Effect of Charcoal Quantity on Microbial Biomass and Activity in Temperate Soils

Wildfire-produced charcoal is a common component of soils, affecting a range of important abiotic and biotic soil processes. Our ability to predict the effects of charcoal addition to soil is currently limited, however, by our understanding of how charcoal affects the soil microbial community mediating many of these processes. This study sought to improve our understanding of the relationship between charcoal addition and soil microbial biomass and activity among temperate soils. Charcoal was added to four distinct temperate soils, a Mollisol, an Alfisol, an Entisol, and a Spodosol, at five application levels ranging from 0 to 0.1 kg charcoal kg(-1) soil, and incubated at 25 degrees C with measurements at approximately 0, 1.5, and 3 mo. We hypothesized that microbial biomass and activity would increase with increasing charcoal application in all soils, but the relative magnitude of the response would depend on the texture and fertility of each soil. As hypothesized, microbial biomass and activity and Bray P increased significantly with increasing charcoal application, while extractable N decreased. The coniferous forest soil provided a notable exception to the general patterns of N availability; having the highest total extractable N at the highest charcoal application level. Our results suggest that charcoal additions affected microbial biomass, microbial activity; and nutrient availability in relatively similar ways in all four soils that we studied, suggesting considerable predictability in response to charcoal application. Differences in the magnitude of the microbial response, however, appeared dependent on differences in nutrient availability among soils.