Microbial Biomass Carbon (MBC)

AUS-TMI-CON-SMB General Moderate confidence

Benchmark Value

1000 mg/kg

Direction: Higher is desirable ↑

Form: Point

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

A benchmark value of 1000 mg⋅kg−1 is proposed. This value is consistent with direct measurements in analogous high-health natural forests and falls within the range calculated from expected high SOC levels.

Metric Definition:

Microbial Biomass Carbon (MBC) is a measure of the carbon contained within the living component of soil organic matter, primarily bacteria and fungi.

Benchmark Definition:

This benchmark represents the carbon content in living soil microbes in a high-health, mature, protected subtropical rainforest ecosystem, indicating a healthy soil microbial community.

Justification:

The benchmark is derived via a proxy-based triangulation due to a lack of direct field data, combining data from analogous forest ecosystems with established soil science principles (MBC/SOC ratios).

Sources (3)

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). Journal

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

View Source

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

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

View Source

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)

View Source

Context

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

Lifecycle

Status Active
Version 1
Effective From 5 Jun 2026

Notes

No upper detrimental threshold — higher values are always better up to natural saturation. This benchmark represents a high-health, mature, protected subtropical rainforest ecosystem on fine-textured volcanic soils. Anomalously high MBC values, especially if associated with invasive species dominance, may indicate degradation.

Related Benchmarks

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