Biochar affects taxonomic and functional community composition of protists

Biochar-induced changes in microbial communities are exclusively derived from the studies on the soil bacterial and fungal communities, and we lack an understanding of how biochar can affect taxonomic and functional communities of protists. Here, the short-term effects of two biochars originating from rice husk and poultry litter (hereinafter referred to as RH and PL, respectively) on taxonomic and functional community compositions of protists in a rice rhizosphere were studied using high-throughput sequencing. Soil physicochemical properties were differentially affected by the RH and PL amendments. The relative abundance of Stramenopiles, mainly oomycetes (Peronosporomycetes), was increased in the RH-amended soil, which was correlated with the increased total pore volume and C/N ratio. In the PL amended soil, the relative abundances of Amoebozoa, Alveolata, and Excavata were increased, and those increases were correlated with the enhanced pH and nutrient conditions. Among functional groups, the relative abundance of phagotrophic protists increased by the PL amendment, while the relative abundance of plant pathogens was decreased by both the RH and PL amendments. Network analysis indicated that phagotrophs were the keystone group and were sensitive to the biochar amendments. The keystone taxa in each biochar treatment were different: Cercozoa (Rhizaria) in control, Conosa (Amoebozoa) in RH, and Discoba (Excavata) in PL. The impact of biochar on protist communities correlated with its physicochemical properties, which depends on the source material.