Potassium Fertilizer Formulations Modulate Starch Content and Biosynthetic Gene Expression in Potato Tubers

In Inner Mongolia, a major potato-producing region in China, excessive and unbalanced potassium (K) fertilizer application by farmers in pursuit of higher yields compromises tuber quality and environmental sustainability. To establish a rational K fertilization strategy, two-year field trials were conducted using the medium-late maturing cultivar 'Dafeng No. 10'. The experiments evaluated different K rates and blending ratios with polyhalite (POLY4). Key results show that a moderate K reduction (K₂O 200 kg ha⁻¹) combined with a low POLY4 proportion (18.5%, treatments 2T4 and 3T4) did not cause yield loss but instead achieved the highest yield increases (35.6% in 2022, 22.6% in 2023) and significantly enhanced tuber starch content. This was mechanistically supported by the up-regulation of key starch-synthesis enzymes (AGPase, SBE, SSS, GBSS) and their related genes at transcriptional level under the optimal treatments (particularly 2T3, 2T4, 3T4). The study concludes that a tailored K-POLY4 blend, specifically a reduced K rate with 18.5% POLY4, is an optimal strategy for synergistically improving potato yield, starch quality, and potassium use efficiency, providing a theoretical foundation for sustainable intensification of potato production in China.