Les invasions biologiques sont une cause majeure de perte de biodiversité à l’échelle mondiale. L’impact direct des espèces exotiques envahissantes (EEE) sur la structure et la composition des communautés a été bien documenté. Par contre, leur impact sur le fonctionnement des écosystèmes a été comparativement moins étudié. Dans le présent travail, j’ai mesuré sur le terrain et en conditions expérimentales l’impact de 7 espèces de plantes exotiques particulièrement envahissantes en Europe sur les propriétés chimiques du sol, sur la productivité et sur le stock d’éléments minéraux dans la biomasse. Malgré la diversité des groupes fonctionnels considérés dans notre échantillon (des espèces annuelles aux arbres), des impacts récurrents ont pu être mis en évidence. Les EEE ont toujours une biomasse et une productivité supérieures à celles de la végétation qu’elles envahissent. Il en va de même pour le stock d’éléments minéraux dans la biomasse aérienne. En ce qui concerne le sol, les traits fonctionnels des espèces ne permettent pas de prédire la direction et l’amplitude des impacts. Par contre, ces impacts sur le sol se sont révélés partiellement prévisibles en fonction des conditions écologiques initiales (contexte pédologique). La disponibilité des cations et du P et la concentration en C et N organiques augmentent suite à l’invasion dans les sites initialement pauvres alors que ces mêmes paramètres baissent dans les sites plus eutrophes au départ. Les EEE entraînent, dans une certaine mesure, une homogénéisation des conditions écologiques dans les écosystèmes envahis. Dans un deuxième temps, je me suis attaché à identifier les mécanismes de l’impact de Fallopia japonica sur le cycle de l’azote. Cette espèce, perenne rhizomateuse, adopte une gestion très conservatrice de l’azote en retransloquant jusqu’à 80 % de l’azote des tiges et des feuilles vers le système racinaire en automne avant l’abscission des feuilles. La litière restituée est, de ce fait, pauvre en azote. Ce paramètre, combiné à une teneur élevée en lignine, explique sa faible vitesse de décomposition par rapport à celle de la végétation non envahie. Une grande partie de l’azote de l’écosystème tourne donc en cycle quasi fermé entre les organes de réserve et les parties aériennes de la plante, tandis que l’azote restant est en grande partie bloqué dans la nécromasse de la plante et est donc non disponible pour les espèces concurrentes indigènes. Ce mécanisme explique, sans doute, en partie le succès invasif de l’espèce. A l’avenir, les implications des impacts sur le sol en terme de restauration des communautés devront être étudiées. L’hypothèse d’une influence positive de ces impacts sur l’aptitude compétitive des espèces envahissantes devra être testée. Enfin, une étude plus fonctionnelle des impacts de ces espèces dans des sites contrastés devrait permettre d’identifier les mécanismes impliqués./Biological invasions are a major cause of biodiversity loss worldwide. The direct impact of alien invasive species (AIS) on community structure and composition has been well documented. On the other hand, their impact on ecosystem functioning has been comparatively less studied. In this work, I measured, on the field and in experimental conditions, the impact of 7 highly invasive alien plant species in Europe on soil chemical properties, biomass and aboveground nutrient stock. Despite the high diversity in considered functional groups (from annuals to trees), recurring impacts have been found. AIS had always higher biomass and aboveground nutrient stocks than invaded resident vegetation. Concerning soil, species functional traits did not allow us to predict impact direction and intensity. On the other hand, impacts on soil were partially predictable based on initial ecological conditions (pedologic context). Thus, cations and P availability and organic C and N concentrations increased in initially poor sites and decreased in eutrophic ones. AIS tend to homogenize soil properties across invaded landscapes. In a second part, i tried to identify the mechanisms of the impacts of Fallopia japonica on N cycling. This perrennial rhizomatous species manage N in a very conservative way. About 80 % of aboveground N is translocated to rhizomes before leaves abscission. The litter is therefore poor in N. This parameter combined with a high lignin concentration explains its slow decomposition rate compared to that of uninvaded vegetation. A big part of the ecosystem N is engaged in a nearly closed cycle between above and belowground organs while the remaining N is blocked in the necromass and is thus not available for the indigenous competitors. This mechanism probably explains the invasive success of this species. In the future, the implications of soil properties modifications in terms of community restoration should be studied. The hypothesis of a positive influence of these modifications on the competitive ability of AIS should be tested. At last, a functional study of these soil impacts in contrasted sites should allow us to identify the implied mechanisms.

