Amino acid based biostimulants mitigate salinity-induced yield loss and modulate phytochemical composition in hydroponic flat leaf parsley (Petroselinum crispum var. neapolitanum)

Background Soil salinization is a major constraint in horticulture, reducing yield and resource-use efficiency in high-value crops. While salinity generally inhibits plant growth, it can enhance the accumulation of bioactive compounds in medicinal and aromatic species. This study aimed to evaluate the effects of salinity and amino acid–based biostimulants on yield and phytochemical composition of hydroponically grown flat-leaf parsley ( Petroselinum crispum var. neapolitanum ). We hypothesized that salinity would reduce biomass while increasing phenolic and volatile compounds, and that biostimulants would mitigate yield loss under stress. Results Salinity (40 mM NaCl) reduced yield nearly fivefold compared to control plants. Biostimulant application partially alleviated this effect, increasing yield by 73.3 and 54.6% relative to untreated salt-stressed plants. Salinity increased total phenolic content, particularly hydroxycinnamic acids and flavones (e.g., apigenin-6,8-di-C-glucoside), while decreasing chrysoeriol pentose-hexose. Volatile compounds, mainly monoterpenes, also increased under salinity, with higher levels of p -1,3,8-menthatriene and α -phellandrene. Biostimulants moderated these changes while supporting biomass recovery. Conclusions Salinity reduced yield but enhanced phenolic and volatile compound accumulation in parsley. Amino acid–based biostimulants partially mitigated yield loss while maintaining phytochemical quality, highlighting their potential for hydroponic production under saline conditions.