Effects of fermented vermicompost on the physiological and biochemical responses of plants subjected to abiotic stress

Abstract

Tomato holds a crucial position on both economic and nutritional scales worldwide. However, its production is severely limited by various biotic and abiotic stresses, particularly salt stress. To cope with these constraints, plants have developed adaptive strategies enabling them to maintain their homeostasis and viability under unfavourable conditions. To strengthen these defence mechanisms, the use of natural products, commonly referred to as biostimulants, has been widely developed. Among modern bio-ecological approaches, vermicompost-derived fermentations represent a promising technology, valorising agricultural residues while contributing to the sustainable management of plant health. The general objective of this study is to evaluate the effect of three types of fermentations, namely a vermicompost tea-based fermentation, a fermentation of aromatic plants (Eucalyptus, Bermuda grass, nettle, rosemary, fleabane, and wild mustard), and a combined fermentation of vermicompost tea and aromatic plants. Each of these fermentations is applied as a liquid extract at two concentrations (5 PERCENT and 10 PERCENT) on various morphological parameters, photosynthetic pigments (chlorophylls a, b, and total), phenolic and flavonoid compounds, as well as the accumulation of soluble solutes (proline and total sugars) in tomato seedlings (*Solanum lycopersicum* L., 1753) subjected to salt stress. The results obtained demonstrate that the application of the different biostimulants exerted a beneficial effect on all morphological parameters of tomato, compared to the control. In particular, the growth parameters revealed a notable improvement in vegetative growth in treated plants subjected to salt stress, relative to the control plants. Furthermore, the analysis of physiobiochemical leaf parameters highlighted a stimulating effect of the biostimulants on chlorophyll, polyphenol, and flavonoid contents. Among the treatments tested, the biostimulant based on vermicompost combined with fermented aromatic plants proved to be the most effective. It was followed by fermented vermicompost, and then by plant-based fermented biostimulants. In addition, the evaluation of microbial activity revealed a higher microbial load in biostimulants containing vermicompost, which could explain, at least in part, their superior efficacy on the growth and physiological responses of tomato seedlings.