This review synthesises current research findings and modelling approaches to explore the impact of elevated atmospheric carbon dioxide (eCO₂) concentrations on crop productivity, water and nutrient use efficiency, plant nutritional quality, and the implications for global food security. Over recent decades, rising atmospheric CO₂ levels have sparked significant concern due to their role in driving climate change. While some studies highlight the potential benefits of eCO₂, such as increased crop yields and improved water-use efficiency, many recent investigations reveal a concerning decline in crop nutritional quality. eCO₂ has been shown to reduce concentrations of key nutrients, including nitrogen, minerals, vitamins, polyphenols, and other non-nutrient compounds, as well as alter gene expression. These changes are further complicated by interactions with heat stress and drought, presenting significant challenges in predicting sustainable future crop productivity. These nutritional declines exacerbate the global crisis of malnutrition and hidden hunger, threatening the achievement of Sustainable Development Goal 2 (SDG2), which aims to end hunger and ensure food security. Addressing these challenges requires further research, interdisciplinary collaboration, and innovative approaches to mitigate the adverse effects of eCO₂ on crop physiology and nutritional content while maximising agricultural sustainability. This review aims to provide insights into the complex mechanisms governing crop responses to eCO₂ using wheat as a model and proposes pathways for future research and agricultural practices. These strategies are critical for tackling the intricate dynamics of climate variability, ensuring nutrient-rich food production, and securing food security in the face of a rapidly changing climate.

Amaranth (Amaranthus tricolor), an underutilized climate smart crop, is highly nutritious and possesses diverse drought tolerance traits, making it an ideal crop to thrive in a rapidly changing climate. Despite considerable studies on the growth and physiology of plants subjected to drought stress, a precise trait phenotyping strategy for drought tolerance in vegetable amaranth is still not well documented. In this study, two drought screening trials were carried out on 44 A. tricolor accessions in order to identify potential drought-tolerant A. tricolor germplasm and to discern their physiological responses to drought stress. The findings revealed that a change in stem biomass was most likely the main mechanism of drought adaptation for stress recovery, and dark-adapted quantum yield (Fv/Fm) could be a useful parameter for identifying drought tolerance in amaranth. Three drought tolerance indices: geometric mean productivity (GMP), mean productivity (MP) and stress tolerance index (STI) identified eight drought-tolerant accessions with stable performance across the two screening trials. The highly significant genotypic differences observed in several physiological traits among the amaranth accessions indicate that the amaranth panel used in this study could be a rich source of genetic diversity for breeding purposes for drought tolerance traits.

Amaranth (Amaranthus spp.) is a highly nutritious, underutilized vegetable and pseudo-cereal crop. It possesses diverse abiotic stress tolerance traits, is genetically diverse and highly phenotypically plastic, making it an ideal crop to thrive in a rapidly changing climate. Despite considerable genetic diversity there is a lack of detailed characterization of germplasm or population structures. The present study utilized the DArTSeq platform to determine the genetic relationships and population structure between 188 amaranth accessions from 18 agronomically important vegetable, grain, and weedy species. A total of 74, 303 SNP alleles were generated of which 63, 821 were physically mapped to the genome of the grain species A. hypochondriacus. Population structure was inferred in two steps. First, all 188 amaranth accessions comprised of 18 species and second, only 120 A. tricolor accessions. After SNP filtering, a total of 8,688 SNPs were generated on 181 amaranth accessions of 16 species and 9,789 SNPs generated on 118 A. tricolor accessions. Both SNP datasets produced three major sub-populations (K = 3) and generate consistent taxonomic classification of the amaranth sub-genera (Amaranthus Amaranthus, Amaranthus Acnida and Amaranthus albersia), although the accessions were poorly demarcated by geographical origin and morphological traits. A. tricolor accessions were well discriminated from other amaranth species. A genome-wide association study (GWAS) of 10 qualitative traits revealed an association between specific phenotypes and genetic variants within the genome and identified 22 marker trait associations (MTAs) and 100 MTAs (P≤0.01, P≤0.001) on 16 amaranth species and 118 A.tricolor datasets, respectively. The release of SNP markers from this panel has produced invaluable preliminary genetic information for phenotyping and cultivar improvement in amaranth species.

Drought is a major abiotic stress responsible for severe crop losses worldwide. Development of new crop varieties with increased drought tolerance is one way to increase crop productivity. The aim of this study was to characterise the diversity of nine accessions belonging to Amaranthus tricolor and A. cruentus, in response to drought stress using a dry-down protocol to characterise the transpiration efficiency (TE). Plants were subjected to either a gradual dry down or well-watered conditions. Results showed that TE was significantly higher (P < 0.01) in water-deficient (WD) plants compared to water-sufficient (WS) plants, 2.40 g kg⁻¹–7.13 g kg⁻¹ and 2.19 g kg⁻¹–4.84 g kg⁻¹, respectively. There was no significant difference in the fraction of transpirable soil water (FTSW) threshold decline between the amaranth genotypes. TE was highly correlated with yield under both WS (r = 0.89, P < 0.001) and WD conditions (r = 0.662, P < 0.001), and negatively correlated with root-to-shoot ratio under both WS (r = −0.488, P < 0.05) and WD conditions (r = −0.460, P < 0.05). Significant genotypic differences were seen for growth rate and stress susceptibility index (SSI). The result obtained in this investigation underline the need to identify genotypic variation in water use efficiency in amaranth. Abbreviations: FTSW: Fraction of transpirable soil water; NTR: normalised transpiration rate; SSI: Stress susceptibility index; TE: transpiration efficiency; WHC: water holding capacity; WD: water-deficient; WS: water-sufficient.

Elevated atmospheric CO₂ is known to alter plant physiology, yet its specific effects on nutrient-rich leafy vegetables remain insufficiently quantified. This study aimed to examine how eCO₂ influences yield and nutritional quality in kale (Brassica oleracea) and spinach (Spinacia oleracea) through the first meta-analysis focused exclusively on these crops. Following the Collaboration for Environmental Evidence (CEE) guidelines, we systematically reviewed eligible studies and conducted a random-effects meta-analysis to evaluate overall and subgroup responses based on CO₂ concentration, crop type and exposure duration. Effect sizes were calculated using Hedges’ g with 95% confidence intervals. The analysis showed that eCO₂ significantly increased biomass in spinach (g = 1.21) and kale (g = 0.97). However, protein content declined in both crops (spinach: g = −0.76; kale: g = −0.61), and mineral concentrations, particularly calcium and magnesium, were reduced, with spinach exhibiting stronger nutrient losses overall. The variability in response across different CO₂ concentrations and exposure times further underscores the complexity of eCO₂ effects. These results highlight a trade-off between productivity and nutritional quality under future CO₂ conditions. Addressing this challenge will require strategies such as targeted breeding programmes, biofortification, precision agriculture and improved sustainable agricultural practices to maintain nutrient density. This research provides critical evidence for policymakers and scientists to design sustainable food systems that safeguard public health in a changing climate.