Macrófitas flutuantes causam supressão do fitoplâncton independente do estado trófico.

Abstract

The degradation of inland aquatic ecosystems, driven by eutrophication, frequently alters the dominance dynamics among primary producers. This study aimed to evaluate the competitive interaction between the free-floating aquatic macrophyte Pontederia crassipes and the phytoplankton community under different nutrient availability levels. To achieve this, an experimental design was conducted to evaluate three trophic states (oligotrophic, mesotrophic, and hypertrophic) subjected to interaction treatments (species in isolation and in combination). Macrophyte biomass gain, chlorophyll a concentrations, and limnological variables were quantified. Analysis of Variance (ANOVA) demonstrated that the biomass gain of P. crassipes showed no significant differences regarding trophic state or the presence of phytoplankton, evidencing its high physiological resilience and efficient clonal biomass allocation even under severe nutritional restriction. In contrast, the phytoplankton community was severely impacted, showing drastic and significant reductions (𝑝 < 0.05) in chlorophyll 𝑎 concentrations in treatments containing the macrophyte, regardless of nutrient enrichment. The data indicate that the rapid formation of the floating mat by P. crassipes exerts rigorous temporal control through a physical barrier, making light attenuation the primary limiting factor for pelagic producers. Additionally, multivariate ordering (PCA) confirmed that the presence of the macrophyte substantially restructures the physicochemical characteristics of the water. It is concluded that the dominance of P. crassipes over the phytoplankton community is independent of the nutrient enrichment of the medium. The asymmetry of this interaction warns of the ecological complexity of managing invaded environments and reinforces the urgency of preventive policies aimed at mitigating nutrient input.