Reduced carbon use efficiency and increased microbial turnover with soil warming.

Area of Science:

• Soil science
• Microbial ecology
• Climate change research

Background:

• Global soil carbon stocks are projected to decrease with rising temperatures.
• Microbial processes, including carbon use efficiency (CUE) and biomass turnover (rB), are critical to soil carbon cycling but their warming responses remain unclear.

Purpose of the Study:

• To determine the temperature sensitivities of microbial CUE and rB using long-term field data.
• To assess the impact of these microbial parameters on soil carbon flux and pool changes under warming.
• To project the long-term effects of soil warming on carbon storage.

Main Methods:

• A probabilistic inversion approach was employed, integrating a microbial-enzyme model with 22 years of carbon cycling measurements.
• Temperature sensitivities of CUE and rB were derived from multidecadal field observations.
• Soil carbon flux and pool changes were analyzed in relation to temperature sensitivities.

Main Results:

• Increasing temperature was found to decrease CUE and increase rB.
• Two decades of soil warming enhanced the temperature sensitivities of both CUE and rB.
• Long-term soil carbon changes under warming were more influenced by the temperature sensitivity of CUE than rB.

Conclusions:

• Estimates of microbial CUE and rB temperature sensitivities can be rigorously obtained and evaluated using multidecadal datasets.
• The developed approach can be applied to broader scales to improve projections of soil carbon feedbacks to climate change.
• Chronic soil warming at Harvard Forest is projected to result in a small average soil carbon gain in the surface mineral horizon over six decades.