| Moso bamboo(Phyllostachys edulis) is an economically and ecologically important species characterized by short growth cycle, high yield and large soil nutrient demand in southern China, but under the influence of their growth characteristics and harvest method, the nutrient return is less. As a result, fertilizers were usually used to supplement the soil fertility, and nitrogen(N) fertilizer was widely used. However, in terms of the current management of bamboo forests, in order to obtain the greater economic benefits, large N fertilizer was used, which caused the reduction of nitrogen use efficiency(NUE) and a great environment pressure. Under this background, how to improve the NUE, reduce the loss of N, and reduce the adverse effects of N fertilizer on the environment, has become the key to achieving the sustainable management of Phyllostachys edulis forest.In this paper, four fertilization treatments included furrow application at 0~20 cm(T1) and 20~40 cm(T2) and hole application at 0~20 cm(T3) and 20~40 cm(T4) and a control treatment with no fertilizer were set in Huangshan public forest farm in Anhui Province of China. The 15 N isotope tracer technique was used to study the fate of fertilizer N. The effects of root type, root layer and age were studied and the rules of N uptake and utilization were investigated in moso bamboo forest. Then, the soil nutrient efficient response layer, root type and the key manage age were determined. Furthermore, the environmental factors in soil and their spatio-tempora characteristics at four key physiological stages were monitored and the index library was established. The relevance between soil index and NUE was conducted using the methods of grey correlation analysis, canonical correlation analysis and stepwise regression analysis, and the key factors affecting NUE of moso bamboo forest were screened. Furthermore, the way and rule of N loss were studied by subtraction method in moso bamboo forests. The main results were as follows.1. The fates of fertilizer N were uptake and utilization, residual in soil and N loss. The fates were different between different fertilization treatments.(1) After fertilization, the NUE showed a trend of first increasing and then decreasing with the growth of moso bamboo, and the NUE in stage S1~S2 was the largest. The NUE of different fertilization treatments was different, and the NUE for the furrow application at 20~40 cm(T2) was the largest, up to 30.36%.(2) The residual amount of fertilizer N decreased gradually with the absorption by bamboo roots and the N loss. Obvious vertical distribution characteristics were observed from the residual fertilizer N in moso bamboo forest soil. At the end of the test(184 d after fertilization), the residual ratios of fertilizer N of different fertilization treatments were 15.20%, 18.22%, 20.59% and 14.77%, respectively.(3) N loss is an important part of N fates in moso bamboo forest. The total loss ratio of fertilizer N in moso bamboo forest of four treatments were 51.42%~57.16%. Ammonia(NH3) volatilization, leaching and nitrification-dentrification were the main ways of N loss, and the loss ratios were 13.30%~16.57%, 18.08%~20.99% and 15.27%~21.35%, respectively. However, the ratio of runoff loss was the lowest, only 1.43%~2.02%. At the same fertilization method, N losses through NH3 volatilization and leaching by deep application were lower than that by shallow application. At the same fertilization depth, N losses through NH3 volatilization and leaching by rhizome root fertilization were lower than that by stump root fertilization. N losses through leaching showed the opposite trend. In terms of nitrification-dentrification loss, no consistent trend was observed under the same fertilization method or depth.2. Obvious effects of root type, root layer and age were found in NUE in moso bamboo forest.(1) Significant difference was found in N uptake and utilization between different root type fertilizations in moso bamboo forest. The absorption efficiency and NUE by rhizome root fertilization were significantly higher than that by stump root fertilization. When the experiment was over, the NUE by rhizome root fertilization and stump root fertilization were 28.07% and 26.93%, respectively.(2) Significant difference was found in N uptake and utilization between different root layer fertilizations in moso bamboo forest. The total absorption efficiency and NUE in fertilization depth of 20~40 cm were significantly higher than that in fertilization depth of 20~40 cm. At the end of the experiment, the NUE in fertilization depth of 0~20 cm and 20~40 cm were 27.09% and 29.41%, respectively.(3) N uptake and utilization among different ages in moso bamboo forest were different. The stage absorption efficiency ofâ… , â…¡ and â…¢ du moso bamboo increased first and then decreased, and the stage absorption efficiency ofâ… du moso bamboo was higher in various stages. The total absorption efficiency of different ages decreased with the increase of age. The NUE ofâ… , â…¡ and â…¢ du moso bamboo were 13.29%, 5.12% and 3.55%, respectively.3. Among 29 soil environmental factors, soil moisture content, total porosity, organic matter content, total phosphorus, urease activity, bacterial PLFAs, C:N, N:P and cumulative temperature were the key factors that affecting NUE in moso bamboo forest.Soil physical and chemical properties, enzyme activities and microbial biomass were determined through collecting moso bamboo forest soil at different physiological stages, and ecological stoichiometry characteristics of carbon(C), N and phosphorus(P) were calculated. The index database of soil environmental factors in moso bamboo forest was established, and the temporal and spatial variations of soil environmental factors were analyzed. The key factors that affecting NUE of moso bamboo forest were determined using the main factor screening technology, which including the methods of grey correlation analysis, canonical correlation analysis and stepwise regression analysis. Researches showed that soil environmental conditions and soil depth were closely related. The key factors affecting NUE were different in different soil layers. Comperhensive analysis showed that soil moisture content, total porosity, organic matter content, total phosphorus, urease activity, bacterial PLFAs, C:N, N:P and cumulative temperature were the key factors that affecting NUE in moso bamboo forest.An obvious regularity was found in the utilization of N in moso bamboo forest, and the utilization rate was directly affected by soil environmental factors. The results provided a strong theoretical support for the improvement of fertilization technology. Significant difference was found in N utilization between different root layer fertilizations in moso bamboo forest. Rhizome root at 20~40 cm soil layer, which could significantly improve the NUE and reduce N loss, should be recommended as the key application placement in moso bamboo forest. N utilization among different ages in moso bamboo forest were different and the NUE ofâ… du moso bamboo by hole application was the highest. Therefore,â… du moso bamboo should be recognized as the key object to be fertilized by hole application at soil depth of 30 cm. Moreover, NUE was closely related to soil environmental factors, especially for soil moisture content, total porosity and urease activity, and they should be the key point in fertilization practice. |
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