Abstract
The utilization of saline-alkali land is undergoing a paradigm shift from traditional soil remediation-driven strategies to the adaptive cultivation of salt-tolerant plants. Okra Abelmoschus esculentus L. (Moench), a species with strong salt tolerance, offers dual benefits when cultivated in moderately to severely saline-alkali soils: it enhances soil desalination and fertility while generating economic value. However, the dynamic changes in okra fruit quality traits in saline-alkali habitats, particularly the coordinated response patterns of yield components, color development, and nutritional metabolites across different growth stages, remain poorly understood. This gap limits the development of targeted quality regulation strategies for high-value agricultural products in such marginal environments. To address this, a field study was conducted in the saline-alkali regions of Nandagang, Cangzhou (with the total salt content of about 4‰), analyzing the traits of okra fruits at different growth stages. Key traits included yield parameters (transverse and longitudinal diameters, fresh and dry weight), chlorophyll content (chlorophyll a, chlorophyll b, and total chlorophyll), and nutritional components flavonoids, soluble sugars, total dietary fiber, and mineral elements (Ca, Fe, Zn). The universality of observed patterns was further validated across different harvesting months (July–September). Principal component analysis (PCA) and membership function methods were employed to calculate composite scores for these traits, guiding the determination of the optimal harvest time for okra. The results indicated that as the okra fruits developed, the fresh weight and dry weight progressively increased, peaking at 15d post-anthesis (dry weight: 12.31±0.27 g in July, 11.97±0.24 g in August, and 7.45±0.19 g in September). Fruit size (transverse and longitudinal diameters) exhibited rapid initial growth followed by stabilization at 11 d post-anthesis (2.12–2.30 cm and 14.0–17.75 cm, respectively). Chlorophyll a content showed a slight upward trend, while chlorophyll b content gradually decreased over time. Total chlorophyll content remained stable with low variability Coefficient of Variation (CV) = 3.56% in July, CV = 3.04% in August, and CV = 10.07% in September. Soluble sugar and flavonoid contents first rose and then fell, peaking at 5-7 days post-anthesis (158.92±4.69 mg·g-1 and 33.07±2.74 mg·g-1, respectively), whereas total dietary fiber content accumulated linearly. Mineral elements exhibited distinct patterns: calcium decreased initially before stabilizing, while iron and zinc showed no significant changes. The fruit size, weight, and accumulation patterns of chlorophyll b, total chlorophyll, and mineral elements in okra fruits were consistent across the three harvesting cycles from July to September. In contrast, the developmental trends of chlorophyll a content, soluble sugar content, flavonoid content, and total dietary fiber demonstrated month-specific variations. A trade-off relationship was observed among yield, color and nutritional components, but the timing of the optimal balance point varied among the months. The results indicated that in saline-alkali environments, okra fruits exhibit delayed morphological development but enhanced accumulation of osmotic substances. Recommended plucking periods were 5 days post-anthesis for July and August, and 7 days post-anthesis for September. These findings provide theoretical support for developing saline-alkali-adapted agricultural products, advance the practical implementation of the "planting suitable crops for specific lands" ecological agriculture model, and support the sustainable exploitation of saline-alkali lands.
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