A Comparative Study of Conventional and Nano-NPK on the Growth, Flowering, Bioactive Compounds, and Anatomical Characters of Solidago virgaurea

Nano fertilization helps improve the efficiency of nutrient absorption, thus reducing the harmful effects of overuse of chemical fertilizers and reducing toxicity to plants and soil. Solidago virgaurea, a perennial herb, is widely used as an attractive addition to floral arrangements and as a source of valuable compounds. A pot experiment was carried out using a randomized complete block design to investigate the effect of nitrogen, phosphorus, and potassium (NPK) fertilizers on the growth, flowering, bioactive metabolites, and anatomical attributes of S. virgaurea. Two sources of NPK, conventional NPK (conv-NPK) and nanoparticle NPK (nano-NPK), were sprayed at three levels (conv-NPK; 1, 1.5, and 2 g/l, nano-NPK; 1, 1.5, and 2 ml/l). The highest significant values for growth parameters (plant height, leaf number, branch number, plant biomass), flowering metrics (flowering start, flower length, full flowering duration, fresh and dry flower weights), photosynthetic pigments (chlorophyll and carotenoids), nutrient (N, P, and K), and carbohydrates contents were attained by the highest level of nano-NPK. Subsequently, the moderate level of nano-NPK followed suit in performance. Furthermore, a moderate level of nano-NPK demonstrated significant superiority or equivalence to a high level of conv-NPK in enhancing various parameters, with the exception of total flavonoid content and total antioxidant capacity. Increasing NPK levels generally increased the accumulation of total phenolics, flavonoids, and antioxidant capacity, with the moderate and highest levels showing the most pronounced effects. Different concentrations of conv-NPK and nano-NPK impacted tissue thickness, vessel dimensions, and midrib zone thickness distinctly. Nano-NPK consistently outperformed conv-NPK in enhancing palisade and spongy tissue thickness, while both fertilizers showed similar improvements in xylem vessel dimensions. Utilizing nano-NPK at moderate to high levels could optimize growth, flowering, and bioactive constituents content in S. virgaurea. These findings suggest that nano-fertilizers can be a promising strategy for sustainable agriculture, improving the productivity and quality of high-value plants like S. virgaurea while minimizing environmental impact by reducing fertilizer application rates.