Enhanced growth and photosynthetic efficiency in wild rocket (Diplotaxis tenuifolia L.) following multi-species microalgal biostimulant application.

Foliar spraying is a simple and efficient technique that enables targeted delivery of biostimulants directly onto plant surfaces, minimizing losses and environmental dispersion. Among biostimulant categories, microalgae-based formulations represent an eco-friendly solution to improve crop productivity, thanks to their richness in bioactive compounds and rapid growth in low-input systems. In this study, the crude extract of three green microalgae with high commercial value and broad biotechnological potential-Auxenochlorella protothecoides, Tetradesmus obliquus and Chlamydomonas reinhardtii-along with their consortium, was tested as foliar biostimulants for the first time on wild rocket (Diplotaxis tenuifolia L.) at an early vegetative stage. Plants received three sequential treatments, and physiological and biochemical responses were evaluated at 24, 48, and 72 h after the final application. Biostimulation led to up to 32 % increases in fresh biomass and significantly enhanced photosynthetic efficiency (F/F, PI), particularly in consortium-treated plants. The multi-step application also triggered a late and transient rise in antioxidant compounds (carotenoids and phenolics), potentially improving post-harvest quality. Remarkably, these effects were observed even in the absence of abiotic stress, highlighting the intrinsic biostimulant potential of the treatments. Notably, when the consortium crude extract was applied, higher chlorophyll content, nitrate accumulation, and enhanced nitrogen assimilation (indicated by lower δ¹⁵N values) were also observed. These results suggest a compositional and functional uniqueness of the consortium, likely due to interspecies interactions. Overall, early-stage, multi-step foliar biostimulation with selected microalgal species or consortia represents a promising and sustainable strategy to improve crop performance and modulate quality traits in leafy vegetables.