betula nana) hummock tundra ecosystem and an ecosystem of dense, tall, birch (B. nana) shrubs. Nitrogen cycling and availability was enhanced at the tall shrub ecosystem compared to the birch hummock ecosystem. Net nitrogen immobilization by microbes was approximately threefold greater at the tall shrub ecosystem. This was in part because of larger microbial biomass nitrogen and carbon (interpreted as a larger microbial community) at the tall shrub ecosystem. Nitrogen inputs via litter were significantly larger at the tall shrub ecosystem and were hypothesized to be the major contributor to the higher dissolved organic and inorganic nitrogen pools in the soil at the tall shrub ecosystem. The results from this study suggest a positive feedback mechanism between litter nitrogen inputs and the enhancement of nitrogen cycling and availability as a driver of shrub expansion across the Arctic.; Summary 1. Nitrogen cycling was enhanced at the tall shrub ecosystem. The immobilization rate was approximately three times higher at the tall shrub ecosystem than at the birch hummock ecosystem. There was a net nitrogen immobilization by microbes in the soil at both the birch hummock and the tall shrub ecosystem late in the growing season. 2. Microbial biomass carbon (MBC) and nitrogen (MBN) were greater at the tall shrub ecosystem. The greater MBC and MBN at the tall shrub ecosystem may explain why net immobilization was greater at the tall shrub ecosystem because the greater microbial biomass at the tall shrub ecosystem can be expected to immobilize more nitrogen. 3. MBC:MBN was lower at the tall shrub ecosystem...

Nematode abundance and diversity in relation to soil nitrogen dynamics within three Canadian low arctic ecosystems

Laidlaw, Meghan Jr
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 2929974 bytes; application/pdf
EN
Relevância na Pesquisa
46.49%
Soil nematode predation on microbial populations can speed up microbial turnover rates, increase nitrogen mineralization and the availability of N in soils, and ultimately enhance plant N uptake. However, this soil food web interaction has not been tested in arctic soils, where plants are limited by N and there is often net immobilization of N by soil microbes during the growing season. Experiments were conducted to determine the spatial and temporal factors regulating nematode abundance and diversity in the arctic, and to establish whether the interaction between nematode grazing and microbial N cycling is also evident in arctic ecosystems. The field experiment was conducted in tall birch, birch hummock and lichen heath low arctic ecosystems over a growing season. Nematode abundances were highest in the tall birch plots, corresponding with the largest pools of DON and NH4+-N and previously recorded higher rates of N cycling. Microbial biomass did not differ significantly between ecosystem types. Therefore, larger soil N pool sizes in tall birch sites may be explained by faster N cycling rates due to nematode grazing on microbes at these sites. Nematode communities were strongly dominated by bacterial and fungal feeders in generally equal proportions...

Regimes de desfolhação sobre a ciclagem de nitrogênio e produção da forragem em pastos consorciados

Gomes, Fernanda de Kássia
Fonte: Universidade Federal de Lavras; Programa de Pós-Graduação em Zootecnia; UFLA; brasil; Departamento de Zootecnia Publicador: Universidade Federal de Lavras; Programa de Pós-Graduação em Zootecnia; UFLA; brasil; Departamento de Zootecnia
Tipo: Dissertação
Publicado em 23/10/2015 POR
Relevância na Pesquisa
46.42%
Defoliation frequencies of dossal managed in intermittent grazing may cause changes in the production, persistence and nitrogen cycling in mixed pastures. In this study, we aimed to define the management that optimizes the input and cycling of nitrogen, favoring greater production and forage intake in pastures containing Brachiaria brizantha cv. Marandu and Arachis pintoi cv. Mandobi. Four defoliation frequencies were tested, defined by variable time intervals for dossal reaches 90%, 95% and 100% light interception (LI) and a fixed interval of 42 days (42DF). The experiment was performed in completely randomized design. The forage weight (FW) of grass in pre-pasturing was greater in dossal at 100% and 95% LI. The N and FW accumulation in grasses was greater at 90% LI, while the N and FW accumulation in leguminous was greater at 42DF. The accumulation of N and leaf litter was greater in dossal at 42DF, as well as the accumulation of total N in the leaf litter. The accumulation of total N (FW + leaf litter) in grasses was greater in dossal at 90% LI, while in leguminous, was greater at 42DF. The content of crude protein in grasses and leguminous was greater in dossal at 42DF. There was greater production of microbial protein in animals that grazed forage from dossal at 90% and 95% LI...