Submitted by (edna.saturno@ufrpe.br) on 2016-06-21T13:10:04Z No. of bitstreams: 1 Juliana de Santana Ribeiro.pdf: 950223 bytes, checksum: 57e807982bb7047332843fb4e28ff0ab (MD5) / Made available in DSpace on 2016-06-21T13:10:04Z (GMT). No. of bitstreams: 1 Juliana de Santana Ribeiro.pdf: 950223 bytes, checksum: 57e807982bb7047332843fb4e28ff0ab (MD5) Previous issue date: 2008-02-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Bamboo is a quite promising crop in Brazil. It is employed for diverse purposes, from simple craftwork to high-resistance paper and energy production. However, literature in Brazil on fertilizing this crop is scarce. Among the essential elements for the plant, potassium is responsible for the activation of more than 60 enzymes. A lack of potassium causes a substantial imbalance in vegetal development. The aim of the present study was to assess the responses of bamboo to different levels of potassium and obtain data for estimating a recommendation formula for the rational fertilization of bamboo crops. The experiment was conducted in a greenhouse at the Chemistry Department of the Universidade Federal Rural de Pernambuco (Brazil) in a randomized block design, with six replications and six doses of potassium: zero, 0.5, 1.0, 2.0, 5.0 and 10.0 mmol.L-1. Bamboo plants were cultivated for 90 days in pots, employing a hydroponic system with static aeration. Growth variables and organic solute contents were assessed. The addition of potassium led to an increase in plant height, tiller and sprouts, and shoots biomass and the allocation of biomass in the roots; a reduction in both fresh and dry biomass of the leaves, stalk and roots, the allocation of biomass in the leaves and stalk, and in growth rates comparing to the treatments with 0.0 and 10.0 mmol.L-1 of potassium. Regarding to solute content, bamboo plants had different answer to potassium treatments. Chlorophyll a, b and total chlorophyll, there was a reduction proportionate to the increase in potassium content in the nutritive solution. The chlorophyll a/chlorophyll b ratio changed from 0.98 to 1.42. The increase in organic solutes was proportional to the potassium content in the nutrient solution. The 5.0 and 10.0 mmol.L-1 potassium treatments provided the highest increases in total soluble carbohydrates, reducing sugars, nonreducing sugars, total free amino acids, soluble proteins and free proline. The best potassium content in the nutritive medium for hydroponic cultivation is between 0.5and 1.0 mmol.L-1, where as 10.0 mmol.L-1 is considered a stressing dose. / O bambu é uma cultura bastante promissora no Brasil, a qual está sendo empregada para diversos fins, desde simples artesanato até a produção de papel de alta resistência e produção de energia. Porém ainda é escassa a literatura no Brasil sobre a adubação desta cultura. Dentre os elementos essenciais para o vegetal, o potássio é responsável pela ativação de mais de 60 enzimas e sua falta provoca um substancial desequilíbrio no desenvolvimento vegetal. O objetivo deste trabalho foi avaliar as respostas da cultura do bambu a doses de potássio, bem como obter subsídios para estimar uma fórmula de recomendação para uma adubação racional da cultura do bambu. O experimento foi conduzido na casa de vegetação do Departamento de Química da UFRPE, em delineamento de blocos ao acaso, com 6 repetições e 6 doses de potássio, a saber: zero, 0,5, 1,0, 2,0, 5,0 e 10,0 mmol.L-1. Plantas de bambu foram cultivadas por 90 dias em vasos empregando-se o sistema de hidroponia por aeração estática. Avaliou-se variáveis de crescimento e teores de solutos orgânicos. A adição de potássio provocou aumento na altura das plantas, no número de folhas, perfilhos e brotos e na alocação de biomassa nas raízes; redução na biomassa fresca e seca de folhas, colmo e raízes, alocação de biomassa nas folhas e colmo, e nas taxas de crescimento quando comparados os tratamentos 0,0 e 10,0 mmol.L-1 de potássio. As plantas de bambu responderam de forma diferenciada aos tratamentos aplicados quando relacionado os teores dos solutos analisados. Para os teores de clorofila a, b e total houve uma redução proporcionalmente ao aumento no teor de potássio na solução nutritiva. A relação clorofila a:clorofila b oscilou entre 0,98 e 1,42. O aumento nos solutos orgânicos analisados foi proporcional ao teor de potássio no meio de cultivo. Os tratamentos 5,0 e 10,0 mmol.L-1 de potássio proporcionaram os maiores incrementos nos teores de carboidratos solúveis totais, açúcares redutores, açúcares não-redutores, aminoácidos livres totais, proteínas solúveis e prolina livre. O teor de potássio no meio nutritivo, mais adequado para o cultivo hidropônico fica na faixa de 0,5 e 1,0mmol.L-1, enquanto que 10,0 mmol.L-1 é considerada uma dose estressante.

