Increased periods of water shortage and higher temperatures, together with a reduction in nutrient availability, have been proposed as major factors that negatively impact plant development. Photosynthetic CO₂ assimilation is the basis of crop production for animal and human food, and for this reason, it has been selected as a primary target for crop phenotyping/breeding studies. Within this context, knowledge of the mechanisms involved in the response and acclimation of photosynthetic CO₂ assimilation to multiple changing environmental conditions (including nutrients, water availability, and rising temperature) is a matter of great concern for the understanding of plant behavior under stress conditions, and for the development of new strategies and tools for enhancing plant growth in the future. The current review aims to analyze, from a multi-perspective approach (ranging across breeding, gas exchange, genomics, etc.) the impact of changing environmental conditions on the performance of the photosynthetic apparatus and, consequently, plant growth.

Cereal yield and grain quality may be impaired by environmental factors associated with climate change. Major factors, including elevated CO₂ concentration ([CO₂]), elevated temperature, and drought stress, have been identified as affecting C₃ crop production and quality. A meta-analysis of existing literature was performed to study the impact of these three environmental factors on the yield and nutritional traits of C₃ cereals. Elevated [CO₂] stimulates grain production (through larger grain numbers) and starch accumulation but negatively affects nutritional traits such as protein and mineral content. In contrast to [CO₂], increased temperature and drought cause significant grain yield loss, with stronger effects observed from the latter. Elevated temperature decreases grain yield by decreasing the thousand grain weight (TGW). Nutritional quality is also negatively influenced by the changing climate, which will impact human health. Similar to drought, heat stress decreases starch content but increases grain protein and mineral concentrations. Despite the positive effect of elevated [CO₂], increases to grain yield seem to be counterbalanced by heat and drought stress. Regarding grain nutritional value and within the three environmental factors, the increase in [CO₂] is possibly the more detrimental to face because it will affect cereal quality independently of the region.

The availability and management of N are major determinants of crop productivity, but N excessive use has an associated agro-ecosystems environmental impact. The aim of this work was to investigate the influence of N fertilization on yield and grain quality of 6 durum wheat genotypes, selected from 20 genotypes as high- and low-yielding genotypes. Two N levels were applied from anthesis to maturity: high (½ Hoagland nutrient solution) and low (modified ½ Hoagland with one-third of N). Together with the agronomic characterization, grain quality analyses were assessed to characterize carbohydrates concentration, mineral composition, glutenin and gliadin concentrations, polyphenol profile, and anti-radical activity. Nitrogen supply improved wheat grain yield with no effect on thousand-grain weight. Grain soluble sugars and gluten fractions were increased, but starch concentration was reduced, under high N. Mineral composition and polyphenol concentrations were also improved by N application. High-yielding genotypes had higher grain carbohydrates concentrations, while higher concentrations in grain minerals, gluten fractions, and polyphenols were recorded in the low-yielding ones. Decreasing the amount of N to one-third ensured a better N use efficiency but reduced durum wheat agronomic and quality traits.

Grain development in cereals depends on synthesis and remobilisation compounds such as water-soluble carbohydrates (WSCs), amino acids (AAs), minerals and environmental conditions during pre- and post-anthesis. This study analyses the impact of water stress on metabolite (WSCs, AAs and nitrogen) dynamics between the source (leaves and stems) and sink (grain) organs in triticale, bread wheat, durum wheat and barley. Plants were grown in glasshouse conditions under well-watered (WW) and water-limited (WL) regimes (from flag leaf fully expanded until maturity). The results showed that the stem WSC content and the apparent mobilisation of WSC to the grain were much higher in triticale and were associated with its larger grain size and grain number. In the four cereals, grain weight and the number of kernels per spike were positively associated with stem WSC mobilisation. After anthesis, the AA concentration in leaves was much lower than in the grain. In grain, the main AAs in terms of concentration were Asn, Pro and Gln in triticale, bread, and durum wheat, and Asn, Pro and Val in barley. The water-limited regime reduced grain weight per plant in the four cereal species, but it had no clear effects on WSC content and AAs in leaves and grain. In general, triticale was less affected by WL than the other cereals.

