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Figure captions
Fig. 1 | Schematic representation of two
mineral protection mechanisms.a, A diagram of each mechanism: surface adsorption (top panels)
and pore entrapment of SOM (bottom panels) by different types of clay
minerals. Litter residues are associated with clay minerals to a higher
strength through surface adsorption than through pore entrapment and
decomposed to different degrees by microorganisms. b, Temporal
changes in the chemical composition of labile (yellow) versus
recalcitrant (brown) litter residues and the compositions of microbial
functional communities and necromass (blue, bacteria; red, fungi) for
each mechanism.
Fig. 2 | Chemical structures and composition
of litter-derived SOM. a, CP/TOSS 13C NMR spectra of
maize and soya litter and their derived SOM in four model soils.b , Differences in the chemical composition of litter-derived
SOM between litter and clay mineral types. Principal component analysis
of the relative abundance of functional C groups determined by13C NMR among four model soils by two litter types in
comparison with original maize and soya litters (top panel) and the
loadings of individual functional C groups to the first two principal
components (bottom panel). Open symbols are for soya litter and filled
symbols for maize litter.
Fig. 3 | Community compositions of microbial
biomass and necromass. a, b, Microbial biomass (represented by total
phospholipid fatty acids) and microbial necromass (represented by amino
sugars) of different communities in model soils mixed with maize litter
(left column) and soya litter (right column). Lower case letters
indicate differences in total microbial biomass or necromass among model
soils for each litter type and * indicates difference between litter
types for each model soil P < 0.05 (n = 3). Error bars
represent standard errors (n=3).
Fig. 4 | Main controls over the SOM formation
efficiency during litter decomposition within clay mineral matrices.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 mineral
selectivity 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), showing 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 ).
Supplementary Figure 1: Correlations of SOM formation efficiency
with different mineralogical, microbial and litter compositional
properties. a, Specific surface area (SSA); b,mineral pH; c, PC2 in Fig. 2; d , fungal PLFAs;e, fungal to bacterial PLFAs; and e, fungal amimo
sugars. Filled and open symbols represented maize and soya litters,
respectively.
Supplementary Table 1:Particle size (Φ ), pH, iron
oxide content measured using oxalate (Feo) or dithionite
(Fed) extraction as well as specific surface area (SSA)
measured using Brunauer–Emmett–Teller (N2-BET)
adsorption method for pure clay minerals and natural soil material.
Supplementary Table 2: Measured total respiration,
post-incubation soil C and C contents (defined as the SOM formation
efficiency) and C loss rate due to hydrofluoric acid (HF) treatment,
modeled mineral-organic association extent (δ ), pool sizes and
decomposition rate constants (k 1 andk 2) of free litter and mineral-protected litter
residue pools, respectively, and determination coefficient
(r 2) of the best fitting to the new
mineral-driven decomposition model.
Supplementary Table 3: Assignments and relative abundancess of
C functional groups in soil organic matter of the model soils and
original litters obtained by 13C cross
polarization/total sideband suppression (CP/TOSS) nuclear magnetic
renosance spectroscopy at the end of incubation.