Les plantes sont au centre d’une grande diversité d’interactions biotiques entre organismes plus ou moins proches qui les exploitent en tant que ressources. L’objectif de cette thèse a été de comprendre comment les infections fongiques de la plante et la diversité des arbres en forêt modifient les interactions arbres-insectes. Nous avons tout d’abord effectué une méta-analyse pour poser le cadre théorique des effets indirects des infections fongiques sur les insectes herbivores associés aux mêmes plantes hôtes. L'effet de l’infection préalable des plantes par les champignons sur les préférences et performances des insectes s’avère généralement négatif. Cependant, la magnitude de cet effet délétère varie selon le mode de vie du champignon, la guilde trophique de l’insecte et la spatialité des interactions (interactions locales vs distantes). Nous avons ensuite analysé de façon empirique les interactions tripartites entre le châtaignier européen (Castanea sativa) et deux de ses bioagresseurs exotiques: le cynips (Dryocosmus kuriphilus), insecte galligène, et Cryphonectria parasitica, champignon pathogène responsable de la maladie du chancre. L'effet sur les taux d’infestation par le cynips de la composition spécifique en essences forestières des forêts de châtaigniers atteintes de chancre a été également étudié. Afin d'identifier les mécanismes sous-jacents aux effets de la diversité des forêts sur cet insecte invasif, les communautés d'insectes parasitoïdes et de champignons endophytes présents dans les galles ont été décrites. Les taux d’infection par le cynips étaient plus faibles dans les mélanges de châtaignier avec du chêne et du frêne que dans des parcelles de châtaignier monospécifiques ou dans les mélanges avec du pin. La composition des forêts influence aussi la composition des communautés de parasitoïdes associés aux galles du cynips mais pas leur abondance, richesse ou diversité. Les communautés de champignons endophytes des galles, étudiées par des méthodes de séquençage de nouvelle génération, sont indépendantes de la composition forestière. Par contre, celles présentes dans les galles différent fortement de celles des tissus foliaires adjacents. Nous avons ainsi apporté de nouvelles preuves que la diversité des plantes et les champignons pathogènes sont des facteurs clés déterminant les interactions plantes-insectes. Etudier comment les plantes interagissent avec leurs insectes et champignons associés, et les mécanismes sous-jacents à l’effet de la diversité des plantes sur ces interactions, doit permettre de mieux comprendre les relations entre diversité et fonctionnement des écosystèmes et de proposer des applications pour la gestion des bio-agresseurs forestiers natifs et exotiques. / Plants are the playground of a large diversity of biotic interactions between related and unrelated organisms exploiting them as common resources. The aim of this thesis was to understand how plant-insect interactions vary with fungal infection of their host plant and plant diversity. I first performed a meta-analysis to provide a theoretical background for plant-mediated effects of fungal infection on herbivorous insects. Overall, I found a negative plant-mediated effect of fungi on both insect preference and performance. However, this effect varied according to fungus lifestyle, insect feeding guild and spatial location of the interactions (local vs distant). Then I experimentally tested plant-fungus-insect tripartite interactions in the particular case of exotic bio-aggressors of the European chestnut (Castanea sativa): the Asian chestnut Gall Wasp (ACGW, Dryocosmus kuriphilus), and the fungal pathogen Cryphonectria parasitica, the causal agent of chestnut blight. I performed an observational study, in natural chestnut forest stands in Italy, where I tested how ACGW infestation rates vary with the tree species composition. I also investigated the mechanisms underlying plant diversity effects on the invasive pest, with a particular focus on its natural enemies such as insect parasitoids and endophytic fungi. ACGW infestation rates was lower in oak and ash chestnut mixtures compared to monocultures or pine-chestnut mixtures. Plot composition also influenced ACGW parasitoid community composition but not their abundances, diversity or richness. Endophytic communities of galls, described by using next generation sequencing methods, did not vary with plot composition. However, they strongly differed from surrounding leaf tissues. We thus provided evidence that plant diversity and fungal pathogens are key drivers of plant-insect interactions. Understanding how plants interact with associated insects and fungi, and mechanisms underlying plant diversity effect on these interactions, will improve our knowledge on diversity-ecosystem functioning relationships and will have practical applications for the management of native and exotic forest pests.

