Elevated CO2 has concurrent effects on leaf and grain metabolism but minimal effects on yield in wheat.

While the general effect of CO2 enrichment on photosynthesis, stomatal conductance, N content, and yield has been documented, there is still some uncertainty as to whether there are interactive effects between CO2 enrichment and other factors, such as temperature, geographical location, water availability, and cultivar. In addition, the metabolic coordination between leaves and grains, which is crucial for crop responsiveness to elevated CO2, has never been examined closely. Here, we address these two aspects by multi-level analyses of data from several free-air CO2 enrichment experiments conducted in five different countries. There was little effect of elevated CO2 on yield (except in the USA), likely due to photosynthetic capacity acclimation, as reflected by protein profiles. In addition, there was a significant decrease in leaf amino acids (threonine) and macroelements (e.g. K) at elevated CO2, while other elements, such as Mg or S, increased. Despite the non-significant effect of CO2 enrichment on yield, grains appeared to be significantly depleted in N (as expected), but also in threonine, the S-containing amino acid methionine, and Mg. Overall, our results suggest a strong detrimental effect of CO2 enrichment on nutrient availability and remobilization from leaves to grains.

Differential effects of elevated CO2 on awn and glume metabolism in durum wheat (Triticum durum).

While the effect of CO2 enrichment on wheat (Triticum spp.) photosynthesis, nitrogen content or yield has been well-studied, the impact of elevated CO2 on metabolic pathways in organs other than leaves is poorly documented. In particular, glumes and awns, which may refix CO2 respired by developing grains and be naturally exposed to higher-than-ambient CO2 mole fraction, could show specific responses to elevated CO2 . Here, we took advantage of a free-air CO2 enrichment experiment and performed multilevel analyses, including metabolomics, ionomics, proteomics, major hormones and isotopes in Triticum durum . While in leaves, elevated CO2 tended to accelerate amino acid metabolism with many significantly affected metabolites, the effect on glumes and awns metabolites was modest. There was a lower content in compounds of the polyamine pathway (along with uracile and allantoin) under elevated CO2 , suggesting a change in secondary N metabolism. Also, cytokinin metabolism appeared to be significantly affected under elevated CO2 . Despite this, elevated CO2 did not affect the final composition of awn and glume organic matter, with the same content in carbon, nitrogen and other elements. We conclude that elevated CO2 mostly impacts on leaf metabolism but has little effect in awns and glumes, including their composition at maturity.

Climate Change, Crop Yields, and Grain Quality of C3 Cereals: A Meta-Analysis of [CO2], Temperature, and Drought Effects.

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.

Photosynthetic Metabolism under Stressful Growth Conditions as a Bases for Crop Breeding and Yield Improvement.

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.

Metabolic Effects of Elevated CO2 on Wheat Grain Development and Composition.

The increase in the atmospheric CO2 concentration is predicted to influence wheat production and grain quality and nutritional properties. In the present study, durum wheat (Triticum durum Desf. cv. Sula) was grown under two different CO2 (400 versus 700 µmol mol-1) concentrations to examine effects on the crop yield and grain quality at different phenological stages (from grain filling to maturity). Exposure to elevated CO2 significantly increased aboveground biomass and grain yield components. Growth at elevated CO2 diminished the elemental N content as well as protein and free amino acids, with a typical decrease in glutamine, which is the most represented amino acid in grain proteins. Such a general decrease in nitrogenous compounds was associated with altered kinetics of protein accumulation, N remobilization, and N partitioning. Our results highlight important modifications of grain metabolism that have implications for its nutritional quality.