Comprehensive Assessment of Low Potassium Tolerance in Mature Chinese Cabbage and Physiological Differences in Responses to Potassium Deficiency

Chinese cabbage (Brassica rapa ssp. pekinensis) is a typical potassium (K)-demanding crop that is highly sensitive to soil K availability. Severe soil potassium deficiency in production fields frequently impairs both yield and quality. Therefore, screening for potassium-efficient varieties is essential for identifying germplasm resources and breeding materials tolerant to low-K conditions. To evaluate genetic variation in potassium utilization efficiency, 12 Chinese cabbage germplasms were assessed under two field conditions: with adequate potassium supply (K2O 165 kg/ha) and without potassium application (K2O 0 kg/ha). Fourteen parameters, including yield, plant growth, potassium content, and potassium accumulation, were measured and compared. Principal component analysis (PCA) was employed to identify key indicators influencing K-use efficiency, and cluster analysis was subsequently performed to classify the 12 germplasms. The results demonstrated that under K-deficient conditions, the mean values of yield, fresh plant weight, shoot K accumulation, and total plant K accumulation were significantly reduced compared to those under adequate K supply. Based on three principal components (root fresh weight, shoot potassium utilization efficiency, and yield), membership function values, and comprehensive evaluation scores (D-values), the 12 genotypes were classified into four categories: low-K tolerant (‘HK8’); moderately low-K tolerant (‘HK1’, ‘HK6’, ‘HK12’, ‘HK42’); intermediate low-K sensitive (‘HK18’, ‘HK25’, ‘HK27’, ‘HK40’); and low-K sensitive (‘HK45’, ‘HK48’, ‘HK54’). Under K-deficiency stress, significant differences were observed between the low-K tolerant genotype ‘HK8’ and the low-K sensitive genotype ‘HK48’ in terms of yield, dry matter accumulation across plant organs, potassium distribution patterns, and K+/Na+ and Ca2+/Na+ ratios. Notably, the low-K tolerant genotype ‘HK8’ exhibited markedly superior salt tolerance compared to the low-K sensitive genotype ‘HK48’, suggesting a potential physiological link between low-K tolerance and ionic homeostasis.