Pyrolysis temperature during biochar production alters its subsequent utilization by microorganisms in an acid arable soil

Abstract Biochar amendment of agricultural soils can have a significant impact on microbial carbon (C) metabolism by providing C substrates and altering soil properties, including amelioration of soil acidity. It remains unclear whether available C of biochar or its pH effects determines the utilization of biochar by microorganisms. Compound-specific stable 13C isotope analysis of phospholipid fatty acids (13C-phospholipid fatty acid analysis) was used to explore which microbial group utilized biochar distinguished with pHs and C availability. C4 Miscanthus biochar (δ13C = −12.2‰) was prepared at 2 pyrolysis temperatures (350 °C and 700 °C) and applied (50 mg C g−1 soil) to a very acid soil (pH 3.7, δ13C = −27.7‰), which was sampled from the long term Hoosfield Acid Strip experiment at Rothamsted Research, and incubated for 14 months. Biochar700 increased soil pH to 5.1 and biochar350 increased soil pH to 4.3. All microbial groups (Gram-positive bacteria, Gram-negative bacteria, actinobacteria, and fungi) were more abundant in the biochar-treated soils. The 13C values of biomarker phospholipid fatty acid analysis suggested that all groups of microorganisms, and especially Gram-positive bacteria, were using the C from the biochar350, but not the biochar700, as a substrate. We conclude that its utilization of biochar by microorganisms after 14 months was largely determined by the pyrolysis temperature controlling the availability of biochar C, instead of the pH effects, in a very acidic soil.