Sustainable agriculture with cyanobacterial biomass: Soil experiments on spinach and radish plants

To support sustainable food production and improve crop yields, it is essential to explore bio-based plant growth-promoting products. Cyanobacterial biomass has shown potential to enhance soil quality and agricultural productivity. However, some cyanobacteria produce cyanotoxins, such as microcystins, cylindrospermopsin and anatoxin-a, which can adversely affect plant development depending on their concentration. This study evaluated the potential of cyanobacterial biomass as a soil amendment and plant growth stimulant by assessing growth, nutrient content and toxin accumulation in spinach and radish plants. Plants were cultivated in soil treated with no amendment, commercial fertilizer, or cyanobacterial biomass from Microcystis aeruginosa (microcystins-producer), Anabaena sp. (anatoxin-a-producer), Raphidiopsis raciborskii (non-cylindrospermopsin producer), and R. raciborskii (cylindrospermopsin-producer). While biomass additions supplied nutrients to the soil, spinach showed increased sensitivity to microcystins and anatoxin-a, with significantly reduced growth. Overall, mineral concentrations in plant tissues did not increase; most macro- and micronutrients declined, particularly in spinach shoots and radish roots (p ≥ 0.05). Vitamin C content also decreased in most treatments, except in plants treated with the non-cylindrospermopsin-producing R. raciborskii strain, where a significant increase was observed (p ≥ 0.05). Toxic biomass amendments led to the uptake of microcystins-LR and cylindrospermopsin in spinach, and cylindrospermopsin in radish, with cylindrospermopsin levels in spinach exceeding Word Health Organization's tolerable daily intake. These findings underscore the need for a previous detailed characterization of both nutrients and toxins in cyanobacterial biomass to ensure its safe and effective agricultural use, maximizing benefits while protecting food safety.