Effects Of Amino Acid Additions On Nitrogen Transformation In Subtropical Broad-leaved Forest Soil

Enough inorganic nitrogen were from decomposition of a great number of organic nitrogen,as one of which the role of amino acids played in keeping decomposition of organic nitrogen and transformation of inorganic nitrogen is one of most importance step to understand the relationship between nitrogen transformation and benefit of ecological and environment.To study the effects of amino acids on nitrogen transformation in forest soil,a subtropical broad-leaved forest soil was collected from Wan Mulin natural reserve located at Fujian province,Southeast China.This study was carried out with addition of four different amino acids in incubation under two water levels,at 60%WHC(Water-holding capacity)or 90%WHC.Soil ammonium,nitrate,soluble organic nitrogen and nitrous oxide,soil pH and soluble organic C content were determined.In order to found which path of soil nitrification did inhibited by methionine,we respectively added the substance for autotrophic nitrification and heterotrophic nitrification into soil and then analyzed the response of nitrate and nitrite content to them.In order to know the mineralization rate of amino acids in soil and the priming effect of it on soil organic nitrogen,we used method of 15N trace to determine the 15N enrichments in NH4+,NO3-,and N2O after labeled amino acid addition.Results showed as follows:(1)Soil NH4+contents was significantly(P<0.05)increased by acidic amino acid,basic amino acid and neutral amino acid,but similar effects were not found on NO3-and N2O.However,addition of methionine not only increased N44+-N(P<0.05),but also decreased NO3--N(P<0.05)and to some extent increased nitrous oxide emission from soil as a whole.The nitrogen transformation in forest soil is likely related to the decomposed product of amino acids mineralization,rather than the charge of amino acids.Amino acids might become the intermediate products between organic nitrogen and mineral nitrogen,which regulate the nitrogen transformation in forest soils.(2)Soil nitrification was significantly inhibited by methionine addition(P<0.05),which is probably not relative to the low soil potential nitrification rate in acid soil.Methionine not only inhibited the process of autotrophic nitrification,but also the heterotrophic nitrification.While the process of transfer from nitrite to nitrate was significantly inhibited by methionine at 90%WHC condition.And the degree of inhibition in autotrophic nitrification was much more than that of heterotrophic nitrification.(3)Compared with other amino acids,the rate of mineralization of methionine was small.The rate of mineralization of amino acids was negatively related with C/N of them.Alanine and methionine both had a positive priming effect on the soil NH4+ production.And there was more NH4+ originated from soil organic nitrogen at mineralization treatment than at alanine treatment.But the majority of NH4+ immensely originated from mineralization of amino acids.With soil moisture content increasing,the priming effect of amino acid on soil NH4+ were declined.Alanine also had a positive priming effect on the soil NO3-production,in which there was much more NO3-were generated from soil organic nitrogen at start of experiment.On the contrary,methionine had a great negative priming effect on the soil NO3-production.The nitrification of methionine was strictly inhibited.Moreover,alanine and methionine had a positive priming effect on N2O production.The emission of N2O was greatly originated from the decomposition of soil nitrogen rather than amino acid themselves,particularly for methionine added treatment.