Phyllosphere of senescent crops as a microbial N₂O source.

Area of Science:

• Agricultural Science
• Environmental Microbiology
• Biogeochemistry

Background:

• Plant residues are nutrient sources in terrestrial ecosystems, impacting the nitrogen cycle.
• The role of phyllosphere microbes in plant residue nitrogen cycling, particularly N2O emissions, is unclear.
• Agricultural crop residues contribute to global nitrous oxide (N2O) emissions, a potent greenhouse gas.

Purpose of the Study:

• To investigate direct N2O emissions from aboveground cabbage leaf residues.
• To identify and characterize indigenous microbial communities in the phyllosphere responsible for denitrification.
• To understand the mechanisms and ecological significance of N2O production on senescent plant leaves.

Main Methods:

• Field experiments to measure N2O emissions from cabbage leaf residues.
• Isolation and identification of denitrifying bacteria from senescent leaves.
• Multi-omics analyses to investigate microbial gene expression and metabolic pathways.

Main Results:

• Cabbage leaves accumulated significant nitrate levels (3.0–11.3 mg NO3⁻-N g⁻¹ dry weight) after fertilizer application.
• Leaf senescence induced N2O emissions ranging from 8.62 to 415.35 μg N2O-N m⁻² h⁻¹.
• Denitrifiers, including *Agrobacterium* sp. 6Ca8, were isolated and shown to utilize leaf-derived nutrients for N2O production, even in aerobic conditions.

Conclusions:

• The plant phyllosphere acts as a microbial hotspot for N2O emissions in agricultural fields.
• Denitrifying bacteria on senescent leaves actively contribute to N2O production, expanding the known ecological niche of denitrification.
• Denitrification can occur on leaf surfaces, challenging the traditional view of it being solely an anaerobic soil process.