Litter decomposition is a fundamental ecosystem process. It is responsible for nutrient cycling and influences carbon (C) sequestration, and soil physical and chemical properties. In nature, litter is usually heterogeneous and may not decompose the way homogeneous litter does. For example, heterogeneous litter decomposition is frequently non-additive. This makes the rate of nutrient cycling as well as fluxes of C into and out of soil C pools impossible to predict. The most frequently proposed mechanisms for positive, non-additive decomposition include the supply of limiting mineral nutrients, the supply of available C (priming), and the improvement of micro-environmental conditions. However, all three mechanisms are controversial in the sense that no single mechanism accounts for all cases of non-additive decomposition. In mesic ecosystems, both soil microbes and soil fauna are the major causes of decomposition. Microbes decompose litter by producing extracellular enzymes. The comminution of litter by soil animals interacts with microbial activities by increasing substrate surface area. In our study, positive, non-additive decomposition of oat straw when mixed with clover was not due to enhancing microarthropod density in oat straw but associated with significantly increased microbial activity in oat straw. We further investigated the factors that contribute to positive, non-additive decomposition by testing several common hypotheses used to explain non-additive decomposition (increased water content, and the transfer of C and/or nitrogen (N) compounds from clover to oat straw). We also tested a new hypothesis, which is that C, N and other nutrients are simultaneously supplied by clover to stimulate the decomposition of oat straw. Our study indicated that the addition of water to oat straw did not increase oat straw decomposition and adding ammonium chloride only or glucose and ammonium chloride together to oat straw had no significant effect on oat straw decomposition. Glucose addition alone (Low concentration) increased oat straw decomposition but was not sufficient to predict the effect of clover litter. Either the addition of glucose, ammonium chloride and other minerals together to oat straw, or soil was in contact with oat straw and glucose and ammonium chloride were added, oat straw decomposition was stimulated as if clover were present. These results suggest that the limiting resources are some combination of C, N and other mineral nutrients and that soil itself may be a source of limiting nutrients in litter decomposition. In nature, some combination of high quality litter and soil itself may supply resources that stimulate the decomposing organisms’ activity on low quality litter and then the decomposition of low quality litter. Our research provides insight into the dynamics of heterogeneous litter decomposition and will allow us to better model nutrient cycling.

