The Response Of Ecological Stoichiometric Characteristics Of Natural Secondary Forest Leaves To Nitrogen Deposition

As an important manifestation of global climate change,nitrogen deposition caused by human activities can not be ignored.As an important forest type of temperate forest,natural secondary forest is sensitive to atmospheric N deposition because of its special demand for nutrients for succession and regeneration.The effects of nitrogen deposition on nutrient stoichiometric characteristics of natural secondary forest are studied.It provides a reference for further understanding the effect of nitrogen deposition on the community structure and function of natural secondary forest,and has high service function value.In view of this,an artificial simulated nitrogen deposition control experiment was set up in the experimental forest farm of Lushuihe Forestry Bureau,Fusong County,Jilin Province in May 2006.Three?N?adding gradients of nitrogen were set up as the control(CK 0 g N m^-2a^-1).Two species of natural secondary forest,Betula platyphylla and Populus davidiana,and three shrub species were determined with low N(LN 2.5 g N m^-2a^-1)and high N(HN 5.0 g N m^-2a^-1).The contents of C,N,P and stoichiometric ratio of Philadelphus schrenkii fresh leaves and litter leaves in Acanthopanax senticosus,of Syringareticulatavar amurensis,were studied in order to explore the effects of N deposition on the stoichiometric characteristics and nutrient reabsorption of leaves and litter of five species of plants.And the correlation between leaf reabsorption and soil,leaf stoichiometric characteristics.It provides a theoretical basis for the growth and stoichiometry of natural secondary forest under nitrogen application.Try The main findings are as follows:?1?Nitrogen application could significantly increase the N content of soil and decrease the N content of soil C:N,and the N content of fresh leaves of B.platyphylla,A.senticosus and P.schrenkii in Northeast China showed an increasing trend with the increase of N deposition concentration.C:P decreased significantly,and N:P in fresh leaves of dominant plants was still less than 14,indicating that the secondary forest was restricted by N.Before N input continued to increase until saturation,N application promoted N uptake and P absorption in fresh leaves of plants,and exogenous N input could alleviate the N restriction on plants.Scientific and reasonable application of N can benefit the growth of secondary forest plants and improve the soil nutrient structure.?2?The changes of NRE and PRE in the leaves of the dominant species were species specific.Under LN treatment,NRE?PRE decreased in leaves of P.davidiana and A.senticosus and PRE decreased in leaves of S.amurensis,showing low reabsorption ability to N and P in fresh leaves.Soil nutrients and exogeno us N can be absorbed quickly and promote the growth of trees,without the nee d to absorb nutrients from senescent leaf tissues.However,there was no signific ant change in the reabsorption rate of the five plants under HN treatment,which may promote the growth of natural secondary forest in Changbai Mountain und er the treatment of HN(5.0 g N m^-22 a^-1).?3?The NRE?PRE and stoichiometric characteristics of the leaves of the five plants were different.The results were as follows:B.platyphylla NRE was negatively correlated with N content and N:P,but the correlation between PRE and C:N:P stoichiometric ratio was not obvious.There was no significant correlation between NRE and its C:N:P in fresh leaves of P.davidiana.There was a very significant positive correlation between PRE and its N content,There was no significant correlation with C:P and C:N,but there was a significant positive correlation with N:P.There was no significant correlation between NRE and C:N:P stoichiometric ratio of the leaves of the S.amurensis,but there was a significant negative correlation between PRE and N:P,and a significant positive correlation between NRE and PRE in fresh leaves of A.senticosus and P.davidiana.There was a significant positive correlation between N reabsorption rate and N content in fresh leaves of P.schrenkii,and a significant positive correlation between P reabsorption rate and P content in fresh leaves of P.schrenkii,and a significant positive correlation between PRE rate and P content in fresh leaves of P.schrenkii.