Metabolic and morpho-physiological responses of Salvia officinalis to superabsorbent polymer in combination with chemical and biological nitrogen nutrition

Sage ( Salvia officinalis L . ) contains valuable bioactive compounds, including polyphenols and terpenoids. This plant, which exhibits numerous medicinal properties, is utilized in the treatment of various diseases. In recent decades, the application of superabsorbent polymers (SAP) or hydrogels, along with optimal nutrition strategies, to enhance water availability for medicinal plants has garnered significant attention. This study was conducted between 2022 and 2023 using a randomized complete block design (RCBD) to investigate the effects of nitrogen, plant growth-promoting bacteria (PGPB), superabsorbent polymer, and their interactions on the morphological, physiological, and phytochemical parameters of sage. Nitrogen, applied as 46 % urea at a rate of 200 kg/ha, bacterial inoculation with Pantoea agglomerans , and superabsorbent polymer at 1500 kg/ha were utilized in the experiment. The results demonstrated positive effects of the superabsorbent polymer and bacterial treatment on the biological yield of sage. Moreover, bacterial inoculation significantly enhanced cell membrane stability, resulting in reduced electrolyte leakage. Photosynthetic activity was markedly improved following superabsorbent polymer application. Biochemical parameters, including phenolic compounds, flavonoids, and antioxidant capacity, were enhanced by the combined application of nitrogen and bacterial inoculation. Analysis revealed that nitrogen application increased thujone content while reducing 1,8-cineole and camphor levels. Conversely, superabsorbent polymer application elevated 1,8-cineole and camphor concentrations. Collectively, these results demonstrate that optimized water and nitrogen availability—the latter being the most extensively utilized nutritional element—enhanced both growth and biochemical parameters in sage. • Nitrogen and superabsorbent polymer co-application boosted sage growth and phytochemicals traits. • Co-application of nitrogen and superabsorbent polymer resulted in maximum sage biomass. • Nitrogen and superabsorbent polymer synergy maximized essential oil yield in Salvia officinalis . • Terpenoid chemical profiles varied under different treatments in sage.