Avaliação da distância máxima de absorção de nutrientes em formações florestais tropicais usando 15N como marcador
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Data
2019-04-02
Autores
Pinheiro, Rafael Costa [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As mudanças climáticas têm causado alterações na temperatura e também nos regimes de precipitação do planeta, aumentando a probabilidade de ocorrência de secas mais severas, o que, no cenário florestal, pode resultar na mortalidade de florestas ao redor do mundo. Assim, é necessário um conhecimento mais detalhado sobre a dinâmica de absorção de água e nitratos pelas raízes das árvores, que explique o comportamento das árvores sob extrema seca. O objetivo do estudo foi avaliar a distância máxima do tronco e a profundidade máxima de absorção de nutrientes e água pelas raízes das árvores em florestas crescendo sobre Neossolos Quartzarênicos muito profundos, utilizando o 15N como marcador. As consequências do status social das árvores, comparando árvores dominantes e dominadas do mesmo genótipo numa floresta monoclonal foram estudadas em plantios de um clone híbrido de Eucalyptus urophylla x Eucalyptus grandis durante a estação seca. Os efeitos da sazonalidade (comparando as estações seca e chuvosa) foram estudados em três espécies do Cerrado: i) Xylopia aromatica (Lam.) Mart.; ii) Coussarea hydrangeifolia (Benth.) Müll.Arg.; and iii) Miconia albicans (Sw.) Steud. Além disso, foi avaliada a existência de uma complementaridade de nicho no solo entre essas espécies do Cerrado, com uma absorção do marcador em camadas diferentes. O marcador NO3--15N foi aplicado em talhões de eucalipto com 7 meses, 1,2 anos, 2,2 anos e 6,4 anos de idade, a várias profundidades do solo em 60 pontos, sendo 3 repetições por profundidade. No Cerrado, o marcador NO3--15N foi aplicado em 36 pontos: 2 estações do ano (seca e chuvosa), 6 profundidades (até 12 m) e 3 repetições. Todas as parcelas foram alocadas a uma distância maior que 50 m entre elas. O marcador foi aplicado em apenas um ponto no centro de cada parcela. Cinco meses após a aplicação do marcador, o 15N foi determinado a partir do valor de δ15N nas folhas amostradas em árvores a diferentes distâncias de cada área de injeção. Os resultados mostram que os fertilizantes em plantios comerciais de eucalipto devem ser aplicados próximos aos troncos para serem absorvidos por todas as árvores (dentro de 2 m), independentemente da idade do povoamento e do status social das árvores. A fertilização (e o controle de ervas daninhas) em metade das entrelinhas de plantios de eucalipto durante a estação chuvosa pode ser suficiente para permitir que todas as árvores absorvam os nutrientes aplicados, o que poderia reduzir o custo de uma adubação comercial convencional. Os íons de nitrato lixiviados em Latossolos profundos podem ser absorvidos pelas raízes das árvores a uma profundidade de 6 metros entre 0,6 e 2,5 anos após o plantio. Entretanto, a velocidade de exploração das camadas profundas do solo depende do status social das árvores. Na área de Cerrado, o nitrato marcado foi absorvido em diferentes profundidades e distâncias do tronco, dependendo da espécie estudada, o que sugere uma complementaridade de nicho em todo o perfil do solo até uma profundidade de pelo menos 6 metros. Apenas as árvores com um diâmetro à altura do peito maior que 5 cm foram capazes de absorver o marcador injetado em profundidades de mais de 1,5 metros. Inesperadamente, as árvores não absorveram os nitratos marcados mais profundamente na estação seca do que na estação chuvosa.
