Aggregate size mediates temperature sensitivity of soil organic matter decomposition in response to soil management

Temperature sensitivity (Q₁₀) of soil organic matter (SOM) decomposition is a crucial parameter to predict soil carbon (C) dynamics and its feedback to climate change. Soil management affects aggregate formation and decomposition, where the impact on Q₁₀ of SOM decomposition within aggregates remains unknown. Using a 14-year field experiment, we demonstrate that maize straw-amended soil had lower SOM stability and higher Q₁₀ than biochar-amended soil, with aggregate size playing a central role in response to the management. Biochar-derived stable compounds accumulate in small macroaggregates (SMA) and microaggregates (MA), as indicated by the increased benzene polycarboxylic acids and decreased ¹⁴C age and δ¹³C. Besides, biochar facilitated C sequestration by increasing mineral protection, microbial C use efficiency, and microbial necromass C accumulation in these smaller aggregates, while large macroaggregates (LMA) were less effective to sequester SOM (high Q₁₀) than smaller aggregate sizes. Maize straw primarily sequestered soil C through SMA by raising mineral protection and decreasing microbial C decomposition. However, it was less effective than biochar in soil C sequestration due to the greater susceptibility of maize straw-derived C to decomposition under warming conditions (high Q₁₀). As such, soil management practices mediate the stability and Q₁₀ of SOM through specific aggregate sizes. Our findings contribute to a better understanding of the impact of aggregate sizes on the carbon-climate feedback in agriculture.