B13F-0694
Quantifying the effect of fire disturbance on free-living nitrogen fixation in tropical ecosystems

Monday, 14 December 2015
Poster Hall (Moscone South)
Barbara De Oliveira Bomfim1, Lucas C.R. Silva2, Ben Hur Marimon Junior3, Beatriz Marimon3 and William R Horwath2, (1)University of California Davis, Davis, CA, United States, (2)University of California Davis, Land, Air, and Water Resources, Davis, CA, United States, (3)Universidade Estadual do Mato Grosso, Laboratorio de Biologia Vegetal, Nova Xavantina, Brazil
Abstract:
Tropical forests and savannas are among the most important biomes on Earth, supporting more than half of all plant and animal species on the planet. Despite growing interest in biogeochemical processes that affect tropical forest dynamics, many, including biological nitrogen fixation (BNF), are still poorly understood. Free-living N-fixers are thought to play a key role in tropical ecosystems, alleviating N and P limitation, supporting above and below ground biomass production, as well as carbon storage in plants and soil, but this influence has yet to be quantified. Of particular interest, the spatial distribution and identity of free-living BNF under disturbance regimes that commonly lead to the conversion of forests to savannas is currently unknown. To address this critical gap in knowledge, we measured free-living BNF quantifying rates of N fixation under contrasting fire regimes in the Amazon-Cerrado transition of central Brazil. Samples were collected in 4 ha of floodable forests affected by fire and 1 ha of unburned (seasonally flooded) forest located at the Araguaia State Park, Mato Grosso State, Brazil. Free-living N-fixation rates were measured by both 15N2 (98 atom% 15N) and acethylene reduction assay (ARA). Samples were incubated in the field and left in the dark at room temperature for 12 hours. In the next few weeks we will quantify N fixation rates that will be presented in the upcoming AGU meeting.