Abstract: Taking five typical forests (Betula platyphylla forest, Quercus mongolica forest, B. platyphylla + Pinus koraiensis + Acer mono mixed forest, P. koraiensis forest, and Larix olgensis forest) in Xiaoxing'an Mountains as test objects, we investigated the effects of forest types (broadleaved forest, mixed forest, and coniferous forest) and soil layers (0-10 cm, 10-20 cm, 20-30 cm) on the turnover of exogenous alanine. The results showed that the turnover of soil exogenous alanine varied across different forest types, with significant difference in time and profile. The turnover rate was the highest in the broadleaved forest, followed by the mixed forest, and the lowest in the coniferous forest, with the half-life being 2.6-4.2, 3.6-5.5, and 4.3-7.0 h, respectively. With increasing soil depth, the potential turnover rate of exogenous alanine decreased, the half-life became longer, and soil adsorption of alanine weakened. With the addition of exogenous alanine, the content of ammonium and nitrate significantly increased, with the former being increased by 83.8%-95.3%, 80.9%-94.6% and 73.7%-93.2%, and the latter being increased by 82.9%-94.7%, 82.3%-93.8% and 78.1%-92.5% in the broadleaved forest, mixed forest, and coniferous forest, respectively. The net ammoniation and nitrification rates increased sharply at first and then decreased slowly, which were both positive. Soil layer and forest type as well as their interaction significantly affected the turnover, half-life, ammoniation, and nitrification of exogenous alanine.

Key words: exogenous alanine, turnover, half-life, ammoniation, nitrification