Mitigation effects of solar-driven metalloporphyrins on CO₂ and N₂O emissions from an agricultural soil

Developing green technologies to mitigate soil carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions is critical for sustainable agriculture. Here, we investigated the effects of two water-soluble metalloporphyrins (FeTPPS and MnTPPS), with and without glucose addition, on CO₂ and N₂O emissions and the associated mechanisms in an agricultural soil under natural solar irradiation. Metalloporphyrin effects depended on metal identity and labile carbon (C) availability. FeTPPS alone significantly reduced cumulative CO₂ emissions by 9.9%, and FeTPPS with glucose reduced emissions by 7.2% relative to the glucose treatment. These effects were accompanied by redistribution of organic C into < 250 μm aggregates, suppressed cellulase activity, and decreased humic-like DOM components, suggesting altered organic C accessibility and aggregate-associated C distribution. However, FeTPPS did not significantly alter cumulative N₂O emissions. MnTPPS exhibited a biphasic effect on CO₂ flux, but still significantly reduced cumulative CO₂ emissions by 13.3%, consistent with increased abundances of cbbL/cbbM. MnTPPS also significantly reduced cumulative N₂O emissions by 63.3%, despite increased urease activity and abundances of nitrification-related genes, and this reduction coincided with increased nosZII abundance. However, glucose addition eliminated the suppressive effects of MnTPPS on CO₂ and N₂O emissions, recovered cellulase activity, and did not alter cbbL/cbbM abundances, indicating that labile C can override MnTPPS-induced changes in CO₂ and N₂O emissions. Overall, these results demonstrate that solar-driven metalloporphyrin catalysis can regulate soil CO₂ and N₂O emissions, and its effectiveness depends on labile C availability. These findings provide useful information for developing innovative strategies to mitigate soil CO₂ and N₂O emissions.