Climate changes have caused alterations in temperature and in precipitation regimes around the world. This increases the probability of exceptional drought periods, which may result in tree mortality over large areas. Therefore, it is necessary to improve our knowledge about the the dynamics of water and nitrate uptake by the rootsthat explain the tree behaviour under extreme drought. This study aimed to assess the maximum distance of the trunk and the maximum depth of nutrient and water uptake by tree roots in forests growing on very deep Ferralic Arenosols through 15N tracer. The consequences of the social status of trees, comparing dominant and suppressed trees of the same genotype in a monoclonal forest, were studied in plantations of the same clone of the Eucalyptus urophylla x Eucalyptus grandis hybrid over the dry season. The effects of seasonality (comparing dry and rainy seasons) were studied in three native savanna (Cerrado) species: i) Xylopia aromatica (Lam.) Mart.; ii) Coussarea hydrangeifolia (Benth.) Müll.Arg.; and iii) Miconia albicans (Sw.) Steud,. Furthermore, the existence of a niche complementarity in the soil among the three studied Cerrado species was evaluated, with the analysis of the tracer uptake in different soil layers, depending on the species. The NO3--15N tracer was applied in 7-month-old, 1.2-year-old, 2.2-year-old and 6.4-year-old eucalypt stands at several soil depths, with three repetitions per depth at 60 positions. In the Cerrado, NO3--15N tracer was applied at 36 positions: 2 seasons (dry and rainy), 6 depths (down to 12 m) and 3 repetitions. All the plots were allocated at a distance > 50 m between them. The tracer was applied at only one location in the centre of each plot. Five months after tracer application, 15N was determined from the δ15N values in leaves sampled in dominant and supressed trees at different distances from each injection area. The results show that fertilizers must be applied close to the trunks (within 2 m) in Eucalyptus plantations to be taken up by all trees, regardless of stand age and tree social status. Fertilization (and weed control) in half of the inter-rows during the rainy season could be sufficient to make it possible for all the trees to take up the applied nutrients which could reduce the cost of a conventional commercial fertilization., Nitrates leached in deep sandy soils can be taken up by tree roots at a depth of 6 m between 0.6 and 2.5 years after planting in commercial Eucalyptus plantations. However, the velocity of exploration of deep soil layers depends on the social status of the trees. The labelled nitrates were taken up at different depths and distances from the trunk depending on the species in the Brazilian savanna studied, which showed a niche complementarity throughout the soil profile down to a depth of at least 6 m. Only trees with a DBH of more than 5 cm were able to take up the NO3--15N tracer injected at depths of more than 1.5 m. Unexpectedly, trees did not take up the labelled nitrates more deeply in the dry season than in the rainy season.
Climate changes have caused alterations in temperature and in precipitation regimes around the world. This increases the probability of exceptional drought periods, which may result in tree mortality over large areas. Therefore, it is necessary to improve our knowledge about the the dynamics of water and nitrate uptake by the rootsthat explain the tree behaviour under extreme drought. This study aimed to assess the maximum distance of the trunk and the maximum depth of nutrient and water uptake by tree roots in forests growing on very deep Ferralic Arenosols through 15N tracer. The consequences of the social status of trees, comparing dominant and suppressed trees of the same genotype in a monoclonal forest, were studied in plantations of the same clone of the Eucalyptus urophylla x Eucalyptus grandis hybrid over the dry season. The effects of seasonality (comparing dry and rainy seasons) were studied in three native savanna (Cerrado) species: i) Xylopia aromatica (Lam.) Mart.; ii) Coussarea hydrangeifolia (Benth.) Müll.Arg.; and iii) Miconia albicans (Sw.) Steud,. Furthermore, the existence of a niche complementarity in the soil among the three studied Cerrado species was evaluated, with the analysis of the tracer uptake in different soil layers, depending on the species. The NO3--15N tracer was applied in 7-month-old, 1.2-year-old, 2.2-year-old and 6.4-year-old eucalypt stands at several soil depths, with three repetitions per depth at 60 positions. In the Cerrado, NO3--15N tracer was applied at 36 positions: 2 seasons (dry and rainy), 6 depths (down to 12 m) and 3 repetitions. All the plots were allocated at a distance > 50 m between them. The tracer was applied at only one location in the centre of each plot. Five months after tracer application, 15N was determined from the δ15N values in leaves sampled in dominant and supressed trees at different distances from each injection area. The results show that fertilizers must be applied close to the trunks (within 2 m) in Eucalyptus plantations to be taken up by all trees, regardless of stand age and tree social status. Fertilization (and weed control) in half of the inter-rows during the rainy season could be sufficient to make it possible for all the trees to take up the applied nutrients which could reduce the cost of a conventional commercial fertilization., Nitrates leached in deep sandy soils can be taken up by tree roots at a depth of 6 m between 0.6 and 2.5 years after planting in commercial Eucalyptus plantations. However, the velocity of exploration of deep soil layers depends on the social status of the trees. The labelled nitrates were taken up at different depths and distances from the trunk depending on the species in the Brazilian savanna studied, which showed a niche complementarity throughout the soil profile down to a depth of at least 6 m. Only trees with a DBH of more than 5 cm were able to take up the NO3--15N tracer injected at depths of more than 1.5 m. Unexpectedly, trees did not take up the labelled nitrates more deeply in the dry season than in the rainy season.
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Palavras-chave
Absorção de água, Raízes (Botânica), Isótopos, Eucalipto, Cerrados, Water uptake, Fine roots, Labelled nitrate, Eucalypt plantations