● This study identified four key aroma components in ‘Tianhong No 2′ apples. ● Nitrogen reduction (20%) and bio-organic fertilizer enhanced aroma synthesis. ● This study revealed how soil factors hierarchically regulate aroma synthesis. ● This study built a soil-based model to quantitatively predict apple flavor quality. To elucidate the regulatory mechanisms of pre-harvest root-zone management on post‑harvest aroma quality in apples, this study used ‘Tianhong No 2′ apples as experimental material. A field experiment was conducted with treatments including conventional nitrogen application (T1) and nitrogen reduction by 20% (T2), 40% (T3), and 60% (T4) combined with humic acid and Bacillus subtilis , aiming to compare the effects of different treatments on soil nutrients, enzyme activities, and volatile compounds in apple fruit. The results showed that nitrogen reduction combined with bio‑organic fertilizer significantly improved the root‑zone soil environment, increasing soil organic matter, available phosphorus, and available potassium in the 0–20 cm layer by 73.80%, 69.76%, and 60.51%, respectively. A total of 62 volatile compounds were identified in the fruit, among which hexyl butanoate, hexyl hexanoate, hexyl 2‑methylbutanoate, and α‑farnesene were identified as key aroma components. Redundancy analysis further revealed that aroma synthesis was regulated by soil depth: available nutrients played a direct driving role in the surface layer, while organic matter and enzyme activity exerted indirect effects in deeper layers. A predictive model constructed based on core soil factors screened by variable importance in projection demonstrated excellent predictive capability for hexyl 2‑methylbutanoate (R 2 = 0.91). This study indicates that 20% nitrogen reduction combined with bio‑organic fertilizer can promote the synthesis of key aroma substances by synergistically optimizing the root‑zone microenvironment. The established model provides a novel approach for the targeted regulation of apple flavor quality and offers important guidance for green orchard production.
Yao et al. (Sun,) studied this question.