The Nutrient Biological Cycling In4Kinds Urban Forest Ecosystems In Karst Region

With the accelerated process of urbanization, the urban forests that could beautify and improve the urban ecological environment have became increasingly prominent. The concept of the city going into the forest-the forest embracing the city is more and more in-depth and the research work of urban forest carry out extensively. Guizhou located in the hinterland of China's karst region of southwestern has uniqueness and fragility geological environment. Karst rocky desertification in Guizhou constrains the economy development and human life. Nutrient cycling based on forest vegetation, litter and soil is less, so the research of urban forest nutrient biological circulation of karst areas has important practical significance and guiding role.As the research object of typical Guiyang urban forest, the main content of this paper is the nutrient distribution and biological circulation characteristics of four urban forest (Poplar forest, Betula luminifera and Italian Poplar mixed forest, Sawtooth Oak forest, Black Locust and Ovate Catalpa mixed forest), and the results show that:(1) The nutrient elements content in soil of Poplar forest and Sawtooth Oak forest is TK>TN>TP>TCa>TMg, and it is TK>TN>TP>TMg>TCa in Black Locust and Ovate Catalpa mixed forest and Betula luminifera and Italian Poplar mixed forest. The nutrient elements accumulation is Poplar forest (65.69t-hm-2)> Betula luminifera and Italian Poplar mixed forest (59.22t-hm-2)> Black Locust and Ovate Catalpa mixed forest (54.71t-hm-2)>Sawtooth Oak forest (35.63t-hm-2)(2) The nutrient elements content of arbor is most in leaf and least in trunk. The nutrient elements accumulation is Poplar tree (1095.96kg·hm-2)>Ovate Catalpa tree (897.99kg-hm-2)>Black Locust tree(853.81kg-hm-2)>Sawtooth Oak tree(726.48kg·hm-2)>Betula luminifera tree (36.28kg-hm-2)>Italian Poplar tree. The nutrient element accumulation of leaves is highest. Due to the nutrient accumulation of trunk taking up4.16%to25.69%of total, so deforestion based on trunk has litter effect to forest nutrient cycling and productivity.(3) The nutrient elements accumulation of ground cover is Sawtooth Oak forest (164.16kg-hm-2)>Poplar forest (112.96kg-hm-2)>Black Locust and Ovate Catalpa mixed forest (102.57kg-hm-2)>Betula luminifera and Italian Poplar mixed forest (83.46kg·hm-2) (4) The nutrient elements accumulation in biological cycling is Poplar forest (65130.14kg-hm-2)>Betula luminifera and Italian Poplar mixed forest (58537.86kg·hm-2)>Black Locust and Ovate Catalpa mixed forest (56174.95kg-hm-2) Sawtooth Oak forest (35871.91kg-hm-2)(5) The nutrient elements uptake of forest ecosystem is46.10kg-hm-2·a-1in Black Locust and Ovate Catalpa mixed forest,43.84kg-hm-2·a-1in Poplar forest,22.01kg-hm-2·a-1in Sawtooth Oak forest,6.36kg-hm-2·a-1in Betula luminifera and Italian Poplar mixed forest.(6) The nutrient elements cycling rate in biological cycling is Betula luminifera and Italian Poplar mixed forest (0.49)> Poplar forest (0.42)> Black Locust and Ovate Catalpa mixed forest (0.37)> Sawtooth Oak forest (0.28).N cycling rate is highest and Ca cycling rate is slowest.(7) Poplar forest have the highest nutrient content, nutrient accumulation, and nutrient return, the higher nutrient circulation rate. Poplar grows well in Guiyang City, which is worth promoting planting.