O caramujo africano ou caramujo gigante, Achatina fulica, é considerado uma das cem piores espécies invasoras do mundo, causando prejuízos ambientais, econômicos e à saúde humana e animal, sendo relatado como hospedeiro intermediário de nematoides. Este estudo teve por objetivo descrever a distribuição do caramujo em Palmas, Tocantins, e pesquisar a ocorrência das larvas de nematoides, considerando os fatores climáticos da região. No período de outubro de 2014 a março de 2017 foram coletados 380 caramujos em hortas comunitárias e lotes baldios. Os caramujos foram identificados e processados por digestão. Os helmintos recuperados foram identificados morfologicamente. Foram encontradas larvas de Aelurostrongylus abstrusus nos caramujos provenientes de 35,6% dos terrenos baldios estudados e também a forma adulta de Rhabditis sp, em 7,14% dos lotes baldios. Foi possível observar que o local da coleta dos caramujos influenciou na presença de larvas de nematoides. Durante o estudo, as condições climáticas foram evidenciadas pela baixa umidade e altas temperaturas, podendo ter influenciado na ocorrência de caramujos, durante o período analisado, visto que estes costumam enterrar-se e estivar em condições desfavoráveis de temperatura e umidade. Este estudo demonstra a ocorrência do caramujo em diversas regiões da cidade de Palmas e seu papel como hospedeiro de nematoides, o que evidencia a necessidade de medidas de controle e vigilância epidemiológica para zoonoses transmitidas por este caramujo. / The African snail or giant snail, Achatina fulica, is considered one of the hundred worst invasive species in the world, causing environmental, economic and human health damage, being reported as an intermediate host of nematodes. This study was intended to describe the distribution of the snail in Palmas, Tocantins, and to research the occurrence of the larvae of nematodes, considering the climatic factors of the region. In the period from October 2014 to March 2017, 380 snails were collected in community gardens and vacant lots. The snails were identified and processed by digestion. The helminth recovered have been identified morphologically. Larvae of Aelurostrongylus abstrusus were found in snails from 35.6% of the studied vacant land and also the adult form of Rhabditis sp, in 7.14% of the vacant lots. It was possible to observe that the site of the collection of snails influenced in the presence of larvae of nematodes. During the study, the climatic conditions were evidenced by low humidity and high temperatures, may have influenced the occurrence of snails during the analyzed period, since they usually bury themselves and stowed in unfavorable conditions of temperature and Moisture. This study demonstrates the occurrence of the snail in several regions of the city of Palmas and its role as host of nematodes, which shows the need for measures of control and epidemiological surveillance for zoonoses transmitted by this snail.

Knowledge of natal environments and dispersal of Silver Carp (Hypophthalmichthys molitrix) inhabiting the Ohio River, and Kentucky and Barkley lakes would inform development of strategies to control established and emerging populations. However, the principal natal environments supporting the emerging bigheaded carp population in the Ohio River basin are unknown. There is also a need to assess the role of tributaries as nursery sites to increase understanding of dispersal patterns and better target young fish. The goal of this study was to identify recruitment sources and determine dispersal patterns of Silver Carp in the Ohio River basin using evidence from otolith core trace element compositions relative to ambient water elemental measurements. Fish were collected from the Ohio River, and Kentucky and Barkley lakes from 2014-2017 and water samples were taken during summer 2012-2017. Water samples maintained temporal stability and spatial differentiation for the Ohio River and tributaries during the sampling period. Results suggest that most Silver Carp in the Ohio River are utilizing tributaries during early life. Results also suggest there is passage of carp through the locks into the lakes from the Ohio River and natural reproduction is occurring in or above Kentucky and Barkley lakes. Results will inform development of efforts to target and remove spawning and young bigheaded carps as well as direct management efforts in the Tennessee and Cumberland River systems.

