氮添加对戴云山黄山松林土壤有机氮解聚酶活性的影响及其调控因素

解聚作用是控制土壤有机氮矿化和氮素有效性供应的关键，然而氮沉降对亚热带森林土壤有机氮解聚作用的影响机制尚不明确。以福建戴云山黄山松林为研究对象，设置对照（CT）、低氮（LN）和高氮（HN）3个氮添加水平，进行为期2年的氮沉降模拟试验。通过分析土壤化学性质、微生物生物量和土壤8种有机氮解聚酶活性的变化，探究土壤有机氮解聚作用响应氮沉降的机理过程。结果表明：短期氮添加显著增加0-10 cm和10-20 cm土层矿质氮含量，并显著增加了10-20 cm土层微生物生物量碳（MBC）的含量。同时，0-10 cm土壤锰过氧化物酶活性随氮添加量增加而显著提高，HN处理下土壤漆酶活性显著高于LN和CT；10-20 cm土壤的酸性蛋白酶、碱性蛋白酶、中性蛋白酶和漆酶活性均随氮添加量增加而显著提高，但是谷氨酰胺酶活性变化相反。冗余分析表明两个土层有机氮解聚酶活性影响因素不同，土壤硝态氮（NO₃^--N）是0-10 cm土层有机氮解聚酶活性的主要影响因素，而10-20 cm土层有机氮解聚酶活性由NO₃^--N和MBC共同影响。综上所述，亚热带黄山松林土壤不同有机氮解聚酶对氮添加的响应不一致，主要受土壤NO₃^--N和MBC调节。该研究有助于拓宽土壤氮循环对氮沉降的响应机理，同时对维持土壤有效氮含量和提高黄山松生态系统生产力具有重要意义。

Effects of nitrogen addition and associated regulatory factors of the organic nitrogen depolymerizing enzyme activity of Pinus taiwanensis forest soils in Daiyun Mountain

Depolymerization is a key process to control soil organic nitrogen mineralization and nitrogen availability supply. However, it is unclear that the affecting mechanism of nitrogen deposition on soil organic nitrogen depolymerization in subtropical forest. In this study, taking Pinus taiwanensis forest as the research object, a two-year nitrogen addition simulation experiment was set up by three levels including control (CT), low nitrogen (LN) and high nitrogen (HN) in Daiyun Mountain, Fujian Province. The mechanism of soil organic nitrogen depolymerization in response to nitrogen deposition was explored by analyzing the changes of soil chemical properties, microbial biomass and eight soil organic nitrogen depolymerizing enzyme activities. The results showed that short-term nitrogen addition significantly increased the content of mineral nitrogen in 0-10 cm and 10-20 cm soil layers, and significantly increased the content of microbial biomass carbon (MBC) in 10-20 cm soil layers. Simultaneously, the activity of Manganese Peroxidase in 0-10 cm soil layer increased significantly with nitrogen addition, and Laccase in HN was significantly higher than that of CT and LN. The activities of Acid Protease, Alkaline protease, Neutral protease and Laccase in 10-20 cm soil layer were increased significantly with the nitrogen addition, but the D-glutaminase activity was the opposite. Redundancy analysis showed that different influencing factors dominated the activities of organic nitrogen depolymerase in the two soil layers. Soil nitrate nitrogen (NO₃^--N) was the main influence factor of organic nitrogen depolymerase activities of 0-10 cm soil layer, while the organic nitrogen depolymerase activities of 10-20 cm soil layer was jointly affected by NO₃^--N and microbial biomass carbon (MBC) content. In conclusion, the responses of soil organic nitrogen depolymerization enzymes to nitrogen addition were inconsistent in subtropical Pinus taiwanensis forest soil, which were mainly regulated by soil NO₃^--N and MBC content. The mechanism of soil organic nitrogen depolymerization under nitrogen addition is very complex, and it will be an important direction in the future to study the process and mechanism of organic nitrogen depolymerization from the perspective of their polymerization effect. This study is helpful to broaden the response mechanism of soil nitrogen cycle to nitrogen deposition, and it has important implications for maintaining soil available nitrogen content and improving ecosystem productivity in Pinus taiwanensis forest.