Assessing Hg Accumulation in Leaves and Fluxes between Vegetation and Soil in Tropical Dry and Moist Broadleaf Forests: Investigating the Role of Vegetation and Seasonality in the Tropical Forest Mercury Cycle

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Recent findings suggest that tropical ecosystems, particularly tropical forests, are a major component in the global Hg cycle. Because of the high productivity and litter production in tropical forests, 70% of the global atmospheric (dry) deposition of Hg to forest topsoils occur in these environments. There has been an increasing interest of the significance of determining the relationship between Hg accumulation in leaves and leaf/canopy characteristics, such as specific leaf area (SLA) and leaf area index (LAI), respectively, to update global Hg models. However, these parameters and Hg accumulation in tropical forest vegetation has been never studied. Another crucial factor that has never been evaluated is the connection between leaf Hg accumulation and water use efficiency (WUE), which is the amount of carbon produced as biomass per unit of water used by the plant. Stomatal regulation plays a crucial role in WUE as stomatal aperture affects water losses through transpiration and the amount of CO2 obtained. Due to Hg uptake is also dependent of stomatal regulation, establishing the relationship can provide valuable insights into the role that drought and better adaptation to drought by plants with higher WUE will play in Hg assimilation in vegetation in the future and at the same time provide valuable data to support future large scale models on Hg cycling. This study aims to provide a more detailed characterization of the Hg cycle in tropical forests, including two different forest types Tropical Dry Broadleaf Forest (TDBF) and Tropical Moist Broadleaf Forest (TMBF). By doing so, we aim to contribute to a better assessment of the importance of tropical forests compared to non tropical forests as Hg sinks. A comprehensive understanding of the role of vegetation Hg uptake and litterfall–driven Hg deposition in a range of tropical forest types would not only clarify the importance of the tropical forests, but also shed light on the potential effects of climate change on them. The proposed study aims to determine how different tropical forest types and associated climatic conditions drive Hg accumulation in vegetation, as well as its transport from the atmosphere to the soil. Finally, this study will quantify Hg accumulation in the organic topsoil and its relationship to C accumulation and Hg fluxes in litterfall providing which will provide valuable additional data for future global Hg models. The study will involve characterizing Hg accumulation in vegetation and assessing the seasonal and spatial variability in Hg deposition through litterfall. By comparing the TDBF and TMBF biomes, which represent two (near-)extreme tropical systems, we can gain a unique perspective on the functioning of tropical forests and the extent to which they differ in terms of Hg accumulation.