Forest Diversity and Environmental Factors Shape Contrasting Soil-Litter BVOC and Methane Fluxes in Three Central Amazonian Ecosystems

Abstract. Biogenic volatile organic compounds (BVOCs) play a crucial role in biosphere-atmosphere interactions and the global carbon cycle. While vegetation is recognized as the primary source of BVOC fluxes in forest ecosystems, recent studies suggest that the carbon-rich soil-litter compartment contributes significantly. However, these fluxes, their underlying drivers, and their variability across forest types remain poorly understood, with measurements still scarce—particularly in the Amazon rainforest, the world’s largest source of BVOCs. In this study, we investigated soil-litter BVOC and methane fluxes and their potential drivers—including nutrient content, microbial biomass, soil temperature and moisture—across three forest types in central Amazonia: white sand forest (WS), upland forest (UP), and ancient river terrace forest (AR). Our results showed distinct flux patterns among forest types. WS exhibited both high emissions and consumption of gases, notably high acetaldehyde and methane emissions, and strong isoprene and monoterpene uptake. UP showed lower overall fluxes, with moderate emission and consumption of DMS, isoprene, and acetaldehyde. AR presented no significant fluxes. Linear models identified soil moisture and temperature as the primary drivers of fluxes in WS, while microbial biomass was the main driver in UP. Our measurements suggest that, despite covering a relatively small area in the Amazon basin, WS can be a significant ecosystem for BVOC and methane fluxes, regulated by soil moisture and temperature. Our findings underscore the need to account for forest-type-specific fluxes when modeling BVOC and methane emissions in the Amazon, particularly under changing climate conditions.