In a context of the expanding world population and global climate change, food security is becoming a challenge for worldwide society. To meet the increasing global agricultural demands, crop yields enhancement has been attempted since the green revolution and cereals production, in particular wheat, has increased since then by releasing high yielding new cultivars. However, improvement in crop yields has slowed since the 1990s and the recent gains in global crop production fall short of the expected demands mainly due to global warming. At a global scale, the relatively decrease in wheat production is principally because of the adverse effects of abiotic stresses that are increasing in intensity and frequency under climate change scenario. Low water availability and extreme temperatures will negatively affect the growth and productivity of major crop species including durum wheat. In the Mediterranean area, the process of grain filling is coinciding with dry and hot environmental conditions affecting final yield quantitatively and qualitatively as well. Moreover, studies conducted recently remarked that grain mineral composition is shifted and total protein content in grains is reduced when durum wheat grows in the presence of high CO2 concentration ([CO2]). It is clear that commercialised wheat genotypes are becoming more vulnerable to global climate change which is affecting not only grain yield but also quality. Thus, the understanding of physiological mechanisms that enable plants to adapt to drought stress and increasing atmospheric [CO2] could help in screening and selection of genotypes with suitable grain yield and quality, and using these traits in breeding programs. On the other hand, the increase in nitrogen fertilizers application in wheat crops is consequently stimulating plant growth and increasing grain yield, nitrogen and protein concentration in kernels ensuring, thereby, good bread/pasta making quality and mitigating the negative effect of changing climate on grain production. Nevertheless, the excessive nitrogen supply can lead to environment pollution and may probably accentuate climate warming by increasing nitrous oxide (N2O) emission. For this reason, optimizing nitrogen use efficiency (NUE) is a tool to increase crop yields while preserving the environment. Within this context, the main objective of this work is the use of new wheat selection criteria to identify, in an integrative manner, genotypes and crop management practices conferring high nitrogen use efficiency to reach higher yield and better grain quality under increasing [CO2] and low water availability. For this purpose, in the first chapter (I), a meta-analysis study was carried out to provide an overview of the effects and interactions of multiple climate factors, specifically high [CO2], drought, and elevated temperature on the productivity and grain quality of C3 cereals. Findings presented in this chapter showed that despite of the positive effect of elevate [CO2] on grain yield, this trait seems to be mitigated by heat and drought stress. Grain quality was also impacted by changing climate, characterized by an increase in carbohydrates and decrease in protein and minerals. In the second chapter (II), we assessed the grain quality trait of wheat archived samples since 1850 collected from many countries to evaluate the nutritional quality changes in grain under changing climate. This study confirmed the results foundin the previous chapter and showed an imbalance in carbohydrate/protein content marked after the 60s, adding to an impoverishment in minerals. Yield results from Broadbalk wheat experiment in Rothamsted (UK) showed an improvement of wheat yield since the green revolution attributed mainly to the introducing of semi-dwarf high yielding genotypes. In chapter (III), to investigate the impact of nitrogen fertilization on yield and grain quality, an experiment was performed where 20 durum wheat genotypes were fertilized since anthesis with two N fertilization levels under greenhouse conditions. Within these genotypes, only 6 lines were selected with high and low nitrogen use efficiency to characterize agronomic and quality traits. As expected, nitrogen supply increased grain yield while no effect was detected in thousand-grain weight. Grain soluble sugars, gluten fractions, mineral composition, and polyphenol concentrations were also improved by N application. The comparison among genotypes revealed that high yielding genotypes had higher grain carbohydrate concentrations while higher concentrations in grain minerals, gluten fractions, and polyphenols were recorded in low yielding cultivars. Finally, in chapter (IV), 4 durum wheat genotypes and 6 tritordeum lines with higher and lower NUE were exposed to high [CO2] and drought stress in greenhouses, in order to characterize post-anthesis nutrient remobilization from leaves and ears sustaining grain filling, together with agronomic characterization under such conditions. It seems that the increase of atmospheric [CO2] could attenuate the negative effect of drought on grain yield. Carbon and nitrogen metabolism in leaves and ears were altered under high CO2 enrichment and larger effect was observed when it was combined with drought, and the relative contribution of each organ to grain filling was strongly affected by growing conditions.