The Upper River Paraná Floodplain System comprises the rivers Ivinheima, Baía and Paraná, which with their associated waterbodies form three subsystems, each showing individual characteristics.

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RESUMO A qualidade do resíduo vegetal e a disponibilidade de nitrogênio (N) mineral 00-30-90, (iii)30-30-60, (iv)60-30-30 e (v) 00-00-00, (2) 00-30-90, (3) 30-30-60, (4) 60-30-30, (5) 90-30-00

Summary 1. Invasion biologists use two main approaches to evaluate the effects of non‐native species (NNS) on diversity of native species (DNS), namely space‐for‐time and time approaches. These approaches have pitfalls related to lack of controls: the former lacks pre‐invasion data, while the latter often lacks data from non‐invaded sites. 2. We propose a framework that combines space‐for‐time and time approaches and which should result in more focused mechanistic hypotheses and experiments to test the causes of invasibility and the effects of NNS on DNS. We illustrate the usefulness of our framework using two case studies: one with the submersed macrophyte, Hydrilla verticillata, in reservoir and the other with the fish, Geophagus proximus, in a large river–floodplain system. 3. Hydrilla verticillata invaded sites with DNS similar to that found in non‐invaded sites, indicating that biotic and/or abiotic factors did not influence invasion success; however, DNS increased over time in invaded sites compared with non‐invaded sites, suggesting that H. verticillata facilitated natives. In contrast, G. proximus invaded sites with higher DNS than non‐invaded sites, suggesting that biotic and/or abiotic factors favouring natives were important for invasion success, but DNS increased in invaded and non‐invaded sites over time, indicating that an independent factor contributed to DNS increases. 4. Conclusions from both studies would have been inaccurate or incomplete if the space‐for‐time and time approaches had not been used in combination as proposed in our framework.

The number of citations that papers receive has become significant in measuring researchers' scientific productivity, and such measurements are important when one seeks career opportunities and research funding. Skewed citation practices can thus have profound effects on academic careers. We investigated (i) how frequently authors misinterpret original information and (ii) how frequently authors inappropriately cite reviews instead of the articles upon which the reviews are based. To reach this aim, we carried a survey of ecology journals indexed in the Web of Science and assessed the appropriateness of citations of review papers. Reviews were significantly more often cited than regular articles. In addition, 22% of citations were inaccurate, and another 15% unfairly gave credit to the review authors for other scientists' ideas. These practices should be stopped, mainly through more open discussion among mentors, researchers and students.

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We tested the effects of desiccation and type of sediment (clay or sand) on the regeneration of fragments of the apical shoots of three species of Hydrocharitaceae: Egeria najas, E. densa and Hydrilla verticillata. The shoots were left to dry on clay or sand from zero to four days, and were then returned to aquaria containing water. To approximate natural conditions, the aquaria containing clay had higher turbidity and nutrient (P and N) concentrations than did the aquaria with sand. All species dried faster on sand substrate, which led to lower regeneration (in terms of dry weight, length, sprout and root formation) in this treatment. H. verticillata fragments elongated faster than the other species, but E. najas was the most successful species (in terms of increase in dry weight) in the sand treatment. Our results indicate that the exotic H. verticillata has a competitive advantage, at least in its early stages of regeneration, over the other two, native species, especially in more eutrophic and turbid habitats; whereas E. najas fragments have a competitive advantage in less-turbid, oligotrophic and sand-dominated sites.

Resumo -Os objetivos deste trabalho foram determinar, na sucessão aveia-preta/milho, a produção de matéria seca e o acúmulo de N pela aveia-preta e sua relação com a produtividade do milho em sucessão; a influência de épocas de aplicação de N sobre os teores de N no solo e a produtividade de grãos do milho. Os tratamentos foram: 15-0-20-55, 30-0-20-40, 45-0-20-25, 0-35-20-35, 0-70-20-0, 0-0-20-70 e 0-0-0-0, correspondendo, respectivamente, às quantidades de N (kg ha -1 ), aplicadas no perfilhamento da aveia-preta, na pré-semeadura, na semeadura e na cobertura do milho. O aumento na produção de matéria seca e de N acumulado pela aveia-preta, com as aplicações de N no seu perfilhamento, não alteraram a produtividade de grãos de milho. Apesar da aplicação de N em pré-semeadura do milho ter proporcionado maior teor de N no solo no início do desenvolvimento, a aplicação de N em cobertura propicia a obtenção de maiores produtividades de grãos.Termos para indexação: grão, rendimento de cultura, matéria seca, nitrogênio, época de aplicação. Management of nitrogen fertilization in the succession black oat/corn in the no-tillage systemAbstract -The objectives of this study were to evaluate, in the succession black oat/corn, the dry matter production and N accumulation by black oat and their corn productivity, the influence of applied N on soil N content and the best application time of mineral N for corn production. The treatments were: 15-0-20-55, 30-0-20-40, 45-0-20-25, 0-35-20-35, 0-70-20-0, 0-0-20-70 and 0-0-0-0, corresponding, respectively, to the amounts of N (kg ha -1 ) applied at black oat tillering, before corn seeding, at corn seeding and corn sidedress. The increase in the dry matter production and of N accumulated in the black oat, with the applications of N in the black oat tillering, did not affect corn grain productivity. Although the application of N before corn seeding provided greater soil N content at the beginning of corn development, the application of N as sidedress provided the highest corn grain yield.Index terms: grain, crop yield, dry matter, nitrogen, application date.(1) Aceito para publicação em 20 de setembro de 2002. IntroduçãoUm dos aspectos determinantes do sucesso do plantio direto é a rotação de culturas capaz de produzir e manter grande quantidade de matéria seca sobre o solo por maior período. Esse é um dos motivos pelos quais as gramíneas devem compor sistemas de culturas no plantio direto. Grande parte das áreas sob plantio direto na região Sul do Brasil utilizam a aveia-preta como cobertura de inverno, antecedendo ao milho no verão. A aveia-preta propicia elevada produção de matéria seca, menor custo da semente, rápido desenvolvimento inicial, eficiência