Many freshwater ecosystems sustain several invasive species. Here I examine multiple invasions in two highly invaded and well catalogued catchments; Lake Naivasha, Kenya and River Thames, England. New metrics, derived from stable isotope analysis, are used to provide measures of trophic diversity and to examine dietary interactions among species. I test the hypothesis that functionally similar sympatric species will occupy a smaller niche than their allopatric counterparts. Additionally, I quantify the impact of multiple invasive species on ecosystem structure and functioning in order to address the question; do interactions among species amplify or mitigate one another's impact? In Lake Naivasha, the stable isotope metrics revealed serial replacement of invasive species due to dietary interactions. Invasive red swamp crayfish were eventually excluded from the lake due to niche restriction in the presence of a more recent invader, the common carp. Now, the crayfish have migrated into the catchment where they overlap with a species of native river crab. Here, I found a novel mechanism of invasion, whereby the crayfish restricted their niche at the invasion front in order to reduce competition with crabs. Crayfish also caused significant changes in invertebrate community structure and increased decomposition rates, which indirectly resulted in displacement of the crabs. In the Thames catchment, I catalogue the non-indigenous species and show how invasion rates have increased significantly since 1800 due to globalisation. Using the four species of invasive crayfish present (red swamp, signal, Turkish and virile), I demonstrate their extensive diet plasticity using novel measures of niche width and individual specialisation based on stable isotope data. Interactions among the crayfish were examined and this revealed that each species has varying and independent impacts on invertebrate community structure, algal standing stock and decomposition rates. Hence, interactions among invaders are not expected to amplify or mitigate one another's impact and instead, the combined impact will be the sum of their allopatric impacts.

Salt marshes provide a range of ecosystem services and yet are subjected to anthropogenic impacts that alter the biogeochemical processes underlying these services. In particular, human activities may modify salt marsh greenhouse gas (carbon dioxide, methane, nitrous oxide) emissions by changing plant and microbial communities, hydrological regime, and sediment chemistry. Quantifying the effects of human impacts on greenhouse gas emissions is important for complete carbon budgets, and for effective management of salt marshes and the ecosystem services they provide. In Chapters 1 and 2, I investigate the effects of hydrology and plant invasion on greenhouse gas emissions. First, I show how the restriction and restoration history of four salt marshes influence methane flux in unpredictable ways. Despite comparable salinity, methane emissions from one partially restored marsh were 25 times higher than unimpacted reference sites 13+ years after restoration, but emissions from other restored sites were equal or lower. Next, I show that greenhouse gas emissions associated with invasive Phragmites australis are not different from those associated with native Spartina alterniflora. These Chapters demonstrate the de-coupling of greenhouse gas emissions, and carbon sequestration more generally, from ecosystem degradation and restoration. In Chapters 3 and 4, I quantify greenhouse gas fluxes and microbial community structure under precipitation changes that may occur with global climate change. In a field experiment, doubled rainfall and drought had significant transient impacts on porewater salinity following storms, and on the community structure of plants (doubled rainfall) or microbes (drought), yet greenhouse gas fluxes and other biogeochemical processes were not affected. The absence of biogeochemical change indicates functional redundancy and resistance or resilience exist in the microbial community, suggesting marshes may continue providing services as precipitation changes. In a lab experiment, rewetting intact cores to simulate tidal inundation or rainstorms produced a nitrous oxide pulse 10-20x the baseline flux rates, without changing the microbial community. A model of rewetting event frequency suggests that pulsed emissions may be responsible for the majority of marsh nitrous oxide emission. Precipitation change may increase coastal nitrous oxide emission if it causes more or stronger storms, and thus more rewetting events.

