Humic substances (HS) act as biostimulants for terrestrial photosynthetic organisms. Their effects on plants are related to specific HS features: pH and redox buffering activities, (pseudo)emulsifying and surfactant characteristics, capacity to bind metallic ions and to encapsulate labile hydrophobic molecules, ability to adsorb to the wall structures of cells. The specific properties of HS result from the complexity of their supramolecular structure. This structure is more dynamic in aqueous solutions/suspensions than in soil, which enhances the specific characteristics of HS. Therefore, HS effects on microalgae are more pronounced than on terrestrial plants. The reported HS effects on microalgae include increased ionic nutrient availability, improved protection against abiotic stress, including against various chemical pollutants and ionic species of potentially toxic elements, higher accumulation of value-added ingredients, and enhanced bio-flocculation. These HS effects are similar to those on terrestrial plants and could be considered microalgal biostimulant effects. Such biostimulant effects are underutilized in current microalgal biotechnology. This review presents knowledge related to interactions between microalgae and humic substances and analyzes the potential of HS to enhance the productivity and profitability of microalgal biotechnology.

This review aims to evaluate the scientific evidences for siliceous natural nanomaterials (SNNMs), natural zeolites, and diatomaceous earth, as biorationals. Both SNNMs are multifaceted agricultural inputs—plant protectants, plant biostimulants/plant strengtheners, soil improvers. The effects depend on the plant parts, where such siliceous natural nanomaterials (SNNMs) are applied. For stored grains, SNNMs act as plant protectants. Foliar applied SNNMs protect plants against biotic and abiotic stress—plant protectant and plant strengtheners. When applied to soil/roots, SNNMs stimulate root development and improve soil characteristics. These effects are related to the composition and porous (nano)structure of SNNMs. The large active siliceous surfaces of SNNMs are involved in: desiccation of the insects damaging stored grains, fungistatic effects against mycotoxigenic fungi and adsorption of their mycotoxins, desiccation of foliar pathogens and pests, stimulation of photosynthesis, release of soluble silicon species, improved soil characteristics. Similar to other biorationals from the category of basic substances with low risk, the SNNMs efficacy as plant protectants and plant health strengtheners is rather low. Complementary active ingredients should be used to enhance the effects of SNNMs on treated plants. For SNNMs applied as protectants of stored seeds, such strategy, of using complementary biorationals/low risk substances, proved to be highly effective.

Siliceous natural nanomaterials (SNNMs), i.e., diatomaceous earth and natural zeolites, have a nanoporous structure with large active surfaces that adsorb cations or polarized molecules. Such nanoporous feature determines the effects related to SNNM utilization as low-risk plant protectants and soil improvers. This work used SNNMs from Romanian quarries as carriers for foliar fertilizers applied to stone-fruit trees, apricot and peach. We determined the effects of SNNMs on the physiology, yield and fruit quality of the treated stone-fruit trees. SNNM application determined impacts specific to the formation of particle films on leaves: reduced leaf temperature (up to 4.5 °C) and enhanced water use efficiency (up to 30%). Foliar fertilizers’ effects on yield are amplified by their application with SNNMs. Yield is increased up to 8.1% by the utilization of SNNMs with foliar fertilizers, compared to applying foliar fertilizer alone. Diatomaceous earth and natural zeolites promote the accumulation of polyphenols in apricot and peach fruits. The combined application of SNNMs and foliar fertilizer enhance the performance of peach and apricot trees.

The increasing need for sustainable waste management and food fortification requires continuous agri-food biotechnological innovation. Spent brewer’s yeast (SBY) is a mass-produced underutilized by-product of the brewery industry and has elevated bioactive potential. The current study presents a streamlined ultrasonic SBY cell lysis method, with the main goal of bioactive compound valorization. The influence of selected ultrasonication parameters on protein release and, implicitly, on the cell disruption efficiency, was assessed. The SBY derivatives resulting from the ultrasonic cell lysis were SBY extracts (SBYEs) and cell walls (SBYCWs), which were evaluated in terms of protein content, antioxidant activity (AOA) and total polyphenol content. Scanning electron microscopy (SEM) and FT-IR spectroscopy were used to characterize SBYCWs in relation to the morphological and chemical transformations that follow ultrasonic yeast cell disruption. The optimal ultrasonication conditions of 6.25% SBY concentration, 40 °C and 33.33% duty cycle (DC) ensured the most efficient lysis. The SBY derivatives with the most elevated antioxidant activity were obtained at temperatures below 60 °C. SBYCWs had the highest polyphenol content and a relatively high content of β-glucan under these parameters. Optical microscopy and SEM confirmed the release of intracellular content and separation of SBYCWs.

This study aimed to evaluate the impact of a more cost-efficient strigolactone mimic SL-6 on Chlorella sorokiniana NIVA-CHL 176 growth in comparison with the strigolactone analog GR24 and the plant biostimulant functions of microalgal extracts. Three molar SL-6 concentrations were tested: 10⁻⁷ M, 10⁻⁸ M, and 10⁻⁹ M, respectively. Five parameters of microalgal growth were assessed: optical density, turbidity, biomass production, chlorophyll fluorescence, and pigment concentration. Results after 15 days of culturing revealed that the SL-6 treatments significantly enhanced biomass production (13.53% at 10⁻⁹ M), pigment synthesis, and photosystem II activity (14.38% at 10⁻⁹ M). The highest increases in pigments induced by SL-6 were 15.7% for chlorophyll a (at 10⁻⁸ M SL-6), 12.87% for chlorophyll b (at 10⁻⁹ M SL-6), 2.3% for carotenoids (at 10⁻⁸ M SL-6), and 10.78% for total pigments (at 10⁻⁸ M SL-6) per gram biomass compared to the solvent control (DMSO). Higher doses of GR24 and SL-6 (10⁻⁷ M) inhibited microalgal growth, reducing cell density, biomass production, and pigment synthesis. The microalgal extracts acted as plant biostimulants, stimulating root and shoot elongation and proton pump functioning of mung seedlings in the presence and absence of salt stress. The extracts from SL-6 biostimulated C. sorokiniana were more active as plant biostimulants than the extracts from the non-stimulated C. sorokiniana.

Shilajit, also known in the north of India as salajit, shilajatu, mimie, or mummiyo, is a blackish-brown powder or an exudate from high mountain rocks, especially in the Himalayans mountains between India and Nepal