TABLE 2.
Results of general mixed models that assess relationships between the SOM characteristics and soil age, mean temperature of warmest quarter (T) and precipitation of warmest quarter (P). Two types of mixed models were tested: models with random intercept (RI) and random slope (RS). The table includes results only for the mixed models with the lowest AICs values (cells in gray correspond to the variables discarded). Symbols for p values: ***p < 0.001; **p < 0.01; *p < 0.05; † p < 0.1; NS >0.1. B values indicating the direction of the relationships are in brackets. Other models tested and detailed results are presented in Tables S1 and S3
| Model | Soil age | T | P | Age:T | Age:P | R2 | |
|---|---|---|---|---|---|---|---|
| SOC (g C kg−1) | RS | *** (0.85) | * (0.70) | * (0.26) | 0.51 | ||
| Ntot (g N kg−1) | RI | *** (0.66) | † (0.47) | ** (0.27) | † (0.14) | 0.41 | |
| C/N | RI | *** (2.39) | * (1.88) | † (0.56) | † (−0.46) | 0.54 | |
| δ13C (‰) | RS | ** (−0.82) | 0.20 | ||||
| δ15N (‰) | RI | ** (0.71) | * (−0.82) | † (0.49) | 0.26 | ||
| POC 1 (g C kg−1) | RI | ** (0.32) | * (0.38) | * (0.37) | 0.36 | ||
| POC 2 (g C kg−1) | RI | *** (0.90) | * (0.67) | * (0.64) | * (0.43) | † (0.41) | 0.57 |
| ROC (g C kg−1) | RI | *** (0.95) | * (0.68) | * (0.60) | * (0.45) | NS | 0.62 |
| POC 1 (% of total SOC) | RI | *** (−0.48) | † (−0.31) | * (−0.35) | 0.50 | ||
| POC 2 (% of total SOC) | RI | † (−0.06) | * (0.09) | 0.17 | |||
| ROC (% of total SOC) | RI | *** (0.13) | † (0.05) | ** (−0.10) | 0.38 | ||
| T50‐POC 2 (°C) | RI | *** (−0.03) | 0.33 | ||||
| T50‐ROC (°C) | RI | *** (−0.02) | 0.08 | ||||
| CH‐POC 1 | RI | *** (−0.39) | NS | * (−0.37) | NS | 0.30 | |
| CH‐POC 2 | RI | * (0.18) | † (0.13) | * (0.29) | ** (0.36) | 0.38 | |
| FTIR C=C | RS | ** (0.04) | * (0.02) | * (0.03) | 0.36 | ||
| FTIR C=O | RS | * (−0.02) | † (0.02) | * (−0.01) | 0.29 | ||
| FTIR C‐H | RI | *** (−0.02) | ** (−0.02) | 0.29 |