A deficiência de nitrogênio tem sido apontada como uma das principais causas da degradação de pastagens, mas o suprimento de enxofre também é relevante nessa situação. Objetivou-se avaliar os efeitos das combinações entre doses de nitrogênio e de enxofre em características produtivas, fisiológicas e nutricionais da planta e nos atributos químicos do solo, na implantação do capim-Marandu (Brachiaria brizantha cv. Marandu) em Neossolo Quartzarenico proveniente de área de capim-Braquiária (Brachiaria decumbens) em degradação, com baixo teor de matéria orgânica. O experimento foi conduzido em casa-de-vegetação, em Piracicaba, Estado de São Paulo, no período de dezembro de 2004 a abril de 2005. Utilizou-se esquema fatorial 52 fracionado, com 13 combinações para as doses de nitrogênio e enxofre, em mg dm-3: 0-0; 0-20; 0-40; 100-10; 100-30; 200-0; 200-20; 200-40; 300-10; 300-30; 400-0; 400- 20 e 400-40, as quais foram distribuídas em delineamento estatístico de blocos ao acaso, com quatro repetições. Foram realizados três cortes nas plantas e a cada corte era coletada uma amostra de solo de cada unidade experimental. Após o terceiro corte as raízes foram separadas do solo e tiveram o comprimento e a superfície avaliados. Os resultados demonstraram que o fornecimento de nitrogênio foi fundamental para o crescimento inicial e adequado estabelecimento do capim-Marandu. Quando o nitrogênio foi fornecido em altas doses foi necessário cuidar do fornecimento de enxofre para a maximização da produção do capim- Marandu, bem como para o valor SPAD, a concentração de nitrogênio e de enxofre nas lâminas de folhas recém-expandidas e parte aérea e para a relação N:S na parte aérea. O valor SPAD refletiu diretamente a concentração de nitrogênio nas lâminas de folhas recém-expandidas do capim. O nitrogênio foi determinante para a maximização da massa seca de raízes, do comprimento do sistema radicular, da relação nitrogênio e enxofre no sistema radicular do capim- Marandu e dos teores de nitrato e amônio no solo suportando o capim-Marandu. A aplicação de enxofre proporcionou aumento da concentração de enxofre na parte aérea e no sistema radicular do capim, e dos teores de sulfato e enxofre total no solo com a presença do capim. A relação adequada entre as doses de nitrogênio e de enxofre para a maximização das características produtivas do capim-Marandu esteve no intervalo entre doses de 8:1 a 11:1. / Nitrogen deficiency has been mentioned as one of the main reasons for pasture degradation, but sulphur supply also is considerable in such cases. The objective was to evaluate the effects of combinations between nitrogen and sulphur rates in productive, physiological and nutritional plant characteristics and in some soil parameters at the establishment of Marandu grass in Typic Quartzipsamment with low organic matter concentration taken from a degrading Signal grass pasture. The experiment was carried out in a greenhouse, at Piracicaba, Satate of São Paulo, Brazil, from December 2004 to April 2005. A fractionated 52 factorial was used, with 13 combinations for the nitrogen and sulfur rates, in mg dm-3: 0-0; 0-20; 0-40; 100-10; 100-30; 200- 0; 200-20; 200-40; 300-10; 300-30; 400-0; 400-20 e 400-40, which were set in a randomized block design, with four replications. Plants were harvested three times, and at each harvest a soil sample was taken from each experimental unit. Following the third harvest, roots were separated from the soil and their length and surface were measured. The results showed that nitrogen supply was essential for the initial growth and adequate establishment of Marandu grass. When nitrogen was supplied at high rates, it was necessary a special care with sulphur supply to maximize dry matter yield, SPAD value, nitrogen and sulphur concentrations in the newly expanded leaves and plant tops and N:S ratio in plant tops. SPAD value was directly related to nitrogen concentration in the newly expanded leaves. Nitrogen was also decisive for maximizing roots dry weight and length, N:S ratio in the roots, and nitrate and ammonium in the soil with the grass. Sulphur application resulted in increase in the sulphur concentration in the grass tops and roots, and in the sulphate and total sulphur in the soil supporting the grass. Adequate ratio between nitrogen and sulphur rates to maximize the productive characteristics of Marandu grass was in the range of 8:1 a 11:1.

