Seasonal changes of leaf Nitrogen content in trees of Amazonian floodplains

Abstract

-In Amazonian floodplains the trees are exposed to extreme flooding of up to 230 days a year. Waterlogging of the roots and stems affects growth and metabolic activity of the trees. An increased leaf fall in the aquatic period and annual increment rings in the wood indicate periodical growth reductions. The present study aims at documenting seasonal changes of content. Leaves of six tree species common in floodplains in Central Amazonia and typical representants of different growth strategies were collected every month between May 1994 and June 1995 in the vicinity of Manaus, Brazil. Mean leaf nitrogen content varied between 1.3% and 3.2% in the non-flooded trees. Three species showed significantly lower Ν content in the flooded period (p=0.05, 0.001, 0.001), the difference ranging 20-25% lower than in the nonflooded period. Two species showed no significant difference while Nectandra amazonum showed 32% more Ν in the flooded season (p=0.001). Leaf nitrogen content was generally high when new leaves were flushed (in the flooded period) and decreased continuously thereafter in all species. Three species showed an additional peak of nitrogen during the first month of the terrestrial phase, in leaves which had flushed earlier, indicating that flooding may disturb nitrogen uptake.Key-words: leaf nitrogen, growth strategy, waterlogging, várzea, floodplain, Amazonia. Mudanças Sazonais do Conteúdo de Nitrogênio nas Folhas de Arvores das Áreas Inundáveis da Amazônia.Resumo -Em áreas inundáveis da Amazônia as árvores estão expostas a extremos de inundação de até 230 dias por ano. A submersão das raízes e do tronco afeta o crescimento e as atividades metabólicas das árvores. O aumento da queda de folhas na fase aquática e o incremento anual nos anéis do lenho, indicam reduções de crescimento periódicas. O presente estudo visa documentar em um ciclo anual mudanças sazonais no metabolismo e vitalidade de árvores adultas, expressas pelas mudanças no conteúdo de nitrogênio das folhas. Seis espécies de árvores comuns em áreas inundáveis da Amazônia Central e típicos representantes de diferentes estratégias de crescimento, tiveram suas folhas coletadas a cada mês entre maio de 1994 e junho de 1995, nas cercanias da cidade de Manaus, Brasil. A média do conteúdo de nitrogênio variou entre 1,3% e 3,2% em árvores não inundadas. Três espécies tiveram concentrações de Ν significativamente menores no período de inundação (p = 0,05, 0,01, 0,01), sendo 20 a 25% menores que as concentrações no período não inundado. Duas espécies não tiveram diferenças significativas, enquanto Nectandra amazonum teve 32 % mais Ν quando inundada (p = 0.001). O conteúdo de nitrogênio foliar foi geralmente alto quando brotaram folhas novas (no período inundado) seguido por um decréscimo contínuo, embora três espécies atingiram seu pico de conteúdo de Ν no primeiro mês da fase terrestre, em folhas que haviam brotadas antes, indicando que a inundação possivelmente inibe a assimilação de nitrogênio.Palavras-chave: nitrogênio, folhas, estratégias de cre...

Responses to flooding of plant water relations and leaf gas exchange in tropical tolerant trees of a black-water wetland

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