The surveillance and control of introduced species has become an increasingly important, yet often controversial, form of environmental management. I investigate why and how introduced species management is initiated; whether, why and how it is contested; and what relations and outcomes emerge ‘in practice’. I examine how introduced species management is being done in the United Kingdom through detailed social scientific analyses of the processes, practices, and disputes involved in a series of management case studies. First, I demonstrate how some established approaches to the design and delivery of management initiatives can render them conflict-prone, ineffective and potentially unjust. Then, examining a disputesurrounding a state-initiated eradication of monk parakeets (Myiopsitta monachus), I show why and how ‘parakeet protectors’ opposed the initiative. I identify the significance of divergent evaluations of the risks posed by introduced wildlife; personal and community attachments between people and parakeets; and campaigners’ dissatisfaction with central government’s approach to the issue. By following the story of an unauthorised (re)introduction of Eurasian beavers (Castor fiber) to England, I show how adiverse collective has, at least temporarily, been united and empowered by a shared understanding of beavers as ‘belonging’ in the UK. I consider how nonhuman citizenship is socio-politically negotiated, and how the beavers have become enrolled in a ‘wild experiment’. Finally, through a multi- sited study of grey squirrel (Sciuruscarolinensis) control initiatives, I find important variations in management practitioners’ approaches to killing squirrels, and identify several ‘modes of killing’ that comprise different primary motivations, moral principles, ultimate aims, and practical methods. I identify multiple ways in which people respond and relate to introduced wildlife, and demonstrate how this multiplicity produces both socio-political tensions and accords. Furthermore, throughout this thesis I make a series of propositions for re-configuring the management of introduced species in ways that explicitly incorporate inclusive, constructive, and context-appropriate socio-political deliberations into its design and implementation.

Large carnivores are in global decline, chiefly resultant of anthropogenic persecution, habitat reduction and disturbance. Fosas represent Madagascar's largest carnivore, occupying much of the island's forest. This thesis examines the threats of bushmeat hunting, retaliatory killing, habitat alteration and exotic species using sociological and remote-sensing methodologies. Habitat degradation was not associated with reduced fosa occupancy, indicating some resilience within large, contiguous forests. However, competition with exotic species (cats, dogs) was associated with reduced fosa occupancy and potential temporal shifts towards greater nocturnality. Poor households were more likely to consume protected species. Conversely, wealthier households consumed more fish and eel. This pattern is reflected in Malagasy reported taste preference to consume domesticated animals and certain legally hunted wild species. Protected areas were not associated with reduced protected species consumption. Fosas' predation was a major cause of rural poultry mortality. Predation was more likely to occur in deciduous forests, in the dry season, during the evening. Fosa predation, and lower education was associated with negative Malagasy attitudes. Wealthy households, and those that had experienced fosa predation were most likely to retaliatory kill a fosa. Strategies to safeguard fosas' long-term persistence should seek to improve domestic husbandry, build robust coops with the use of watchdogs, promote education, and reduce exotic species abundance.

Submitted by Jean Medeiros (jeanletras@uepb.edu.br) on 2016-02-29T13:38:50Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) PDF - Romilda Narciza Mendonça de Queiroz.pdf: 1184612 bytes, checksum: c662ab49132bf777a48debcd6101143e (MD5) / Approved for entry into archive by Secta BC (secta.csu.bc@uepb.edu.br) on 2016-04-12T17:18:00Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) PDF - Romilda Narciza Mendonça de Queiroz.pdf: 1184612 bytes, checksum: c662ab49132bf777a48debcd6101143e (MD5) / Made available in DSpace on 2016-04-12T17:18:00Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) PDF - Romilda Narciza Mendonça de Queiroz.pdf: 1184612 bytes, checksum: c662ab49132bf777a48debcd6101143e (MD5) Previous issue date: 2015-02-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The invasive bivalve Isognomon