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Microbial Soil Temperature Index (v3.0c, 3.1g)

Microbial Soil Temperature Index helps identify where soil temperature limits carbon assimilation, reveals regions with optimal microbial activity, and supports refining degree-day calculations for agroecosystem analysis and future crop modeling using Global Climate Projections.

The temperature of soil is important for soil carbon sequestration; temperatures that are too high or too low slow down the assimilation of organic matter into the soil. Throughout a year, the duration of time that soils spent within the optimal range of moderate temperatures will enable the highest potential for carbon assimilation into the soil, which is what is captured by the microbial soil temperature index. This index is a dimensionless index that accounts for the duration of time spent within an optimal temperature threshold for sequestering carbon.

To access high-resolution data for your area(s) of interest, contact our team.

High-Level Description

Within SOCSPOT 3.0c and 3.1g, the Microbial Soil Temperature Index (MSTI) is a dimensionless gridded data product that captures the cumulative time throughout the year that a soil lies within the optimal temperature range for microbial activity. The calculations are similar to the formulae for Growing Degree Days (GDD) as applied in agronomic research for crops. As such, values scale linearly and directly with the duration of time that a given soil spends within the optimal temperature range. Version 3.0c extends across rangelands and croplands within the Continental US (CONUS, 'c'), while 3.1g includes both across a global extent. This product leverages understanding from both agronomy alongside contemporary studies of microbial activity responses to varying temperature (Alster et al., 2023; Yan et al., 2024) alongside high-quality and temporal frequency geospatial data inputs to generate a global map of annual MSTI.

Use Cases

With MSTI, a customer can:

  • Gauge where soil temperature may be limiting carbon assimilation relative to soil moisture or pH, suggesting they could not improve SOC sequestration unless they have a way to ubiquitously increase/decrease soil temperatures throughout the year.
  • Understand regions with soil temperatures that consistently stay within a range that is optimal for microbial activity.

Technical Specifications

  • Native Resolution: 100-250m
  • Spatial extent: 3.0c = CONUS, 3.1g = Global
  • Domain: Croplands and/or rangelands
  • Units: Dimensionless (0-10)
  • Inputs: 8-day soil temperature
  • Temporal frequency and range: Annual, 2018-2022

Algorithm Theoretical Basis

The theoretical basis for algorithms underpinning Microbial Degree Days (MSTI) lies in the understanding that temperature influences the growth, respiration and carbon sequestered by microbial communities. The concept is rooted in the observation that biological processes are temperature-dependent and occur within specific thermal thresholds, and further that these processes are cumulative with heat over time. This theoretical basis is also underpinning Growing Degree Days (GDD) from agronomic research, which we transfer to the field of microbial biogeochemistry to predict the relative rate of carbon processing and assimilation by microbial communities in response to an array of soil temperatures.

Model Assumptions & Constraints

A number of assumptions and methodological choices are important to consider when using MSTI.

  • We currently assume all microbial communities respond similarly to present-day soil temperatures, regardless of historical conditions.
  • Input data is constrained by the use of land surface temperature availability and quality. Further, we assume land surface temperatures are equivalent to soil temperatures within the top 10 cm of soil.
  • In order to account for spatial variability in image counts (e.g., some areas have more missing input LST data than others), we normalize MSTI by the number of image counts to avoid biasing areas with more/less inputs relative to others.

Known Issues

No known issues exist for MSTI.

What’s New?

Within the frameworks of SOCSPOT 3.0c, 3.0r, and 3.1g, updates include:

  • SOCSPOT 3.0c, 3.0r, and 3.1g all implement an improved set of temperature ranges used for predicting microbial responses.

  • Within SOCSPOT 3.1g, the extent has gone beyond CONUS to include global coverage.

Data Partners, Providers, and References

NASA Land Processes Distributed Active Archive Center (LP DAAC), USGS/Earth Resources Observation and Science (EROS) Center : Wan, Z., Hook, S., & Hulley, G. 2015. MOD11A1 MODIS/Terra Land Surface Temperature/Emissivity Daily L3 Global 1km SIN Grid V006. NASA EOSDIS Land Processes DAAC. DOI: 10.5067/MODIS/MOD11A1.006

Accessing Data

Contact our team to request high-resolution data for your area(s) of interest.