Phosphorus Absorption And Physiological Response Of Salix To Eutrophic Water

The eutrophication caused by Non-point source pollution has become the main problem of water environment.The mechanism of water eutrophication is the blooming of algae and plankton and leading to aquatic organism mass mortality subsequently as a result of oxygen deficit which caused by nitrogen and phosphorus concentration excessively increasing.Nitrogen and phosphorus are essential macronutrient for plant growth and development and play an important role,but they also are the key limiting factor of water eutrophication.The previous research mostly focused on nitrogen pollutant,but only decreasing nitrogen concentration is invalid to harness eutrophication.So it's necessary to remove the excess phosphorus in eutrophic water,too.As it has low investment,long-term effect and less secondary pollution,phytoremediation has a broad prospect to heal polluted environment.Compared with aquatic herb,woody plant has more biomass and longer growth cycle and stronger stress resistance and more manageable.Hence using woody plant harnessing eutrophic water is especially significant.However,there have been few studies on the purification of water by woody plant,and it is difficult to conduct a systematic research because of its long growth cycle.In this research,we focused on the phosphorus in eutrophic water and chose Salix matsudana new variety“Shidiliu 1”as experimental material,set fivesimulated eutrophic water treatment with different phosphorus concentrations(0.1 mg·L^-1,0.2 mg·L^-1,1 mg·L^-1,2 mg·L^-1,10 mg·L^-1)to fostered willow seedlings.We also used radioisotope tracing and autoradiography method to study the migration mechanism of phosphorus in the water-plant and its transportation and distribution rules in willow,analyzed the phosphorus purification mechanism and the physiological response to different phosphorus concentrations.The following main conclusion are obtained:?1?Phosphorus was transported and distributed in the root system after being absorbed by the roots and it was transported to the above-ground part after about 24 hours.At beginning phosphorus in the above-ground part was initially concentrated in the leaves and transported to the leaves near the root firstly,but the general tendency was that phosphorus was transported to the young leaves at the top of growth.The growth of leaf near the top was affected by the apical effect,and the distribution of phosphorus was inhibited.There was no significant difference in the content of phosphorus in the leaves at the late stage of absorption,the distribution ratio of phosphorus to the stem increased but remained lower than that of the leaves at this stage. ?2?Phosphorus content in each parts of willow increased over time.The absorptivity of phosphorus in stock reached 21.43%at 14 d and the translocation coefficient was 2.389,which indicated that it could remove phosphorus from the water by assimilation and transport it to the ground.This provided a theoretical basis to treat phosphorus in eutrophic water by the tree.?3?This willow could grow normally in all set eutrophic waters.At the meantime,there were no apparent phosphorus deficiency symptoms in the stockfor low-phosphorus waters,and the growth of the seedlings in high-phosphorus waters were not inhibited.As well the plant height increased by 70%after three months and biomass increased by 101%,and there was no significant difference among the all groups.Moreover there was no significant difference in total biomass,above-ground morphology,and leaf soluble sugar concentration between different treatments.On the other hand,the response of the root system of the stock to low P concentration showed that the allocation of biomass was inclined to the underground but did not change significantly,and the root/shoot ratio,root length,root surface area,root volume,root acid phosphatase and other indicators all increased with decreasing P concentrations.And for the purification efficiency,in the low-phosphorus environment,the plant was rapid with high removal ratio,but leaf nitrogen and phosphorus concentrations,chlorophyll concentration,photosynthetic rate,leaf soluble protein concentration of willow were reduced,thus the tree is suitable for short-term healing in low P concentration eutrophic water;for the high phosphorus environment,this one had slow absorption but high enrichment which making it suitable for long-term applying.