Influences Of Emerging Organic Pollutant Of DEHP (Bis (2-ethylhexyl) Phthalate) On Soil N Transformation And Gaseous Of N Emissions

?Objective?Bis?2-ethylhexyl?phthalate?DEHP?is one of emerging organic pollutants,which belongs to a typical environmental endocrine disruptor,and possess the characteristic of persistent resisting to degradation in soil environment.As an effective plasticizer,DEHP has been extensively used in industry and agriculture.In agriculture systems,due to long-term widespread application of plastic films,the occurrences of soil DEHP pollution have been detected in diverse agricultural sectors including vegetable fields,cotton fields,and commonly happened in agricultural soils.It has been proved that DEHP exerts a significant negative impact on the quality of agricultural products,soil health,soil biological processes and soil microbial community diversity as well.Therefore,to date,the problem of soil DEHP pollution has attracted a growing attention.Calcareous soil is a widely distributed in arid and semi-arid regions in northern China.The agriculture management pattern of plastic film mulching cultivation has been extensively used in these areas.However,how and to what degree DEHP influence on soil nitrogen biological transformation process,and further affect gaseous of N release from calcareous soils have not been well explored.Therefore,in the present study,the effects DEHP addition with low or high dosage on soil N biological transformation characteristics and N₂O and NH₃emissions were explored.The objectives of this research were to decipher the soil nitrogen conversion characteristics gaseous forms of N emissions as affected by DEHP subjected to calcareous soil.?Method?A batch microcosm incubation experiment was conducted at 25?,Four treatments contain:?1?CK?without urea?;?2?Urea(urea pure nitrogen dosage is 0.30 g·kg^-1);?3?Urea+10 mg·kg^-1DEHP;?4?Urea+100 mg·kg^-1DEHP,expressed as CK,U,U+LDEHP and U+HDEHP,respectively.Each treatment has four replicates.Different soil N forms?Urea-N,NH⁺₄,NO₃^-,and NO₂^-?were measured by flow injection analyzer,the enzymatic methods were used to study the enzyme activities which closed related with soil N transformation namely,urease,nitrate reductase,nitrite reductase,and hydroxylamine reductase).Emission fluxes of gaseous forms of N₂O and NH₃ were real-time determined on-line through Picarro?G2508?apparatus.?Result??1?Compared with CK,the addition of U significantly increased concentrations of soil NH₄⁺,NO₃^-and NO₂^-.For instance,the average concentrations of NH₄⁺,NO₃^-and NO₂^-in the urea-added treatments increased by 48.8⁶8.2 mg·kg^-1?33.5³7.6 mg·kg^-11 and151.5¹67.9 mg·kg^-1,respectively,those were significantly higher than that in the CK treatment during the whole incubation period.However,DEHP merely slightly increased soil NH₄⁺,and reduced NO₂^-and NO₃^-concentrations,while had no effect on soil urea-N even at high-dosage,implying DEHP addition hardly influenced on soil N transformation.?2?The treatment of DEHP addition significantly reduced soil MBC and MBN?P<0.05?.Compared with the treatment with U,soil MBC and MBN contents were decreased by29⁵3.6%and 11.3⁴4%,respectively.?3?The addition of DEHP had no obvious influence on soil urease activity,but presented an inhibitory effect on soil nitrite reductase?P<0.05?.Compared with the U treatment,the treatments of DEHP amendment with low and high dosages significantly reduced soil nitrite reductase activities by 37.3%and 33.4%,respectively.At initial incubation stage,the activity of soil hydroxylamine reductase was significantly increased in the low-dose spiked DEHP soil?P<0.05?.In contrast,the activity of soil nitrate reductase increased by 21.0%and 23.3%,respectively,relative to the U treatment at end of incubation time.Moreover,Pearson correlation results demonstrated that urease exhibited a negative correlation with soil MBC and MBN,but hydroxylamine reductase had a positive correlation with MBN.?4?The treatment of DEHP addition at high-dose strengthened the soil N₂O negative emission and increases the volatilization of soil NH₃.Compared with the U treatment,soil total N₂O and NH₃ emissions increased by 67.7%and 13.7%,respectively.However,the treatment of DEHP at low-dosage had no significant effect on soil N₂O and NH₃ emissions.The linear regression results showed that soil NH₄⁺positively correlated with NH₃ emission fluxes.?Conclusion??1?The addition of DEHP had no obvious effect on soil N transformation processes,but significantly reduced soil microbial biomass?MBC and MBN?.Furthermore,a significant dose effect was found in high-dose DEHP treated soil.In addition,the inhibitory effect of DEHP on MBC and MBN exhibited a attenuating tendency along with the increase of incubation time.?2?The addition of DEHP had no effect on soil urease activity,but had an inhibitory effect on soil nitrite reductase?P<0.05?.The addition of DEHP at low-dose significantly increased the activity of soil hydroxylamine reductase at initial stage of incubation?P<0.05?,while the activity of soil nitrate reductase was increased by the high-dose of DEHP added treatment at the end of incubation period.?3?The addition of DEHP at high-dose enhanced the negative emission of N₂O,but increased the volatilization of NH₃ from calcareous soil.