Vegetable fermentation as an overlooked source of greenhouse gases: from microbial mechanisms to global budget implications

Vegetable fermentation represents a globally ubiquitous yet overlooked source of greenhouse gas (GHG) emissions. This study quantified GHG fluxes and integrated 16S rRNA sequencing to elucidate the potential microbial mechanisms using a 90-day cabbage fermentation model. High-salt conditions enhanced cumulative CO₂ emissions 2.1-fold relative to the low-salt treatment. This amplification was driven by salt-induced osmotic dehydration accelerating dissolved organic carbon release from vegetable tissues, which likely fueled heterofermentative guilds (e.g., Leuconostoc) and resulted in elevated CO₂ production. Conversely, low-to-medium salt concentrations favored N₂O generation via nitrification and denitrification by salt-sensitive Proteobacteria (e.g., Enterobacter), whereas high salinity shifted nitrogen flux toward dissimilatory nitrate reduction to ammonium (DNRA), thereby minimizing gaseous losses. Globally, vegetable fermentation is estimated to contribute between 16,483 and 56,872 tonnes of CO₂-equivalent annually. These findings establish vegetable fermentation as an important GHG source, offering new insights for mitigating the food industry's environmental footprint.