外源氮添加对森林土壤二氧化碳排放及酶活性的影响

Effects of exogenous nitrogen addition on carbon dioxide emission and enzyme activities of a forest soil

为研究不同外源氮添加量对森林土壤CO2排放及酶活性的影响，设置了室内土壤培养实验。在野外采集落叶阔叶林土壤，设置了17个外源氮添加水平，分别在添加外源氮后的第1、2、4、6、8、15、18、22天观测土壤CO2排放通量，分析不同外源氮量对土壤CO2排放动态变化的影响。于培养实验结束后测量土壤脲酶、转化酶、过氧化氢酶活性和土壤可溶性有机碳（DOC）等指标，分析不同施氮量对土壤脲酶、转化酶、过氧化氢酶活性和土壤可溶性有机碳（DOC）等的影响。结果表明：随着培养天数的增加，各处理的土壤CO2排放量持续增加且处理间差异逐渐增大。大部分氮添加处理的土壤CO2排放量低于对照，表明外源氮添加抑制了土壤CO2排放。外源氮添加增加了土壤脲酶活性，脲酶活性与外源氮添加量之间存在极显著的线性关系（P〈0.001）。在0～0.0067 g外源氮添加量范围内，转化酶活性的对数值随氮添加量的增加呈线性增加；但在0.0078～0.1000 g氮添加量条件下，土壤转化酶活性的对数值与氮添加量无显著线性关系。施加外源氮对土壤过氧化氢酶影响不明显。外源氮添加显著增加了土壤DOC含量，在0～0.0055 g氮范围内，土壤DOC与氮添加量呈极显著线性相关（P〈0.001）。

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.