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变暖和氮（N）添加都会影响土壤有机质（SOM）的化学性质和特性。然而，它们的交互作用对农业生态系统中分子组成和来源（植物或微生物衍生）的影响仍不确定。
该研究在中国北方进行了为期九年的实地试验研究，通过使用生物标志物（即游离脂质、木质素酚和氨基糖）和13C核磁共振以量化增温（+2°C）、氮添加（ kg N ha−1yr−1）以及它们的交互作用对SOM含量及其组成的影响。
结果表明，在进行增温或氮添加处理后非根系土的SOM含量变化不大，但表层土壤（0~10 cm）SOM特征（即分子组成、不稳定性和来源）受到的变暖和/或氮添加的显著影响，而深层土壤（10~20 cm）则没有显著影响。SOM由大约18-27%的微生物残留物组成，其大部分来自真菌（比细菌高4倍）。单独增温可减少总游离脂质（主要是短链脂质，<C20）21%，但木质素酚（香草基和丁香酚）增加了37%，微生物残留物（量化为氨基糖）增加了31%。单独氮添加使表层土壤中的木质素酚增加了28%，微生物残留增加了30%，但对游离脂质含量的影响有限。增温和氮添加结合使总游离脂质增加40%，木质素酚增加42%，并使地表土壤中真菌/细菌微生物残留物的比例增加。总的来说，增温和氮添加通过木质素酚和微生物残留物的积累对温带农业生态系统中SOM的持久性具有协同的积极作用。
Fig. 1. Effects of warming and nitrogen addition on lipid degradation proxies: ratio of short-chain lipids (<c20) to long-chain lipids (≥C20) (i.e., SCA/LCA: a); the ratio of acyclic to cyclic lipids (i.e., Acyclic/Cyclic: b); lignin oxidation indices: ratio of acid to aldehyde for syringyls [(Ad/Al)s: c], and the ratio of acid to aldehyde for vanillyls [(Ad/Al)v: d] in the 0–10 and 10–20 cm layers. The treatments include: CK, Control; W, Warming; N, Nitrogen addition; WN, Warming with N addition. Different lowercase and uppercase letters indicate a significant difference between treatments and soil layer, respectively (P < 0.05). W and N denote the effects of warming and nitrogen addition treatments, respectively (based on results of two-way ANOVA). Values in bold indicate significant treatment effects at P < 0.05).
Fig. 2. Effects of warming and nitrogen addition on fungal (a), bacterial (c), and total (e) microbial residual C (MRC), and their contribution to soil organic C (SOC) accumulation (b, d, f) in the 0–10 and 10–20 cm layers. The treatments include: CK, Control; W, Warming; N, N addition; WN, Warming with N addition. Different lowercase and uppercase letters indicate a significant difference between treatments and soil layer, respectively (P < 0.05). W and N denote the effects of warming and nitrogen addition treatments, respectively (based on results of two-way ANOVA). Values in bold indicate significant treatment effects at P < 0.05).
Fig. 3. Biplots of the principal component analysis (PCA) between compounds and related degradation proxies (i.e., free lipids, lignin phenols, and amino sugars) and the control (CK), soil warming (W), N addition (N), and soil warming plus N addition (WN) in the 0–10 and 10–20 cm layer. ACLtot: average chain length of total acyclic lipids; SCA/LCA: ratio of short-chain lipids (<c20; SCA) to long-chain lipids (≥C20; LCA); (Ad/Al)s: the ratio of acid to aldehyde for syringyls; (Ad/Al)v: the ratio of acid to aldehyde for vanillyls; VSC: total lignin phenols; AS: total amino sugars; MRC: microbial residual C; F-MRC: fungal microbial residual C; B-MRC: bacterial microbial residual C.https://doi.org/10.1016/j.soilbio.2022.108693
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