Impacts of fire on sources of soil CO efflux in a dry Amazon rain forest.

Fire at the dry southern margin of the Amazon rainforest could have major consequences for regional soil carbon (C) storage and ecosystem carbon dioxide (CO ) emissions, but relatively little information exists about impacts of fire on soil C cycling within this sensitive ecotone. We measured CO effluxes from different soil components (ground surface litter, roots, mycorrhizae, soil organic matter) at a large-scale burn experiment designed to simulate a severe but realistic potential future scenario for the region (Fire plot) in Mato Grosso, Brazil, over 1 year, and compared these measurements to replicated data from a nearby, unmodified Control plot. After four burns over 5 years, soil CO efflux (R ) was ~5.5 t C ha  year lower on the Fire plot compared to the Control. Most of the Fire plot R reduction was specifically due to lower ground surface litter and root respiration. Mycorrhizal respiration on both plots was around ~20% of R . Soil surface temperature appeared to be more important than moisture as a driver of seasonal patterns in R at the site. Regular fire events decreased the seasonality of R at the study site, due to apparent differences in environmental sensitivities among biotic and abiotic soil components. These findings may contribute toward improved predictions of the amount and temporal pattern of C emissions across the large areas of tropical forest facing increasing fire disturbances associated with climate change and human activities.