ABSTRACT
Impacts of potassium (K) deficiency and elevated
carbon dioxide (eCO2) 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 (aCO2) and
eCO2 (400 and 800 μmol·mol-1,
respectively). Both treatments significantly affected several constituents,
with the K deficiency having stronger impacts than eCO2. Out of 49
seed constituents, K deficiency and eCO2 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 eCO2 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 eCO2 on several amino
acids appeared to be dependent on the severity of K deficiency. For instance,
eCO2 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 × CO2 interaction.
Results showed that CO2 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.