Calcium application coordinates seedling heat tolerance and yield-quality formation in ginger under summer...

Summer heat stress constrains ginger production. Although calcium (Ca) enhances stress tolerance in various crops, its effects on heat tolerance, yield, and quality in ginger remain unclear. A pot experiment was conducted using Zingiber officinale cv. 'Laiwu Big Ginger' to evaluate Ca effects on plant growth and quality under natural summer high-temperature conditions. Six Ca rates (0, 15.2, 30.5, 45.7, 60.9, and 76.2 mmol Ca²⁺ plant^-1) were established using calcium nitrate tetrahydrate [Ca(NO₃)₂·4H₂O]. Seedling-stage physiological and biochemical parameters were analyzed with linear mixed-effects models; harvest-stage growth, biomass, and quality parameters were analyzed with ANOVA or non-parametric tests. PCA, correlation analysis, and membership function analysis were used for multivariate evaluation. At Day 16, the 60.9 mmol Ca²⁺ plant^-1 treatment significantly improved photosynthetic capacity (chlorophyll +23.3%, Pn +13.0%), antioxidant enzyme activities (SOD, POD, CAT), and proline content, while reducing oxidative damage (MDA, REC) and ROS (O₂ ^·-, H₂O₂). These adjustments promoted biomass and rhizome quality, with the highest rhizome fresh weight (727.7 vs. 447.3 g plant^-1), dry matter (+3.6%), soluble sugars (+28.1%), soluble protein (+36.5%), free amino acids (+19.1%), and vitamin C (+17.5%). Multivariate analyses confirmed positive correlations among photosynthetic traits, antioxidant activity, biomass, and quality parameters, with the 60.9 mmolCa²⁺ plant^-1 treatment ranking highest in comprehensive evaluation by membership function analysis. Calcium application at this optimal rate, as determined under our experimental conditions, was associated with enhanced heat tolerance and subsequent growth and quality formation. These findings provide practical insights for sustaining ginger productivity under heat stress within the scope of our experimental conditions.