Feedstock determines biochar-induced soil priming effects by stimulating the activity of specific microorganisms

Uncertainty remains over what properties of biochar and which groups of microorganisms are responsible for the direction and magnitude of observed biochar-induced priming effects (PE). We selected maize straw, grass, peanut shells and sugar cane as feedstocks to produce biochar at 300, 400 and 500 degrees C by slow pyrolysis, and carried out an 80-day soil-biochar incubation experiment to investigate biochar-induced soil PE by adopting isotopic techniques. Irrespective of pyrolysis temperature, grass-derived biochar (Grass-B) induced the largest PE (348 to 1214mgCkg(-1)soil), whereas peanut shell-derived biochar (Peanut-B) induced the smallest (-135 to 261mgCkg(-1)soil) PE. The intensity of PE was largely determined by the feedstock and was closely related to the proportion of cellulose and lignin in it. The bacterial and fungal communities at days 8 and 40 were investigated by high-throughput sequencing of 16S rRNA and ITS genes. Biochar additions explained 54.0 and 52.9% of the total variation in bacterial and fungal community structure, respectively. The bacterial Actinobacteria and Firmicutes were dominant during the initial phase of the PE (at day 8), whereas the fungal Sordariomycetes and Tremellomycetes were abundant after the longer phase of incubation at day 40. A succession from bacterial community (used the available C fraction of biochar) to fungal community (used the recalcitrant C fraction of biochar and soil organic C) might occur during the PE, together with the alternation of apparent PE to real PE.