Characterization of soil-litter fluxes of Biogenic Volatile Organic Compounds and Greenhouse gases from different forest types in central Amazonia

Abstract

The Amazon rainforest, characterized by its vast biodiversity and diversity of 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). However, the specific contributions of soil and litter to these gas fluxes remain poorly understood. Focusing on the influences of microbial biomass, soil and litter nutrients, and soil moisture and temperature, this study investigates the fluxes of BVOCs and GHGs (methane and carbon dioxide) in three forest types in Central Amazonia: upland forest (terra firme); ancient river terrace forest (terraço fluvial) and white sand forest (campinaranas). It also analyzes the possible drivers that could influence these fluxes, such as nutrients and microbial biomass in the soil and litter. In a second phase, we focused on white sand forests, examining gas fluxes during the dry-to-wet transition and wet seasons, and relating seasonal differences to the same drivers identified in the first study. The results showed that gas fluxes vary between forest types. The white sand forest showed high emissions of various gases, especially acetaldehyde and sesquiterpenes. The upland forest showed lower fluxes than the white sand forest but stood out for its emission and consumption of dimethyl sulfide (DMS) and isoprene. The ancient river terrace forest showed no significant fluxes. Soil moisture and temperature were the main drivers in determining gas fluxes for the white sand forest, while microbial biomass was the determining factor for the upland forest. The results of the influence of seasonality in the white sand forest showed that the direction of the fluxes shifted from one season to the next. In the dry-to-wet transition season, we observed high rates of BVOCs emissions; in the wet season, we observed the consumption of these gases and a substantial increase in methane emissions. Soil phosphorus microbial biomass was a predictor of the fluxes of most of the BVOCs. Soil phosphorus was selected as a driver of CH4 emissions, demonstrating that phosphorus played an important role in the wet season. This study offers a significant contribution to broadening the understanding of gas fluxes in Amazonian forest types, highlighting how nutrient factors, soil and litter microbial biomass, and seasonality affect BVOC and GHG emissions. These findings can help predict how environmental changes will impact biogeochemical cycles in the Amazon, providing valuable information for the conservation and management of tropical forests.