Effects of Glucose Addition on Soil Nitrogen Transformation and Net Mineralization and Nitrification in Chinese Fir Plantation

In view of the significant role of litter played in regulating forest soil nitrogen transformation, simulating the influence of matrix carbon sources on nitrogen transform in the subtropical coniferous forest acid soil is helpful to deeply understand the mechanism between carbon and nitrogen. The effects of glucose addition (as C of 0, 100, 300, 1 000, 2 000, and 5 000 mg·kg-1) on soil nitrogen content, nitrogen mineralization and nitrification were studied in the soil under subtropical Chinese fir plantation. The results showed that the glucose addition reduced the soil inorganic nitrogen content and proportion in total soluble nitrogen, and the nitrate nitrogen decreased more than ammonium nitrogen; but the decrease of soluble organic nitrogen (SON) and pH was not found, even the ratio of SON in total soluble nitrogen increased. Glucose addition decreased the net nitrogen mineralization and the nitrification rates for nitrogen mineralization were inhibited. The results showed that hydrophilic nitrogen proportion decreased significantly with the addition of glucose, which was related to nitrogen immobilization and transformation to result in the enhancement of SON proportion. Correlation analysis showed that there was a significantly negative linear relationship (R2 = 0.902) between the proportions of nitrate and dissolved organic nitrogen in the total nitrogen of the extract from soil, which indirectly give a evidence of glucose likely promoting the nitrate retaining and transformation by microorganisms involved in soil. The research discovered that the glucose amount (as C) of 1 000 mg ·kg-1 was the threshold affecting the nitrogen transforms in forest soil under subtropical Chinese fir plantation.