A vegetação campestre em gradientes inundáveis: composição florística, dinâmica do banco de sementes e de plântulas
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Data
2017-10-10
Autores
Bao, Francielli [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Espécies exóticas como Urochloa humidicola são introduzidas em pastagens nativas e ameaçam a diversidade de áreas úmidas, como o Pantanal. Áreas com eventos sazonais, a reserva de sementes no solo é uma importante fonte de regeneração. A influência de plantas exóticas e da inundação com relação à dinâmica do banco de sementes, distribuição e composição da vegetação campestre elucidam as características adaptativas voltadas para germinação, crescimento e estabelecimento das espécies. O objetivo foi avaliar as fontes primárias de regeneração: o banco de sementes e de plântulas, em diferentes níveis de topografia e sazonalidade e, estabelecimento de plantas exóticas. As coletas ocorreram em dois campos de pastagem, um dominado por espécies nativas e outro dominado por U.humidicola, no Pantanal de Mato Grosso do Sul. A amostragem ocorreu em lagoas sazonais em três níveis topográficos (baixo, intermediário e alto), para analisar o efeito da sazonalidade, as coletas foram realizadas ao final das estações de seca e de cheia, em dois anos. Os dados da vegetação, do banco de plântulas e de sementes foram analisados separadamente, para avaliar cada estágio de vida em função da sazonalidade, topografia e influência de plantas exóticas. Em seguida os dados de vegetação e banco de sementes foram relacionados para verificarmos a importância do banco de sementes na manutenção da flora nativa. O primeiro capítulo abordou a influência da U.humidicola sobre a pastagem nativa. Observamos alta cobertura vegetal no período de seca, e queda na cobertura vegetal de U. humidicola posterior a inundação. Para complementarmos este estudo foi elaborado o segundo capítulo, com um experimento em laboratório que simulou a inundação e a influência de macrófitas aquáticas na sobrevivência de mudas de U. humidicola. Verificamos que a associação com macrófitas promove a mortalidade de mais de 50% da cobertura aérea de U. humidicola. No terceiro capítulo foi avaliado o banco de sementes de nativas, as estratégias de germinação e as previsões de espécies que podem ocorrer na vegetação quando ocorre inundação e seca foram avaliados, com tratamentos de inundação e pós-inundação do solo. Encontramos rica comunidade de macrófitas durante a inundação e emergentes anuais e perenes pós-inundação. No quarto, avaliamos a regeneração em campo, a distribuição do banco de plântulas sob influência da inundação foi avaliada junto a formação de detritos orgânicos, a influência dos detritos sobre a distribuição de plântulas foi avaliada nos diferentes níveis de topografia. Diferentes concentrações de detritos orgânicos sugerem diferentes estratégias de colonização, variando a distribuição de plântulas entre os níveis. Já a importância do banco de sementes na manutenção da comunidade nativa foi analisada no último capítulo, o banco apresenta diversidade e pode ser uma importante fonte de manutenção da comunidade de espécies nativas, a U. humidicola deve ser tratada com cuidado, pois promove diminuição de macrófitas, este grupo de espécies é particularmente importante no controle de colonização de U. humidicola. Os resultados encontrados neste estudo podem auxiliar em planos de conservação e preservação de áreas úmidas frente à invasão de espécies exóticas.
