Fig. 4. Root effects on the decomposition of native soil organic carbon (SOC) across soil column depth.

a Depth variation in living root density, respiration of root-derived organic carbon (OC), native SOC decomposition rate and net rhizodeposition at the soil core scale in the second incubation series 279 days after planting (n = 144 soil core incubations). Symbols with error bars show treatment means ± standard errors (n = 4 replicate soil cores). b–e Response of native SOC decomposition rate (b, d, e, k_SOC, n = 144 soil core incubations) and rhizosphere priming effect (c, RPE, n = 72 soil core incubations) to the variation in living root density (b, c), respiration of root-derived OC (d) and net rhizodeposition (e) across soil column depth in the second incubation series. The respiration of root-derived OC includes both root autotrophic respiration and soil microbial heterotrophic respiration derived from rhizodeposits, and was used here to estimate plant energy supply to soil by root activity (Methods section). Symbols with error bars along the horizontal dashed line in (a) and along the vertical dashed line in (b, d, e) show treatment means ± standard errors of unplanted controls (n = 24 soil core incubations). Polygons around regression lines represent 95% confidence intervals. Grey symbols represent outliers. Statistical results are shown in Supplementary Table 4.