Effects of biochar amendment on tomato rhizosphere bacterial communities and their utilization of plant-derived carbon in a calcareous soil

Abstract

Rhizosphere microbes play a significant role in nutrient cycling and in plant health. Biochar soil amendment can enhance carbon sequestration and alter soil edaphic features (e.g., increase pH and water holding capacity) in terrestrial ecosystems. However, the effect of biochar amendment on rhizosphere microbiome is still an open question, especially for calcareous soils, which generally have neutral or alkaline pH. We investigated the impacts of biochar amendment on tomato rhizosphere bacterial community composition and diversity in alkaline calcareous soil. To characterize the bacterial communities that consume root-exudates, we grew tomato plants with and without the biochar amendment in plant growth chambers supplied with and without 13CO2 labeled gas for 35 days. Biochar amendment increased soil pH and total carbon (C) concentration but had little impacts on soil NO3–-N, NH4+-N, OlsenP concentrations, and total vegetative tomato biomass compared with unamended soil. Furthermore, the tomato rhizosphere bacterial community composition did not significantly change after biochar amendment. We observed 76 and 82 13C-labeled amplicon sequence variants (ASVs) in the control and biochar treated rhizospheres, respectively, and 60 of the 98 ASVs were shared between the two treatment samples. The bacterial taxonomic composition of the 13C-labeled ASVs was similar between control and biochar treatments, and mainly belonged to the phylum Proteobacteria (e.g., Acinetobacter and Kaistia). Additionally, the relative abundance of 13C-labeled bacteria only accounted for approximately 2% of the total rhizosphere bacterial communities for both treatments. These results demonstrate that biochar amendment may have limited impacts on rhizosphere bacterial community composition and their utilization of plant-derived carbon in alkaline calcareous soils. Our study furthers our understanding of the association of plant and bacterial communities in response to biochar amendment in agricultural systems.