Microbial Biomass Carbon (MBC)

AUS-TSR-CON-SMB General High confidence

Benchmark Value

No specific value — see range
Range: 1120 to 4400 mg/kg
Thresholds: Lower: 560, Upper: —
Optimal Range: 1120 to 4400
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 3 benchmarks together — the OptimalRange form drives the primary score, while 2 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary Point Guard Point Guard

Evidence & Context

The benchmark range is derived from field measurements of Soil Organic Carbon (SOC) from 20 protected rainforest sites within the Australian Wet Tropics World Heritage Area, converted to Microbial Biomass Carbon (MBC) using a scientifically validated, biome-specific MBC:SOC ratio of 2.53% for tropical forests.

Metric Definition:

Microbial Biomass Carbon (MBC) in soil top 0-10 cm layer

Benchmark Definition:

This benchmark represents the range of Microbial Biomass Carbon (MBC) in the topsoil of Australian tropical and subtropical rainforests under conservation land use, indicating a state of high ecological health and function.

Justification:

Derived from high-quality Soil Organic Carbon data from 20 protected rainforest sites and a biome-specific microbial quotient of 2.53%, representing the best available condition in functionally intact, high-carbon conservation areas.

Sources (2)

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A meta-analysis of soil microbial biomass responses to forest disturbances - OSTI Journal

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Far North Queensland, Soil Chemistry Data, 2019 - TERN Data Discovery Portal Government

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Supporting Sources (25)

Additional references from the underlying research that informed this benchmark.

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A Compilation of Global Soil Microbial Biomass Carbon, Nitrogen ..., accessed July 23, 2025
Contextual Support GreyLiterature

A Compilation of Global Soil Microbial Biomass Carbon, Nitrogen ..., accessed July 23, 2025

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A meta-analysis of soil microbial biomass responses to forest ..., accessed July 23, 2025
Contextual Support GreyLiterature

A meta-analysis of soil microbial biomass responses to forest ..., accessed July 23, 2025

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Preview of A review on effective soil health bio-indicators for ecosystem restoration and sustainability, accessed July 23, 2025
A review on effective soil health bio-indicators for ecosystem restoration and sustainability, accessed July 23, 2025
Contextual Support Journal

A review on effective soil health bio-indicators for ecosystem restoration and sustainability, accessed July 23, 2025

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Alexander CHEESMAN | Senior Research Fellow | PhD University of Florida, accessed July 23, 2025
Contextual Support GreyLiterature

Alexander CHEESMAN | Senior Research Fellow | PhD University of Florida, accessed July 23, 2025

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Arun SINGH RAMESH | Research Data Analyst | Doctor of Philosophy | The University of Queensland, Brisbane - ResearchGate, accessed July 23, 2025
Irrelevant

Arun SINGH RAMESH | Research Data Analyst | Doctor of Philosophy | The University of Queensland, Brisbane - ResearchGate, accessed July 23, 2025

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CSIRO Permanent Rainforest Plots of North Queensland, accessed July 20, 2025,
Contextual Support Government

Estimating the relative magnitude of expected increases in soil ..., accessed July 18, 2025

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Preview of Differences in the ratio of soil microbial biomass carbon (MBC) and soil organic carbon (SOC) at various altitudes of Hyperalic Alisol in the Amazon region of Ecuador - PubMed Central, accessed July 23, 2025
Differences in the ratio of soil microbial biomass carbon (MBC) and soil organic carbon (SOC) at various altitudes of Hyperalic Alisol in the Amazon region of Ecuador - PubMed Central, accessed July 23, 2025
Contextual Support

Differences in the ratio of soil microbial biomass carbon (MBC) and soil organic carbon (SOC) at various altitudes of Hyperalic Alisol in the Amazon region of Ecuador - PubMed Central, accessed July 23, 2025

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Preview of Drought effects on microbial biomass C, N and P Colour indicates soil... - ResearchGate, accessed July 23, 2025
Drought effects on microbial biomass C, N and P Colour indicates soil... - ResearchGate, accessed July 23, 2025
Contextual Support Journal

Drought effects on microbial biomass C, N and P Colour indicates soil... - ResearchGate, accessed July 23, 2025

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Preview of Drought Shifts the Type of Carbon Emitted by Soil Microbes, accessed July 23, 2025
Drought Shifts the Type of Carbon Emitted by Soil Microbes, accessed July 23, 2025
Contextual Support Journal

Drought Shifts the Type of Carbon Emitted by Soil Microbes, accessed July 23, 2025

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Preview of Editorial: The Role of Microbial Communities in Tropical Ecosystems - PMC, accessed July 23, 2025
Editorial: The Role of Microbial Communities in Tropical Ecosystems - PMC, accessed July 23, 2025
Contextual Support Journal

Editorial: The Role of Microbial Communities in Tropical Ecosystems - PMC, accessed July 23, 2025