A deficiência de nitrogênio tem sido apontada como uma das principais causas da degradação de pastagens, mas o suprimento de enxofre também é relevante nessa situação. Objetivou-se avaliar os efeitos das combinações entre doses de nitrogênio e de enxofre em características produtivas, fisiológicas e nutricionais da planta e nos atributos químicos do solo, na implantação do capim-Marandu (Brachiaria brizantha cv. Marandu) em Neossolo Quartzarenico proveniente de área de capim-Braquiária (Brachiaria decumbens) em degradação, com baixo teor de matéria orgânica. O experimento foi conduzido em casa-de-vegetação, em Piracicaba, Estado de São Paulo, no período de dezembro de 2004 a abril de 2005. Utilizou-se esquema fatorial 52 fracionado, com 13 combinações para as doses de nitrogênio e enxofre, em mg dm-3: 0-0; 0-20; 0-40; 100-10; 100-30; 200-0; 200-20; 200-40; 300-10; 300-30; 400-0; 400- 20 e 400-40, as quais foram distribuídas em delineamento estatístico de blocos ao acaso, com quatro repetições. Foram realizados três cortes nas plantas e a cada corte era coletada uma amostra de solo de cada unidade experimental. Após o terceiro corte as raízes foram separadas do solo e tiveram o comprimento e a superfície avaliados. Os resultados demonstraram que o fornecimento de nitrogênio foi fundamental para o crescimento inicial e adequado estabelecimento do capim-Marandu. Quando o nitrogênio foi fornecido em altas doses foi necessário cuidar do fornecimento de enxofre para a maximização da produção do capim- Marandu, bem como para o valor SPAD, a concentração de nitrogênio e de enxofre nas lâminas de folhas recém-expandidas e parte aérea e para a relação N:S na parte aérea. O valor SPAD refletiu diretamente a concentração de nitrogênio nas lâminas de folhas recém-expandidas do capim. O nitrogênio foi determinante para a maximização da massa seca de raízes, do comprimento do sistema radicular, da relação nitrogênio e enxofre no sistema radicular do capim- Marandu e dos teores de nitrato e amônio no solo suportando o capim-Marandu. A aplicação de enxofre proporcionou aumento da concentração de enxofre na parte aérea e no sistema radicular do capim, e dos teores de sulfato e enxofre total no solo com a presença do capim. A relação adequada entre as doses de nitrogênio e de enxofre para a maximização das características produtivas do capim-Marandu esteve no intervalo entre doses de 8:1 a 11:1. / Nitrogen deficiency has been mentioned as one of the main reasons for pasture degradation, but sulphur supply also is considerable in such cases. The objective was to evaluate the effects of combinations between nitrogen and sulphur rates in productive, physiological and nutritional plant characteristics and in some soil parameters at the establishment of Marandu grass in Typic Quartzipsamment with low organic matter concentration taken from a degrading Signal grass pasture. The experiment was carried out in a greenhouse, at Piracicaba, Satate of São Paulo, Brazil, from December 2004 to April 2005. A fractionated 52 factorial was used, with 13 combinations for the nitrogen and sulfur rates, in mg dm-3: 0-0; 0-20; 0-40; 100-10; 100-30; 200- 0; 200-20; 200-40; 300-10; 300-30; 400-0; 400-20 e 400-40, which were set in a randomized block design, with four replications. Plants were harvested three times, and at each harvest a soil sample was taken from each experimental unit. Following the third harvest, roots were separated from the soil and their length and surface were measured. The results showed that nitrogen supply was essential for the initial growth and adequate establishment of Marandu grass. When nitrogen was supplied at high rates, it was necessary a special care with sulphur supply to maximize dry matter yield, SPAD value, nitrogen and sulphur concentrations in the newly expanded leaves and plant tops and N:S ratio in plant tops. SPAD value was directly related to nitrogen concentration in the newly expanded leaves. Nitrogen was also decisive for maximizing roots dry weight and length, N:S ratio in the roots, and nitrate and ammonium in the soil with the grass. Sulphur application resulted in increase in the sulphur concentration in the grass tops and roots, and in the sulphate and total sulphur in the soil supporting the grass. Adequate ratio between nitrogen and sulphur rates to maximize the productive characteristics of Marandu grass was in the range of 8:1 a 11:1.

