Floating-leaved and submerged macrophytes suppress filamentous cyanobacteria blooms and 2-MIB episodes in eutrophic shallow lakes

Although macrophytes can control filamentous cyanobacteria that produce 2-methylisoborneol (2-MIB) in lakes, there is a lack of evidence regarding the inhibitory effects of different macrophyte growth forms on 2-MIB producers, as well as the underlying mechanisms. To address this knowledge gap, this study compared the impact of floating-leaved and submerged macrophytes on Pseudanabaena growth and 2-MIB release, combing a field investigation and culture experiments. The field survey showed that both the Pseudanabaena cell density and 2-MIB concentrations were significantly lower in areas dominated by floating-leaved or submerged macrophytes than in phytoplankton-dominated areas. In the culture experiments, floating-leaved macrophytes exhibited overall stronger inhibitory effects on Pseudanabaena than submerged macrophytes. Allelopathic effects emerged as a more critical mechanism than nutrient competition and light limitation in controlling Pseudanabaena growth and 2-MIB release by regulating the photosynthetic activity, gene abundance, and cell density. Allelopathic experiments further confirmed that the dissolved organic matter released from Nymphoides peltate, Trapa bispinosa and Myriophyllum spicatum contained higher concentrations of allelochemicals than that released from Vallisneria natans and Ceratophyllum demersum, driving the photosynthetic inhibition pathway. These findings demonstrate that biological control has great promise as an effective method for odorant management in eutrophic shallow lakes.