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

最近的研究结果表明，热带生态系统，特别是热带森林，是全球汞循环的主要组成部分。由于热带森林的高生产力和凋落物的产生，全球大气（干）汞沉积到森林表层土壤中的70%发生在这些环境中。确定叶片中汞累积量与叶/冠层特征（如比叶面积（SLA）和叶面积指数（LAI））之间的关系，以更新全球汞模型的重要性越来越受到关注。然而，这些参数和汞在热带森林植被中的积累从来没有研究过。另一个从未评估过的关键因素是叶片汞积累与水分利用效率（WUE）之间的关系，WUE是指植物每单位用水产生的碳生物量。气孔调节在水分利用效率中起着至关重要的作用，因为气孔开度影响通过蒸腾作用的水分损失和获得的CO2的量。由于汞的吸收也依赖于气孔的调节，建立这种关系可以提供有价值的见解，干旱和更好地适应干旱的植物具有较高的WUE将发挥在未来的汞在植被中的同化作用，同时提供有价值的数据，以支持未来的大尺度模型的汞循环。本研究旨在对热带森林（包括两种不同的森林类型：热带干阔叶林和热带湿阔叶林）中的汞循环进行更详细的描述。通过这样做，我们的目标是更好地评估热带森林与非热带森林相比在汞汇方面的重要性。全面了解各种热带森林类型中植被吸收汞和凋落物驱动汞沉积的作用，不仅可以澄清热带森林的重要性，还可以阐明气候变化对热带森林的潜在影响。拟议的研究旨在确定不同的热带森林类型和相关的气候条件如何驱动汞在植被中的积累，以及汞从大气到土壤的迁移。最后，本研究将量化汞在有机表土中的积累及其与C积累和凋落物中汞通量的关系，这将为未来的全球汞模型提供有价值的额外数据。这项研究将包括描述汞在植被中的积累情况，并评估通过凋落物汞沉积的季节和空间变化。通过比较TDBF和TMBF生物群落，这代表了两个（近）极端的热带系统，我们可以获得一个独特的角度对热带森林的功能和程度，他们不同的汞积累。

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.