Plant Biostimulants and Crop Yield and Quality under Climate Change: A Critical Review of Mechanisms, Field Evidence and Translational Constraints

Abstract

Climate change is reducing the stability of crop production through more frequent drought, heat, salinity and combined stresses, while rising atmospheric carbon dioxide threatens the nutritional quality of staple crops. Plant biostimulants, defined by their capacity to improve nutrient use efficiency, abiotic stress tolerance, quality traits or nutrient availability independently of their nutrient content, are increasingly promoted as adaptation tools. The evidence underpinning these claims is extensive but fragmented across controlled-environment physiology, product-specific field trials, meta-analyses of heterogeneous studies and a small number of multi-site agronomic networks. This critical narrative review evaluates how far the available evidence supports the use of plant biostimulants to protect or enhance crop yield and quality under climate-related stress. Peer-reviewed literature published between January 2014 and July 2026 was identified through searches of agricultural, biomedical and multidisciplinary scholarly indexes, supplemented by citation tracking and institutional sources, and was appraised thematically with attention to study design, scale, heterogeneity and conflicts of evidence. The synthesis indicates that mechanistic plausibility is well established for several categories, particularly seaweed extracts, protein hydrolysates, humic substances and beneficial microorganisms, which modulate hormonal signalling, water relations, osmotic adjustment, antioxidant capacity and root function. Quantitative syntheses consistently report mean yield gains in the mid-teens, with larger responses in arid environments, degraded or nutrient-poor soils and low-yielding systems. These averages conceal very high heterogeneity, and large regional field networks have reported negligible or modest responses for some commercial products. Quality responses are frequently positive for antioxidants, vitamins and micronutrients but can involve trade-offs such as nitrate accumulation. Inconsistent product composition, poor viability of some microbial inoculants, limited reporting of stress intensity, publication bias, geographical concentration and scarce multi-season data substantially constrain confidence. Evidence concerning combined stresses, elevated carbon dioxide, waterlogging and long-term soil effects remains particularly thin. Plant biostimulants are best regarded as context-dependent complements to breeding, water management and nutrient stewardship rather than as generic climate solutions. Standardised stress-explicit field protocols, independent multi-environment testing, product characterisation and integrated yield-quality-economic assessment are required before strong adaptation claims can be justified.