Potassium is one of the most important elements for crop growth and development. However, potassium deficiencies are common in the cultivated land of oil crops in the world, which limits the increase in their yields. The photosynthesis, fluorescence, and physiological indexes of peanut plants were affected by low K stress to varying degrees, and finally the yield decreased. However, the effect of low K stress on the photosynthetic physiological mechanism of peanut plants remains unclear. In this study, in order to explore the response mechanism of peanuts to low K stress, NH18 (tolerance to low K) and HY20 (intolerance to low K) were used to explore the effects of different peanut varieties under low K stress on the dry matter accumulation, protective enzyme activities, osmotic regulatory substance accumulation capacity, fluorescence characteristics, nutrient content, grain quality, and yield. The results of the 2-year experiment showed that under the stress of low K, the content of malondialdehyde in peanut leaves increased and the activities of NH18 superoxide dismutase (SOD) and peroxidase (POD) in the low-K-tolerant variety were higher than those in the low-K-intolerant variety HY20. The decrease in osmotic regulation caused by low K was compensated for by an increase in the soluble protein content. As a result, the chlorophyll content decreased significantly, F0 increased under dark adaptation, and Fm, Fv, and Fv/Fm decreased. The photosynthetic and fluorescence physiology of low-K-tolerant NH18 was less affected by low K stress. Furthermore, under low K stress, the dry matter accumulation of NH18 was reduced less, so that the final yield was less affected by low K stress than that of HY20. Under low K stress, the potassium content in the roots, stems, leaves, and fruit needles decreased significantly, and the decreasing range of stems and leaves gradually increased with the growth period, while that of the pod gradually decreased with the growth period. Under low K stress, the sodium content in the root system significantly increased and was significantly higher than that in the stem, leaf, pod, and fruit needle, indicating that the peanut plants actively absorbed more Na⁺ to replace the K⁺ function. This study clarified the mechanism of photosynthesis and the physiology of peanut plants under low K stress, which is of great significance for the breeding and cultivation of peanut resistance.

Auxin plays a crucial role in regulating root growth and development, and its distribution pattern under environmental stimuli significantly influences root plasticity. Under K deficiency, the interaction between K⁺ transporters and auxin can modulate root development. This study compared the differences in root morphology and physiological mechanisms of the low-K-tolerant maize inbred line 90-21-3 and K-sensitive maize inbred line D937 under K-deficiency (K⁺ = 0.2 mM) with exogenous NAA (1-naphthaleneacetic acid, NAA = 0.01 mM) treatment. Root systems of 90-21-3 exhibited higher K⁺ absorption efficiency. Conversely, D937 seedling roots demonstrated greater plasticity and higher K⁺ content. In-depth analysis through transcriptomics and metabolomics revealed that 90-21-3 and D937 seedling roots showed differential responses to exogenous NAA under K-deficiency. In 90-21-3, upregulation of the expression of K⁺ absorption and transport-related proteins (proton-exporting ATPase and potassium transporter) and the enrichment of antioxidant-related functional genes were observed. In D937, exogenous NAA promoted the responses of genes related to intercellular ethylene and cation transport to K-deficiency. Differential metabolite enrichment analysis primarily revealed significant enrichment in flavonoid biosynthesis, tryptophan metabolism, and hormone signaling pathways. Integrated transcriptomic and metabolomic analyses revealed that phenylpropanoid biosynthesis is a crucial pathway, with core genes (related to peroxidase enzyme) and core metabolites upregulated in 90-21-3. The findings suggest that under K-deficiency, exogenous NAA induces substantial changes in maize roots, with the phenylpropanoid biosynthesis pathway playing a crucial role in the maize root’s response to exogenous NAA regulation under K-deficiency.