Effect of applying nitrogen fertilizer on nitrogen metabolism and distribution in grapevine under magnetic treatment of water

The aim of this study was to investigate nitrogen (N) absorption and distribution, as well as nitrogen-use efficiency, of grape seedlings grown in magnetic and non-magnetic water treatments. One-year-old grape (Vitis vinifera×V. labrusca L. hybrid) seedlings were planted in pots and fertilized with exogenous ¹⁵N, and then grown under different magnetic water treatments or a control (untreated irrigated water). The proportional content of different forms of N, the activities of key enzymes relative to N metabolism, and the fate of N in leaves, stems, and roots of treated grape seedlings were analyzed. Under N application, we found that compared with the non-magnetic treatment (NMT), the magnetic treatment of water (MTW) appeared to promote N uptake and N-use efficiency in treated grape seedlings, while also optimizing the N allocation pattern and improving N assimilation ability of N fertilizer. We also identified that the total content of N in the leaves and roots (and in the plant generally) of treated seedlings were significantly increased when grown in the MTW. Conversely, the degree of contribution by N fertilizer (Ndff) to total N was not significantly different. Notably, the N utilization efficiencies of leaves and roots was significantly increased under MTW compared to that of the NMT treatment. The N allocation rate in leaves showed a marked increase under MTW, while that in stems showed a significant decrease. Additionally, it was found that the activities of glutamine syntheses and glutamic synthase increased significantly in the leaves, but decreased in the roots of treated seedlings. Finally, we identified that MTW increased the N-use efficiency and fixing capacity of plants and, additionally, alleviated the loss of N fertilizer in grape seedlings. Compared with treatments applying N fertilizer, the content of inorganic N and total N were promoted by 3.03%-3.45% in soil when exposed to MTW with N application. The utilization rate, residual rate, and recovery rate of seedlings increased by 36.39%-76.50% under MTW after the addition of ¹⁵N, and the loss rate of ¹⁵N decreased significantly (35.33% reduction). Based on our findings, it appears that the magnetic treatment of water can be effective in promoting N absorption and allocation in grape seedlings while also improving the plant fertilizer use efficiency from soil.