Exploring the relationships between soil fauna, different tillage regimes and CO2 and N2O emissions from black soil in China

Recent studies have shown that soil fauna can significantly affect greenhouse gas emissions. However, different functional groups and different soils can influence soil CO2 and N2O emissions to different extents. To date, little attention has been paid to whether soil fauna interactions with each other and their predators play a significant role in CO2 and N2O emissions under different tillage systems. Therefore, we studied how the interactions between soil fauna and their predators affect soil CO2 and N2O emissions from black soil following 13 years of conservation tillage (no-till) (NT) and conventional tillage (CT). We conducted a 35-day microcosm experiment with black arable soil and hay residue. The results indicated that the presence of earthworms and predator mites (EP) significantly increased the soil CO2 and N2O emissions in both NT and CT systems (P < 0.05). However, the addition of predator mites to microcosms with earthworms and Collembola treatments (ESP) did not significantly increase the soil CO2 (900.7 mg CO2-C kg−1 soil in NT, 991.0 mg CO2-C kg−1 soil in CT) or N2O (75.9 μg N2O-N kg−1 soil in NT, 79.0 μg N2O-N kg−1 soil in CT) emissions compared to earthworms and springtail (ES) treatments (CO2: 924.7 mg CO2-C kg−1 soil in NT, 914.4 mg CO2-C kg−1 soil in CT; N2O: 72.5 μg N2O-N kg−1 soil in NT, 251.4 μg N2O-N kg−1 soil in CT). Therefore, adding predators does not always increase the CO2 and N2O emissions, and the different body lengths of predators and the effect of predator-prey interactions on soil physicochemical properties should be considered. We found much higher dissolved organic carbon and nitrate availability in the E, ES and EP treatments at the time of high gas emissions on day 18, indicating that the major increase in CO2 and N2O emissions in these treatments may be due to enhanced denitrification. Our study indicates that under different tillage regimes, the interaction between soil fauna functional groups on the availability of C and N can decrease or increase soil CO2 and N2O emissions. Compared with CT soils, CO2 and N2O emissions from NT soils were lower, which demonstrates that long-term conservation tillage can reduce CO2 and N2O emissions from soil. The findings indicate that a more stable soil environment and food web with more intact functional groups are built in NT and may be more conducive to carbon and nitrogen sequestration for reducing soil CO2 and N2O emissions in the black soil region of Northeast China.