Effects of Combined Application of Phosphorus and Zinc on Root Configuration, Rhizosphere Soil Nutrients, and Environment of Apple Rootstock M9-T337 Seedlings

Abstract

This study aimed to investigate the impacts of the combined application of phosphorus (P) and zinc (Zn) on the root development and the rhizosphere soil environment of apple trees. A pot experiment was implemented with nine treatments, encompassing three P levels (0, 100, 200 mg kg⁻¹) and three Zn levels (0, 15, 30 mg kg⁻¹). The research focused on the effects of the combined application of P and Zn on root morphology, rhizosphere soil nutrients, soil enzyme activities, and the soil environment of M9-T337 apple rootstock seedlings. This was done to provide a scientific basis for the optimal application of P and Zn fertilizers in apple orchards. The results indicated that parameters such as the average root diameter, soil phosphatase activity, fractal dimension, total root length, total root volume, total root surface area, soil bacteria count, and catalase activity all increased first and then decreased as the zinc application rate increased. The highest values were observed in the P₂₀₀Zn₁₅ treatment. The number of root tips, total number of internal connections, root topological index, soil available Zn, available P, urease activity, actinomycetes count, fungi counts, and sucrase activity exhibited different trends with increasing Zn dosage, but the parameter values for each index were significantly higher than those of the control treatment. The synergistic application of P and Zn has notably influenced the root morphology and the rhizosphere soil environment of M9-T337 apple rootstock seedlings. The optimal effect was observed under the P₂₀₀Zn₁₅ treatment, demonstrating a synergistic interaction between P and Zn, thereby promoting root development and soil health. This improvement was manifested in the increased root diameter, enhanced soil phosphatase activity, expanded root length and volume, augmented root surface area, and heightened soil bacterial count and catalase activity. Moreover, the levels of available Zn, available P, and urease activity in the soil were elevated. Concurrently, the diversity of soil microbiota was also improved. These findings lay a solid foundation for maximizing the utility of P and Zn fertilizers in apple orchards, thus, aiding in the realization of sustainable agricultural practices and boosting apple production.