Fig. 4 | Main contorls over the SOM formation efficiency identified using structure equation modelling. Optimized structure equation model shows no effects of litter chemistry and three independent (P = 0.16, n = 18) pathways from clay minerals to the SOM formation efficiency. Path coefficient (k p), with a significance at P < 0.05 (*) or P< 0.05 (**) and the proportion of the variance (R2) are presented for each pathway, with the line width proportional to kp . The chemical composition of litter residues is reflected by the score of the second principal component of principal component analysis of functional C groups estimated by 13C NMR (Fig. 2) as it demonstrates the effects of clay mineral types irrespective of litter type.
Fig. 5 | Mineral-organic association effects on the X-ray diffractograms of clay minerals. a, b , Original minerals (thick lines) before incubation and model soils without H2O2 treatment (thin lines) and with H2O2 treatment (dotted lines) after incubation with maize and soya litter.
Fig. 6 | Quantification and application of mineral-protection strength. a, Cumulative respiration measured (symbols) and modeled (lines) using the novel model describing the mineral-protection strength (δ ) (inserted equation). Error bars represent standard errors (n=3). b, Correlation between SOM formation efficiency and mineral-protection strength (δ ).