Microbial Biomass Carbon (MBC)

AUS-ASC-LVG-SMB General Moderate confidence

Benchmark Value

300 µg MBC/g soil

Direction: Higher is desirable ↑

Form: MinimumOnly

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 4 benchmarks together — the OptimalRange form drives the primary score, while 3 guard(s) constrain the result.

Contributing Benchmarks

OptimalRange Primary MinimumOnly Guard OptimalRange Guard MinimumOnly Guard

Evidence & Context

For Australian alpine/subalpine mineral soils (0-10 cm), MBC values consistently below 200-300 µg MBC/g soil, or an MBC:SOC ratio persistently less than 1%, could be considered a lower critical threshold, warranting concern and investigation.

Metric Definition:

Microbial Biomass Carbon (MBC) in soil, measured in micrograms of microbial carbon per gram of soil at 0-10 cm depth.

Benchmark Definition:

This benchmark represents the minimum Microbial Biomass Carbon level in Australian alpine and subalpine mineral soils below which soil health and ecosystem function are impaired.

Justification:

Values below this threshold indicate a tipping point where soil microbial activity and nutrient cycling are significantly compromised, leading to degradation.

Sources (2)

Preview of Grazing Regulates Changes in Soil Microbial Communities in Plant-Soil Systems - MDPI

Grazing Regulates Changes in Soil Microbial Communities in Plant-Soil Systems - MDPI Journal

Drought decreases incorporation of recent plant photosynthate into soil food webs regardless of their trophic complexity - PMC, accessed May 10, 2026

View Source

Preview of Microbial Biomass - Qld | Fact Sheets | soilquality.org.au

Microbial Biomass - Qld | Fact Sheets | soilquality.org.au GreyLiterature

Global negative effects of nitrogen deposition on soil microbes - PMC, accessed July 31, 2025

View Source

Supporting Sources (9)

Additional references from the underlying research that informed this benchmark.

Carbon Cycling in Sub-alpine Ecosystems

Contextual Support GreyLiterature

The composition of organic phosphorus in soils of the Snowy Mountains region of south-eastern Australia - Semantic Scholar

View Source

Crop and Pasture Science - CSIRO PUBLISHING

Contextual Support Journal

Temperature response of soil respiration largely unaltered with experimental warming

View Source

Fire Effects on Soils and Restoration Strategies - National Academic Digital Library of Ethiopia, accessed May 10, 2026

Contextual Support Journal

Grover, S.E., et al. (2023). Nitrogen dynamics in alpine soils of south-eastern Australia. Soil Research, 61(6), 560-568. 1

View Source

Impacts of Agricultural Management Practices on Soil Health - NCBI, accessed May 11, 2025

Contextual Support

Impacts of Agricultural Management Practices on Soil Health - NCBI, accessed August 28, 2025

View Source

Local Land Services

Contextual Support Government

Microbial Biomass Carbon - 0 - 10cm | Victoria | Examine ...

View Source

Management-intensive Grazing (MiG) impacts on soil biological health - Semantic Scholar, accessed May 10, 2026

Direct Evidence Journal

Management-intensive Grazing (MiG) impacts on soil biological health - Semantic Scholar, accessed May 10, 2026

View Source

Microbe Biomass in Relation to Organic Carbon and Clay in Soil - MDPI, accessed August 28, 2025,

Contextual Support Journal

Forest Soil Microbiomes: A Review of Key Research from 2003 to 2023 - MDPI

View Source

openresearch-repository.anu.edu.au, accessed on May 31, 2025

Contextual Support Journal

openresearch-repository.anu.edu.au, accessed on May 31, 2025,

View Source

www.zobodat.at, accessed on June 5, 2025

Direct Evidence

www.zobodat.at

View Source

Context

Region Australia
Biome Alpine and Subalpine Complex
Land Use Livestock Grazing & Pasture
Assessment Conservation Target
Evidence Type DegradationThreshold

Lifecycle

Status Active
Version 1
Effective From 3 Jun 2026

Notes

This threshold is based on observed declines in MBC in degraded systems and is a warning level for management intervention. No upper detrimental threshold — higher values are always better up to natural saturation.

Related Benchmarks

Other benchmarks in the AUS-ASC-LVG-SMB family.