Extracellular enzymes in the soil are pivotal to nutrient cycling in the ecosystem. Simulated nitrogen (N) deposition has resulted in positive, negative, and neutral effects of added N on soil extracellular enzyme activity (EEA).

A field experiment involving two levels (50 and 150 kg ha⁻¹ yr⁻¹) and three forms (NaNO₃, NH₄NO₃, (NH₄)₂SO₄) of added N was conducted in a northern temperate forest. Over 8 years beginning in 2011, we measured the extracellular enzyme activity of six soil-based enzymes involved in C- (β-glucosidase, BG; polyphenol oxidase, PPO; catalase, CAT), N- (urease, UR) and P- (acid phosphatase, ACP; alkaline phosphatase, AKP) cycling during the growing season (March to September).

High-level N addition produced a more obvious effect in promoting the activity of C-cycling enzymes and ACP, while the activities of UR and AKP under high-level N addition decreased significantly at rates of 10.0 and 26.8%, respectively. NH₄⁺-N had a stronger effect on soil EEAs than NO₃⁻-N, except UR activity. Furthermore, N addition induced a time-lag effect on the activity of BG, PPO, and ACP. BG activity achieved a maximum value in 2016 after increasing at an average rate of 21.2%. Furthermore, additional N produced nonlinear effects in the inter-annual variation of BG and CAT activity, which emphasized the importance of long-term monitoring.

The effects of N addition on soil EEAs depended on the forms and levels of N added. The stimulatory effects of N addition on the activity of C-cycling enzymes may lead to instability in the soil C pool.

土壤中的细胞外酶对于生态系统中的养分循环至关重要。模拟的氮（N）沉积已导致添加N对土壤细胞外酶活性（EEA）的正，负和中性作用。

在北部温带森林中进行了涉及两种水平（50和150 kg ha ^-1 yr ^-1）和三种形式（NaNO ₃，NH ₄ NO ₃，（NH ₄）₂ SO ₄）添加的N的田间试验。从2011年开始的8年中，我们测量了六种涉及C-（β-葡萄糖苷酶，BG；多酚氧化酶，PPO；过氧化氢酶，CAT），N-（脲酶，UR）和P-的土壤基酶的细胞外酶活性。 （酸性磷酸酶，ACP；碱性磷酸酶，AKP）在生长期（3月至9月）循环。

高氮添加对促进C-循环酶和ACP的活性具有更明显的作用，而高氮添加下UR和AKP的活性分别以10.0和26.8％的速率显着降低。除UR活性外，NH ₄ ⁺ -N对土壤EEA的影响比NO ₃ ^-- N强。此外，氮的添加对BG，PPO和ACP的活性具有时滞效应。BG活动在以平均21.2％的速度增长后在2016年达到了最大值。此外，另外的N在BG和CAT活性的年际变化中产生了非线性影响，从而强调了长期监测的重要性。

氮素对土壤EEA的影响取决于氮素的形式和含量。氮的添加对碳循环酶活性的刺激作用可能导致土壤碳库的不稳定。