Assessing the growth dynamics of alfalfa varieties ( Medicago sativa cv. Bilensoy 80 and Nimet) response to varied carbon dioxide (CO 2 ) concentrations.

Rising atmospheric CO2 levels drive greenhouse effects, elevating temperatures, and diminishing water accessibility in semi-arid regions, affecting agriculture. Alfalfa contributes to climate change mitigation by sequestering carbon, enhancing soil fertility and carbon storage, reducing synthetic nitrogen fertilizer use, preventing soil erosion, supplying high-quality livestock feed, and serving as a bioenergy source. This research examined the effects of elevated CO2 levels in climate change scenarios (600, 800, and 1000 ppm, with control at 400 ppm) on two alfalfa varieties, Medicago sativa cv. Nimet and Bilensoy-80. The experiments were conducted in specialized Climate Change Simulation Greenhouses, allowing control of CO2 , water, and temperature variables. Results revealed a positive relationship between higher CO2 concentrations and increased photosynthesis ( P ≤ 0.001), promoting the plant growth leaf area ( P ≤ 0.001), yields and both leaf ( P ≤ 0.05) and stem dry biomass ( P ≤ 0.001). At 1000 ppm CO2 , a saturation point was reached, halting further photosynthesis. This down-regulation was linked to decreased intercellular CO2 levels, which expedited chlorophyll and breakdown and potentially induced leaf senescence. High CO2 levels led to greater biomass, as anticipated. However, total protein levels, a forage quality indicator, initially decreased with high CO2 concentrations (up to 1000 ppm) due to an inverse relationship with shoot yield. Surprisingly, the 1000 ppm CO2 concentration mitigated this protein reduction in both alfalfa varieties.