Submitted by Mario BC (mario@bc.ufrpe.br) on 2016-07-28T16:39:44Z No. of bitstreams: 1 Sandra Maria do Nascimento.pdf: 553060 bytes, checksum: af162526240a5bf78aa1ac5c4f3cbba7 (MD5) / Made available in DSpace on 2016-07-28T16:39:44Z (GMT). No. of bitstreams: 1 Sandra Maria do Nascimento.pdf: 553060 bytes, checksum: af162526240a5bf78aa1ac5c4f3cbba7 (MD5) Previous issue date: 2006-05-31 / The Atlantic rainforest is one of the richest biomasses of the planet in terms of biodiversity, but has been compromised by considerable anthropogenic action. The present study investigated a managed fragment of the Atlantic rainforest in the city of Goiana, PE, Brazil, on the Megaó farmland, with the aim of evaluating the distribution and exportation of mineral nutrients in Tapirira guianensis Aulb. (cupiúva), a perennial, pioneering halophyte species belonging to the family Anacardiaceae. Analysis of the mineral nutrients in the vegetal biomass and litter was carried out at the Mineral Nutrition of Plant Laboratory (Chemistry Department) and the Soil Chemistry Laboratory (Agronomy Department); soil analysis was carried out at the Soil Physics and Soil Fertility Laboratories (Agronomy Department) of the Rural Federal University of Pernambuco. Macronutrient (N, P, K, Ca, Mg, S) and micronutrient (Cu, Fe, Mn, Zn) determinations were performed on the leaves, branches, bark and trunk. Pre-dried samples were submitted to nitro-perchloric digestion, with the exception of N, for which sulfuric digestion was performed. Colorimetry was used for the analytic determination of P, whereas turbidimetry was used for S; K was assessed using the flame photometric technique, and the Ca, Mg, Cu, Fe, Mn and Zn contents were determined by the atomic absorption spectrophotometric method. N concentration was determined by the Kjeldahl method. Results were submitted to variance analysis and the averages were compared through the Tukey test at 5 % probability. The concentration of nutrients in the Tapirira guianensis Aulb. biomass obeyed the following order: leaves>bark>branches>trunk. The distribution of macronutrients in the leaves, bark and branch were distributed in N>Ca>Mg>K>S>P, and in the trunk in N>Ca>S>P>Mg>K. Micronutrients followed the distribution sequence for all arboreal components: Fe>Zn>Mn. The leaves presented a greater accumulation of nutrients, despite their biomass being smaller than the remaining components. Leaf maintenance is therefore important in the management area, thereby ensuring the cycling of nutrients through litter and the adequate maintenance of the management area. The total of exported nutrients was 71 % at the time of the cutting of the tree when the trunk, bark and branches are removed from the site, which could compromise the sustainability of the site. / A mata Atlântica é um dos biomas mais ricos em biodiversidade do planeta, diversidade esta que se encontra comprometida por causa da forte ação antrópica, que entre outros problemas, produz a degradação do solo. O presente trabalho teve como área de estudo um fragmento manejado de mata Atlântica no município de Goiana – PE, na fazenda Megaó. O objetivo foi avaliar a distribuição e exportação de nutrientes minerais em Tapirira guianensis Aulb. (cupiúva), espécie perenifólia, pioneira, e heliófita, pertencente à família Anacardiaceae. As análises dos nutrientes minerais na biomassa vegetal e na serrapilheira foram realizadas no Laboratório de Nutrição Mineral de Plantas (Departamento de Química) e no Laboratório de Química do Solo (Departamento de Agronomia), e as análises do solo foram realizadas nos Laboratórios de Física do solo e Fertilidade do Solo (Departamento de Agronomia), da Universidade Federal Rural de Pernambuco. As determinações dos macronutrientes (N, P, K, Ca, Mg, S) e micronutrientes (Cu, Fe, Mn, Zn), foram realizadas nas folhas, galhos, casca e fuste. As amostras pré-secas foram submetidas à digestão nitroperclórica, com exceção do N, onde foi feita a digestão sulfúrica. A determinação analítica de P se deu por colorimetria e S por turbidimetria; K, foi avaliado através da técnica de fotometria de chama e os teores de Ca, Mg, Cu, Fe, Mn e Zn foram determinados pelo método de espectrofotometria de absorção atômica. Os teores de N foram determinados pelo método de Kjeldahl. Os resultados foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey a 5 % de probabilidade. A concentração de nutrientes na biomassa da cupiúva obedeceu a seguinte ordem folhas>casca>galhos>fuste. A distribuição de macronutrientes nas folhas, casca e galho foi distribuídos em N>Ca>Mg>K>S>P e no fuste foi N>Ca>S>P>Mg>K. Os micronutrientes seguiram a seqüência de distribuição para todos os componentes arbóreos Fe>Zn>Mn. As folhas apresentaram maior concentração de nutrientes, apesar de sua biomassa ser menor que os outros componentes, sendo assim importante sua manutenção na área de manejo, garantindo a ciclagem de nutrientes via serrapilheira e a boa manutenção da área de manejo. O total de nutrientes exportados no momento do corte da árvore, em que são retirados o fuste, a casca e os galhos do sítio, é de 71 %, o que representa uma grande perda no total de nutrientes da área de manejo, e pode comprometer a sustentabilidade do sítio.

