Understanding how environmental factors drive community assembly remains a major challenge in community ecology, especially in biodiverse tropical forests. We investigated how environmental filters affect functional trait distribution in two contrasting types of floodplain forest in the Brazilian Amazon: white-water forest (várzea) and black-water forest (igapó). We placed 40 plots of 625 m2 along a flooding gradient in Central Amazonia and measured for edaphic variables and 11 functional traits related to use of resources and flooding tolerance/avoidance. We assessed functional distribution by calculating community-trait mean values and trait kurtosis. Analysis of community mean trait values showed that nutrient-rich white-water forests favored trees with productive leaves and fast growth, whereas nutrient-poor black-water forests favored trees with nutrient conservation traits and slow growth. Functional diversity was not related to environmental gradients. Edaphic characteristics act, therefore, as a strong environmental filter leading to trait convergence in these floodplain tree communities.