Effects Of Nitrogen-Water Interaction On Fine Roots And Mycorrhizal Fungal Mycelium In A Mixed Pinus Koraiensis Forest In Changbai Mountains, Northeastern China

Fine roots are the important organs of plants for water and nutrient absorption.Symbiotic mycorrhizal fungal can promote plants to acquire water and nutrients.With increasing atmospheric nitrogen deposition and decreasing precipitation on the global level,the changes in soil water and nutrient availabilities will strongly influence resource acquisition strategy of plants.In this study,we conducted a three-year nitrogen addition and reduced rainfall experiment in a mixed Pinus koraiensis forest in Changbai Mountains.We used a double layer in-growth bag method to reveal the effects of nitrogen-water interaction on fine roots and mycorrhizal fungal mycelium,in order to reveal the response characteristics of temperate forest underground system with increasing atmospheric nitrogen deposition and decreasing precipitation.Our results will help to deeply understand carbon allocation strategy and carbon cycle characteristic in the future global climate change.The results showed that:(1)Nitrogen addition(N),reduced rainfall(D)and nitrogen-water interaction(DN)can decrease the number of the mixed Pinus koraiensis forest in Changbai Mountains and can decrease the length of the fine root?the superficial area of the fine root and the number of root tips.However,in the 0-10 cm soil layer,if the rainfall reduced after the application of nitrogen,the number?the length and the superficial area of the fine root and the number of root tips can reduced by 74.6%,52.4%,59.6%,78.6%,respectively.In the 10-20 cm soil layer,if the rainfall reduced after the application of nitrogen,the length of the fine root and the number of root tips can increased by 118.1%,136.9%,respectively.(2)In the morphology of fine roots,nitrogen application(N)increased the diameter of the fine root and decreased the SRL in the 0-10 cm soil layer by 12.3% and 25.3%,respectively.Reduced rainfall(D)increased the SRL by 29.6%-43.8% and decreased the diameter of fine roots in the 20-30 cm soil layer by 29.6%-43.8%,and the branching ratio of fine roots increased in the 0-10 cm soil layer by 25.5%;The SRL of fine roots decreased in the 0-10 cm soil layer by 32.3% and the branching ratio of fine roots increased by 29.2% under the nitrogen-water interaction(DN).Compared with the application of nitrogen(N)and the reduced rainfall(D),the branching ratio of fine roots increased by 25.2% and 45.5% in the 0-10 cm soil layer under the nitrogen-water interaction(DN).However,the nitrogen application after the rainfall decreased,the SRL of fine roots decreased by 15.4% in the 0-10 cm soil layer.(3)In the chemical constituents of fine roots,after nitrogen application(N),the N concentration of fine roots increased,the P and K concentration decreased,and N:P increased;The reduced rainfall(D)led to the decrease of the N concentration and the increase of the K concentration of fine roots;The N,P and K concentration of fine roots decreased under the nitrogen-water interaction(DN).If the rainfall reduced after the application of nitrogen,the N,P,K concentration and N:P of fine roots can decrease;Moreover,the nitrogen application after the rainfall decreased,the P?K concentration can decrease and the N:P of fine roots can increase.(4)In the growth of mycorrhizal fungal mycelium,the n itrogen addition(N)and reduced rainfall(D)and their interaction will decrease the length of the mycelium and increase the diameter of the mycelium.If the rainfall reduced after the application of nitrogen,the diameter of mycelium in the 0-10 cm soil layer can increased by 68.8%,and the diameter of mycelium in the 10-20 cm soil layer can decreased by 16.0%;What's more,the nitrogen application after the rainfall decreased,the length of the mycelium decreased by 43.0%and the diameter increased by 39.2% in the 0-10 cm soil layer.