Effects Of Nitrogen Addition On Fine Root Turnover In Natural Secondary Forests

The turnover of fine roots is an important way for the carbon(C)in plants to enter the soil.Quantifying the distribution and turnover of fine roots plays an important role in accurately estimating the C budget of forest ecosystems.In recent years,the global atmospheric nitrogen(N)deposition has shown a gradual increase trend due to global industrialization,causing changes in the distribution pattern of soil nutrients,the morphology of fine roots,and the dynamic of fine roots.However,little research has been done on how plants obtain nutrients by adjusting the morphology and dynamic patterns of fine roots to achieve optimal growth under different nutrient conditions.Given the uncertain impact of N deposition on fine root turnover,this study conducted an experiment of N addition in the natural secondary forest of Lushui River to simulate the effect on the morphology and dynamics of fine roots when the N deposition in the future atmosphere increased by 1-2 times.The production,mortality and turnover dynamics of fine roots in the natural secondary forest of Lushui River were measured over two years period by using minirhizotrons.The results of the study showed that:(1)Simulated N deposition has a significant impact on the fine root morphology of natural secondary forests.The addition of N significantly increased the diameter,length,number and surface area of the live fine roots,and with the increase of N application level,morphological characteristics of fine roots first increased and then decreased.Soil layer,year,N application level and their interactions all affect the morphological characteristics of fine roots.(2)Simulated N deposition has a significant impact on fine root production(FRP)and mortality(FRM)of natural secondary forests.With the increase of N application level,both FRP and FRM showed a trend of first increase and then decrease;in different soil layers,compared with the sample plot without N application,low concentration of N significantly increased FRP and FRM,while high concentration of N only increased the FRM of the topsoil(10?20cm).N addition did not change the seasonal dynamics of FRP,Fine roots production vigorously in summer and gradually decrease in autumn.There is no obvious regularity in the changes of fine root FRM.N treatment,soil depth,year and their interaction also have significant effects on FRP and FRM.Different soil layers FRP and FRM have different changing laws,which may be caused by environmental differences in different soil layers.(3)Simulated N deposition significantly reduced the fine root turnover rate(FRT)of natural secondary forests.The annual turnover rate of fine roots in the plots without N application was about 1.91 times,and the turnover rate showed a downward trend with the increase of N application.The effect of FRT on N addition is different in different soil layers.Soil layer,year and the level of N administration and its interaction also affect FRT.In short,N addition changes the morphological characteristics of fine roots,which means that plants can change the morphology of fine roots to adjust nutrient absorption strategies in order to grow better in different soil nutrient environments.Exogenous N addition decreased the FRT of natural secondary forests and increased the life of fine roots,which indicated that N application increased the residence time of nutrients in fine roots and affected the C distribution pattern of terrestrial ecosystems.