Global sublinear scaling between soil microbial biomass carbon and soil organic carbon across biomes

Authors: Chatterjee, Amitava

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2026
Publication Date: 6/24/2026
Citation: Chatterjee, A. 2026. Global sublinear scaling between soil microbial biomass carbon and soil organic carbon across biomes. Applied Soil Ecology. https://doi.org/10.1016/j.apsoil.2026.107238.
DOI: https://doi.org/10.1016/j.apsoil.2026.107238

Interpretive Summary: Soil microbial biomass carbon (MBC) represents the total amount of living microorganisms responsible for nutrient cycling in the soil and supporting plant growth. Because direct measurement of MBC is expensive and labor-intensive, it is difficult for researchers to determine soil microbial communities with change in response to changes in crop and soil management practices. By analyzing a global dataset of 2,000 soil samples, this study developed a simple equation to estimate MBC using only soil organic carbon content (SOC) and soil acidity (pH). Farmers and managers can now use routine SOC and pH measurement to easily estimate their soil’s MBC, helping them to make more effective management decisions tailoring their management practices to maintain crop productivity while ensuring robust soil health. This reduces production costs while improving farm profits and ensuring American agriculture continues to thrive.

Technical Abstract: Soil microbial biomass carbon (MBC) plays a central role in predicting soil health, yet global-scale relationships between MBC and soil organic carbon (SOC) across biomes remain insufficiently quantified. Using a global surface (0-30 cm depth) soil dataset (n=2008), how MBC scales with SOC and soil pH were evaluated using pedotransfer functions, metabolic scaling concepts, and machine learning approaches. On a log-log scale, MBC exhibited consistent sublinear scaling with SOC (ß = 0.75), indicating diminishing microbial biomass accumulation with increasing SOC levels. The scaling exponent remained stable after excluding pH (ß = 0.69) and bootstrap resampling confirmed statistical robustness (95% CI: 0.68-0.77). A parsimonious log-linear model explained 61.7% of global variation in MBC and performed comparably to Random Forest models evaluated using spatial cross-validation model (R2=0.54), suggesting that the dominant SOC-MBC relationship is fundamentally linear after logarithmic transformation. Biome-specific interaction models produced modest improvements in model fit (R2=0.68), indicating ecosystem modulation of scaling strength while preserving a consistent global pattern. Variance partitioning identified SOC as the primary driver of spatial variation in MBC. These findings revealed a globally conserved but sublinear coupling between MBC and SOC, implying decreasing microbial biomass accumulation efficiency at higher SOC levels. Incorporating empirically derived scaling relationships into Earth system models may improve predictions of microbial contributions to SOC dynamics.