Effects of Long-Term Biochar Addition On Soil Microbial Community Composition and Carbon Use Efficiency.

Biochar addition to soil is proposed as a management strategy to improve soil fertility and sequester C. However, information on the long-term effects of biochar additions on soils and, in particular, on soil microbial community composition and activity are limited. For example, biochar additions could modify microbial Carbon Use Efficiency (CUE), i.e. the fraction of assimilated C allocated to microbial growth, affecting the balance between C losses and storage in soils. We will present results from 900 days laboratory incubation, where oak-derived biochar was added at 0, 1, 5, 10, and 20% rate by weight to four soils varying in texture and SOC content. At harvest, microbial community composition and CUE were determined on all soils, using PLFA biomarkers and ¹³C labeled glucose additions, respectively. Contrary to our hypothesis, results showed that the highest CUE occurred at 1% or 5% biochar addition rates, depending on soil type, and not at the highest rates. We will illustrate the effect of biochar addition on CUE and microbial community abundance and composition, and the relationship between CUE and microbial community composition.