Les invasions biologiques sont une cause majeure de perte de biodiversité à l’échelle mondiale. L’impact direct des espèces exotiques envahissantes (EEE) sur la structure et la composition des communautés a été bien documenté. Par contre, leur impact sur le fonctionnement des écosystèmes a été comparativement moins étudié. Dans le présent travail, j’ai mesuré sur le terrain et en conditions expérimentales l’impact de 7 espèces de plantes exotiques particulièrement envahissantes en Europe sur les propriétés chimiques du sol, sur la productivité et sur le stock d’éléments minéraux dans la biomasse. Malgré la diversité des groupes fonctionnels considérés dans notre échantillon (des espèces annuelles aux arbres), des impacts récurrents ont pu être mis en évidence. Les EEE ont toujours une biomasse et une productivité supérieures à celles de la végétation qu’elles envahissent. Il en va de même pour le stock d’éléments minéraux dans la biomasse aérienne. En ce qui concerne le sol, les traits fonctionnels des espèces ne permettent pas de prédire la direction et l’amplitude des impacts. Par contre, ces impacts sur le sol se sont révélés partiellement prévisibles en fonction des conditions écologiques initiales (contexte pédologique). La disponibilité des cations et du P et la concentration en C et N organiques augmentent suite à l’invasion dans les sites initialement pauvres alors que ces mêmes paramètres baissent dans les sites plus eutrophes au départ. Les EEE entraînent, dans une certaine mesure, une homogénéisation des conditions écologiques dans les écosystèmes envahis. <p>Dans un deuxième temps, je me suis attaché à identifier les mécanismes de l’impact de Fallopia japonica sur le cycle de l’azote. Cette espèce, perenne rhizomateuse, adopte une gestion très conservatrice de l’azote en retransloquant jusqu’à 80 % de l’azote des tiges et des feuilles vers le système racinaire en automne avant l’abscission des feuilles. La litière restituée est, de ce fait, pauvre en azote. Ce paramètre, combiné à une teneur élevée en lignine, explique sa faible vitesse de décomposition par rapport à celle de la végétation non envahie. Une grande partie de l’azote de l’écosystème tourne donc en cycle quasi fermé entre les organes de réserve et les parties aériennes de la plante, tandis que l’azote restant est en grande partie bloqué dans la nécromasse de la plante et est donc non disponible pour les espèces concurrentes indigènes. Ce mécanisme explique, sans doute, en partie le succès invasif de l’espèce.<p><p>A l’avenir, les implications des impacts sur le sol en terme de restauration des communautés devront être étudiées. L’hypothèse d’une influence positive de ces impacts sur l’aptitude compétitive des espèces envahissantes devra être testée. Enfin, une étude plus fonctionnelle des impacts de ces espèces dans des sites contrastés devrait permettre d’identifier les mécanismes impliqués./Biological invasions are a major cause of biodiversity loss worldwide. The direct impact of alien invasive species (AIS) on community structure and composition has been well documented. On the other hand, their impact on ecosystem functioning has been comparatively less studied. In this work, I measured, on the field and in experimental conditions, the impact of 7 highly invasive alien plant species in Europe on soil chemical properties, biomass and aboveground nutrient stock. Despite the high diversity in considered functional groups (from annuals to trees), recurring impacts have been found. AIS had always higher biomass and aboveground nutrient stocks than invaded resident vegetation. Concerning soil, species functional traits did not allow us to predict impact direction and intensity. On the other hand, impacts on soil were partially predictable based on initial ecological conditions (pedologic context). Thus, cations and P availability and organic C and N concentrations increased in initially poor sites and decreased in eutrophic ones. AIS tend to homogenize soil properties across invaded landscapes.<p>In a second part, i tried to identify the mechanisms of the impacts of Fallopia japonica on N cycling. This perrennial rhizomatous species manage N in a very conservative way. About 80 % of aboveground N is translocated to rhizomes before leaves abscission. The litter is therefore poor in N. This parameter combined with a high lignin concentration explains its slow decomposition rate compared to that of uninvaded vegetation. A big part of the ecosystem N is engaged in a nearly closed cycle between above and belowground organs while the remaining N is blocked in the necromass and is thus not available for the indigenous competitors. This mechanism probably explains the invasive success of this species.<p><p>In the future, the implications of soil properties modifications in terms of community restoration should be studied. The hypothesis of a positive influence of these modifications on the competitive ability of AIS should be tested. At last, a functional study of these soil impacts in contrasted sites should allow us to identify the implied mechanisms.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished