Abstract: In order to investigate the effects of exogenous nitrogen addition on carbon dioxide emission and enzyme activities of a forest soil, an incubation experiment was performed with soil collected from a broadleave forest. There was 60 g dry soil in each jar used for soil incubation and there were 17 exogenous nitrogen addition treatments. Soil CO₂ emission rates were measured 1, 2, 4, 6, 8, 15, 18, and 22 days after the exogenous nitrogen addition by using an infrared gas analyzer. Urease, invertase and catalase activities, dissolved organic carbon (DOC) were also measured. Results showed that the accumulative soil CO₂ emissions for all treatments increased significantly with the increase of incubation days. Soil CO₂ emissions for most nitrogen treatments were lower than that for CK treatment, which indicated that the addition of exogenous nitrogen inhibited soil CO₂ emission. The addition of nitrogen increased soil urease activity; a linear regression function could be used to fit the relationship between soil urease activity and the amount of exogenous nitrogen added. Within the range of 0-0.0067 g nitrogen addition, soil invertase activity increased significantly with the increase of exogenous nitrogen. There was no significant linear relationship between soil catalase activity and exogenous nitrogen addition. Furthermore, within the range of 0-0.0055 g nitrogen addition, the relationship between DOC content and the amount of exogenous nitrogen could be significantly fitted with a linear function.

Key words: shoot, exogenous growth regulator, rice, Sub1, survival percentage, submergence