Improved root development leads to higher root derived carbon stocks in formerly deep-plough soils - A biomarker-based approach

Roots can add significant amounts of carbon (C) to the subsoil, which enhances soil fertility and can mitigate climate change. About 5% of agricultural soils in Germany have been deep-ploughed (ploughing depth 30-120 cm) at least once. This technique can provide better root access to the subsoil and may help to increase yields. Studies on deep-ploughed soils focused on C stability, whereas not much is known about root-derived C in the subsoil (>0.3 m). We hypothesized that five decades after deep-ploughing, root-derived C stocks were higher compared to conventionally ploughed treatments due to better root development. This was measured by analysing suberin and cutin monomers as tracers for root- and shoot-derived C at three former deep-ploughed sites in N Germany with different soil textures and different deep-ploughing depths. Concentrations of suberin monomers in the soil were positively correlated with root biomass, this was especially strong at one sandy site. Suberin contributed more to the bulk soil organic carbon (SOC) stocks than cutin throughout the soil profile, independently of the ploughing depth. The three sites responded differently to deep-ploughing. The contribution of suberin monomers to the bulk SOC stock at silty site Banteln and the sandy site Essemühle was 38% higher in the deep-ploughed plots than at the reference plot, respectively, these differences were most visible in the subsoil of Essemühle. We conclude that when deep-ploughing enhances C stocks and root development, suberin SOC stocks increase as well, especially in the subsoil of sandy sites with low pH.