Enhanced mite grazing leads to pattern shifts in soil N2O emissions after organic fertilizer application

Studies have reported inconsistent (or even opposing) effects of soil mesofauna, such as mites, on net soil N2O emissions. Here we show that whether mites affect net N2O emissions positively, negatively, or neutrally depends on the microbial guild that dominates the emissions. We found that enhanced mite grazing, following artificially elevated mite populations, led to shifts in N2O emission patterns in soils applied with organic fertilizer: N2O emissions decreased under low soil moisture conditions, whereas those under high soil moisture conditions increased. Since the dominant microbial processes underlying N2O emissions shift from fungal to bacterial denitrification with increasing soil moisture, our results imply that enhanced mite grazing tends to decrease net soil N2O emissions dominated by fungi, whereas increase those dominated by bacteria. Furthermore, we observed that mite grazing largely suppressed fungal mycelial growth after organic fertilizer application but promoted the dispersal and decomposition of fertilizer granules and N mineralization. These findings suggested that the distinct effect of enhanced mite grazing on N2O emissions dominated by fungi and bacteria could occur because high-intensity mite grazing affects fungi-derived N2O emissions mainly by consuming the biomass of N2O-producing fungi, which has a negative effect, whereas affects bacteria-derived N2O emissions mainly by stimulating bacterial N2O-producing processes via the promotion of N diffusion from the fertilizer to the soil, which has a positive effect.