Characteristics Of Soil Soluble Organic Nitrogen Components And Their Regulation On Mineralization In Three Vegetation Types In The Interforest Zone Of Forest And Grassland

Soluble Organic Nitrogen?SON?is one of the most active components of soil nitrogen compositions and plays an important role in the nitrogen cycle and nutrient balance of terrestrial ecosystems.Studies have shown that SON can be converted into mineral nitrogen by mineralization,and can also be directly absorbed and utilized by plants.In addition,SON losses may cause eutrophication of aquatic ecosystems and exacerbate emissions of the greenhouse gas N2 O in the soil system.Therefore,SON has received extensive attention from many disciplines at home and abroad.SON can only be absorbed and utilized by plants if it is mineralized to inorganic nitrogen under the action of soil microorganisms.Soil nitrogen mineralization is affected by various factors such as climate,soil,vegetation and microorganisms.The forest grassland interlaced zone is located in the middle of the two vegetation types in the forest and grassland.It is dominated by the middle and dry hay shrubs and herbaceous plants.The precipitation and average temperature are higher than other grassland types.In order to grasp the SON compositions of different vegetation types,the characteristics of soil nitrogen mineralization and the regulation of mineralization by protease and urease in the intertwined zone of forest grassland,this study is based on the Aerxiang Teaching and Research Base of Shenyang Agricultural University,located in the north of Zhangwu County,Fuxin City,Liaoning Province.The township teaching and research base is the platform.The soil of shrub grassland,poplar broadleaf forest land and Pinus sylvestris var.mongolica forest are taken as the research objects.The soil ammoniation and nitrification rates are calculated by measuring the content of NH₄⁺-N and NO₃^--N in different periods.The seasonal dynamic characteristics were analyzed.The contents of soluble organic nitrogen?SON?and compositions of soils in three vegetation types and the role of nitrogen mineralization were analyzed.The regulation of protease and urease on soil nitrogen mineralization was discussed.The main relults are as follows:1 During the whole growing season,the NH₄⁺-N content in different soil layers of grassland,broad-leaved forest and coniferous forest in the inter-forested steppe showed an increase in summer and a decrease in autumn,while NO₃^--N content showed a corresponding opposite trend.The inorganic nitrogen content of the three vegetation types was dominated by NO₃^--N content,accounting for 53.62%?grass?,56.83%?broad-leaved forest land?and 53.53%?coniferous forest land?.The net ammoniation rate,net nitrification rate and net mineralization rate of different soil types in the three vegetation types reached the maximum in the growing season in August.At the beginning of summer?May?,the mineralization of surface soil in grassland and broad-leaved forest was dominated by nitrification,while the soil in coniferous forest was dominated by ammoniation.In June and August,the topsoil mineralization of the three vegetation types was dominated by nitrification,and ammoniaification was dominant in July.At the end of autumn vegetation growth?September?,mineralization is dominated by ammoniation.In the deep soil,the soil mineralization of the three vegetation types in the early summer was dominated by ammoniation,and the mineralization characteristics of other periods were the same as those of the topsoil.2 Among the three vegetation types,the inorganic nitrogen content accounts for 5% of the total nitrogen content of the soil.The proportion of acid-soluble organic nitrogen to total nitrogen was 24.82%?grass?,18.95%?broad-leaved forest land?and 23.7%?coniferous forest land?.In the grassland soil,the size of each acid-soluble nitrogen component and the proportion of acid-soluble nitrogen were acid-decomposed ammonia nitrogen?43%?,amino acid nitrogen?34%?,amino sugar nitrogen?12%?,acid hydrolysis.Unknown nitrogen?11%?;broad-leaved woodland showed acid-decomposed ammonia nitrogen?52%?,amino acid nitrogen?39%?,amino sugar nitrogen?4%?,acidolysis unknown nitrogen?5%?;In the forest land,it is characterized by acid hydrolysis of ammonia nitrogen?50%?,amino acid nitrogen?36%?,amino sugar nitrogen?9%?,and acid hydrolysis of unknown nitrogen?5%?.The ratio of acid-decomposed ammonia nitrogen in the soil of the two forests was significantly higher than that in the grassland.3 There was a significant positive correlation between NH₄⁺-N content and aminoglycemia in grassland soil?P<0.01?,which may be the main participant in soil nitrogenation.Acid-dissolved ammonium nitrogen was significantly positively correlated with NO₃^--N content and had no correlation with ammonium nitrogen.Acidolysis of ammonia nitrogen may be a major player in nitrogen mineralization and directly generate NO₃^--N,ie nitrogen.The mineralization was dominated by heterotrophic nitrification;in the broad-leaved forest soil,the content of acid-decomposed ammonia nitrogen and NH₄⁺-N were significantly negatively correlated.The aminoglycemia nitrogen was in the broad-leaved soil with NH₄⁺-N,NO₃^--N content showed a very significant positive correlation in broad-leaved soil and a very significantly negativly correlation in coniferous soil.In the broad-leaved forest soil,acid-salted ammonium nitrogen may be the main participant,and amino sugar nitrogen is the main contributor;in the coniferous soil,acid-decomposed ammonia nitrogen and amino sugar nitrogen may be the main participants.4 The protease activity and urease activity in the grassland soil were lower than those in the forest soil,and there was no significant difference between the two forest soils.In the grassland soil,with the increase of enzyme activity,NO₃^--N and acid-decomposed ammonia nitrogen showed a decreasing trend.Urease in grassland soil promoted soil nitrogen mineralization.In the broad-leaved forest soil,both protease and urease activities can promote soil nitrogen mineralization.In the coniferous forest soil,the protease activity increased,the ammonia nitrogen increased,and the acid hydrolysis ammonium decreased.This indicates that protease may be involved in nitrogen mineralization in the soil of coniferous forests.