The Pathway Of Nutrient Absorption And Utilization Of Submerged Macrophyte Potamogeton Crispus And Its Effect On Water Purification Efficiency

Submerged macrophytes,involved in the cycles of nitrogen and phosphorus nutrients,are important primary producers in freshwater ecosystems.Replanting submerged macrophytes is a common technology for restoration of eutrophic water.Therefore,it is of great significance to study the adsorption processes of nitrogen and phosphorus nutrients via submerged macrophytes.In this study,a typical submerged macrophytes,Potamogeton crispus?P.crispus?,was selected to investigate the nutrient adsorption efficiency by its stems and leaves?fragments?,through a series of laboratory simulation experiments.The adsorption pathway of P.crispus under eutrophication condition was analyzed and its discrepancy between trophic states was compared.The main results were as follows:?1?The P.crispus fragments significantly grew via adsorbing nutrients,as evidenced by the maximal length of stems and their fresh weights?p < 0.05?.At the end of the experiment,the numbers of the turions in the treatment of 100% coverage of P.crispus fragments?2.67 ind.-1?were slightly higher than the treatment of 50% coverage?2.09 ind.-1?.The reduction rate of nitrogen and phosphorus in the water became faster with the increase of the coverage of P.crispus fragments.The TN and TP concentrations were significantly decreased in the treatments of 50% and 100% coverage at day 3?p <0.01?.When the concertation of NH₄⁺-N was more than 0.35 mg·L-1,P.crispus was preferential to absorb NH₄⁺-N and followed by NO3--N.In addition,algae biomass,including planktonic and benthic algae,significantly declined with the increase of fragment biomass.Given the increase of fragment biomass,the dominated green algae Cosmarium and Chlorella vulgaris of the phytoplankton shifted to cyanobacteria Microcystis and green algae.The dominated green algae Cosmarium in the control system changed to the green algae Scenedesmus,which is dominated in the benthic algae.?2?The reduction rate of nitrogen and phosphorus in the water was fastest in the treatment of wrapped sediments?B?.On Day 18,the TN and TP removal rates of B reached 62.58% and 90.07%,respectively.The TN removal rates of other four groups were less than 60%.The main nitrogen form was NH₄⁺-N in the sediments.The reduction rate of NH₄⁺-N and TP in the sediments of the treatment of exposed sediments is higher than the treatment of wrapped sediments.In the treatment of wrapped sediments,the NH₄⁺-N and TP removal rates of sediments reached 39.05% and 10.95%,respectively,suggesting that nutrients in the sediments were released into the water.Therefore,the roots of P.crispus in the eutrophic water can absorb the nitrogen and phosphorus nutrients in the sediments,while the nitrogen and phosphorus nutrients in the sediments can be released into the water for the absorption of P.crispus stems and leaves.?3?Under oligotrophic and eutrophic levels,the maximal length of stems,average fresh weights,relative growth rate?RGR?and actual photochemical fluorescence yield of P.crispus were not significantly different.The nitrogen and phosphorus contents of P.crispus increased gradually at the beginning of the experiment,and the PTN and PTP reached the maximum on Days 42 and 60,respectively,with no significant difference between the two groups?p > 0.05?.There was a significant negative correlation between the nitrogen and phosphorus nutrient in the water and the PTN and PTP of P.crispus?p < 0.05?,while the nitrogen and phosphorus in P.crispus and the nitrogen and phosphorus in the water were not significantly related.On Day 30,the reduction rate of TN in the eutrophic group reached 73.57%,and the reduction rate of TP reached 87.05% on Day 18.The reduction rate of TP in the control reached 51.02%,and TN increased slightly on Day 18.In oligotrophic and eutrophic conditions,P.crispus can absorb nutrients via roots,stems and leaves.However,in the condition of oligotrophic state,P.crispus can only adsorb nutrients from sediments by roots.The change of trophic state can change the absorption pathway of nutrients by P.crispus.Therefore,P.crispus can shift the absorption pathway of nutrients in difference trophic states.