Effect of Exogenous Potassium on Physiological Characteristics and Fruit Setting of Torreya grandis ‘Xifei’ Fruiting Branch

To investigate the effect of potassium fertilizer on the physiological characteristics of leaves, fruit setting rate and expansion rate of Torreya grandis ‘Xifei’ fruiting branches, this study conducted a foliar spraying experiment on 15-year-old T. grandis ‘Xifei’ trees with potassium chloride (KCl), focusing on the slow growth stage and seed-filling stage. The results showed that there were significant differences (P<0.05) in N, P, K mineral elements, chlorophyll, nutritional indicators, fruit setting rate, morphological characteristics of seeds, oil content and fatty acid composition of fruiting branch leaves. The contents of N, P and K reached the highest value in A2 treatment, and the contents of chlorophyll a, b and total chlorophyll were the best in A3 treatment. Starch content reached the peak in B1 treatment, while those of soluble sugar and soluble protein were the highest in A3 treatment. The first-generation fruit setting rate and the second-generation fruit expansion rate reached the maximum in A2 and B3 treatments, respectively. The seed shape index, single seed weight, kernel shape index, single kernel weight and kernel yield rate were the highest in B3 treatment. The oil content was the best in B1 treatment, while the relative contents of linoleic acid, arachidonic acid and picric acid were significantly higher in A3 treatment than those in the control (P<0.05). Principal component analysis showed that the comprehensive score (spraying 0.6% KCl at seed-filling stage) was the highest in B3 treatment. This study demonstrates that exogenous potassium can significantly enhance the physiological indicators, fruit setting rate and seed oil content of T. grandis ‘Xifei’ fruiting branch leaves. B3 treatment exhibited the most favorable performance, indicating high potential for practical application.