| Submerged machophytes are not only one of the most important aquatic plants in building water ecosystems,but also are essential to the ecological remediation in eutrophic waters such as Lakes and ponds.Therefore,this paper choose growing fast,environmental adaptability,resistance to barren sediment,three kinds of common submerged machophytes----Eloeda nuttallii,Ceratophyllum demersum, and Myriophyllum spicatum as study object,studied on their growth,absorption and physiological changes through indoor ecological experiment.The results showed that the optimal combination of phosphorus and iron concentration of Eloeda nuttallii and Myriophyllum spicatum growth are P(0.4mg·L-1)×Fe(1.25mg·L-1),and Ceratophyllum demersum are P(0.2mg·L-1)×Fe (0.28mg·L-1) or P(0.4mg·L-1)×Fe(0.28mg·L-1);under this concentration,the growth rate and absorption rate significantly higher than other combinations and single-factor phosphorus or iron of three kinds of submerged plant (p<0.05),furthermore,their chlorophyll content reached the largest,SOD activity and MDA content is the lowest.A fitting kinetic equation displayed the phosphorus and iron absorption of three submerged macrophytes have a higher correlation coefficient of 0.9395.The results on the absorption and utilization of phosphorus and iron of Microcystis aeruginosa indicated that:five kinds of phosphorus sources(dipotassium hydrogen phosphate,β-glycerol phosphate,adenosine triphosphate sodium,sodium pyrophosphate, partial sodium) can be absorbed and utilised by Microcystis aeruginosa;the ratio of inorganic phosphorus(dipotassium hydrogen phosphate)and organic phosphorus(β-glycerol phosphate or adenosine triphosphate sodium)of 6:1 was the most favorable growth period and the fastest uptake of solubility of reactive phosphorus(SRP),and reached the maximum biomass of 2.586×106cells·mL-1,increased by about 65.3%than that of pure inorganic phosphorus group;the optimal combination of phosphorus and iron concentration of Microcystis aeruginosa growth are P(0.4mg·L-1)×Fe(1.25mg·L-1) or P(1mg·L-1)×Fe(0.28mg·L-1),at this concentration,the growth rate and absorption rate significantly higher than other combinations and single-factor phosphorus or iron of Microcystis aeruginosa(p<0.05),furthermore,their chlorophyll content reached the largest, SOD activity and MDA content were the lowest. At the same time,their chlorophyll content reached the largest,SOD activity and MDA content were the lowest.Co-culture system of the competition on nutrients of submerged machophytes and Microcystis aeruginosa showed that:under the condition of P(1mg·L-1)and Fe(0.28mg·L-1),the growth inhibitation rates of 1×104,105cells·mL-1 Microcystis aeruginosa were 71.16% and 69.32% through the competition on nutrients of 2.5±0.05g·L-1 Ceratophyllum demersum;Under the same condition, the growth inhibition rate of different initial concentrations of Microcystis aeruginosa(1×104,1×105和1×106cells·mL-1)were 88.33%,72.52%and 59.36%; In co-culture system of the competition on nutrients,since the fourth days,Microcystis aeruginosa's alkaline phosphatase activity and secretion of siderophore increasing reflected that the competition of submerged machophytes and Microcystis aeruginosa is fierce;The physiological and biochemical changes such as SOD activity and MDA contents raising demonstrated that Microcystis aeruginosa were in oxidative stress,but in ten days the physiological and biomass indicators showed that the algal cells were in seriously injured and toward death.Through this experiment,we found the optimal combination of phosphorus and iron concentration on growth and absorption of three kinds of submerged machophytes and Microcystis aeruginosa,as well as the conclusions that submerged machophytes can effectively inhibit the growth of Microcystis aeruginosa,in co-culture systems through the competition on nutrients of phosphorus and iron.thereby, this paper is to lay the foundation for cultivate submerged machophytes abundantly in eutrophic waters and create a healthy and harmonious aquatic ecosystems,and provide a theoretical basis for make better use of submerged machophytes remediation in eutrophic waters.
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