Microalgae carbon capture waste acts as a biostimulant in strawberry (Fragaria x ananassa cv. Albion), altering the soil microbiome and improving soil nutrient availability

Microalgae are the basis of many modern-day carbon capture bioreactors. These bioreactors result in production of spent media waste, or cell-free supernatant, whose application has previously been found to increases soil nutrient and promote plant growth. The mechanism for this activity is not fully understood, but one possible driver is changes to the soil microbiome. This study aimed to assess the impacts of a cell-free supernatant, from a Chlorella vulgaris-based bioreactor, on vegetative and reproductive growth of greenhouse grown day-neutral strawberries (Fragaria x ananassa cv. 'Albion'), soil nutrients, and soil microbiome. At a 1:1 dilution, the bioenhancer significantly decreased reproductive growth (yield) and increased vegetative growth (production of runners and crowns, fresh weight, and chlorophyll content). Available soil nutrient levels significantly increased, notably a 100-fold increase in soil nitrate and an almost 4-fold increase in soil inorganic phosphorus, well beyond what would be anticipated based on the NPK of the product alone. Investigation of the soil microbiome via 16S metagenomics found that in the treated plants there was lower microbial community diversity, with a shift towards nutrient cyclers and beneficial microbes in the phyla Actinobacteriota, Proteobacteria, and Verrucomicrobiota, which may be drivers of increased soil available nutrients. These findings provide new insights into function and mechanisms of cell-free supernatants in mediating plant growth and soil nutrient status and their potential for use in agricultural and horticultural systems.