Despite the importance of subsoil carbon (C) deposition by deep-rooted crops in mitigating climate change and maintaining soil health, the quantification of root C input and its microbial utilization and stabilization below 1 m depth remains unexplored. We studied C input by three perennial deep-rooted plants (lucerne, kernza, and rosinweed) grown in a unique 4-m deep RootTower facility. 13C multiple pulse labeling was applied to trace C flows in roots, rhizodeposition, and soil as well as 13C incorporation into microbial groups by phospholipid fatty acids and the long-term stabilization of microbial residues by amino sugars. The ratio of rhizodeposited 13C in the PLFA and amino sugar pools was used to compare the relative microbial stability of rhizodeposited C across depths and plant species. Belowground C allocation between roots, rhizodeposits, and living and dead microorganisms indicated depth dependent plant investment. Rhizodeposition as a fraction of the total belowground C input declined from the topsoil (0–25 cm) to the deepest layer (360 cm), i.e., from 35%, 45%, and 36%–8.0%, 2.5%, and 2.7% for lucerne, kernza, and rosinweed, respectively, where lucerne had greater C input than the other species between 340 and 360 cm. The relative microbial stabilization of rhizodeposits in the subsoil across all species showed a dominance of recently assimilated C in microbial necromass, thus indicating a higher microbial stabilization of rhizodeposited C with depth. In conclusion, we traced photosynthates down to 3.6 m soil depth and showed that even relatively small C amounts allocated to deep soil layers will become microbially stabilized. Thus, deep-rooted crops, in particular lucerne are important for stabilization and storage of C over long time scales in deep soil.

尽管根深蒂固的作物在缓解气候变化和维持土壤健康方面的地下土壤碳（C）沉积非常重要，但仍未对根系C输入的定量及其在1 m以下深度的微生物利用和稳定性进行探索。我们研究了在独特的4 m深RootTower设施中生长的三种多年生根系植物（卢塞恩，kernza和rosinweed）的C输入。将13C多脉冲标记应用于根，根状茎和土壤中的痕量C流动，以及通过磷脂脂肪酸将13C掺入微生物基团，并通过氨基糖长期稳定微生物残基。PLFA和氨基糖库中的根际沉积13 C的比率用于比较深度和植物物种中根际沉积C的相对微生物稳定性。根，根状根，活的和死亡的微生物表明植物的深度依赖于投资。根际沉积占地下总碳输入的一部分从表土（0–25 cm）下降到最深层（360 cm），即从35％，45％和36％–8.0％，2.5％和2.7下降分别为卢塞恩，克恩扎和松香，其中卢塞恩的碳输入量高于其他物种，介于340至360 cm之间。在所有物种中，土壤中根际菌丝的相对微生物稳定性表现出在微生物坏死瘤中最近被同化的C占主导地位，因此表明随着深度的变化，根际沉积菌C的微生物稳定性更高。总之，我们追踪了低至3.6 m的土壤深度的光合产物，并表明，即使分配给土壤深层的相对较小的C量也会被微生物稳定。因此，根深蒂固的农作物