Forest soils are an important carbon (C) sink and critical component of the global C cycle. Warmer temperatures and increased atmospheric nitrogen (N) deposition are altering the biogeochemistry in forest soils and disrupting the intricate balance between C storage and C respired across the globe. The molecular biogeochemistry of soil organic matter (SOM) with warming, N-addition, and simultaneous warming and N-addition was analyzed in soil samples from the Soil Warming × Nitrogen Addition Study at the Harvard Forest Long-term Ecological Research Site using advanced techniques. The results unequivocally demonstrate that warming and N-addition alter the molecular composition of SOM as individual stressors uniquely and in combination. Warming alone and in combination with N-addition accelerated SOM decomposition while N-addition alone slowed SOM degradation. The two-factor N-addition and warming plots contain SOM more like the warming only plots but exhibited unique changes over time (from 4 to 10 years) that could not be predicted by studying N-addition or warming alone. The specific SOM components and the overall SOM decomposition suggests that N-addition and warming impacts are not additive. N-addition may hinder warming impacts antagonistically over time but not to the extent where advanced SOM decomposition from warming is supplanted. As such, the results from warming alone and N-addition alone are not necessarily additive compared to the observed SOM molecular compositional changes when these treatments are applied simultaneously. Marked evolution in the molecular biogeochemistry of SOM demonstrates the sensitivity of SOM trajectories to multiple interactive global environmental changes and the continued need to study long-term impacts more holistically.

森林土壤是重要的碳（C）汇和全球碳循环的关键组成部分。气温升高和大气氮 (N) 沉积增加正在改变森林土壤中的生物地球化学，并破坏全球碳储存和碳呼吸之间的复杂平衡。使用先进技术在哈佛森林长期生态研究站点的土壤变暖×氮添加研究的土壤样品中分析了土壤有机质 (SOM) 的分子生物地球化学，其中包括变暖、N-添加以及同时变暖和 N-添加. 结果明确表明，变暖和 N-添加改变了 SOM 的分子组成，作为单独的压力源并结合在一起。单独加热以及与 N-添加相结合加速了 SOM 分解，而单独添加 N 会减缓 SOM 降解。双因素添加氮和变暖图包含 SOM，更像是仅变暖图，但随着时间（从 4 到 10 年）表现出独特的变化，这无法通过单独研究添加氮或变暖来预测。特定的 SOM 成分和整体的 SOM 分解表明，氮添加和变暖影响不是相加的。随着时间的推移，N-添加可能会对抗性地阻碍变暖的影响，但不会达到由变暖导致的高级 SOM 分解被取代的程度。因此，与同时应用这些处理时观察到的 SOM 分子组成变化相比，单独加热和单独添加 N 的结果不一定是相加的。