Soil and Litter BVOC and GHG Fluxes in Central Amazonia: Variability Across Forest Types and Seasons

The Amazon rainforest, characterized by its vast biodiversity and diverse vegetation formations, plays a crucial role in global biogeochemical cycles, including the emission and consumption of biogenic volatile organic compounds (BVOCs) and greenhouse gases (GHGs). Soil and litter fluxes have been suggested as important contributors to the overall forest BVOC budget, but these fluxes remain understudied and are therefore poorly understood. Moreover, only a few observations exist from the Amazon rainforest, an ecosystem expected to be the largest BVOC source in the global atmosphere. Even less studied is the influence of the diversity of soils and vegetation types on BVOC and GHG flux (emission and consumption) patterns. This study aimed to assess the fluxes of BVOCs and GHGs, and their potential drivers, in three dominant forest types in Central Amazonia: upland forest (terra firme), ancient river terrace forest (terraço fluvial), and white sand forest (campinaranas). Soil fluxes were determined using flux chambers, from which sampling bags were collected and subsequently analyzed by a PTR-MS (isoprene, monoterpenes, sesquiterpenes) and a Los Gatos Analyzer (CO₂, CH₄). In addition, soil temperature and moisture were determined, and soil and litter samples were taken to analyze nutrients and microbial biomass. Measurements were conducted in the dry-to-wet transition period, and repeated for the white sand forest in the wet season. In the dry-to-wet season, the highest BVOC fluxes, predominantly emission, were found in the white sand forest, particularly for acetaldehyde and sesquiterpenes. The upland forest exhibited lower fluxes than the white sand forest but stood out for emission and consumption of dimethyl sulfide (DMS) and isoprene. The ancient river terrace forest showed no significant fluxes. Soil moisture and temperature were identified as the primary drivers in the white sand forest, while microbial biomass was the determining factor in the upland forest. In the wet season, fluxes in the white sand forest shifted strongly toward dominance of BVOC consumption and increased methane emissions. Soil phosphorus microbial biomass was identified as a predictor of most BVOC fluxes and CH4 emissions, highlighting the critical role of phosphorus in the wet season. This study offers a significant contribution to the understanding of gas fluxes in Amazonian forest types, emphasizing how nutrients, soil, litter microbial biomass, and seasonality affect BVOC and GHG emissions. These findings provide valuable insights into how environmental changes may impact biogeochemical cycles on the Amazon, providing valuable information for the conservation and management of tropical forests.