Evaluating aeration rate modulation to restructure denitrifier communities for nitrous oxide mitigation in cattle...

Area of Science:

• Environmental Science
• Microbiology
• Agricultural Science

Background:

• Livestock manure composting is a major source of nitrous oxide (N2O), a potent greenhouse gas.
• Aeration is known to mitigate anaerobic conditions but its specific impact on N2O emissions via microbial pathways requires clarification.

Purpose of the Study:

• To investigate the effects of different aeration rates on N2O emissions, enzyme activity, and denitrifier communities during cattle manure composting.
• To elucidate the mechanistic linkages between aeration, microbial pathways, and N2O mitigation using an integrated analytical framework.

Main Methods:

• Composting experiments were conducted with three aeration rates: 0.1 (AR1), 0.2 (AR2), and 0.3 L kg-1 DM·min-1 (AR3).
• A novel integrated analytical framework (NIAF), incorporating redundancy, Spearman, network, Mantel, and Path analyses, was employed.
• Measurements included N2O emissions, enzyme activities, and the nirK-gene denitrifier community structure.

Main Results:

• The optimal aeration rate of 0.2 L kg-1 DM·min-1 (AR2) reduced N2O emissions by 75.25% and ensured compost maturity.
• Peak N2O emissions occurred during the mesophilic phase, correlating strongly with nitrite accumulation.
• NIAF analysis revealed that AR2 mitigated N2O by suppressing key N2O-producing genera, reducing nitrite reductase activity, and enhancing denitrifier interactions.

Conclusions:

• An aeration rate of 0.2 L kg-1 DM·min-1 is optimal for minimizing N2O emissions in cattle manure composting while achieving compost maturity.
• Microbial regulation pathways, including suppression of specific genera and enhanced denitrifier interactions, are key to N2O mitigation under optimal aeration.
• This study provides a microbial ecological blueprint for precise aeration control to reduce greenhouse gas emissions from composting.