Date of Defense
9-4-2026 2:00 PM
Location
Microsoft Teams
Document Type
Dissertation Defense
Degree Name
Doctor of Philosophy (PhD)
College
College of Agriculture and Veterinary Medicine
Department
Integrative Agriculture
First Advisor
Mohammed A. Alyafei
Keywords
Climate change; Barley (Hordeum vulgare), elevated CO₂, UV-B radiation, elevated temperature; antioxidants responses, treated wastewater, green fodder
Abstract
Climate change presents a complex risk to crop productivity, with elevated temperatures, rising CO2 and UV-B enhancement profoundly impacting growth. Although the effects of individual stressors are well-documented, limited information is available regarding the combined effects of variables such as elevated CO₂ (eCO2), UV-B radiation, and elevated temperature (eT). This knowledge gap is especially critical for major cereal crops such as barley (Hordeum vulgare L.), which ranks fourth in global production and serves as a valuable source of forage for livestock. However, traditional forage production is unsustainable in arid regions, where water shortage and extreme weather conditions are present, as most forage crops require large amounts of freshwater. Under climate change conditions, the shortage of forages, particularly during the dry season, is a significant factor that contributes to low animal productivity. Integrating innovative techniques, such as utilizing nonconventional water resources such as treated wastewater (TWW), are necessary to achieve adequate animal feeds in arid regions. Therefore, the objective of this study was to study to study the effect of climate change factors on the productivity of three different barley genotypes, namely "CM 72, 60 1A, and 58 1A" and the potential to improve production by municipal treated wastewater utilization, to achieve these objectives, three experiments were conducted. In the first experiment, eCO₂ significantly increased plant growth parameters, such as fertile tillers, spike number, grain weight, flag leaf area, and chlorophyll concentration, indicating higher photosynthetic efficiency and biomass accumulation. However, these advantages were markedly reduced under simultaneous stress conditions (eCO₂ + UV-B + eT). The genotype 60 1A showed the strongest resilience in tiller and spike formation under elevated CO₂, whereas 58 1A achieved the highest grain weight. Combined stresses markedly increased oxidative stress, as indicated by heightened malondialdehyde (MDA) concentrations, and modified cell wall composition, evidenced by increased neutral detergent fiber (NDF) and acid detergent fiber (ADF) levels. Plants subjected to stress initiated strong antioxidant defenses, characterized by high levels of glutathione-S-transferase (GST), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), thioredoxin-dependent glutathione reductase (Tgsh), and glutathione peroxidase (GPX). Polyphenols reached their maximum under UV-B, but flavonoid concentration was highest under elevated CO₂. Crude protein levels decreased markedly under combined stress. Overall, the results show that while eCO₂ promotes growth and photosynthesis, concurrent exposure to UV-B radiation and high temperatures can diminish these advantages, cause oxidative damage, and modify fodder quality, highlighting the complexity of plant responses in future climate conditions. In the second experiment, TWW applications substantially improved biological yield, grain yield, straw yield, number of spikes, and 1000 grain weight compared to potable water application (PW). The genotype "58 1A" steadily showed the highest grain yield, 1000 grain weight and harvest index, while genotype "60 1A" gave the highest biological yield, straw yield and tillers. Under 100%TWW irrigation, the genotype 58 1A exhibited the highest grain yield when irrigated with 100% TWW, producing 4.51- and 5.16-ton ha-1in 2022 and 2023, respectively. This corresponds to a 40.64% - 44.20% increase compared with the control treatment. Furthermore, TWW application enhanced photosynthetic pigments, crude proteins, fiber content, and nutrients. However, the heavy metals concentrations remained within the acceptable limits for forage crops. In the third experiment, the study indicated that TWW irrigation treatment had a positive effect, significantly enhancing the quantity and quality of green fodder compared to other treatments. Irrigation with TWW improved plant height, fresh weight, dry weight, and nutrient content compared with irrigation with PW. Furthermore, TWW irrigation enhanced the levels of photosynthetic pigments, crude proteins, and fiber. Overall, the use of TWW enhances barley performance, and nutritional value while maintaining heavy metal concentrations within safe limits.
