Glycine max (L.) Merr. (Soybean) metabolome responses to potassium availability

Potassium (K+) has vital physiological and metabolic functions in plants and its availability can impact tolerance to biotic and abiotic stress conditions. Limited studies have investigated the effect of K+ fertilization on soybean metabolism. Using integrated omics, ionomics and metabolomics, we investigated the field-grown Glycine max (soybean) response, after four K+ soil fertilization rates. Soybean leaf and pod tissue (valves and immature seeds) extracts were analysed by ultra-performance liquid chromatography coupled to high-resolution mass spectrometry (UPLC-HRMS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Multivariate analyses (PCA-X&Y e O2PLS-DA) showed that 51 compounds of 19 metabolic pathways were regulated in response to K+ availability. Under very low potassium availability, soybean plants accumulated of Ca2+, Mg2+, Fe2+, Cu2+, and B in young and old leaves. Potassium fertilization upregulated carbohydrate, galactolipid, and flavonol glycoside biosynthesis in leaves and pod valves, while K+ deficient pod tissues showed increasing amino acids, oligosaccharides, benzoic acid derivatives, and isoflavones contents. Severely K+ deficient soils elicited isoflavones, coumestans, pterocarpans, and soyasaponins in trifoliate leaves, likely associated to oxidative and photodynamic stress status. Additionally, results demonstrate that L-asparagine content is higher in potassium deficient tissues, suggesting this compound as a biomarker of K+ deficiency in soybean plants. These results demonstrate that potassium soil fertilization did not linearly contribute to changes in specialised constitutive metabolites of soybean. Altogether, this work provides a reference for improving the understanding of soybean metabolism as dependent on K+ availability.

Automated summary

Potassium availability significantly impacts soybean metabolism, leading to changes in the composition of various metabolites in different tissues. The deficiency of potassium in soil can cause the accumulation of certain elements in soybean leaves, while potassium fertilization promotes the synthesis of carbohydrates, galactolipids, and flavonol glycosides in leaves and pod valves. In contrast, potassium-deficient pod tissues show increased contents of amino acids, oligosaccharides, benzoic acid derivatives, and isoflavones. The results also suggest that L-asparagine can be used as a biomarker for potassium deficiency in soybean plants.