Exploring the effects of CO2 elevation on seedlings' growth of Acacia senegal in the era of changes

Acacia senegal is a priority and important C3 tree species in drylands of Sudan and across the gum belt. Investigation of its seedlings response to elevated carbon dioxide (eCO2) is important as atmospheric ([CO2]) has increased and predicted to continue to rise. Many studies showed that eCO2 causes increased photosynthesis in plants, which leads to greater production of carbohydrates and biomass, and increased soil organic matter and carbon content. This study investigated the effects of eCO2 on A. senegal seedlings grown in sand and silt soils under irrigation intervals of every day and every two days. Seven days old seedlings were assigned to the treatments in Split - spilt plot design for 4 weeks. The main plot is eCO2 (600-800 ppm) and ambient ([≤]400 ppm) under Free Air CO2 Enrichment (FACE) system. Subplots are irrigation intervals and soil types. Seedling height and number of leaves were measured weekly, and seedlings were harvested after 4 weeks where growth parameters and soil properties were measured. The eCO2 showed no effect on the measured parameters except the significant increase in tap-root length. However, the irrigation every day showed significant increase than every two days in seedlings height, number of leaves, root length and seedlings dry weight but not seedlings and soil C% & N%. Soil treatment showed effects on stem height, leaf number, seedlings dry weight, leaves and root N% and soil C% but not root length, seedling C% and soil N%. The results indicate the importance of soil moisture, physical and chemical properties that reflects adaptation of the species to its dry land environment.