Physical protection of soil carbon in macroaggregates does not reduce the temperature dependence of soil CO2 emissions

In a warmer world, soil CO₂ emissions are likely to increase. There is still much discussion about which soil organic C (SOC) pools are more sensitive to increasing temperatures. While the temperature sensitivity of C stabilized by biochemical recalcitrance or by sorption to mineral surfaces has been characterized, few studies have been carried out on the temperature sensitivity—expressed as Q₁₀—of C physically protected inside soil macroaggregates (0.2–2 mm). It has been suggested that increasing the availability of labile SOC by exposing C through macroaggregate crushing would decrease Q₁₀, i.e., the temperature dependence of soil CO₂ emissions. To test this hypothesis, the temperature dependence of CO₂ emissions from C physically protected in macroaggregates was measured through 21‐d laboratory incubations of crushed and uncrushed soils, at 18°C and 28°C. 199 topsoil samples, acidic or calcareous, with SOC ranging from 2 to 121 g kg⁻¹ soil were investigated. The CO₂ emissions were slightly more sensible to temperature than to C deprotection: about 0.3 mg C g⁻¹ soil (= 13 mg C g⁻¹ SOC) and 0.2 mg C g⁻¹ (= 12 mg C g⁻¹ SOC) were additionally mineralized, in average, by increasing the temperature or by disrupting the soil structure, respectively. The mean Q₁₀ index ratio of CO₂ emitted at 28°C and 18°C was similar for crushed and uncrushed soil samples and equaled 1.6. This was partly explained because Q₁₀ of macro‐aggregate‐protected C was 1. The results did not support the initial hypothesis of lower temperature dependence of soil CO₂ emissions after macroaggregate disruption, although a slight decrease of Q₁₀ was noticeable after crushing for soils with high amounts of macroaggregate‐protected C. Field research is now needed to confirm that soil tillage might have no effect on the temperature sensitivity of SOC stocks.