Lipidomics reveals divergent root and shoot responses to combined nitrogen deficiency and heat stress.

Introduction: Soybean productivity is highly sensitive to heat and insufficient nitrogen supply, stresses that can occur simultaneously. However, organ-specific lipid responses to this stress combination remain poorly resolved. Methods: We exposed hydroponically grown soybean plants to nitrogen deficiency, heat stress (HS) and their combination and compared physiological, lipidomic and gene-expression responses in roots and leaves. Results: Combined stress caused the largest reductions in biomass and photosynthetic performance and the highest H₂O₂ and MDA accumulation and relative total abundance of candidate oxylipin features. Untargeted LC-MS lipid profiling coupled with WGCNA revealed distinct organ-specific lipid abundance patterns. HS produced the strongest root lipidomic response, characterized by increased abundances of features putatively annotated as polyunsaturated diacylglycerols, lysophospholipids and a gibberellin A12-related compound. Leaves showed their largest lipidomic shift under combined stress, with decreased abundances of photosynthetic membrane-lipid features, increased linoleic-acid- and digalactosylmonoacylglycerol-related features and divergent changes among jasmonate-related features, including cis-jasmone. RT-qPCR showed higher Discussion: These findings reveal pronounced tissue specificity in soybean lipid responses to combined nitrogen deficiency and HS and highlight candidate membrane-lipid- and oxylipin-associated responses for further investigation. However, they do not establish direct root-shoot lipid transport or metabolic coordination.