Soil mesofauna promote mineral-associated organic matter formation under ambient and future climates

The diverse life strategies of soil fauna may substantially affect the persistence of carbon (C) in soil. However, experimental evidence linking soil fauna to C in less (particulate organic matter, POM) and more persistent pools (mineral-associated organic matter, MAOM) of soil organic matter is scarce. This hampers predictions of soil C dynamics in the face of global change and the implementation of management strategies focused on maintaining or establishing soils as C sinks. Here, we follow the transformation of isotopically labeled litter into POM and MAOM in replicated plots under grassland and agricultural management and ambient and simulated future climates. We show that access of mesofauna to agricultural–but not grassland–soil significantly increases the transfer of litter-derived C to MAOM relative to soil accessible only to microfauna (p ˂ 0.05; effect size [Cohen’s d ], 2.1; confidence interval, 0.5–3.6 %) under both ambient and future climates, while not affecting C contents in POM (p ˃ 0.05). Notably, additional access of earthworms, which are considered strong drivers of MAOM formation, did not boost this transfer (p ˃ 0.05). Our findings suggest that conceptualizations of C dynamics and the accuracy of terrestrial C models will improve by including mesofaunal activity. This activity may be particularly relevant in soils with a large capacity to store additional C in MAOM, such as those under agricultural management. • Soil mesofauna increased transfer of litter-C to MAOM under ambient and future climates. • This transfer was more pronounced in agricultural than grassland soils. • Additional access of earthworms to soils did not substantially increase MAOM-C.