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Preview of Impact of drought on soil microbial biomass and extracellular enzyme activity - Frontiers, accessed July 23, 2025
Impact of drought on soil microbial biomass and extracellular enzyme activity - Frontiers, accessed July 23, 2025
Contextual Support Journal

Relative to rainforests and grasslands, banana and sugarcane soils ..., accessed July 23, 2025

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Interpreting Microbial Biomass Carbon | Fact Sheets | soilquality.org.au, accessed August 28, 2025,
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Lucas CERNUSAK | Senior Lecturer | PhD Plant Science, Australian National University, accessed July 23, 2025
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Lucas CERNUSAK | Senior Lecturer | PhD Plant Science, Australian National University, accessed July 23, 2025

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Microbial carbon dynamics in tropical forests: linking soil processes to atmospheric impacts under climate stress - PubMed, accessed July 30, 2025,
Contextual Support Journal

Microbial carbon dynamics in tropical forests: linking soil processes to atmospheric impacts under climate stress - PubMed, accessed July 23, 2025

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Contextual Support Government

Nutrient distribution and cycling in a subtropical rainforest in New South Wales, accessed July 19, 2025,

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Preview of Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter - ResearchGate, accessed July 23, 2025
Ratio of microbial biomass carbon to soil organic carbon as a sensitive indicator of changes in soil organic matter - ResearchGate, accessed July 23, 2025
Contextual Support GreyLiterature

Seasonal Changes of Soil Organic Carbon and Microbial Biomass Carbon in Different Forest Ecosystems - ResearchGate, accessed July 23, 2025

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Preview of Seasonal Dynamics of Soil Microbial Biomass C, N and P along an Altitudinal Gradient in Central Himalaya, India - MDPI, accessed August 28, 2025,
Seasonal Dynamics of Soil Microbial Biomass C, N and P along an Altitudinal Gradient in Central Himalaya, India - MDPI, accessed August 28, 2025,
Contextual Support Journal

Fact Sheets Biological Indicators - Soil Quality

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Soil microbial biomass—what do the numbers really mean? - ResearchGate, accessed August 28, 2025,
Contextual Support

Soil microbial biomass carbon and CO2? - ResearchGate, accessed July 18, 2025,

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Soil Microbial Communities in Tropical Rainforests: Diversity, Fu - Longdom Publishing SL, accessed July 23, 2025
Contextual Support Journal

Soil Microbial Communities in Tropical Rainforests: Diversity, Fu - Longdom Publishing SL, accessed July 23, 2025

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Preview of Soil Organic Carbon Distribution, Enzyme Activities, and the Temperature Sensitivity of a Tropical Rainforest in Wuzhishan, Hainan Island - ResearchGate, accessed July 23, 2025
Soil Organic Carbon Distribution, Enzyme Activities, and the Temperature Sensitivity of a Tropical Rainforest in Wuzhishan, Hainan Island - ResearchGate, accessed July 23, 2025
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Soil organic matter and geochemical characteristics shape microbial community composition and structure across different land us - SciSpace, accessed July 23, 2025
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Soil organic matter and geochemical characteristics shape microbial community composition and structure across different land us - SciSpace, accessed July 23, 2025

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Preview of Topsoil microbial biomass carbon pool and the microbial quotient under distinct land-use types across China, accessed July 23, 2025
Topsoil microbial biomass carbon pool and the microbial quotient under distinct land-use types across China, accessed July 23, 2025
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Topsoil microbial biomass carbon pool and the microbial quotient under distinct land-use types across China, accessed July 23, 2025

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Preview of Variation in soil microbial biomass in the dry tropics: impact of land-use change, accessed on June 7, 2025,
Variation in soil microbial biomass in the dry tropics: impact of land-use change, accessed on June 7, 2025,
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Soil microbial biomass during the early establishment of hoop pine ...

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Preview of Variations and influencing factors of soil organic carbon during the tropical forest succession from plantation to secondary and old–growth forest - Frontiers, accessed July 23, 2025
Variations and influencing factors of soil organic carbon during the tropical forest succession from plantation to secondary and old–growth forest - Frontiers, accessed July 23, 2025
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Variations and influencing factors of soil organic carbon during the tropical forest succession from plantation to secondary and old–growth forest - Frontiers, accessed July 23, 2025

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Wet Tropics of Queensland | World Heritage Outlook - IUCN, accessed July 20, 2025,
Contextual Support Government

Wet Tropics of Queensland | World Heritage Outlook - IUCN

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Context

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

Lifecycle

  • Status Active
  • Version 1
  • Effective From 19 Mar 2026

Notes

Lower Critical Threshold: 560 mg/kg. No upper detrimental threshold — higher values are always better up to natural saturation. Lower critical threshold is a sustained reduction of >30−50% from this benchmark range indicating critical impairment. MBC naturally constrained to less than 5% of total SOC. Higher MBC levels are associated with greater ecosystem health and function.