Agriculture has a significant environmental impact and is simultaneously called to major challenges, such as responding to the need to develop more sustainable cropping systems with higher productivity. In this context, the present study aimed to obtain lignin nanoparticles (LNs) from pomace, a waste product of the olive oil chain, to be used as a nanobiostimulant in tomato plants. The biostimulant effect of this biopolymer is known, but its reduction to nanometer size can emphasize this property. Tomato plants were subjected to different LN dosages (25, 50, and 100 mg L⁻¹) by foliar application, and inductive effects on photosynthetic machinery, aerial and root biomass production, and root morphology were observed. The treated plants showed increased efficiency in catching and using light, while they reduced the fraction dissipated as heat or potentially toxic to cells for the possibility of creating reactive oxygen species (ROS). Finally, this benefit was matched by increased pigment content and a stimulatory action on the content of nitrogen (NBI) and antioxidant substances such as flavonoids. In conclusion, the present study broadens the horizon of substances with biostimulant action by demonstrating the validity and efficacy of nanobiostimulants obtained from biological residues from the olive oil production chain.

Agricultural systems must improve their sustainability and productivity to meet the growing global demand for food. A cost-effective and sustainable way is the development of biostimulants from plants rich in bioactive compounds. This study aimed to test an aqueous extract from Lemna minor L. (duckweed) on tomato plants at different concentrations (LE—0.1, 0.5 and 1.0%—weight/volume, w/v). Photosystem I and II activity, linear electron flow (LEF), electrochemical gradient across the thylakoid membrane (ECSt), shoot biomass production, root phenotyping, pigment and metabolite content were studied. LE improved many of these traits, with LE 0.5% being the most effective dosage. Compared to the untreated samples, LE significantly stimulated photosystems to use light energy while reducing the amount lost as heat (PhiNPQ and NPQt) or potentially toxic to chloroplasts (PhiNO). These results were supported by the improved shoot biomass production (number of leaves and fresh and dry weight) and root traits (number of tips, surface, volume and fresh and dry weight) found for LE-treated samples compared to untreated controls. Finally, the study highlighted that LE increased pigment and flavonoid contents. In conclusion, the research indicates that this species can be an effective and eco-friendly tool to stimulate beneficial responses in tomato.

Water and soil salinization significantly reduce crop yields. Among the strategies developed to counteract salt stress, biostimulants can maintain crop productivity, reversing its impact. In this context, there is interest in finding new substances that could act as biostimulants. Recently, the biostimulatory potential of Lemna minor L. (duckweed) extracts has been shown. This work aimed to highlight whether an extract from duckweed (Lemna extract—LE) could protect maize grown in salinity, exploring the mechanisms induced to improve crop resistance. Plants were grown by applying two concentrations of NaCl (150 and 300 mM), and some physiological, morphological, and biochemical traits were studied in control and salt-stressed samples, treated or not with LE. Salinity decreased shoots, roots, pigment, and soluble protein. LE prompted ameliorative changes at the root level and increased photosynthetic pigment and soluble protein. Furthermore, concerning the oxidative impairment provoked by salt stress, LE enhanced the cellular redox state, contrasting H₂O₂ and MDA accumulation and positively affecting the activity of superoxide dismutase (SOD—EC 1.15.1.1) and catalase (CAT—EC 1.11.1.6). The assessment of some mineral nutrients showed that LE stimulated their acquisition, especially for the highest salt dosage, explaining some benefits found for the parameters investigated.