Straw return methods differentially mitigate N<sub>2</sub>O emissions with reduced AOB <i>amoA</i> abundance and shifted community composition in N-fertilized saline-alkali soils

Figure 1.

During the 90-d incubation period, the temporal variations of (a), (b) N₂O flux and (c), (d) cumulative N₂O emissions in soil under five different straw return methods under low- or high-N conditions. Different letters indicate significant differences among treatments (p < 0.05). Vertical lines represent the standard error of the mean (n = 3).

Figure 2.

After 90 days of cultivation, under low- or high-N conditions, the effects of five different straw return methods on the contents of soil SOC, MBC, MBC/SOC, NH₄⁺-N, NO₃⁻-N and MNN: (MBC/[NH₄⁺-N + NO₃⁻-N]).

Figure 3.

After a 90-d cultivation period, the gene copy numbers of functional genes (a) AOA amoA, (b) AOB amoA, (c) nirK, (d) nirS, (e) nosZ, and (f) nosZ/(nirS + nirK) in the soil under low- or high-N conditions determined for five different straw return methods.

Figure 4.

NMDS analysis of AOB nitrifying bacterial communities under different straw return methods at (a) low-N or (b) high-N conditions.

Figure 5.

The relationship between bacterial communities and soil properties under low-N or high-N conditions for different straw return methods (MNN: MBC/[NH₄⁺-N + NO₃⁻-N]).

Figure 6.

Nitrification and denitrification gene responses to N₂O accumulation emissions. The red line represents a positive effect, while the green line represents a negative effect. The numbers on the arrows indicate the standardized path coefficients. GOF (goodness-of-fit), a measure used for the explanatory power of the entire model as a whole. * p < 0.05; ** p < 0.01; *** p < 0.001.