Oxygen, pH, and Eh microprofiles around submerged macrophyte Vallisneria natans response to growing stages

The periphyton, attached to the surfaces of submerged plants, has important effects on plant growth and development in eutrophic waters. Periphyton complicates the microenvironment of diffusive boundary layer around submerged plants. We researched periphyton characteristics, oxygen (O₂), pH, and Eh microprofiles at various growing stages of Vallisneria natans. The results suggested that during the growing period of V. natans, O₂ concentration and pH decreased from 0 to 2 mm above the leaf surface, whereas the Eh increased. As V. natans grew, O₂ and pH gradually increased until they peaked during stable growing stages, while the Eh decreased. However, during the decline stage, O₂ and pH gradually decreased, and Eh increased. To summarise, O₂ and pH showed a unimodal pattern in response to the life cycle of V. natans, with the maximum levels during the stable growth stage and the minimum levels during the rapid growth and decline stages. Our study demonstrated that V. natans growth induced steep gradients in O₂ concentrations, pH, and Eh at the DBL by increasing the layer's thickness, macrophyte photosynthetic capacity, and periphyton biomass in eutrophic waters.