Effects Of N Addition On Soil Soluble Nitrogen And CH₄ Oxidation Of Upland In Subtropical

Nitrogen addition experiment has been established in Wanmulin Biophere Reserve in three forest types, a natural forest, a coniferous plantation and an Orchard in 2009. The methane oxidation from forest soils were measured using static chamber-gas chromatograph technique and the Soil soluble nitrogen were measured by Flow Injection Analysis (FIA.) for one year. Several key results were given as follows:Nitrogen addition significantly increased the content of soil soluble nitrogen. The contents of ammonium, nitrate and total soluble nitrogen in controls plots in natural forest were 14.30 mg/kg,9.34 mg/kg and 66.32 mg/kg, respectively. The average contents of ammonium, nitrate, and total soluble nitrogen increased by 41%,122%, and 30% when compared to control plots for High-N plots and increased by 76%,95%, and 40% for Low-N plots respectively. For the plantation forest, the contents of ammonium was increased by 35% in High-N and by 17% in Low-N, contents of nitrate were higher 46% and 23% for High-N and Low-N, respectively, and in samples from the nitrogen addition plots, total soluble nitrogen were no significantly increased compared to controls. Annual mean ammonium, nitrate, and total soluble nitrogen were 5.16 mg/kg,6.15 mg/kg, and 26.24 mg/kg, respectively, in Orchard. In the nitrogen addition plots, the contents in High-N were higher 14%,107% and 40%, while in Low-N were higher 12%,94% and 31%, respectively.Means soil CH4 oxidation rates in natural forest, plantation forest, and果园were 45.89μg·-2·h-1,20.02μg·m-2·h-1 and 15.21μg·m-2·h-1,respectively. Soil moisture appears to be an important controller of CH4 oxidation, with increasing water content increased and then decreased. The effect of nitrogen addition on the CH4 oxidation was dependent on forest types and quantity of nitrogen fertilizer added to these soils. The soil CH4 oxidations in natural forest were inhibition in Low-N. There are both significant stimulating of soil CH4 oxidation in plantation forest. There is no significantly difference between the CK, HN and LN in Orchard. Our results suggested that effects of N addition on soil soluble nitrogen and soil CH4 oxidaiton are depends on the contents of nitrogen in soil, forest types, forest management, and N addition levels in subtropical China.