<b>12 年田间氮添加</b><b>通过两种截然不同的微生物酶途径</b>

Soil organic carbon (SOC) decomposition can be significantly influenced by plant C inputs, i.e., the priming effect. However,the current understanding of priming effect under nitrogen (N) addition is overwhelmingly based on short-term incubation studies with simple C addition (e.g., glucose). How long-term N addition in the field affects the priming effect caused by complex C remains unclear, especiallyin boreal forests with severer N limitation.Here, soils were collected from a 12-year in-situN addition field experiment in a boreal forest, and were incubated with 13C-labeled cellulose. Further, a global data synthesis was conducted to compare the effect of N addition on priming between simple and complex C types. The results showed that long-term N addition reduced the priming effectby on average 150%, and meanwhile increased peroxidasebut decreased β-1,4-N-acetylglucosaminidase.The partial least squares path modellingexplained 68.3 % of the variation of the priming effect among all the treatments with two contrasting pathways of hydrolytic enzymes versusoxidases with the extent explainedcomparable. These results suggested that the inhibited effect of long-term N addition on priming could be attributed to changes in microbial utilization of soil C. Based on data synthesis, the N-inhibited effect on priming caused by complex C was higher than by simple C, indicating that the N inhibition might be underestimated by studies with simple C addition. Our results provide insights into accurately assessing SOC decomposition via the priming effect in the context of N deposition in boreal forests.土壤有机碳（Soil Organic Carbon, SOC）的分解过程可显著受植物碳输入调控，即激发效应（priming effect）。然而，当前关于氮（Nitrogen, N）添加下激发效应的认知，绝大多数基于添加简单碳源（如葡萄糖）的短期培养实验。野外长期氮添加对复杂碳源引发的激发效应的影响仍不明晰，尤其是在氮限制更为严重的北方森林中。本研究从某北方森林开展的为期12年的野外原位氮添加田间试验中采集土壤样品，并利用13C标记的纤维素进行培养实验。此外，本研究还开展了全球数据集整合分析，对比不同碳源类型（简单碳与复杂碳）下氮添加对激发效应的影响差异。研究结果显示，长期氮添加可使激发效应平均降低150%，同时过氧化物酶（peroxidase）活性升高，而β-1,4-N-乙酰氨基葡萄糖苷酶（β-1,4-N-acetylglucosaminidase）活性降低。偏最小二乘路径模型（Partial Least Squares Path Modeling, PLS-PM）可解释所有处理下激发效应变异的68.3%，其中水解酶与氧化酶两条相对立的调控路径的解释度相当。上述结果表明，长期氮添加对激发效应的抑制作用，可归因于土壤碳的微生物利用方式发生改变。基于全球数据集整合分析的结果，复杂碳源引发的激发效应所受的氮抑制作用强于简单碳源，这意味着仅采用简单碳源添加的研究可能低估了氮素对激发效应的抑制程度。本研究结果可为在氮沉降背景下，通过激发效应精准评估北方森林土壤有机碳分解过程提供理论依据。