Thirsty for solutions: How potassium drives sugarcane's varietal-specific strategies for drought tolerance

With increasing drought stress impacting plants during critical growth stages, genetic breeding and nutrient management are key strategies for plant's resilience. To investigate how potassium (K) fertilization and drought stress impact biochemical, physiological and nutritional mechanisms of sugarcane, we applied a multitiered approach at a range of leaf- and plant-levels in four sugarcane varieties (IACSP95-5000, CTC7, CTC14, and RB975201) grown under two K-soil availability levels (moderate - MK; high K - HK) and two water regimes (well-watered - WW; drought-stressed - DS). DS reduced leaf water potential at predawn (Ψpd) and midday (Ψmd), and photosynthetic parameters, including CO₂ assimilation (A), stomatal conductance (gs), transpiration (E), instantaneous carboxylation efficiency (k), and Fv/Fm. In contrast, DS enhanced K-uptake efficiency (KUpE), oxidative stress (indicated by H₂O₂ and MDA), and enzymatic antioxidant activities (SOD, CAT, APX, GPX). Regarding K-soil availability levels, the HK increased K-uptake efficiency (KUpE) and K-accumulation, which enhanced photosynthetic parameters, enzymatic antioxidant activities and biomass production, while reduced leaf δ¹³C and oxidative stress relative to MK, regardless the water regimes. Plants under DS x HK showed distinct leaf metabolic profiles, being characterized by the accumulation of stress-resilient metabolites, including organic acids (aconitic, aspartic, benzoic glutonic malic and valeric acid), sugars (ribulose, hexopyranose and turanosis), amino acids (alanine), and polyamines (putrescine), notably in CTC7 variety. Our findings illustrate that enhanced K-accumulation observed in plants under HK (especially in CTC7 variety) supports drought resilience across varieties by upregulating biochemical, physiological and nutritional mechanisms.