Abstract
The effects of water flow on the leaf-biofilm interface of Vallisneria natans and Hydrilla verticillata were investigated using artificial plants as the control. Water flow inhibited the growth of two species of submerged macrophytes, reduced oxygen concentrations in plant leaves and changed oxygen profiles at the leaf-biofilm interface. The results from confocal laser scanning microscopy and multifractal analysis showed that water flow reduced biofilm thickness, changed biofilm topographic characterization and increased the percentages of single colony-like biofilm patches. A cluster analysis revealed that the bacterial compositions in biofilms were determined mainly by substrate types and were different from those in sediments. However, water flow increased the bacterial diversity in biofilms in terms of operational taxonomic unit numbers and Shannon Indices. Our results indicated that water flow can be used to regulate the biomass, distribution and bacterial diversities of epiphytic biofilms in constructed wetlands dominated by submerged macrophytes.
Highlights
Submerged macrophytes growing under water surface play an important role in water environments and in constructed wetlands (CWs)
V. natans and H. verticillata were employed to analyze the response of biofilm-leaves to water flow in a tank-flume cycling system (Supplementary Fig. 1)
The two-way ANOVA analysis showed that both flow treatment and host species influenced the growth rates significantly (Fflow treatment × species = 222.0, p < 0.001; Fflow treatment = 334.7, p < 0.001; and Fspecies = 888.1, p < 0.001). These results suggested that water flow decreased the growth rates of the two species of submerged macrophytes, and the growth rate of V. natans was larger than that of H. verticillata
Summary
Submerged macrophytes growing under water surface play an important role in water environments and in constructed wetlands (CWs) They are able to take up nutrients from both the sediment and the surrounding water column[1], and they show advantages in reducing water turbidity caused by phytoplankton and suspended solids[2]. Submerged macrophytes might provide nutrients as well as allelopathic substances to epiphytic microbes, leading to diverse and host specific epiphytic bacterial communities[7,9]. The animate host would be growing and interacting with epiphytic biofilms throughout its lifetime through physiological activities (e.g. individual growth[8], phyllosphere oxygen profiles[6], allelopathic compounds secretion[9]) Both of these factors make the situation of epiphytic microbes more complex than their counterparts on rigid non-living materials. No studies have systematically investigated the effects of water flow on the biofilms attached to the surface of submerged macrophytes
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