Effects Of Nitrogen Addition And Litter Cover On The Seedlings Growth Of Pinus Tabuliformis And Pinus Armandii

Nitrogen is one of the important nutrient elements that affect the growth and development of forest vegetation.At present,global nitrogen deposition is on the rise.While nitrogen deposition increases soil available nitrogen,it also promotes the accumulation of nitrogen in plants,ultimately affecting the growth and development of forest vegetation.Forest regeneration has always been a very important ecological process.One of the important factors affecting the natural regeneration of forests is litter.Its influence on the growth of seedlings of established species is also a hot topic in the international research on the ecological functions of forest litter.There have been many separate studies on litter and nitrogen deposition in the past.However,in the context of global nitrogen deposition,how will the interaction of nitrogen addition and litter cover affect the growth and physiological and biochemical processes of seedlings?Based on this,this experiment took Pinus tabuliformis and P.armandii,the main forest tree species in the Qinling forest area,as the research object,and carried out a potted control experiment.By simulating nitrogen deposition and different proportions of litter（s leaves,P.tabuliformis and P.armandi needles）cover,to explore the effects of nitrogen addition and litter cover on the growth and stoichiometric characteristics of the seedlings of P.tabuliformis and P.armandi,in order to understand the response of P.tabuliformis and P.armandi seedlings to nitrogen addition and litter cover,And provide scientific basis for the sustainable management of P.tabuliformis and P.armandi forest communities.The main conclusions are as follows:（1）As the nitrogen concentration increases,it will promote the growth of the above-ground part of the seedlings of P.tabuliformis and P.armandi.High nitrogen concentration will inhibit its growth,but it will promote the growth of the roots of the seedlings of P.tabuliformis and P.armandi.Covering litter can promote the growth of the above-ground part of the seedlings of P.tabuliformis and P.armandi,but it can inhibit the growth of their root systems.Adding nitrogen fertilizer under the cover of litter can significantly promote the root system and basal diameter growth of P.armandii seedlings.Adding nitrogen fertilizer when covering（Q.leaves=needle leaves）litter can promote the high growth of P.tabuliformis seedlings.（2）Nitrogen addition will promote the（leaves,above-ground part,roots）biomass and root-shoot ratio of P.tabuliformis and P.armandi seedlings,and the roots biomass and root-shoot ratio will reach the highest value at the medium nitrogen level.Covering H₃（Q.leaves>needle leaves）litter will promote the biomass accumulation and root-shoot ratio of each part of P.tabuliformis seedlings,but only increase the roots biomass and root-shoot ratio of P.armandii seedlings.Covering H₁（needle leaves>Q.leaves）Litter will promote the aboveground part and total biomass of P.armandii seedlings.Adding nitrogen fertilizer under the cover of litter has a"positive effect"on the biomass accumulation and distribution of P.armandi seedlings,and will significantly promote its biomass accumulation and the distribution of root-to-shoot ratio.（3）With the increase of nitrogen fertilizer concentration,the chlorophyll content of P.armandii seedlings decreased first and then increased compared with the control.Covering litter will reduce the chlorophyll content of P.armandii seedlings,and covering H₁（needle leavesr>Q.leaves）litter will increase the chlorophyll content of P.tabuliformis seedlings.Under the treatment of covering different proportions of litter,with the increase of nitrogen fertilizer concentration,the chlorophyll content of P.armandii seedlings would increase,and the H₁N₁,H₂N₂,H₃N₂treatment groups would significantly increase the chlorophyll content of P.tabuliformis seedlings.（4）The content of malondialdehyde in the seedlings of P.tabuliformis and P.armandii with N₂（medium concentration of nitrogen）was the lowest.The MDA content of P.tabuliformis seedlings was the lowest when covered with H₂（Quercus leaves=needle leaves）litter,and the MDA content of P.armandii seedlings was the lowest when the litter was not covered.Under the alternate treatment of nitrogen addition and litter covering,the malondialdehyde content of P.tabuliformis seedlings will decrease as the proportion of covered oak leaves increases,the nitrogen fertilizer concentration decreases.and the malondialdehyde content of P.armandi seedlings will increase as the proportion of covering oak leaves increases,the nitrogen fertilizer concentration increases.（5）Nitrogen addition will increase the C content in the needles of P.tabuliformis seedlings and the N/P in the needles of P.armandi seedlings.The N content in the needles of P.tabuliformis seedlings is the highest when N₃（high concentration of nitrogen）;with the increase of nitrogen fertilizer concentration,the needles of P.tabuliformis seedlings Leaf C/N decreased,N/P increased,and P content in the needles of P.armandii seedlings decreased.Covering litter will increase the P content in the needles of P.tabuliformis seedlings and decrease the N/P.With the increase of the proportion of covered oak leaves,it will significantly increase the C content in the needles of the P.tabuliformis seedlings and the N content in the needles of P.armandi seedlings.Under the alternate treatment of nitrogen addition and litter covering,H₃N₂treatment will increase the C content in the needles of P.tabuliformis and P.armandi seedlings.Adding nitrogen fertilizer under different litter mulching will increase the P content in the needles of the P.tabuliformis seedlings and decrease the N/P.Increase the N content and N/P in the needles of P.armandii seedlings.