Exploring the reinforcing effect of nano-potassium on the antioxidant defense system reflecting the increased yield and quality of salt-stressed squash plants

To explore the reinforcing effects of nano-potassium fertilizer (nano-K) on growth, yield and quality, physiobiochemical responses, antioxidant defense systems, antioxidant gene expressions, and nutrients of saltstressed squash plants, field experiments were performed using normal (EC = 2.34 dS m-1) and saline (EC = 9.38 dS m-1) soils during the 2021 and 2022 seasons. The traditional recommended K at full dose (TRK100) or half dose (TRK50) was used in both soils. Salinity and/or TRK50 significantly decreased photosynthetic pigment contents (by 8.7-22.5%), photosynthetic efficiency (by 6.0-10.9%), relative water content (RWC by 5.0-5.1%), membrane stability index (MSI by 7.2-7.4%), nutrient contents (by 28.4-48.2%), K+/Na+ ratio (by 66.4-67.1%), which contributed to the decrease in growth (by 12.2-25.8%) and yield traits (by 4.2-28.5%), and fruit quality (by 8.5-19.7%) due to an increment of oxidative stress biomarker (O2 center dot- by 32.4-52.9% and H2O2 30.4-57.1%) levels, electrolyte leakage (EL by 23.3-24.5%), malondialdehyde (MDA by 71.4-77.6%), and Na+ (by 55.5-56.9%). Under stress in both soils, foliar-applied 0.50 g nano-K L-1 suppressed the levels of O2 center dot-, H2O2, MDA, EL, and Na+, while noticeably increased photosynthetic pigment contents, photosynthetic efficiency, RWC, MSI, nutrient contents, K+/Na+ ratio, which were positively reflected in growth and yield traits, and fruit quality due to increased osmoprotectant and low-molecular-weight antioxidant contents, antioxidant enzyme activities and enzymatic gene expressions. Therefore, our findings recommend using nano-K as an effective strategy to promote antioxidant and photosynthetic machineries, minimize oxidative stress biomarkers and Na+ levels, boost tolerance to salt stress, and improve squash yield and yield quality under salt stress.