Integrated physiological and transcriptomic analyses reveal adaptive mechanisms of potassium deficiency in Camellia...

Potassium (K⁺) is an essential macronutrient for plant growth, yet Camellia oleifera is often cultivated in red soils severely deficient in available K⁺. Such nutrient limitation has become a major constraint on its growth and productivity, while the physiological and molecular mechanisms underlying K⁺ deficiency responses in this woody species remain unclear. In this study, tissue-cultured seedlings of the C. oleifera cultivar 'Cenruan 3' were employed to examine growth and physiological traits under K⁺ deficiency and to elucidate the underlying transcriptional regulation. Potassium deprivation markedly reduced biomass accumulation, chlorophyll content, photosynthetic capacity, and primary root elongation. Root fresh and dry weights decreased, whereas root Ca²⁺ and Mg²⁺ concentrations increased. Stem lignification was accelerated, and reactive oxygen species (ROS) accumulated in leaves. Transcriptome analysis revealed activation of the Ca²⁺-dependent CBL-CIPK signaling module, which likely modulates K⁺ transport systems such as AKT1 and HAK5 to enhance K⁺ uptake and redistribution. Crosstalk among ROS, ethylene, and auxin signaling appears to contribute to adaptive adjustments of root architecture under ionic stress. Moreover, the phenylpropanoid pathway was significantly upregulated, together with increased expression of lignin biosynthesis-related genes, indicating enhanced structural reinforcement. Overall, C. oleifera adapts to K⁺ limitation through coordinated regulation of ion sensing, signal transduction, and metabolic and structural remodeling. A core Ca²⁺-CBL-CIPK regulatory network integrates K⁺ acquisition with hormonal and ROS signals. These findings improve our understanding of potassium utilization in woody plants and provide valuable references for developing C. oleifera cultivars with enhanced tolerance to low-K⁺ conditions.