Abiotic Stress Combinations in Crops: A Meta-Analysis of Drought and Salinity Responses across Diverse Climatic Zones

Drought and salinity are among the most prevalent abiotic stressors limiting crop productivity, particularly in arid and semi-arid regions where they often co-occur. While many studies have examined these stressors independently, their combined effects remain insufficiently quantified. This meta-analysis synthesizes findings from 22 peer-reviewed experimental studies, yielding 48 trait-level comparisons across 14 crop species and diverse agroecological zones. Using Hedges’ g as the standardized effect size under a random-effects model, we evaluated the impact of combined drought and salinity stress on key physiological and agronomic traits, including yield, photosynthetic efficiency, water status, ion regulation, and antioxidant enzyme activity. Results revealed strong overall negative effects on grain yield (mean Hedges’ g =−4.6) and chlorophyll content, especially in cereals grown in temperate climates. Traits such as proline accumulation and K⁺/Na⁺ ratio showed more variable, crop-dependent responses. Subgroup analyses indicated that climatic zone, crop type, and stress application protocol influenced effect sizes, with crops from arid environments exhibiting greater physiological tolerance. Simultaneous stress application was associated with more pronounced effects than sequential exposure. Due to limited replication per trait, publication bias could not be formally assessed. This synthesis identifies ion homeostasis, antioxidant defense, and root traits as key targets for improving crop resilience. It also highlights knowledge gaps, including underrepresentation of legumes, inconsistent trait reporting, and limited field-based studies. These findings offer quantitative evidence to guide future research and breeding strategies aimed at enhancing tolerance to multiple abiotic stressors under climate variability.