Microbial Biomass Carbon (MBC)

AUS-TMI-CON-SMB General Moderate confidence

Benchmark Value

No specific value — see range

Range: 400 to 1200 mg/kg

Optimal Range: 400 to 1200

Direction: Higher is desirable ↑

Form: OptimalRange

Scoring Curve

This curve shows how a field measurement for this indicator would score across all available benchmark forms in this context. The scoring engine uses 9 benchmarks together — the OptimalRange form drives the primary score, while 8 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary Point Guard Point Guard OptimalRange Guard Point Guard MinimumOnly Guard OptimalRange Guard Point Guard OptimalRange Guard

Evidence & Context

An optimal functional range is one with a high MBC (e.g., 400–1200 mg⋅kg−1), but which is also characterized by a high MBC-to-SOC ratio, high carbon use efficiency (low qCO2), and a fungal-dominated microbial community structure.

Metric Definition:

Optimal functional range of Microbial Biomass Carbon (MBC) indicating a healthy and efficient microbial community.

Benchmark Definition:

This benchmark defines the optimal range of microbial carbon in soil representing a healthy, efficient microbial community in tropical forest ecosystems.

Justification:

Derived from ecological understanding of microbial efficiency and community structure in mature, undisturbed forest ecosystems.

Sources (2)

Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au, accessed August 28, 2025, GreyLiterature

Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au

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Soil microbial biomass, C, N, and P in Chinese subtropical and temperate forests (Zhang et al., 2009)

Soil microbial biomass, C, N, and P in Chinese subtropical and temperate forests (Zhang et al., 2009)

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Supporting Sources (1)

Additional references from the underlying research that informed this benchmark.

Preview of Derived benchmark based on a triangulated analysis of: 1) "Soil microbial biomass, C, N, and P in Chinese subtropical and temperate forests" (Zhang et al., 2009); 2) "Microbial biomass C and N stocks across land uses and soil types in the Brazilian tropical dry forest region" (Menezes et al., 2023); and 3) Established MBC/SOC ratios from "Interpreting Microbial Biomass Carbon" (soilquality.org.au).

Derived benchmark based on a triangulated analysis of: 1) "Soil microbial biomass, C, N, and P in Chinese subtropical and temperate forests" (Zhang et al., 2009); 2) "Microbial biomass C and N stocks across land uses and soil types in the Brazilian tropical dry forest region" (Menezes et al., 2023); and 3) Established MBC/SOC ratios from "Interpreting Microbial Biomass Carbon" (soilquality.org.au).

Contextual Support Journal

Microbial biomass C and N stocks across land uses and soil types in the Brazilian tropical dry forest region (Menezes et al., 2023)

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Context

Region Australia
Biome Tropical & Subtropical Maritime Islands
Land Use Conservation / Protected Natural Areas
Assessment Pristine Reference
Vegetation Forest
Evidence Type HealthyOperationalRange

Lifecycle

Status Active
Version 1
Effective From 5 Jun 2026

Notes

This range reflects a high MBC coupled with high carbon use efficiency and a fungal-dominated microbial community, indicative of a stable and healthy ecosystem. No upper detrimental threshold — higher values are always better up to natural saturation.

Related Benchmarks

Other benchmarks in the AUS-TMI-CON-SMB family.