Enhancing salinity tolerance in Phyla nodiflora L. with potassium humate: crosstalk between osmolytes, antioxidants, and mineral uptake

Abstract

Salinity stress impairs plant growth, nutrient homeostasis, and metabolism, particularly in arid ecosystems. Phyla nodiflora, a ground cover used for erosion control, shows preliminary salinity tolerance, but the mechanistic basis of its long-term adaptation and the potential for enhancement via potassium humate (KH) were unknown. Plant growth, key biochemical attributes, and nutrient uptake were assessed to elucidate how KH modulates physiological performance under increasing salinity. In a 129-day greenhouse experiment, plants were exposed to five salinity levels (0 to 16 dS m⁻¹ NaCl) and three KH concentrations (0, 500, and 1000 mg L⁻¹). Severe salinity (16 dS m⁻¹) without KH provoked oxidative stress, indicated by an 84% increase in malondialdehyde (MDA), and osmotic adjustment, via a 246% rise in proline and a 163% increase in soluble carbohydrates. This coincided with reduced biomass, impaired uptake of nitrogen (N) and potassium (K⁺), and a heightened shoot Na⁺/K⁺ ratio. KH application at 1000 mg L⁻¹ effectively mitigated these disruptions. It reduced oxidative stress (MDA decreased by 76%) and osmotic solute demand (proline lowered by 53%), while enhancing the accumulation of total soluble proteins (121%) and starch (42%). KH improved the acquisition of N, phosphorus (P), and K⁺, restricted sodium (Na⁺) accumulation, and restored a favorable Na⁺/K⁺ balance. We conclude that while P. nodiflora primarily tolerates salinity through osmotic adjustment, KH supplementation confers superior resilience by reinforcing oxidative balance, improving nutrient homeostasis, and supporting key metabolic functions. The 1000 mg L⁻¹ KH treatment was optimal, enabling near-normal growth under high salinity. These findings support the use of KH as a scalable, cost-effective biostimulant to safeguard P. nodiflora productivity in saline soils, offering a strategy for enhancing ecological restoration in salt-affected landscapes.