Exploring the relationship between soil mesofauna, soil structure and N2O emissions.

Agricultural soils are a large source of nitrous oxide (N 2 O) emissions. Soil mesofaunal species can accelerate, delay, increase or decrease N 2 O emissions. However, it is still unknown whether the soil fauna affect N 2 O emissions through trophic interactions or through their effect on soil structure. We explored the role of these two pathways in a 70 day microcosm experiment with a sandy loam subsoil with hay mixed in. Enchytraeids, fungivorous mites and predatory mites were added to the soil in a full factorial design to test for both single species effects as well as interactions between species. We measured N 2 O and CO 2 fluxes and we analysed soil structural parameters using X-ray micro tomography. After 35 days of incubation, enchytraeid presence significantly increased the volumetric air content of the soil (0.049–0.067 cm 3 cm −3 , P = 0.010) as well as the abundance of pores with sizes similar to their body width. At the same time N 2 O emissions, NO 3 − and DOC concentrations were significantly higher when enchytraeids were present (3.6 to 8.4 mg N 2 O-N m −2 , P < 0.001; 6.0 to 17.1 mg NO 3 − - N kg −1 soil, P < 0.001; 121.1 to 135.6 mg C kg −1 soil, and P = 0.017, respectively). Neither fungivorous mites nor predatory mites nor their interactions had a significant effect on soil structure or N 2 O emissions. Enchytraeids accelerated peak N 2 O emissions ( P = 0.001), but did not increase cumulative N 2 O emissions on day 70. Structural equation modelling confirmed that enchytraeids enhanced nitrogen mineralisation directly and also indirectly by creating a higher volumetric air content, and thereby increased N 2 O emissions. We conclude that the soil structure pathway was important in driving N 2 O emissions, and that soil ecosystem engineers such as enchytraeids disproportionately affected N 2 O emissions as compared to other soil fauna. [ABSTRACT FROM AUTHOR]