Effect Of Nitrogen Addition On Nitrogen Acquisition Strategies Of Three Tree Species Of Korean Pine Broadleaved Forests In Xiaoxing’ An Mountains

Global nitrogen deposition has become a key influence factors of forest ecosystem carbon and nitrogen cycle,the most active part of the fine root as the root,Underground nutrient cycling in the forest ecosystem is at the core of global change and has a certain impact on the availability of soil nutrients,fine root morphology on the effectiveness of the change of soil nutrients with high plasticity,it is an important factor to form fine root nutrition strategy.In order to investigate the effect of the nitrogen deposition to the nitrogen absorption strategy of the fine roots.This study takes the korean pine broadleaved forest in the Xiaoxing’ an mountains as the research object and designed the experiment of exogenous N addition.we conducted a N addition experiment by setting four levels of N addition treatment including 0,25,50 and 75 kg hm-2a-1,using stable isotope technique,to reveal the effects of N addition on the fine root morphology,nitrogen absorption preference and rate of three main tree species in temperate forest,Pinus koraiensis,Abies nephrolepis and Acer tegmentosum Maxim.The result of research shows that:N addition significantly affected the physical and chemical properties of undergrowth soil.The ammonium nitrogen,nitrate nitrogen and total organic N in soil were greater with elevated nitrogen application level.The soil pH value decreased significantly with the increasing level of N addition.Nitrogen addition did not change the preference of dominant species for different chemical forms of nitrogen in the temperate forest.Under the same concentration of N addition,the nitrogen acquisition patterns of all species were ammonium>nitrate>glycine.However,we found that dominant tree species shifted their N uptake rate in response to N addition.Regarding the target tree species,N addition with diverse levels had different effects on the N uptake rate of different chemical forms.It was shown that low and medium levels of N addition had a positive effect on the NH4+-N uptake rate of the three target tree species,but had little effect on the Nv3--N uptake rate.High levels of N addition exerted negative effects on NH4+-N and NO3--N uptake rate.The long-term addition of inorganic nitrogen did not inhibit the uptake rate of glycine in 3 species,and the response increased most significantly when nitrogen was added at a low level.High levels of N addition significantly decreased specific root length(SRL)and specific surface area(SRA)in orders 1-2 of PKS and AT,it also significantly decreased the mean root diameter of order 3 of AN and AT;In addition,significantly increased the mean diameter in orders 1-3 of PKS,order 2 of AN,and orders 1-2 of AN.Medium levels of N addition significant increased specific root length(SRL)and specific surface area(SRA)in order 1 of AN,significant increased the mean diameter in orders(1+3)of PKS and orders 1-3 of AT.Low levels of N addition significant increased the mean diameter in orders(1+3)of PKS and oredr 2 of AN.Under the condition of nitrogen addition,the fine root morphology of the three tree species had a correlation with the nitrogen absorption rate.The uptake rate of NH4+-N by PKS was significant positively correlated with the specific root length and specific surface area of the first-and second-order roots(except for the specific surface area of the second order root).The uptake rate of NH4+-N by AN was significant positively correlated with the specific root length and specific surface area of the first order roots;The uptake rate of NO3--N was significant negatively correlated with the mean diameter of the second order root.The uptake rate of NH4+-N by AT was significant negatively correlated with the mean diameter of the first-and second-order roots;The uptake rate of NO3--N was significant positively correlated with the mean diameter of the first-and second-order roots(except for the specific surface area of the second order root).In summary,under the condition of N addition,the uptake of nitrogen by tree species changed,which may be caused by the morphological characteristics of different root orders of fine roots.It can be seen that the fine roots of the three tree species can affect the uptake of nutrients by adjusting their morphological characteristics to adapt to changes in thesurrounding environment.Therefore,comprehensively understanding the response of root morphological traits and nitrogen uptake rate to N addition will help to comprehensively understand the nutrient uptake strategies of different tree species in the forest ecosystem,and has profound significance for predicting biogeochemical cycles in the context of global nitrogen deposition.