Positive soil priming effects are the rule at a global scale.

Area of Science:

• Soil Science
• Biogeochemistry
• Ecology

Background:

• Soil organic matter (SOM) decomposition drives soil carbon budgets and turnover.
• The direction and magnitude of soil priming effects remain debated.
• Understanding priming is crucial for predicting soil carbon dynamics.

Purpose of the Study:

• To quantify the intensity and direction of soil priming effects.
• To investigate how compound type, nutrient availability, and ecosystem influence priming.
• To synthesize global evidence on soil priming.

Main Methods:

• A second-order meta-analysis of 9296 paired observations from 363 studies.
• Analysis of priming effects based on fresh carbon input type, nutrient addition, and ecosystem.
• Statistical synthesis of global data on soil priming.

Main Results:

• Fresh carbon inputs consistently induced positive priming effects (+37%) in 97% of observations.
• Labile organic compounds elicited stronger priming (+73%) than complex compounds (+33%).
• Nutrient addition (N, P) reduced priming intensity, suggesting nutrient mining.
• Tundra, lakebeds, wetlands, and volcanic soils exhibited significantly higher priming (+125%) than forests, croplands, and grasslands (+24–32%).

Conclusions:

• Positive soil priming effects are predominant globally.
• Fresh organic matter inputs accelerate soil carbon turnover.
• Management strategies for organic matter and nutrients are needed to mitigate potential carbon losses.