| With the development of global industry and agriculture, many human activities such as the emission of automobile exhaust, the combusion of fossil fuels and the production and use of chemical fertilizers have produced a large number of reactive nitrogen (N),which leads to the global atmospheric N deposition increased significantly and the problem in the future decades will be further intensified. The increase N deposition may considerably influence the structure and function of forest ecosystems. The studies of N deposition are still in its infancy in China, which is one of the areas of global three biggest N deposition (namely Europe, the United States and China). Pleiobastus amarus is one of the important bamboo used to return the grain plots to forestry in the southern area of China, which plays an irreplaceable ecological and economic effects in Yangtze River shelter-forest with regard to the construction of ecological barrier and economy. Implementing simulated N deposition experiments on P. amarus plantation in Rainy Area of West China, and exploring the responses of litter substrate quality and annual total input of nutrient elements through litter and soil N mineralization of P. amarus plantation to simulated N deposition are helpful to provide important basic data and theoretical basis, which are beneficial for the sustainable management of P. amarus plantation in Rainy Area of West China. Four treatments was installed, i.e., control (0 g N·m-2·a-1), low N (5 g N·m-2a·-1), medium N (15 g N·-2·a-1) and N (30 g N·a-1). The results showed that:(1) Simulated N deposition significantly increased the litter production of P. amarus plantation, and the increasing range was between 8.75% and 28.08%; Both the order on the basis of the content of nutrient elements of litter leaf and litter twig were N>Ca>K>Mg>P, and simulated N deposition significantly increased the content of N、 P、K、Ca and Mg of litter leaf, and the increasing range were 18.10%～32.71%, 16.11%～22.67%,12.86%～22.54%,10.31%～14.70%'13.18%-24.07% respectively. Both the order of annual total input of nutrient elements of litter leaf and litter twig were N>Ca>K>Mg>P. Simulated N deposition significantly increased the annual total input of nutrient elements. The increasing range of annual total input of N, P, Ca, Mg and K were 21.98%～62.12%,50.62%～22.18%,24.02%～50.89%, 28.59%～68.78% and 23.85%～58.66%, respectively. This study shows that the simulated N deposition increased soil nutrient through increasing the annual total input of nutrient elements of litter, which is beneficial to maintain the fertility and remain the long-term growth force of P. amarus plantation.(2) Simulated N deposition significantly increased the content of N and P elements of litter leaf, and MN significantly increased the content of N elements of litter twig, and MN and HN significantly increased the content of P element of litter twig; The impact of simulated N deposition on the content of C element of litter was very weak, which resulted in simulated N deposition significantly reducing the C/N of litter leaf and MN decreasing significantly the C/N of litter twig. Simulated N deposition did not influence the content of lignin and cellulose significantly. Because simulated N deposition increased significantly the content of N and P content and reduced the C/N, so N deposition may promote the initial rate of litter decomposition of P.amarus.(3) Simulated N deposition lowered the soil pH value of P. amarus plantation, and the reducing range was between 0.30% and 7.69%, and significant difference existed between HN and CK (P<0.05). Simulated N deposition increased the content of soil TOC of P. amarus plantation, and compared with CK, LN and HN significantly increased the contents of TOC, and the increasing percentages were 2.63% and 4.03% respectively. Simulated N deposition increased soil TN content of P. amarus plantation, but only HN significantly increased it, and the increasing percentage was 13.2%. Simulated N deposition did not influence soil C/N significantly. Under natural condition (CK), MBC content was 0.23 mg ·g-1, and HN significantly increased the content of MBC by 14.10%. Under natural condition (CK), MBN content was 0.023 mg ·g-1, and simulated N deposition significantly increased the content of soil MBN, and the increasing range was between 12.12% and 25.63%. The content of soil available N of P. amarus plantation showed increasing trend under the treatments of simulated N deposition, and HN significantly increased the content of soil available N. Under the natural condition, the amount of fine root biomass was 616.42 g·m-2, and the difference of fine root biomass between the HN and CK reached a significant level. This study results show that the simulated N deposition helped to improve nutrients cycling, soil quality and increase soil fertility(4) Simulated N deposition significantly increased the net amount of soil N mineralization and the net N mineralization rate of P. amarus plantation, and the net N mineralization rate showed significant positive correlations with initial inorganic N content in soil, soil microbial biological N content, the amount of fine root biomass and litter production respectively, while it showed significant negative correlations with leaf C/N and soil pH value respectively. This study results show that the simulated N deposition influenced the soil N mineralization through affecting soil physical and chemical properties and litter conditions of P. amarus plantation. Due to the fact that the simulated N deposition showed the trend of increasing the amount of soil N mineralization and net N mineralization rate, this is helpful to ease the N limit level and promote the productivity of P. amarus plantation. |
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