Optimizing CO2 - irrigation - nitrogen synergies to ensure short-haired melon growth while improving economic and resource efficiency

CO 2 - Irrigation - Nitrogen synergy is expected to address the imbalance between economic and resource efficiency in arid regions. In this study, we combined principal component analysis and structural equation modeling (SEM) with three consecutive field trials to investigate the key regulatory pathways of yield formation of short-haired melons under CO 2 -Irrigation -Nitrogen synergistic treatments in spring and fall. The optimal treatments were determined by using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) integrated evaluation model and trade-off analysis of economic benefits and resource efficiency. SEM revealed distinct seasonal regulatory pathways: in spring, the photosynthetic rate (Pn) at stretching period (PS) affected the dry matter (DM) accumulation at maturity period (PM) through promoting whole plant leaf area at the blossoming and fruiting period (PBF), thus affecting yield. In contrast, during fall, main stem length (MSL) at PS controlled the MSL and leaf numbers at PBF to further increase DM at PM and impact yield. Based on the TOPSIS model incorporating 11 spring and 9 fall indicators, along with trade-offs among economic efficiency, water use efficiency, and nitrogen fertilizer use efficiency, the T9 (C2 I2 N1) treatment effectively promoted short-haired melon growth while addressing the imbalance between economic and resource efficiency. This study provides a solid theoretical basis for achieving high yield and high efficiency in short-haired melon cultivation. • Enriched CO 2 boosts stem length, leaf area, carboxylation efficiency, and yield under low water and nitrogen. • Spring yields hinge on photosynthesis, while fall yields pivot on morphological growth. • C2 I2 N1 (T9) maximized profit, WUE and NUE in arid melon cultivation. • CO₂-Irrigation-Nitrogen synergy bridges economic/resource gaps under future climate.