Localized Phosphorus Application Promotes the Growth and Nutrient Content of Pitaya (Hylocereus polyrhizus) Seedlings by Improving Root Morphology

Localized phosphorus (P) application stimulates root proliferation in nutrient-rich zones, aligns root growth with soil P distribution, and enhances nutrient uptake efficiency. However, whether localized P supply benefits pitaya remains unclear. In this study, pitaya seedlings were used in a rhizobox experiment with four P treatments: no P (No-P), uniform P (Uniform-P1, 50 mg kg−1), localized P (Local-P1, 50 mg kg−1), and uniform high P (Uniform-P2, 200 mg kg−1). Phosphorus treatments significantly affected shoot growth. Localized P supply produced greater shoot biomass than both uniform and high uniform P. It also increased shoot nitrogen and potassium content but did not significantly affect P content. Localized P application strongly promoted root development. Compared with Uniform-P1, Local-P1 increased root biomass, total root length, root surface area, and root volume by 142.11%, 121.77%, 110.25%, and 100.19%, respectively. Moreover, total root length, root surface area, and root volume were positively correlated with nitrogen and potassium content as well as total biomass. These findings demonstrate that localized P supply improves root morphology, enhances nitrogen and potassium acquisition, and promotes shoot growth in pitaya.