Increased N2O emissions by the soil nematode community cannot be fully explained by enhanced mineral N availability

Soil nematodes, being the most abundant soil fauna, can significantly impact soil N mineralization via interaction with soil microorganisms. As a consequence, nematodes likely also influence soil N₂O production and emissions but the very few studies on this matter were carried out in simplified setups with single nematode species and in (highly) disturbed soil conditions. Here we measured soil N₂O emissions in a 74-day incubation experiment in the presence or absence of the entire soil nematode community with minimal disturbance of the soil microbial community and soil nutrients. This was e.g. evidenced by readily recovery of nitrifiers after the mild and selective sterilization and soil powder inoculation. N₂O emissions increased in the presence of nematodes, varying between soils +747.7 % in a loamy sand, +55.8 % in a loam, and +51.9 % in a silt loam cropland topsoil, in line with nematode abundance in these soils. In particular, the loamy sand soil showed an atypical N₂O emission peak at the time of high nematode abundance. Soil nematodes also increased net N mineralization by +8.4, +6.8 and +4.75 %, in these respective soils and to a smaller extent C mineralization as well. The extra soil nitrate buildup and the overall net stimulation of N mineralization by nematodes could not or just slightly explain the observed increased N₂O emissions. This research revealed the important role of soil nematodes in regulating N₂O emissions, and further stresses the need to consider the change in community composition and activity of denitrifiers, and connectivity of soil pores, rather than the stimulation of N mineralization as potential explanations for this role of nematodes.