bicolor is native to the Caribbean Sea and today is among the key invasive marine species in coastal habitats of the Brazilian coast. Before this problem, this study aims to characterize the structure of the macrobenthic community on beaches in the presence Isognomon bicolor and assess whether their presence may be influencing or being influenced by the distribution and density of native species. The study was conducted in the rocky beaches of Carapibus and Jacumã, Paraíba state (NE Brazil). On Carapibus beach were recorded the highest densities of the invasive I. bicolor (300 ind/m 2 ) and native benthic species (11,372.22 ind/m²). Density of I. bicolor was highest in the mesolittoral zone (347.68 ind/m²) in the rainy season (158.56 ind/m²). However, there was no difference in benthic communities of these beaches between the dry and rainy periods (p = 0.054), but beaches (p = 0.001) and mesolittoral zones (p = 0.005) were significantly different. In characterizing the distribution and zoning of the benthic community, it was observed that in the upper mesolittoral zone these two beaches, the dominant species was the bivalve Brachidontes exustus and the microgastropod Echinolittorina lineolata, and the barnacle Chthamalus sp. In the lower mesolitoral zone, B. exustus, Chthamalus sp., and I. bicolor were the main differentiating factors of the observed zonation. It was also a positive correlation between the density of I. bicolor and some native species. With the results obtained, it can be concluded that certain benthic macroinvetebrates, structural characteristics and benthic cover of the studied beaches are influencing the density and distribution of I. bicolor. / A invasão por espécies exóticas tem causado um grande impacto sobre os ecossistemas, além de prejuízos econômicos, sociais e à saúde humana. Espécie exótica invasora é aquela que foi introduzida a partir de outro ambiente, se estabeleceu, e constitui uma ameaça a biodiversidade nativa, aos recursos naturais ou a saúde humana. O bivalve Isognomon bicolor é uma espécie originária do Caribe e desde seu primeiro registro em 1994, esta espécie tem se expandido e hoje está entre as principais espécies marinhas invasoras que tem causado impactos nas comunidades entremarés na costa brasileira. Mudanças no padrão de distribuição, na disponibilidade de alimento e no tamanho ou estrutura dos substratos e refúgios tem sido ocasionadas pelo I. bicolor. Provavelmente I. bicolor foi introduzido de maneira involuntária na costa do Rio de Janeiro (Sudeste do Brasil) via incrustações em plataformas de petróleo ou nos cascos de navios, e atualmente ele tem sido registrado do litoral do Nordeste até o Sul do país. Para que uma invasão seja bem sucedida, o invasor deve possuir estratégias eficientes para a ocupação do ambiente e tolerância aos fatores abióticos. No caso do I. bicolor, sabe-se que a influência da hidrodinâmica local, temperatura, estrutura do substrato e associação com espécies nativas podem favorecer o estabelecimento deste invasor. Apesar disso, o conhecimento sobre a ecologia e distribuição espaço-temporal do I. bicolor ainda é escasso, principalmente para a região Nordeste do país, que possui características e condições ambientais diferentes dos locais onde ele tem sido estudado. Há muitos questionamentos que ainda precisam ser esclarecidos acerca dos impactos causados por esta espécie e dos fatores que permitem sua expansão relativamente rápida pelos ambientes costeiros no Brasil. Neste contexto, este estudo tem como objetivo principal caracterizar a estrutura da comunidade macrobentônica em praias com a presença do bivalve invasor Isognomon bicolor e avaliar se sua presença pode estar influenciando ou sendo influenciada pela distribuição e densidade das espécies nativas. Os dados fornecidos poderão nortear a elaboração de medidas de controle desta espécie invasora.

Submitted by Francine Silva (francine.silva@unipampa.edu.br) on 2016-06-23T14:11:43Z No. of bitstreams: 1 Dissertação Daiane Valente.pdf: 1062508 bytes, checksum: c859e0c99def78cdd42b20b323c13691 (MD5) / Approved for entry into archive by Vanessa Dias (vanessa.dias@unipampa.edu.br) on 2016-06-25T21:25:13Z (GMT) No. of bitstreams: 1 Dissertação Daiane Valente.pdf: 1062508 bytes, checksum: c859e0c99def78cdd42b20b323c13691 (MD5) / Made available in DSpace on 2016-06-25T21:25:13Z (GMT). No. of bitstreams: 1 Dissertação Daiane Valente.pdf: 1062508 bytes, checksum: c859e0c99def78cdd42b20b323c13691 (MD5) Previous issue date: 2016 / Poa annua L. é a única espécie invasora de plantas com flores que obteve sucesso reprodutivo na Antártica, constituindo uma ameaça para