Included in
Study the Effect of Climate Change on Barley Crop (Hordeum Vulgare L.) and Improving Its Productivity Through Municipal Treated Wastewater Utilization
Microsoft Teams
Climate change presents a complex risk to crop productivity, with elevated temperatures, rising CO2 and UV-B enhancement profoundly impacting growth. Although the effects of individual stressors are well-documented, limited information is available regarding the combined effects of variables such as elevated CO₂ (eCO2), UV-B radiation, and elevated temperature (eT). This knowledge gap is especially critical for major cereal crops such as barley (Hordeum vulgare L.), which ranks fourth in global production and serves as a valuable source of forage for livestock. However, traditional forage production is unsustainable in arid regions, where water shortage and extreme weather conditions are present, as most forage crops require large amounts of freshwater. Under climate change conditions, the shortage of forages, particularly during the dry season, is a significant factor that contributes to low animal productivity. Integrating innovative techniques, such as utilizing nonconventional water resources such as treated wastewater (TWW), are necessary to achieve adequate animal feeds in arid regions. Therefore, the objective of this study was to study to study the effect of climate change factors on the productivity of three different barley genotypes, namely "CM 72, 60 1A, and 58 1A" and the potential to improve production by municipal treated wastewater utilization, to achieve these objectives, three experiments were conducted. In the first experiment, eCO₂ significantly increased plant growth parameters, such as fertile tillers, spike number, grain weight, flag leaf area, and chlorophyll concentration, indicating higher photosynthetic efficiency and biomass accumulation. However, these advantages were markedly reduced under simultaneous stress conditions (eCO₂ + UV-B + eT). The genotype 60 1A showed the strongest resilience in tiller and spike formation under elevated CO₂, whereas 58 1A achieved the highest grain weight. Combined stresses markedly increased oxidative stress, as indicated by heightened malondialdehyde (MDA) concentrations, and modified cell wall composition, evidenced by increased neutral detergent fiber (NDF) and acid detergent fiber (ADF) levels. Plants subjected to stress initiated strong antioxidant defenses, characterized by high levels of glutathione-S-transferase (GST), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), thioredoxin-dependent glutathione reductase (Tgsh), and glutathione peroxidase (GPX). Polyphenols reached their maximum under UV-B, but flavonoid concentration was highest under elevated CO₂. Crude protein levels decreased markedly under combined stress. Overall, the results show that while eCO₂ promotes growth and photosynthesis, concurrent exposure to UV-B radiation and high temperatures can diminish these advantages, cause oxidative damage, and modify fodder quality, highlighting the complexity of plant responses in future climate conditions. In the second experiment, TWW applications substantially improved biological yield, grain yield, straw yield, number of spikes, and 1000 grain weight compared to potable water application (PW). The genotype "58 1A" steadily showed the highest grain yield, 1000 grain weight and harvest index, while genotype "60 1A" gave the highest biological yield, straw yield and tillers. Under 100%TWW irrigation, the genotype 58 1A exhibited the highest grain yield when irrigated with 100% TWW, producing 4.51- and 5.16-ton ha-1in 2022 and 2023, respectively. This corresponds to a 40.64% - 44.20% increase compared with the control treatment. Furthermore, TWW application enhanced photosynthetic pigments, crude proteins, fiber content, and nutrients. However, the heavy metals concentrations remained within the acceptable limits for forage crops. In the third experiment, the study indicated that TWW irrigation treatment had a positive effect, significantly enhancing the quantity and quality of green fodder compared to other treatments. Irrigation with TWW improved plant height, fresh weight, dry weight, and nutrient content compared with irrigation with PW. Furthermore, TWW irrigation enhanced the levels of photosynthetic pigments, crude proteins, and fiber. Overall, the use of TWW enhances barley performance, and nutritional value while maintaining heavy metal concentrations within safe limits.