H2S works synergistically with rhizobia to modify photosynthetic carbon assimilation and metabolism in nitrogen‐deficient soybeans.

Hydrogen sulfide (H2S) performs a crucial role in plant development and abiotic stress responses by interacting with other signalling molecules. However, the synergistic involvement of H2S and rhizobia in photosynthetic carbon (C) metabolism in soybean (Glycine max) under nitrogen (N) deficiency has been largely overlooked. Therefore, we scrutinised how H2S drives photosynthetic C fixation, utilisation, and accumulation in soybean‐rhizobia symbiotic systems. When soybeans encountered N deficiency, organ growth, grain output, and nodule N‐fixation performance were considerably improved owing to H2S and rhizobia. Furthermore, H2S collaborated with rhizobia to actively govern assimilation product generation and transport, modulating C allocation, utilisation, and accumulation. Additionally, H2S and rhizobia profoundly affected critical enzyme activities and coding gene expressions implicated in C fixation, transport, and metabolism. Furthermore, we observed substantial effects of H2S and rhizobia on primary metabolism and C–N coupled metabolic networks in essential organs via C metabolic regulation. Consequently, H2S synergy with rhizobia inspired complex primary metabolism and C–N coupled metabolic pathways by directing the expression of key enzymes and related coding genes involved in C metabolism, stimulating effective C fixation, transport, and distribution, and ultimately improving N fixation, growth, and grain yield in soybeans. Summary Statement: Can H2S effectively modulate photosynthetic C fixation and metabolism in symbiotic soybean‐rhizobia systems? Sufficient and robust data confirmed that H2S synergy with rhizobia promoted the expression of multiple critical enzymes and related coding genes involved in C metabolism to affect crucial primary metabolism and C‐N linked metabolic networks, ensuring efficient C fixation, transport, and allocation and ultimately improving N fixation, growth, and output in N‐deficient soybeans. [ABSTRACT FROM AUTHOR]