Genotype-Specific Physiological Responses of Potassium-Induced Drought Tolerance in Potato: Chlorophyll Protection, Stomatal Regulation, and Proline Accumulation

Abstract

Potassium (K) fertilization is a promising strategy to alleviate drought-induced photosynthetic inhibition in potato. However, cultivar-specific responses remain poorly understood. Six potato cultivars were grown under four treatments: low K, low K + drought, K application, and K application + drought. Chlorophyll content, gas exchange parameters (Pn, Tr, Gs, Ci), and proline (Pro) accumulation were assessed at 50, 70, 90, and 110 days after planting. Drought significantly reduced chlorophyll (up to 37.6% in the sensitive cultivar V7) and suppressed Pn by ~10%, with Gs showing the greatest decline (10–14%). However, Ci did not decrease proportionally to Gs, suggesting the involvement of non-stomatal constraints that merit further investigation. Under drought, K application partially restored chlorophyll (28.5% recovery in SY-2 at 90 DAP), increased Pn and Gs, and substantially elevated Pro accumulation compared with drought alone. Genotypic variation was evident—SY-2 and DXY exhibited strong recovery, whereas V7 and JZS-12 were poorly responsive. K-induced drought tolerance appears to operate via two complementary mechanisms: chlorophyll protection and proline-mediated osmotic adjustment. Both mechanisms are genotype-dependent. These findings provide a physiological basis for genotype-specific K management to sustain potato photosynthesis under water-limited conditions. SY-2 and DXY were identified as promising cultivars for K-enhanced drought resilience. These physiological responses were reflected in final tuber yield, with DXY and SY-2 showing the greatest yield recovery under K-supplemented drought (41.5% and 36.2%, respectively).