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

Elevated atmospheric CO₂ (ECO₂) 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 ECO₂ (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. ECO₂ significantly increased total biomass (17–71 %) and net photosynthetic rate (8–30 %), with optimal growth observed at 100 % fertilization (F2). While ECO₂ 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, ECO₂ 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 ECO₂ decreased soil nitrate (-24 %), available P (-22 %), and K (-16 %), but these effects were mitigated by fertilization. Crucially, a 25 % reduction in fertilization under ECO₂ maintained mulberry biomass and N, P, and K accumulation, whereas a 25 % increase provided no additional benefits. These findings demonstrate that mulberry adapts to ECO₂ 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-CO₂ climates, supporting resource-efficient and climate-resilient horticultural systems.