Purified Tannin From Chinese Fir Litter And The Effect Of Tannic Acid-organic Nitrogen Compounds On Soil Nitrogen

As secondary metabolite of plant,plant tannins were parts of organic carbon.Tannins had active chemical properties that directly or indirectly affect the availability of nitrogen in soil.At incubation and abroad,the reaction of tannins and nitrogen were used to explain the influence of tannin on soil nitrogen as compounds formation,but the nature and function of the compounds were not reported systematically.It is important to understand how reaction of tannins and different organic nitrogen happened and how tannins affected the nitrogen transformation.In this paper,the effects of tannic acid on amino acids and proteins were studied under different pH conditions and proportions,to investigate the influence factors for reaction between tannin and organic nitrogen.A subtropical broad-leaved forest soil was collected from Wanmulin natural reserve located at Fujian province,Southeast China.We selected purified tannin from Chinese fir needles and artificial tannin-protein compounds in two weeks incubation experiment,to study the conditions for the formation of compounds by the reaction of tannin acid and organic nitrogen and the effects of different parts of tannins and different tannin-organic nitrogen compounds on soil nitrogen transformation.Ammonium N,nitrate N,soluble organic N and nitrous oxide were determined.Results showed as follows:(1)The precipitation of the compounds in the reaction of tannin and organic nitrogen was dependent on pH in reaction solution.Low pH was good for tannin reacting with bovine serum albumin and casein to produce precipitation,high pH was good for tannin reacting with lysine and arginine to produce precipitation.The proportion of tannin and organic nitrogen in the reaction can affect the precipitation of the compounds and the limiting factor reaction was organic nitrogen concentration.(2)The main part of purified tannin from Chinese fir needles was F1.The addition of different parts of tannins decreased soluble organic nitrogen content in a short time(0-3 days),while it decreased inorganic nitrogen content in a long time(14 days).F2 and F4 could be the main factors affected nitrogen transformation,because the effects of F2 and F4 on nitrogen content in soil were stronger than F1 and F3.(3)The addition of tannin-arginine compound significantly increased soil ammonium nitrogen,nitrate nitrogen,soluble organic nitrogen and nitrous oxide,which mean it havea positive priming effect in soil.There was no significant effect on the nitrogen content in soil by addition of tannin-bovine serum albumin compound,the compound was a stable nitrogen source,which is difficult to be used directly by microorganisms,and played an important role in the fixation of soil organic nitrogen.The differences in the effects of compounds on nitrogen transformation need to be studied further,it is very important to understand the effect mechanism of tannin in soil.