as espécies nativas desse ecossistema. A hipótese da origem e colonização dessa gramínea nesse ambiente extremo é a de que as plantas pioneiras teriam vindo da Polônia, porém não é descartada a possibilidade de mútiplos eventos de introdução e diferentes fontes de distribuição. A disponibilidade de dados de sequências expressas (EST) tem facilitado o desenvolvimento de marcadores microssatélites (SSR) que podem ser utilizados como ferramentas para estudos populacionais em diferentes níveis, fluxo gênico, níveis de parentesco e informações sobre padrões filogeográficos. O objetivo desse trabalho foi desenvolver marcadores microssatélites a partir de sequências de regiões expressas da família Poaceae, testar o potencial de transferência em P. annua e utilizar esses marcadores para análise filogeográfica de P. annua, a fim de esclarecer a origem e colonização dessa espécie na Antártica. A prospecção de marcadores microssatélites foi desenvolvida com ferramentas de bioinformática, através de análises in sílico SSR em banco de dados EST para família Poaceae, disponíveis no Genbank (NCBI). Foram utilizados os programas CAP3 e SSRLocator para prospecção dos marcadores microssatélites. Uma pesquisa de Termos Gene Ontology (GO) foi realizada no banco de dados de sequências ESTs para avaliar associações entre locus SSR e processos biológicos, componentes celulares e função molecular de genes conhecidos, utilizando os programas Blast2GO e Revigo. O teste de transferência dos primers e análise molecular de P. annua foram conduzidos através da Reação em Cadeia da Polimerase (PCR). Foram prospectadas uma lista de 568 pares de primers, destes foram sintetizados 28 marcadores microssatélites para a transferência em P. annua. 68% dos marcadores EST-SSR tiveram potencial de transferência para esta espécie. A análise sugere que as amostras da Antártica são diferentes das amostras do Chile, Brasil, Irlanda e Argentina. Além disso, foram encontrados 613 transcritos divididos em 302 famílias gênicas. Com esta análise, foi possível desenvolver ferramentas moleculares para a análise genética com P. annua e outras espécies de gramíneas, mapear os motivos mais frequentes e funções dos genes em cada locus SSR, e sugerir que os diásporos de P. annua encontrados na Antártica podem ter vindos de fontes distintas das populações da America do Sul. / Poa annua L. is the only invasive species of flowering plants that reached reproductive success in Antarctica, posing a threat to native species of this ecosystem.The hypothesis of the origin and colonization of grass in this extreme environment is the pioneer plants would have come from Poland, but it is not ruled out event of multiple introduction and different sources of distribution. Recent increase in the availability of expressed sequence data (EST) has facilitated the development of microsatellite markers (SSR) can be used as tools for population studies at different levels, gene flow, relationship of levels and patterns phylogeographical information. The objective of this study was to develop microsatellite markers from expressed sequence regions of the Poaceae family, test the potential transfer in P. annua and use these markers for phylogeographic analysis of P. annua in order to clarify the origin and colonization of this species in Antarctica. The prospect of microsatellite markers was developed with bioinformatics tools, through an analysis in silico SSR in EST database to Poaceae family, available in Genbank (NCBI). Were used the CAP3 and SSRLocator programs for prospecting of microsatellite markers. A Search terms Gene Ontology (GO) were performed in ESTs sequences database to evaluate associations between SSR locus and biological processes, cellular components and molecular function of known genes, using the Blast2GO and Revigo programs. The transfer test of primers and molecular analysis of P. annua was conducted by Polymerase Chain Reaction (PCR). Were prospected a list of 568 primer pairs, these were synthesized 28 microsatellite markers for the transfer in P. annua. 68% of EST-SSR markers have potential transfer for this species. The analysis suggests that the samples from Antarctica are different from samples from Chile, Brazil, Argentina and Ireland. In addition, they found 613 transcripts divided into 302 genic families. With this analysis, it was possible to develop molecular tools for genetic analysis with P. annua and other grass species, mapping the most frequent motifs and functions of genes in each SSR locus, and suggest that the introduction of P. annua found in Antarctica may have come from sources other than South American populations.

