Fine Root Production And Turnover And The Response To Nitrogen Deposition In Metasequoia Glyptostroboides Plantation

In recent years, the gradual increase of nitrogen deposition has an important impact on the underground ecological process. The fine root（<2mm） is the most active part of the plant, and is the most vital organ to absorb nutrients, water and minerals. The impact of nitrogen deposition on the underground ecological process, especially the influence of fine root dynamic, has become one of the hotspots in ecology research. We adopt simulated nitrogen deposition method, and set up five nitrogen concentration treatments(N0=0g·m^-2·a^-1, N1=5g·m^-2·a^-1, N2=10g·m^-2·a^-1, N3=15g·m^-2·a^-1, N4=30g·m^-2·a^-1). We use minirhizotron to monitor the production, mortality and turnover of fine roots, and want to explore the fine roots response mode of to nitrogen deposition in M. glyptostroboides. The following are the main conclusions of this study.（1） Under the natural state, the production of M. glyptostroboides is 0.5267 mm·cm^-2·a^-1, the mortality is 0.6501 mm·cm^-2·a^-1. The production and mortality of fine roots show significantly difference in different months. There are more production of fine roots in spring, and less after the end of summer, and less mortality in spring, and more after the end of summer. The annual production and mortality of fine roots below 1mm diameter are significantly hifher than fine roots above 1mm and show significantly difference in different months. The annual production and mortality of fine roots at second order are significantly hifher than fine roots of high orders and show significantly difference in different months. The first order roots produce more in summer, the second order roots produce more in spring and summer. The maximum mortality of each orders of roots is higher in the end of summer and autumn. The annual production and mortality of fine roots at shallow soil layer are significantly hifher than deep soil layer. But there are no significantly difference in different months. The annual production and mortality of fine roots show different regularity at different soil layers, this may be related to the difference of physical and chemical properties of soil and environmental factors at different soil layers.（2） Nitrogen deposition have no significant effect on fine production in M. glyptostroboides, but have significant effect on fine root mortality. Fine root mortality in N4 sample plot is significantly lower than the control. Fine root production has a high correlation with soil nitrogen availability, but mortality has a low correlation with soil nitrogen availability. The diameter that below 1mm, and the lower orders of fine roots are the most active part of M. glyptostroboides. They are sensitive to nitrogen increasing. The annual production and mortality of fine roots show different regularity at these roots show, this may be related to the comprehensive effects of physical and chemical properties of soil and roots own characteristics. With the increasing of nitrogen availability, there are no significantly different regularity among different soil layers, this may be related to the comprehensive effects of soil nitrogen availability, roots own characteristics, environmental factors and soil fauna.（3） Under the natural state, the turnover of M. glyptostroboides is 1.46 times pre years. With the increasing of nitrogen availability, the turnover of fine roots become faster, then slower, but not significant. We use the summary of fine root production and mortality to estimate turnover, this may be a scientific method to estimate turnover of fine roots. The diameter that below 1mm, and the lower orders of fine roots turnover active. With the increasing of nitrogen availability, all the turnover of different diameter classes fine roots increase at first, then decrease. Except the third order roots, all the turnover of different order fine roots increase at first, then decrease, with the increasing of nitrogen availability. Different fine roots of different diameter classes and root orders has different response regularity to the increasing of nitrogen availability. There are no significantly difference in fine root turnover among different soil layers. There are no significantly difference in fine root of different soil layer turnover between different nitrogen sample plots. This may be related to the comprehensive effects of soil nitrogen availability, roots own characteristics, environmental factors and soil fauna, and still need further study to reveal the mechanism.