Figure S1 Secondary multivariate models that predict patterns of CMic and CMic/COrg. (A) Observed and predicted soil profile CMic estimates from Model-2: slope = 1.0 (± 5.9 × 10−2, β ± 1SEM), intercept: −1.6 × 10−8 (± 1.2 × 10−2), R2 = 43.9%, F1–365 = 285; P < 0.0001. (B) Observed and predicted topsoil CMic/COrg ratios from Model-3: Slope = 1.0(± 5.2 × 10−2; β ± 1SEM), intercept: −1.8 × 10−5, R2 = 49.9%, F1–365 = 363; P < 0.0001. Shadowed area is the 95% C.I and all axes are in log10 scale. Panels (C) and (D) are the relative importance of regressors included in Model 2 and 3, respectively. In both, panels equal lower-case letter indicate that confidence intervals for the difference between the contributions of each regressor includes zero (P < 0.05). Also, metrics are normalized to sum 100% of explained variance and 95% C.I. were obtained after 1000 bootstrap runs. Legend and biome classification as follows: boreal forest (□, BF), desert (○, D), tundra (▵, T), temperate coniferous forest (+, TCF), temperate deciduous forest (×, TDF), tropical forest (◊, TF), and temperate grassland (▿, TG). MAP: mean annual precipitation; ETo: annual evaporative demand; MAT: mean annual temperature; MaxWD: maximum monthly frequencies of wet days; Total N: soil total nitrogen content; CEC: soil cation exchange capacity; pH: soil pH; C-N ratio: soil Carbon-Nitrogen ratio.


Figure S2 Relationship between topsoil total nitrogen and CMic/COrg. Biome category is presented on top of each panel, label is as follows: (BF) boreal forest, (D) desert, (T) tundra, (TCF) temperate coniferous forest, (TDF) temperate deciduous forest, (TF) tropical forest and (TG) temperate grassland. Regression coefficients and standard error (β ± 1SEM) from the corresponding bivariate regressions are as follows: BF: −0.79(± 0.23), P < 0.001; D: +1.22(± 0.44), P < 0.001; T: −0.58(± 0.13), P < 0.0001; TCF: −0.40(± 0.41), P > 0.05; TDF: −1.14(± 0.13), P < 0.0001; TF: −0.38(± 0.13), P < 0.001; TG: −0.76(± 0.14), P < 0.0001. In all graphs, grey lines represent the bivariate regression line and the shaded-area the 95% C.I.


Table S1 Environmental drivers of soil profile microbial biomass carbon (g CMic m−2). Bivariate regressions of annual and seasonal climatic variables versus microbial biomass.


Appendix S1 Supplementary information on materials, methods, and results.


Appendix S2 Scatterplots and Person's correlation factors of both soil microbial biomass carbon (CMic) and soil microbial biomass carbon-soil organic carbon (CMic/COrg), and environmental variables.


Appendix S3 ASCII maps of soil profile microbial biomass carbon (CMic), and for the topsoil soil microbial biomass carbon-soil organic carbon (CMic/COrg).

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