Increasing global temperatures have the potential to stimulate decomposition and alter the composition of soil organic matter (SOM). However, questions remain about the extent to which SOM quality and quantity along the soil profile may change under future warming. In this study we assessed how +4 °C whole-soil warming affected the quantity and quality of SOM down to 90 cm depth in a mixed-coniferous temperate forest using biomarker analyses. Our findings indicate that 4.5 years of soil warming led to divergent responses in subsoils (>20 cm) as compared to surface soils. Warming enhanced the accumulation of plant-derived n-alkanes over the whole soil profile. In the subsoil, this was at the expense of plant- and microorganism-derived fatty acids, and the relative abundance of SOM molecular components shifted from less microbially transformed to more transformed organic matter. Fine root mass declined by 24.0 ± 7.5% with warming over the whole soil profile, accompanied by reduced plant-derived inputs and accelerated decomposition of aromatic compounds and plant-derived fatty acids in the subsoils. Our study suggests that warming accelerated microbial decomposition of plant-derived inputs, leaving behind more degraded organic matter. The non-uniform, and depth dependent SOM composition and warming response implies that subsoil carbon cycling is as sensitive and complex as in surface soils.

全球温度升高有可能刺激分解并改变土壤有机质（SOM）的组成。但是，在未来变暖的情况下，沿土壤剖面的SOM质量和数量可能会变化的程度仍然存在疑问。在这项研究中，我们使用生物标记分析评估了+4°C全土升温如何影响混合针叶温带森林中低至90 cm深度的SOM的数量和质量。我们的发现表明，与表层土壤相比，4.5年的土壤变暖导致地下土壤（> 20 cm）的响应有所不同。变暖促进了植物源性氮的积累-烷烃在整个土壤剖面上。在地下土壤中，这是以植物和微生物衍生的脂肪酸为代价的，并且SOM分子成分的相对丰度从微生物转化较少的有机物转变为更多的有机物。随着整个土壤温度的升高，细根质量下降了24.0±7.5％，伴随着来自植物的投入减少，以及土壤中芳族化合物和植物性脂肪酸的加速分解。我们的研究表明，变暖加速了植物来源输入的微生物分解，而留下了更多的降解有机物。非均匀的，与深度有关的SOM组成和变暖反应表明，地下土壤碳循环与表层土壤一样敏感和复杂。