Shrub expansion in the low Arctic: The influence of snow and vegetation feedbacks on nitrogen cycling

Vankoughnett, Mathew
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 1714435 bytes; application/pdf
EN; EN
Relevância na Pesquisa
56.61%
Climate change has coincided with expansion of deciduous shrub species in the Arctic. Increased deciduous vegetation in the tundra could have profound implications on regional climate, carbon balance, and biogeochemical cycling of nutrients. Winter biological processes may be a mechanism explaining shrub expansion in the Arctic. Tall shrubs accumulate relatively deep snowcover, raising winter soil temperature minima, enhancing microbial activity and promoting nitrogen mobilization that may then be taken up by shrubs. However, it has yet to be determined if shrubs can acquire winter-mobilized nitrogen, and if so, whether they acquire it early in the spring, or over the growing season. The purpose of this study was to test if increased snow alone or the combination of vegetation-type and snow depth affect nitrogen cycling and plant uptake. To test this, inorganic 15nitrogen tracer was added to control and experimentally deepened snow plots (using snowfences) in low birch hummock tundra, and to tall birch-dominated plots near Daring Lake, N.W.T. in the Canadian low Arctic. The first study (Chapter 2) characterizes soil 15nitrogen cycling over a single winter to investigate if experimentally deepened snow in low birch hummock ecosystems enhances nutrient availability to plants in the early spring. In addition...

FEEDBACKS of NITROGEN CYCLING and INVASION with the NON-NATIVE PLANT, MICROSTEGIUM VIMINEUM, in RIPARIAN WETLANDS

DeMeester, Julie E.
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação Formato: 4618705 bytes; application/pdf
Publicado em //2009 EN_US
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Invasive species are rapidly expanding in riparian wetlands while concurrently anthropogenic causes are increasing nitrogen (N) into these ecosystems. Microstegium vimineum (Microstegium) is a particularly abundant invasive grass in the Southeast United States. To evaluate impacts of Microstegium on both plant diversity and N cycling in a riparian floodplain, paired plots of Microstegium hand-weeded and unweeded were established for three years. Plots without Microstegium increased from 4 to 15 species m-2 and 90% of the newly establishing species were native. The Microstegium community accumulated approximately half the annual N in biomass of the diverse community, 5.04 versus 9.36 g-N m-2 year-1, respectively (p=0.05). Decomposition and release of N from Microstegium detritus was much less than in the diverse community, 1.19 versus 5.24 g-N m-2 year-1. Rates of soil N mineralization estimated by in-situ incubations were relatively similar in all plots. While Microstegium invasion appears to greatly diminish within-ecosystem circulation of N through the under-story plants...

Surprisingly rapid nitrogen cycling in tropical forest plantations on volcanically derived soils

James Raich; Ann Russell
Fonte: Nature Preceedings Publicador: Nature Preceedings
Tipo: Conferência ou Objeto de Conferência
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Secondary forests and young forest plantations frequently have high rates of tree growth and NPP – higher even than mature forests in similar situations. The nutrients required to sustain this rapid growth are derived from the soil and by external inputs such as rainfall or, in the case of nitrogen, by biological N fixation. In our study of the effects of tree species within replicated experimental plantations in a moist, lowland tropical environment in Costa Rica, high rates of biomass accumulation and productivity were coupled with high rates of N accumulation and cycling. We applied extensive sampling through time within a mass-balance approach to address the question “Where does all the nitrogen come from?” Rates of N uptake by the vegetation in these plantations were extraordinarily high, even by tropical forest standards, reaching 412 kg N ha^-1^ yr^-1^. Rapid decay coupled to tight nitrogen cycling may have provided large amounts of available N for plant uptake, but do not explain the large quantities of N that accrued in the vegetation, up to 1075 kg N/ha over 16 years. Surface soil organic matter stocks in the plantations increased by as much as 320 kgC/ha in surface soils, but soil nitrogen varied differently. Soil N stocks to 1 m depth were depleted by an average of 2119 kg/ha relative to the mature forest. Thus...