DIFFERENT FUNCTIONAL TYPES OF SUBMERGED MACROPHYTES ON DISSOLVED OXYGEN AND ITS ENVIRONMENTAL EFFECTS

The concentration of dissolved oxygen (DO) in lakes decreases due to eutrophication and climate warming. However, submerged macrophytes can release oxygen through photosynthesis, effectively increasing DO levels in lakes. The process can induce changes in the physicochemical properties of the water column and sediment, subsequently impacting the ecosystem. We conducted a mesocosm experiment to examine the differences in dissolved oxygen and related indexes in water column and sediment across different functional types of submerged macrophytes. Vallisneria spinulosa was assigned to bottom-dwelling species, Hydrilla verticillata was assigned to less rooted canopy-forming species, while Myriophyllum spicatum was assigned to more rooted canopy-forming species. The results showed that significant differences in water column DO among treatment groups. The blank group had significantly lower water column DO compared to the plant treatment group, and it exhibited the least reduction in total nitrogen (TN) and total phosphorus (TP) in the water column. The specific leaf area, leaf area index, net growth biomass, total biomass, relative growth rate and water column DO of H. verticillata were the largest, which can effectively reduce the concentration of TP and TN in the water column. The plant height of M. spicatum was the highest, and its ability to elevate water column DO was significantly higher than that of spiny bittercress, with the greatest reduction in water column TP. V. spinulosa had the largest specific root length, total root length per individual and root shoot ratio among the 3 species. It significantly increased DO concentration in the sediment up to a depth of 6 cm. Additionally, V. spinulosa had the highest sediment iron content and the lowest sediment total nitrogen (TN), total carbon (TC) content and total dissolved phosphorus (TDP) in interstitial water. Therefore, we suggest diverse functional submerged macrophyte types were constructed in the restoration of eutrophic lakes, such as combing bottom-dwelling and canopy-forming species, since it would be conducive to the formation of clear water state.