Purple Nonsulfur Bacteria for Greenhouse Gas Mitigation in Rice Systems: Mechanisms and Future Perspectives

Greenhouse gas (GHG) emissions from flooded rice soils, specifically methane (CH₄) and nitrous oxide (N₂O), are major contributors to agricultural global warming potential. While agronomic strategies, such as water and nutrient management, are used to mitigate, they often involve trade-offs among different gases.

This review synthesizes effective GHG mitigation measures, including water management, rice straw management, chemical fertilizer management, rice cultivar selection, improved cultivation practices, and the role of purple nonsulfur bacteria (PNSB) as a multi-functional microbial solution for simultaneously mitigating CH₄ and N₂O emissions in rice systems.

This review synthesizes current knowledge on GHG emissions from flooded rice systems and evaluates the emerging role of purple nonsulfur bacteria (PNSB) as a microbial strategy for mitigation. While conventional approaches such as water and fertilizer management can reduce emissions, their effectiveness is often constrained by agronomic trade-offs and environmental variability. Recent studies suggest that PNSB may contribute to reducing CH₄ and nitrous oxide N₂O emissions through multiple mechanisms, including modulation of carbon substrate availability, stimulation of methanotrophic activity, competition with methanogens, and enhancement of plant nutrient uptake.

Compared with existing reviews, this study provides a mechanistic synthesis linking microbial metabolism with agronomic outcomes in rice systems. Evidence from laboratory and field studies indicates that PNSB inoculation can reduce CH₄ emissions while improving plant growth. However, results remain inconsistent due to differences in soil type, management practices, and microbial strains. Key knowledge gaps include limited understanding of microbial interactions in situ, scalability of inoculation strategies, and long-term field performance.

Future research should integrate advanced analytical tools, including molecular techniques and data-driven approaches, to better resolve microbial processes and optimize PNSB-based biofertilizers. Overall, PNSB represents a promising but underexplored tool for sustainable rice production and climate change mitigation.