Study On Nitrogen Absorption Characteristics Of Polygonum Hydropiper

The large quantity use of nitrogenous fertilizer in soils usually causes the nitrogen in the soil to easily enter the water body along with leakage and runoff,resulting in an increase in eutrophication of the water body.It is clear that the mechanism of the absorption and accumulation of inorganic nitrogen by the repaired plants can provide a theoretical basis for the extensive use of nitrogen in the environment.To investigate the N accumulation characteristics of the plant can provide a theoretical basis for its application.Previous study showed that the mining ecotype?ME?of Polygonum hygropiper possessed greater removal capability of N than that of the non-mining ecotype?NME?.In this study,sand culture experiments were carried out to investigate the effect of different ammonium nitrogen concentrations and nitrate nitrogen concentration on distribution,root morphology and physiological characteristics of the ME,with the NME as control.The relationship between root morphology,root metabolism and N absorption was also elucidated in this study.The following is a summary of the results.?1?The absorption characteristics of inorganic nitrogen in the two ecotypes of P.hydropiper are in accordance with the Michaelis-Menten equation,and the absorption rate gradually becomes gentle with the increase of nitrogen supply concentration.The maximum absorption rate and affinity of the two types of ecotypes for nitrate nitrogen were significantly higher than that of ammonium nitrogen,which had a stronger preference for nitrate nitrogen absorption.The absorption rate of the two kinds of inorganic nitrogen in the ME is higher than that of the NME.Moreover,the maximum absorption rate of nitrate-like nitrogen in the ME waterlogging is significantly higher than that in NME,and the ME has stronger absorption potential for nitrate nitrogen.The affinity of the ME for ammonium nitrogen is significantly lower than that of the NME.The ME is suitable for a wider range of ammonium nitrogen and nitrogen polluted water bodies.?2?The two ecotypes of P.hydropiper had the highest biomass and nitrogen accumulation at a nitrogen supply concentration of 50 mg L^-1.Nitrate nitrogen treatment has a better effect on the growth of leech,and ammonium nitrogen treatment can increase the nitrogen nutrient content in leech.The biomass,nitrogen content and nitrogen accumulation of the ecological ecotype of the mine are higher than the NME.The ME have better absorption and accumulation capacity for inorganic nitrogen.With the increase of ammonium nitrogen supply concentration,the root growth of leeches was inhibited.When the concentration of nitrate nitrogen was 50 mg L^-1,the root length,root surface area and root volume of P.hydropiper reached the maximum.The parameters of root morphology of ME are better than NME.It can be seen that the ME have stronger adaptability to ammonium nitrogen,and its better root growth also provides a better basis for nitrogen absorption.Under different nitrogen treatments,the lateral root length of the ME accounted for 63%⁷2% of the total root length,and the NME of the lateral root length accounted for 59%⁷0% of the total root length.It indicates that the better lateral root development of the ecological ecotype of the mine provides a good root physiological basis for plant nitrogen uptake.?3?With the increase of nitrogen supply concentration,the nitrate reductase activity of the two ecotypes of P.hydropiper increased,and the activity of glutamine synthetase and glutamate synthetase was the highest at 50 mg L^-1.The free amino acid content of the roots of the two ecotypes was the highest when the nitrogen supply was 75 mg L^-1,and the ammonium nitrogen treatment was higher than that of the nitrate nitrogen treatment.The soluble protein content was the highest when nitrogen was supplied at 50 mg L^-1.Nitrogen supply 50 mg L^-1 is the optimal inorganic nitrogen concentration for nitrogen uptake and assimilation of two ecotypes.Nitrate reductase,glutamine synthetase,glutamate synthetase,free amino acid content and soluble protein content in the roots of ME were higher than NME.The ME have stronger nitrogen absorption and assimilation ability and environmental adaptability.?4?The organic acids secreted by the roots of the two ecotypes of P.hydropiper are mainly oxalic acid,which accounts for more than 60% of the total organic acids,followed by formic acid and propionic acid.Oxalic acid plays a major role in affecting nitrogen uptake by roots;The secretion is mainly serine,and its secretion accounts for 10% to 25% of the total secretion,followed by aspartic acid,threonine,glutamic acid,glycine,alanine,cysteine,and leucine.The secretion of phenylalanine,histidine and threonine plays a major role in affecting nitrogen uptake by P.hydropiper.The content and composition of organic acids and amino acids secreted by the roots of the ME are higher than those of NME.The secretion of more organic acids and amino acids in the roots of the ecological ecotypes also provides more nutrients for rhizosphere microorganisms,which is more conducive to the removal of nitrogen.