Fig. 5. Root effects on the mean age of subsoil organic carbon respired by decomposers.

Response of radiocarbon-based mean age of respired CO₂ derived from the decomposition of native deep soil organic carbon (SOC) to the variation in living root density across soil column depth at the soil core scale in the second incubation series 279 days after planting (n = 24 soil core incubations). The inset show radiocarbon signatures (Δ¹⁴C) of soil-respired CO₂ used to determine the mean age of respired native SOC. Since turnover time and mean age are identical under our model assumption of SOC being a homogeneous one-pool reservoir at steady-state, the mean ages were estimated using the same modelling approach used for turnover time as described in the methods section. Symbols with error bars along the vertical dashed line show treatment means ± standard errors of unplanted controls (n = 4 soil core incubations). Horizontal dotted lines with error bars show the means ± standard errors of mean ages (turnover times) and radiocarbon signatures of initial deep SOC. Polygons around regression lines represent 95% confidence intervals. The grey symbol is an outlier not included in regression model. Statistical results are shown in Supplementary Table 5.