Elevated CO2 and fertilization enhance nutrient use efficiency and carbon allocation in mulberry: A pathway for sustainable horticulture

• ECO₂ boosts mulberry biomass (17–71 %) and photosynthesis (8–30 %), peaking at 100 % fertilizer. • ECO₂ enhances N, P, K use efficiency, enabling 25 % less fertilizer for similar biomass. • ECO₂ reduces leaf N (−15 %), P (−10 %), K (−12 %) but raises root carbohydrates by 30 %. • ECO₂ supports sustainable mulberry cultivation with reduced fertilizer inputs under high-CO₂. Elevated atmospheric CO 2 (ECO 2 ) and fertilization are critical drivers of plant growth and nutrient dynamics, yet their combined effects on nutrient use efficiency (NUE) and carbon allocation in horticultural crops like mulberry ( Morus alba L.) remain underexplored. This study examined how ECO 2 (720/770 ppm vs. ambient 420/470 ppm, daytime/nighttime) and four fertilization levels (0 %, 75 %, 100 %, and 125 % of conventional dose) influence NUE and carbon partitioning in mulberry seedlings, with a focus on nitrogen (N), phosphorus (P), and potassium (K) dynamics. ECO 2 significantly increased total biomass (17–71 %) and net photosynthetic rate (8–30 %), with optimal growth observed at 100 % fertilization (F2). While ECO 2 enhanced root non-structural carbohydrates by 30 %, it reduced leaf N (-15 %), P (-10 %), and K (-12 %) concentrations due to biomass dilution and reduced transpiration. Notably, ECO 2 significantly improved N, P, and K use efficiency, particularly under reduced fertilization (F1), achieving comparable biomass production with 25 % less fertilizer input. Soil analysis revealed that ECO 2 decreased soil nitrate (-24 %), available P (-22 %), and K (-16 %), but these effects were mitigated by fertilization. Crucially, a 25 % reduction in fertilization under ECO 2 maintained mulberry biomass and N, P, and K accumulation, whereas a 25 % increase provided no additional benefits. These findings demonstrate that mulberry adapts to ECO 2 through optimized nutrient allocation and enhanced NUE, enabling sustainable cultivation with reduced fertilizer inputs. This study provides a practical framework for mulberry production in future high-CO 2 climates, supporting resource-efficient and climate-resilient horticultural systems.