Responses Of Leaves And Soil C:N:P Stoichiometry To Nitrogen Addition In A Pinus Koraiensis Plantation

Atmospheric nitrogen(N)deposition has rapidly increased in recent decades due to the combustion of large amounts of fossil fuels and increased agricultural production.Previous studies have focused on how N deposition affects C:N:P stoichiometry in plant leaves,but there are few reports on how C:N:P stoichionetry of plant-soil system responds to N deposition;whether the C:N:P stoichiometry of older leaves,litter and the mineral layer soil is more sensitive to N deposition than the C:N:P stoichiometry of new leaves is still unclear.In May 2014,we established 20 5 m x 3O rn plots with four treatments in a Pinus koraiensis plantation:control(CK,0 Kg·N·ha-1·yr-1),low-N(L,20 Kg-N·ha-1·yr-1),medium-N(M,40 Kg·N·ha-1·yr-1),high-N(H,80 Kg·N·ha-1·yr-1).In September 2017,new leaves(<1 year),older leaves(>1 years)and litter were sampled,and 0-10 cm and 10-20 cm soil was sairpled within lm of the selected Pinus koraiensis.The C,N and P concentrations were determined in the new leaves,older leaves and litter;the total C,total N,total P,available N,and available P concentrations were determined in the 0-10 cm and 10-20 cm soil mineral layers.The results showed that:(1)For forest growth,high N significantly increased the annual growth rate of selected Pinus koraiensis^and the annual growth rates of all trees in the plots was significantly increased under N addition;(2)For plant leaves,N addition significantly increased the C concentration of new leaves but decreased the N concentration of them High N significantly increased the C:N and C:P of litter,significantly decreased the P concentration of the old leaves.The P resorption efficiency was significantly inproved by low N and high N.There was no significant interaction between different leaf stages and different treatments,and there was no significant difference in the coefficient of variation between C:N:P stoichiometry in different leaf stages;(3)For the soil under the forest,with the increase of N addition,the total C,total N,total P,N:P of the two layers of soil showed an inward trend.Soil N availability is significantly iixproved by N addition*There was no significant interaction between different soil layers and different treatments.There was no significant difference in the coefficient of variation between C:N:P stoichiometry in different soil layers;(4)There were no significant correlations between leaf N and soil available N or leaf P and soil available P,but soil total N and P showed a stronger relationship with soil available N and available P than leaf N and P;(5)The coefficient of variation of C:N:P among treatments had an upward trend in new leaves,older leaves,litter,0-10 cm soil layer and 10-20 cm soil layer.Conpared with new leaves,The coefficient of variation of 10-20 cm soil layer C:N:P stoichiometry among treatments was significantly higher than that in the new leaves C:N:P stoichiometry.From these,we conclude that:the Pinus koraiensis plantation was limited deeply by N;conpared to the new leaves,the C:N:P stoichiometry of litter and older leaves did not show a more sensitive response to N addition;the two layers of soil C:N:P stoichiometry respond to N addition earlier than plants due to their ability of homeostatic regulation.