Tengfei Li

Rising atmospheric carbon dioxide (CO₂) enhances C₃ photosynthesis and often improves intrinsic water-use efficiency, yet the extent to which this physiological potential translates into durable agronomic and ecological benefits remains uncertain. This review integrates evidence from controlled environments, free-air CO₂ enrichment experiments, field studies, and modelling to evaluate the mechanisms, constraints, and applications of CO₂ fertilization. We synthesize this evidence within a cascade-filtering framework that follows carbon gain from leaf photosynthesis through whole-plant allocation, resource limitation, environmental stress, and belowground processes to realized outcomes. Three major conclusions emerge from this review. First, leaf-level photosynthetic gains are progressively attenuated by photosynthetic acclimation, source–sink limitation, nutrient shortage, and water and heat stress, so biomass and harvestable-yield responses are smaller and more variable. Second, yield gains can coincide with lower protein, iron, and zinc concentrations, making nutrient yield as important as mass yield. Third, greater carbon input belowground does not guarantee persistent soil-carbon storage because allocation, turnover, and rhizosphere priming determine retention. In controlled-environment agriculture, enrichment is most effective when CO₂ supply is coordinated with light, climate, water, nutrients, crop load, energy use, and gas delivery. Future progress requires multi-factor, multi-year, genotype-resolved studies that link physiology with nutritional quality, soil processes, modelling, life-cycle impacts, and economics.

Elevated CO₂ (eCO₂) is expected to enhance crop productivity but may simultaneously reduce nutritional quality through nutrient dilution. However, responses among crop species with contrasting functional traits and the associated plant–soil responses remain insufficiently understood. Using a multi-crop Free-Air CO₂ Enrichment (FACE) platform, we investigated the effects of eCO₂ on per-plant biomass and yield-component traits, nutritional quality, soil properties, and mineral element dynamics in four representative crops with contrasting functional traits: soybean, peanut, maize, and sweet potato. Elevated CO₂ significantly increased several per-plant biomass and yield-component traits, with the magnitude of these responses varying among crop species and soybean showing pronounced increases in multiple measured traits. Protein concentration decreased significantly by 11.47% in maize and also declined in sweet potato, whereas it remained stable in soybean and increased in peanut, demonstrating crop-specific differences in nutritional responses to eCO₂. Bulk soil responses also differed among crop types, with soybean and sweet potato showing significant decreases in soil pH and crop-specific changes in the total concentrations of Zn and Cu; however, these changes were not consistently accompanied by corresponding increases in elemental concentrations in the harvested plant tissues. These findings indicate that changes in total soil elemental concentrations do not necessarily correspond to higher elemental concentrations in edible organs. Overall, the four crop species exhibited distinct responses to eCO₂, highlighting the importance of integrating crop nutritional quality, nutrient dynamics, and plant–soil interactions when developing adaptive agricultural management strategies under future climate change.