Environmental changes, including climate change, land degradation, and biodiversity loss, pose significant challenges to global food security and nutrition. Atmospheric CO2 concentration has risen significantly since the Industrial Revolution, leading to increased global temperatures and changes in water availability. These shifts have impacted agricultural production, particularly cereal grains, which are crucial sources of carbohydrates, proteins, minerals, and vitamins. While elevated CO2 is generally beneficial for C3 plants like wheat, the combined effects of temperature increases and drought have limited the positive impact on crop yields. Existing studies often rely on controlled environments or field experiments with fixed CO2 levels, potentially failing to fully represent natural conditions. Analyzing historical samples offers a unique way to assess the long-term effects of past growing conditions on wheat quality. This study utilizes archived wheat grain samples spanning 166 years to evaluate the impact of long-term changes in atmospheric CO2, temperature, and rainfall on wheat grain quality traits, including carbohydrates, protein, and mineral concentrations, and their association with increased yield.

Previous research has demonstrated the effects of elevated CO2 on plant mineral content, protein concentration, and lipid composition. Studies using controlled environments (growth chambers) or field experiments (FACE, CGH, OTC) have shown that increased CO2 concentrations can lead to increased starch content, potentially diluting other nutrients. However, these methods may not accurately reflect natural conditions. Other studies have used archived material to analyze changes in plant mineral composition; however, such material often lacks detailed information about growing conditions and cultivars. This study addresses these limitations by analyzing a wide range of samples collected over 166 years, incorporating data from the Broadbalk Continuous Wheat Experiment alongside global samples.

Bread and durum wheat grains were collected from archives in 16 countries (1850-2016). Samples from the Broadbalk Wheat experiment (UK) and herbarium specimens were included. Grain yield data were available for Broadbalk (1850-2016), along with thousand kernel weights (TKW) from 1974-2016. Global atmospheric CO2 values and temperature data were obtained from the European Environment Agency and Intergovernmental Panel on Climate Change, respectively. Average temperature and precipitation data for Rothamsted were provided by the Department of Computational and Analytical Sciences. Grain quality parameters analyzed included carbon isotope discrimination (Δ¹³C), starch and soluble sugar concentrations (glucose, fructose, sucrose), protein content, and mineral composition (C, N, Cu, Zn, Fe, Mn, K, P, Mg, Ca, Na). Statistical analyses included ANOVA to assess the year effect, multiple-range tests (Fisher's LSD), Pearson correlation analyses, and multifactor ANOVA. Data analysis evaluated the trend of grain quality parameters over 166 years by calculating the average per year, without considering the genotype effect.

Analysis of global samples revealed a significant decrease in protein content (23%) and an increase in the C/N ratio (20%) between the periods 1850-1955 and 1965-2016. Starch content showed a non-significant increase (7%). Glucose concentration significantly increased, while other soluble sugars showed no significant change. Mineral concentrations generally decreased with increasing CO2, notably for Mn, Fe, Zn, and Mg. In the Broadbalk experiment, grain yield increased significantly after 1960, while TKW decreased. Carbon isotope discrimination (Δ¹³C) decreased significantly, indicating stress conditions. Starch content increased significantly, while protein content decreased by 26%. Mineral concentrations also decreased, with CO2 having the most significant negative effect. Positive correlations were found between grain yield and CO2, temperature, and precipitation at Rothamsted. Significant negative correlations were observed between protein content and CO2, and between Δ¹³C and CO2 in the Broadbalk experiment.

The findings confirm that wheat grain quality and yield have been impacted by rising atmospheric CO2 and temperature. The increase in CO2 and temperature, along with the introduction of dwarfing genotypes, increased harvest index and wheat yield. The decrease in carbon isotope discrimination at Rothamsted suggests stomatal closure due to stress conditions. Increased carbohydrate concentrations are consistent with findings from controlled environments and FACE experiments. The decreased protein and mineral concentrations are also supported by previous research and may be attributed to dilution effects from increased carbohydrates, reduced transpiration-driven mass flow of nitrogen, changes in crop breeding strategies, and limitations to N assimilation. The more pronounced decreases in mineral concentrations at Rothamsted may be linked to high yield increases and lower Δ¹³C values. Altered nutrient uptake and remobilization, along with lower stomatal opening and decreased transpiration, could also contribute to these changes.

This study demonstrates a global trend of altered wheat grain quality, characterized by increased carbohydrates and decreased protein and mineral content over the past 166 years. This trend is particularly noticeable since the 1960s and is associated with higher-yielding, short-strawed varieties, rising CO2, and increased temperatures. Breeding strategies should focus on developing new genotypes with enhanced resource use efficiency and high nutritional value.

The study's analysis did not account for genotypic variability in the global samples, potentially impacting the interpretation of temporal trends. The use of archived samples presents limitations concerning the precise recording of environmental conditions and cultivar information. The study primarily focuses on the impacts of CO2 and temperature and acknowledges that other factors might have also contributed to the observed changes.