Made available in DSpace on 2017-07-10T14:38:27Z (GMT). No. of bitstreams: 1 dissertacaovandjore pronta.pdf: 1244176 bytes, checksum: 0acde300276a806250001806ca1faae2 (MD5) Previous issue date: 2015-02-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Invasive alien species can interfere with the development of native species for the production and release of chemicals in the environment, a phenomenon known as allelopathy. Thus, the aim of this study was to investigate the allelopathic potential and oxidative stress on seeds and Cucumis sativus seedlings when submitted to aqueous extracts of Leucaena leucocephala. Therefore, we evaluated the germination behavior, early growth and activity of antioxidant enzymes in different soaking time of seeds and target species of seedlings. The results indicated that there was interference from L. leucocephala extracts on the germination of variables, speed index and average germination time, decreased length of root and shoot growth stimulus. Regarding enzymatic activity, it was found high activity of catalase enzyme after 24 hours of soaking seeds, and low activity in the seedlings after 168 hours of soaking. As for the peroxidase enzyme, there was low activity in seeds and high activity in the C. sativus seedlings. They were also investigated the effect of aqueous extracts in the laboratory and powdered extracts, in a greenhouse, Leucaena leucocephala and Hovenia dulcis on the germination and early development of native species Mimosa bimucronata and Peltophorum dubium. Both extracts revealed allelopathic potential on seed germination and initial growth of M. bimucronata. No negative interference of extracts from the donor species on the germination of P. dubium, however, seedlings subjected to L. leucocephala extract had interference in the initial development, and the elongation of the radicle more sensitive to the effects of the extracts. Regarding the effects of the extract powder on the development of the species, it was found that there was no interference in the growth variables for the species M. bimucronata, however, to P. dubium, extracts promoted difference in the height of the seedlings field conditions. According to the methodology used and the results obtained, it observed that the allelopathic effects observed in the laboratory were more significant, suggesting that in a controlled environment, with little variation of environmental factors, the action of allelochemicals interfere more actively on seed germination and seedling development of the recipient species. / As espécies exóticas invasoras podem interferir no desenvolvimento de espécies nativas pela produção e liberação de compostos químicos no ambiente, fenômeno conhecido como alelopatia. Desta forma, o objetivo do presente estudo foi investigar o potencial alelopático e estresse oxidativo sobre sementes e plântulas de Cucumis sativus quando submetidas ao extrato aquoso de Leucaena leucocephala. Para tanto, foram avaliados o comportamento germinativo, crescimento inicial e atividade de enzimas antioxidantes em diferentes tempos de embebição das sementes e plântulas da espécie-alvo. Os resultados indicaram que houve interferência dos extratos de L. leucocephala sobre as variáveis de germinação, índice de velocidade e tempo médio de germinação, diminuição do comprimento de raiz e estímulo de crescimento de parte aérea. Em relação a atividade enzimática, foi verificada alta atividade da enzima catalase, após 24h da embebição das sementes, e baixa atividade nas plântulas, após 168h de embebição. Já para a enzima peroxidase, observou-se baixa atividade nas sementes e alta atividade nas plântulas de C. sativus. Também foram investigados o efeito dos extratos aquosos, em laboratório, e extratos em pó, em casa de vegetação, de Leucaena leucocephala e Hovenia dulcis, sobre a germinação e desenvolvimento inicial das espécies nativas Mimosa bimucronata e Peltophorum dubium. Ambos os extratos evidenciaram potencialidades alelopáticas na germinação das sementes e no crescimento inicial de M. bimucronata. Não foram observadas interferências negativas dos extratos das espécies doadoras sobre o processo germinativo de P. dubium, entretanto, plântulas submetidas ao extrato de L. leucocephala tiveram interferência no desenvolvimento inicial, sendo o alongamento da radícula mais sensível aos efeitos dos extratos. Em relação aos efeitos do extrato em pó sobre o desenvolvimento das espécies, constatou-se que não houve interferência nas variáveis de crescimento analisadas para a espécie M. bimucronata, entretanto, para P. dubium, os extratos promoveram diferença sobre a altura das mudas em condições de campo. De acordo com a metodologia adotada e os resultados obtidos, foi possível verificar que os efeitos alelopáticos observados em laboratório foram mais significativos, sugerindo que em ambiente controlado, com pouca variação de fatores ambientais, a ação dos aleloquímicos interferem mais ativamente sobre a germinação de sementes e o desenvolvimento_de_plântulas_das_espécies_receptoras