Characteristics Of Soil Nitrogen Mineralization Under Different Forest Types In Cold-temperate Forest Areas

Nitrogen is a necessary nutrient element for plant growth and development and nitrogen is also the most important nutrient element in the northern forest ecosystem.It i5 important to study the dynamic changes of soil nitrogen mineralization for further exploring the nutrient mechanism of forest ecosystem.In this paper,the dynamic ehanges of ammonium nitrogen and nitrate nitrogen contents in different forest types of litter and surface mineral soil in Huzhong Primitive Forest Reserve in Daxing'anling Mountains were measured by time series using laboratory incubation methods,so as to explore the relationship between nitrogen mineralization and incubation time,forest types,season,organic carbon,total nitrogen,C/N and PH value in soil.The results as follows:(1)Nitrogen mineralization in litter is predominant by ammoniation and nitrification in soil.In the early stage of culture,the litter layer shows the mineralized nitrogen content increases first and then decreases with time prolonging.The maximum mineralization amount appears in the litter layer around 35 days.Nitrogen mineralization in surface mineral soils increased significantly with the prolongation of incubation time,but there was an obvious lag period of mineralization at the initial stage of incubation.(2)Analysis of forest types at different altitudes showed that nitrogen mineralization in surface mineral soils and litter layers of four forest types decreased with the inereases of altitude(expect for Rhododen-betlaplatyphylla).Mineralized nitrogen content in litter layer increases first and then decreases,and generally decreases rapidly after 40 days.The content of mineralized nitrogen in surface mineral soil decreased first and then increased during the whole cultivation period,and all forest types showed the same mineralization characteristics:longer net mineralization inhibition period,8 days.(3)Soil nitrogen mineralization was different in different months.The four forest types showed two levels in three months:Ledum palustre-Larix dahurica>Rhododen-betla platyphylla>Rhododen-dron-Larix dahurica>Pinus pumila and in August>September>July.The mineralizable nitrogen content in O and A layers in August was significantly different from that in July and September(P<0.05).There was no significant difference between July and September(P>0.05).(4)Effects of soil physicochemical properties on soil nitrogen mineralization:with the increase of pH,soil net nitrogen mineralization rate also increased,and there was a very significant linear correlation between them;soil net nitrogen mineralization rate has a very significant linear correlation with soil total nitrogen and organic carbon;with the increase of C/N content,the net nitrogen mineralization rate of litter layer first increases and then decreases.The maximum value is obtained when C/N is 25.When C/N is less than 25,the net nitrogen mineralization rate increases with the increase of C/N.When C/N more than 25,the net nitrogen mineralization rate decreases with the increase of C/N.There is a linear correlation between C/N and net mineralization rate in surface mineral soil.