NITROGEN FIXATION BY LEGUMES IN FLOODED REGIONS

Maria de Fátima Loureiro, Euan Kevin James, Avílio Antônio Franco

Abstract


Wetlands are often subjected to annual net losses of N from the system via leaching of the soil, which are not balanced by inputs of N via the mineralization of organic matter. These oligotrophic ecosystems are largely dependent on N inputs from biological nitrogen fixation (BNF), and legume-rhizobial symbioses are some of the main contributors. However, legumes are often sensitive to flooding, and soil inundation can have a serious effect on their growth. This is because legume nodules have a requirement for O2 to maintain the aerobic respiration necessary to supply the high amounts of ATP needed for nitrogenase activity. Despite having adaptations such as the O2-carrying protein leghaemoglobin (Lb) to optimize O2 supply, most terrestrial legumes are not capable of increasing the O2 supply and within their nodules sufficiently whilst flooded, and hence BNF is reduced or completely curtailed. By contrast, most legumes that fix N2 in flooded regions have evolved additional mechanisms to optimize the O2 supply to their flooded nodules, as well as the morphological, structural and biochemical adaptations that allow these legumes to fix N2 whilst flooded.


Keywords


plant ecophysiology; nitrogen fixation; oxygen supply

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