Figure 6. Factors influencing microbial metabolic quotients (qCO₂) of soil incubations.

Significant factors included A) microbial C∶P ratios, B) available inorganic P, and C) soil pH. qCO₂ was calculated as the mol/mol ratio of C mineralization rates measured in glass jar incubations per unit microbial biomass C obtained from the same soils, with units of mmol CO₂-C/h/mol MBC-C/g soil. Relationships of qCO₂ with microbial C∶P (A), and inorganic P (B) were fit without data from litter or soil humic horizons. Data were log₁₀ transformed for normality and parameters estimated by SMA are given in Table 1. SMA regressions fit using only forest and pasture soils (parameters in Table S1) are not shown as they were essentially the same as the global relationships.