Exotic species such as Urochloa humidicola (brachiaria) are introduced into native grassland and threaten the diversity of wetlands, such as the Pantanal. In wetlands subjected to extreme seasonal events, seed reserves in the soil are an important source of vegetation regeneration. Information on the influence of exotic plants and flooding in relation to seed bank dynamics, distribution and composition of the field vegetation helps to elucidate the adaptive characteristics aimed at germination, growth and establishment of the species. The aim was to evaluate the primary sources of regeneration: the seed bank and seedlings, under the influence of different levels of topography and seasonality and, establishment of exotic plants. The collections occurred in two grasslands: one dominated by native species and another dominated by U. humidicola, in the Pantanal of Mato Grosso do Sul. Sampling occurred in seasonal ponds where three topographic levels were established (low, mid and high); in addition, to analyze the effect of seasonality, the samples were collected at the end of the dry and flood seasons, in two years. Vegetation, seedling bank and seed data were analyzed separately, where it was possible to evaluate each stage of life due to the seasonality, topography and influence of exotic plants. Then the, vegetation and seed bank data were related to verify the importance of the seed bank in the maintenance of the native flora. Thus, the first chapter addressed the influence of U. humidicola on native grassland and the role of flooding in the control of this exotic species. We observed high vegetation cover in the dry season, but a decrease in U. humidicola vegetation cover after flooding. To complement this study the second chapter was elaborated, where an experiment was carried out in a laboratory that simulated the flood and the influence of aquatic macrophytes on the survival of U. humidicola seedlings. It was possible to verify that the association with macrophytes promotes the mortality of more than 50% of U. humidicola aerial cover, as well as, the persistence of the U. humidicola seed bank, which indicated a high germination potential of post-flood. In the third chapter the seed bank of the native species was evaluated, the germination strategies and the predictions of species that can occur in the vegetation when there is flood and dry were evaluated through greenhouse experiments, with flood and post-flood treatments from soil. A community rich in macrophytes was found during the flood and many emergent annual and post-flood perennials. In the fourth chapter we evaluated the regeneration in the field, the distribution of the seedlings bank under the influence of the flood was evaluated taking into consideration the formation of organic debris from aquatic macrophytes that die in the lowering of the waters, the influence of the debris on the distribution of seedlings was evaluated at different levels of topography. It was observed that different concentrations of organic debris suggest different colonization strategies, varying the distribution of seedlings between the levels. Finally, the importance of the seed bank in the maintenance of the native 4 community was analyzed in the last chapter, where it was possible to verify that the bank presents high diversity and can be an important source of maintenance of the community of native species, but, U. humidicola should be treated with caution, since it promotes a decrease of the macrophytic bank in the cultivated field, and this group of species is particularly important in the control of U. humidicola colonization. The results found in this study can aid in the conservation and preservation of wetlands against the invasion of exotic species.
Exotic species such as Urochloa humidicola (brachiaria) are introduced into native grassland and threaten the diversity of wetlands, such as the Pantanal. In wetlands subjected to extreme seasonal events, seed reserves in the soil are an important source of vegetation regeneration. Information on the influence of exotic plants and flooding in relation to seed bank dynamics, distribution and composition of the field vegetation helps to elucidate the adaptive characteristics aimed at germination, growth and establishment of the species. The aim was to evaluate the primary sources of regeneration: the seed bank and seedlings, under the influence of different levels of topography and seasonality and, establishment of exotic plants. The collections occurred in two grasslands: one dominated by native species and another dominated by U. humidicola, in the Pantanal of Mato Grosso do Sul. Sampling occurred in seasonal ponds where three topographic levels were established (low, mid and high); in addition, to analyze the effect of seasonality, the samples were collected at the end of the dry and flood seasons, in two years. Vegetation, seedling bank and seed data were analyzed separately, where it was possible to evaluate each stage of life due to the seasonality, topography and influence of exotic plants. Then the, vegetation and seed bank data were related to verify the importance of the seed bank in the maintenance of the native flora. Thus, the first chapter addressed the influence of U. humidicola on native grassland and the role of flooding in the control of this exotic species. We observed high vegetation cover in the dry season, but a decrease in U. humidicola vegetation cover after flooding. To complement this study the second chapter was elaborated, where an experiment was carried out in a laboratory that simulated the flood and the influence of aquatic macrophytes on the survival of U. humidicola seedlings. It was possible to verify that the association with macrophytes promotes the mortality of more than 50% of U. humidicola aerial cover, as well as, the persistence of the U. humidicola seed bank, which indicated a high germination potential of post-flood. In the third chapter the seed bank of the native species was evaluated, the germination strategies and the predictions of species that can occur in the vegetation when there is flood and dry were evaluated through greenhouse experiments, with flood and post-flood treatments from soil. A community rich in macrophytes was found during the flood and many emergent annual and post-flood perennials. In the fourth chapter we evaluated the regeneration in the field, the distribution of the seedlings bank under the influence of the flood was evaluated taking into consideration the formation of organic debris from aquatic macrophytes that die in the lowering of the waters, the influence of the debris on the distribution of seedlings was evaluated at different levels of topography. It was observed that different concentrations of organic debris suggest different colonization strategies, varying the distribution of seedlings between the levels. Finally, the importance of the seed bank in the maintenance of the native 4 community was analyzed in the last chapter, where it was possible to verify that the bank presents high diversity and can be an important source of maintenance of the community of native species, but, U. humidicola should be treated with caution, since it promotes a decrease of the macrophytic bank in the cultivated field, and this group of species is particularly important in the control of U. humidicola colonization. The results found in this study can aid in the conservation and preservation of wetlands against the invasion of exotic species.
Descrição
Palavras-chave
Sementes, Espécies exóticas, Inundação, Invasão de espécies, Áreas úmidas, Banco de sementes, Controle de espécies invasoras