High nutrient availability does not mitigate submersion stress in an emergent aquatic macrophyte

Abstract

In floodplains, the depth of water can directly impact the development of aquatic macrophytes. In this study, we used the emergent macrophyte Polygonum ferrugineum Wedd to investigate whether increased nutrient availability in the sediment alleviates submergence stress caused by flood conditions. Using a factorial design, we planted seedlings in two types of sediment (unenriched and enriched with P and N), subjecting them to deep and shallow water treatments. The effects of these treatments on plant attributes were assessed using a two-way ANOVA. The interaction between nutrients and depth significantly influenced most measured attributes (total biomass, shoot length, shoot biomass, leaf area, and root biomass). The highest values for these variables were observed when plants were grown in shallow water with high nutrient concentrations in the sediment. Root length and root:shoot ratios were influenced solely by depth, both of which were greater in the shallow treatment compared to the deep treatment. Our findings demonstrate that the growth of P. ferrugineum only occurs in shallow water where shoots are exposed to the atmosphere. Furthermore, our data indicate that greater depths (> 0.7 m) negatively impact growth regardless of nutrient availability. Therefore, we reject the hypothesis that high nutrient availability mitigates submersion stress. Our results contribute to the discussion on the impact of floods on emergent macrophyte species, highlighting the rapid morphological changes observed due to nutrient conditions in flooded sediments.