Potassium Deficiency Influences Soybean Seed Mineral Compositions and Metabolic Profiles across CO<sub>2</sub>

Abstract

Impacts of potassium (K) deficiency and elevated carbon dioxide (eCO 2) on seed constituents have rarely been explored in most crops including soybean. A controlled environment experiment was conducted with soybean grown under a sufficient (5.0 mM) and two deficient (0.50 and 0.02 mM) levels of K fertilization at ambient (aCO 2) and eCO 2 (400 and 800 µmol•mol −1 , respectively). Both treatments significantly affected several constituents, with the K deficiency having stronger impacts than eCO 2. Out of 49 seed constituents, K deficiency and eCO 2 influenced 41 and 16 constituents, respectively. The K deficiency primarily decreased on average 16 constituents including minerals (e.g., K, P, Mg, Mn, Zn, Fe, B), oil, and essential fatty acids (e.g., linoleic and linolenic acids) but enhanced 25 constituents such as protein, amino acids, simple sugars, and stress-responsive metabolites (e.g., sugar alcohols mannitol and myo-inositol and proline). An accumulation of N while decreased C concentration resulted in the lower C:N ratio in the seeds of K-deficient plants. However, protein:oil, C:K, N:P, and N:K ratios were consistently greater under K deficiency. The eCO 2 also decreased minerals such as P, S, Zn, B, and essential fatty acids but enhanced the concentration of six constituents including alanine, oleic acid, fructose, and sugar alcohols across K fertilization. In addition, the impact of eCO 2 on several amino acids appeared to be dependent on the severity of K deficiency. For instance, eCO 2 decreased essential amino acids (e.g., valine, phenylalanine, isoleucine) in the seeds of severely K-deficient plants but not in the other treatments leading to a K × CO 2 interaction. Results showed that CO 2 enrichment is likely to exacerbate the decline in the concentration of seed minerals such as P, K, S, Zn and B, essential fatty acids, and amino acids under K limited conditions.