Bioscience Methods 2026, Vol.17, No.1, 43-56 http://bioscipublisher.com/index.php/bm 50 6 Effects of Different Potassium Fertilizer Dosages on Sugar Accumulation and Sugar Components 6.1 Changes in sugar components (such as reducing sugar and sucrose) and their significance for flavor/processing The application of potassium fertilizers has a significant impact on the total sugar content and the proportion of various sugar components in the sweet potato tubers (Gao et al., 2021). This experiment monitored the changes in the main sugar components (reducing sugar and sucrose) in the tubers, and the results showed that the sugar composition presented a certain pattern as the potassium application level changed: moderate potassium application helps increase the sucrose content in the tubers, while potassium deficiency leads to insufficient sucrose accumulation in the tubers and a relatively higher proportion of reducing sugar (Shu et al., 2024). Literature reports indicate that moderate potassium fertilizer treatment can promote the accumulation of sucrose in sweet potato tubers, with the sucrose content in the tubers increasing by approximately 18% compared to no potassium application during the growth period (Huang et al., 2025); while in the low potassium treatment, the proportion of reducing sugar (mainly glucose and fructose) in the tubers often increases (Sheng et al., 2023). Changes in sucrose and reducing sugar content are of great significance for the flavor and processing quality of sweet potatoes. Sucrose is the main source of sweetness in sweet potatoes, and an appropriate amount of sucrose makes fresh sweet potatoes taste sweet and delicious; reducing sugar is prone to Maillard reaction during heating and processing (such as baking and frying), and excessive content can lead to overly dark color and abnormal flavor of the products (Huang et al., 2025). Therefore, for fresh and baking-type sweet potatoes, it is necessary to ensure a certain sucrose content to provide sweetness, while avoiding excessive reducing sugar to prevent excessive browning during processing. In summary, reasonable potassium fertilizer management can optimize the sugar component composition of sweet potato tubers: while increasing the total sugar content, it balances the proportion of sucrose and reducing sugar to meet the requirements of sweetness and processing quality. 6.2 Biochemical mechanism of sugar accumulation: starch-sugar conversion and key enzyme regulation The changes in sugar content and composition of sweet potato tubers under different potassium nutrition levels result from the biochemical regulatory effect of potassium on the carbohydrate metabolism pathway of the tubers (Gao et al., 2021). Firstly, potassium affects the balance of starch and sugar conversion. When potassium is sufficient, there is an active conversion of sucrose to starch in the tubers: Adequate potassium promotes the rapid conversion of sucrose to starch for storage, increasing the accumulation of starch in the tubers and moderately reducing free sugars; while in potassium deficiency, this conversion is hindered, leading to the accumulation of soluble sugars such as sucrose and insufficient starch synthesis (Sheng et al., 2023). This process is mediated by multiple metabolic enzymes. Potassium fertilizer can enhance the activity of key enzymes in the sucrose metabolic pathway, among which sucrose synthase (SS) is the key enzyme that breaks down sucrose into substrates for starch synthesis. Experimental observations have found that the SS enzyme activity in potassium-treated tubers significantly increased, averaging an increase of approximately 16% compared to the control (Huang et al., 2025). Higher SS activity promotes the breakdown of sucrose, increasing the sugar concentration gradient between the source and sink. The increase in the gradient accelerates the transport and unloading of assimilates to the tubers, facilitating the deposition of sugar into starch (Jiang et al., 2024). At the same time, potassium may indirectly regulate the activity of sugar metabolism enzyme systems by influencing hormone balance. For example, sufficient potassium supply helps reduce the activity of starch-degrading enzymes (such as amylase, amide sugarase) in the tubers, thereby reducing excessive degradation of starch to sugars; conversely, when potassium is deficient, starch degradation increases, leading to the accumulation of reducing sugars. Other studies have also pointed out that when potassium is sufficient, the activities of enzymes promoting starch synthesis, such as ADP-glucose pyrophosphorylase and starch synthase, increase, converting more sucrose into starch chains (Gao et al., 2021). In summary, potassium fertilizer effectively promotes the conversion of sucrose to starch in the tubers and regulates the sugar accumulation pathway by up-regulating source-end enzymes such as sucrose synthase and down-regulating some sink-end enzymes. This biochemical mechanism explains why appropriate potassium application can simultaneously increase starch content and optimize the composition of sugar components, thereby improving the intrinsic quality of sweet potatoes.
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