Soil mesofauna increases the persistence of soil carbon in agriculturally managed soils under ambient and future climates

Soil fauna can have strong effects on the formation and persistence of soil organic matter (SOM). However, whether these effects are consistent across land uses and modulated by climate change remains unknown. Moreover, experiments on faunal taxa other than earthworms are very scarce.

We thus performed litterbag exclusion experiments in the Global Change Experimental Facility, Germany, in two land uses (agriculture/grassland) and two climate treatments (ambient/future). Litterbags accessible to either macro-, meso-, and microfauna, meso- and microfauna, or microfauna only were filled with soil and ¹³C-labeled maize litter and incubated in replicated plots for ~4 months. At the end of the experiment, we fractionated the soils into less (particulate organic matter) and more persistent (mineral-associated organic matter) SOM, and performed elemental and isotopic analyses.

Our results indicate that the conversion of litter into more persistent SOM was fostered in treatments accessible to meso- and macrofauna but not in those accessible to microfauna only, with this effect being most pronounced for the treatments accessible to mesofauna. Processes such as feces production by earthworms and springtails, which dominated the sites, could have fostered the formation of persistent SOM via stimulating microbial growth and necromass production, which is enriched in persistent SOM. This effect was insensitive to climate change and only perceivable in agriculturally managed soils, in which faunal abundance was lower than in grassland soils. These findings highlight mesofauna as strong regulators of SOM persistence, indicate density-dependent, positive effects of soil fauna on SOM persistence, and hint to a partial insensitivity of these effects to future climates.