Inclusion of biochar in mushroom substrate influences microbial community composition of the substrate and elemental composition of the fruiting bodies.

Due to its structure, biochar makes the soil porous and oxygen-rich, enhancing the water-holding capacity and increasing the cation exchange capacity for a longer duration. These aspects could also be favourable for mushroom production. However, biochar has been considerably less investigated within this context. This study investigated the impact of biochar on mushroom production, quality, and the microbial communities of the substrates. Two different biochar's produced from local feedstocks, plant- or sludge based, were evaluated in the production of oyster mushrooms (Pleurotus ostreatus) at two different concentrations (5 % and 10 %). The results showed that inclusion of biochar in the substrate negatively impacted fruiting body production. The elemental composition of the fruiting body was also affected by inclusion of biochar and partly reflected the elemental composition of the biochar. The metagenomics revealed that inclusion of biochar in the substrate altered the microbial community structure. The bacterial diversity based on Shannon indices was higher in the substrate wherein no biochar was added. Bacterial community richness (Chao 1) was higher in samples with biochar compared to the control with no added biochar. Fungal community richness based on Chao 1 indices displayed an increase in samples with an inclusion of biochar. Overall, this study provides novel insights into the impact of biochar in mushroom production regarding its concentration and the effect of the origin material of the biochar.