Decreased rhizodeposition, but increased microbial carbon stabilization with soil depth down to 3.6 m

• DOI: 10.1016/j.soilbio.2020.108008
• Publication Date: 2020-09-15T09:26:17Z
• Authors: Leanne Peixoto; Lars Elsgaard; Jim Rasmussen; Yakov Kuzyakov; Callum C. Banfield; Michaela A. Dippold; Jørgen E. Olesen
• Keywords: 2. Zero hunger; 550; Nutrient turnover; Carbon stabilization; 04 agricultural and veterinary sciences; 15. Life on land; 630; 6. Clean water; Deep subsoil; Microbial necromass; Soil biology; 13. Climate action; Compound-specific stable isotope probing; Carbon deposition; 0401 agriculture, forestry, and fisheries; Deep-rooted crops

Abstract 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.