Aquatic moss by-products offer an alternative to algal biomasses for phytostimulant bioproduction

Introduction Aquatic mosses are recently gaining attention for commercial use, stimulating the development of new biomass cultivation approaches. This study explores the potential of by-products from aquatic moss propagation as natural plant biostimulants, addressing the need for low-waste production and sustainable agricultural strategies. Methods Using Temporary Immersion Bioreactors, Leptodictyum riparium and Taxiphyllum barbieri were cultivated, yielding solid non-viable biomass and liquid spent culture medium capable of offering a convenient and eco-sustainable alternative to similar products from algal and plant biomasses. Chemical analyses were performed to identify key plant hormones, including cytokinins (e.g., cis-zeatin, N 6 -isopentenyladenosine), auxins (indole-3-acetic acid, 2-oxindole-3-acetic acid), and abscisic acid (ABA). To evaluate efficacy, in vitro Nicotiana tabacum plants were grown under optimal, salt, and osmotic stress conditions and treated with various moss-derived preparations. Results Cytokinins dominated the extract fraction with higher concentrations than auxins in both moss species. Cytokinin totals in the extracts were up to three orders of magnitude above the minimum threshold typically required for cytokinin-responsive phenotypic changes. In some cases, auxin concentrations approached, though remained below, the ~100 nM threshold commonly cited for bioactivity. Under optimal conditions, T. barbieri extract at 0.1% was the most effective treatment, increasing root length by up to 49% and shoot fresh weight by 93%. Under salt stress, L. riparium culture water applied at 3% of medium induced the strongest response, enhancing root length and biomass by up to 260% and 301%, respectively. Under osmotic stress, moderate biomass increases were observed, reaching 94% with L. riparium by-product and 48% with T. barbieri extract. Discussion Overall, biostimulant efficacy was species- and matrix-dependent, with extracts mainly promoting growth under optimal conditions and culture water mitigating salinity stress. These findings indicate that moss-derived by-products are promising candidates for the development of innovative plant biostimulant formulations within a circular and low-input production framework, offering an alternative to other phytohormone-rich biomasses.