Effect of Microbial Biostimulants and Growing System on the Morphological, Nutritional, and Phytochemical Profile of Sonchus oleraceus Plants

The application of biostimulants is a promising tool for enhancing plant growth and crop quality in the context of sustainable and resilient agricultural production. This study evaluated four microbial biostimulants (IMB1–4) on Sonchus oleraceus L. under field and pot cultivation. Our results indicate that the growing system was a more dominant factor than biostimulants in influencing plant performance. For morphological and growth traits, biostimulants generally had a neutral or negative impact compared with untreated plants, with IMB3 consistently showing the lowest performance. Field-grown plants, especially the untreated ones, excelled in plant weight and leaf count, while pot-grown plants treated with IMB2 and IMB4 achieved higher leaf weight per plant, leaf area, and chlorophyll index (SPAD). Specifically, untreated field plants recorded the highest biomass, whereas IMB2 and IMB4 optimized leaf traits in pots. Biostimulant applications enhanced fat content and energetic value, with IMB1 and IMB2 yielding the highest protein levels. Pot cultivation favored the accumulation of nitrogen, phosphorus, and sodium, while IMB2-treated pot plants proved most effective for maximizing overall nutrient content. The phytochemical profile also varied by system: pot-grown plants yielded higher total phenols, particularly with IMB3, while field-grown plants recorded higher flavonoids, especially with IMB4. Furthermore, untreated or IMB3-treated pot plants exhibited the highest antioxidant activity, significantly outperforming field-grown counterparts. In conclusion, while biostimulants did not improve morphological and growth traits, they significantly enhanced the nutritional and phytochemical quality of S. oleraceus L., particularly in the pot cultivation system, where specific biostimulants (IMB2 and IMB3) resulted in nutrient-dense crops with high antioxidant value.