Nitrogen and phosphorus absorption characteristics of Myriophyllum aquaticum under oxygenation method

Aquatic plants often present yellowing and withering at the decline stage, thus seriously deteriorating the aesthetic appearance of the river channel and the purification of water quality. This study aims to investigate the absorption characteristics of nitrogen (N) and phosphorus (P) in plants under oxygenation. Five oxygenation levels were set, namely CK(0min), JO1(4min), JO2(6min), JO3(8min), and JO4(10min). Myriophyllum aquaticum was taken as the research material, due to the rapid growth in summer and slow in winter. Among them, the seedling period of Myriophyllum aquaticum was from July 10 to September 15, while the growth peak period was from September 16 to December 22. The pot experiment was conducted (PVC basin parameters: diameter: 30cm, height: 25cm, dry soil weight: 6.5kg/basin). The spiral pipe system was selected in the soil during the soil loading. Prior to the experiment, Myriophyllum aquaticum was pre-cultured for 1-2 days, washed with distilled water, and appropriately trimmed to 5 cm. The cuttings were cut into the PVC basin on July 10. The nutrient solution was added to the water layer of 10cm on August 22. Mechanical oxygenation treatment was then carried out after the stable growth of the Myriophyllum aquaticuma. The increasing oxygen was attributed to the electromagnetic ventilation pump (rated power: 220V/50Hz, exhaust volume: 20L/min). The spiral pipe system was then ventilated to increase oxygen into Myriophyllum aquaticuma rhizosphere. Oxygenate once a day at 8 am. The samples were tested during t₁ (September 15, 2019), t₂ (October 10, 2019), t₃ (October 27, 2019), t₄ (November 16, 2019) and t₅ (December 22, 2019), in order to determine the winter tolerance and N and P absorption of Myriophyllum aquaticuma after aeration treatment. A systematic analysis was implemented on the N and P absorption content, N and P ratio of plant, N and P form content of bottom mud, and N and P ratio of bottom mud in the seedling and growth peak period of Myriophyllum aquaticum under different oxygenation levels. Results showed that the highest N and P uptake contents of Myriophyllum aquaticum were achieved in the t₁ and t₂ stages, while the highest N uptake content was found in t₅ stage, when the oxygenation level was 8 min; The highest N and P uptake of Myriophyllum aquaticum was found in the t₃ and t₄ stage, while the highest P uptake content was in the t₅ stage, when the oxygenation was 6min. Oxygenation was beneficial to the N absorption in the t₁, t₂ and t₃ stages, while the P absorption in the t₄ stage. The N/P ratio of Myriophyllum aquaticum increased by 5.27%~36.57%, 9.04%~63.07%, and 3.50%~73.45% in the t₁, t₂ and t₃ stage, respectively, whereas, there was the decrease by 1.38%~34.05% in the t₄ stage; The N and P ratio of bottom mud decreased by 64.84% and 54.76% in the t₁ and t₂ stage, respectively, whereas, there was the increased by 138.97% and 47.02% in the t₄ and t₅ stage, respectively; Oxygenation was reduced the chlorophyll a and b, and the total chlorophyll content in the leaves of rice at the t₂ and t₅ stage, while increasing the chlorophyll content at the t₄ stage. Also, the hierarchical cluster analysis and multiple linear regression showed that the duration of 6 min was suitable for the N and P absorption and utilization of Myriophyllum aquaticum; Oxygenation increased the decreased chlorophyll a and b contents in the t₁ stage, alkaline hydrolyzed N content in the t₅ stage and iron-bound P content in the t₄ stage, indicating the high N and P absorption in the t₅ stage. Thereby, Oxygenation was used to regulate the formation of chlorophyll in Myriophyllum aquaticum leaves and the transformation of N and P in sediment. There was an increase in the absorption of N and P in sediment, the absorption and utilization of N and P in Myriophyllum aquaticum. The finding can also be used to inhibit methane and nitrous oxide, carbon dioxide and greenhouse gas emissions.