Are tropical uplands regional hotspots for methane and nitrous oxide?

热带生态系统是温室气体甲烷（CH4）和一氧化二氮（N2O）的主要来源，它们在捕获大气中长波辐射方面的效率分别是二氧化碳（CO2）的25倍和298倍。自工业革命开始以来，CH4和N2O浓度的增加是全球变暖的三分之一以上的原因，这些温室气体大气收支的未来变化对地球的气候和环境条件有影响。特别是N2O的排放量，由于农业扩张和大气氮沉降的增加，预计今后将增加。最近利用卫星图像、大气测量和建模对全球CH4和N2O收支的研究表明，由于CH4和N2O来源不明，热带地区释放的CH4和N2O比以前认为的要多得多。如果我们希望了解热带地区目前对温室气体排放的贡献，那么识别和补充这些“缺失”的排放源是至关重要的。了解这些“缺失”的排放源对于预测热带温室气体排放如何可能对未来的环境或气候变化作出反应也是必要的。这些“失踪”的CH4和N2O源的一个强有力的潜在候选者是热带高地。热带高地在现有的大气预算中明显缺席，因为科学界的注意力主要集中在低地森林、稀树草原或湿地的CH4和N2O排放上。对热带高地的研究表明，它们是甲烷和一氧化二氮的潜在大来源，其排放量等于或大于低地环境的排放量。例如，波多黎各的高地雨林比低地森林排放更多的甲烷，其排放率与北方湿地相当，后者是全世界最大的甲烷自然来源。为了解决这些知识的差距，我们将在秘鲁安第斯山脉进行一项全面的CH4和N2O循环研究，使用现场测量，受控环境研究和数学建模的混合物。具体来说，我们将：1。调查如何CH 4和N2 O通量变化的空间和时间沿着一个环境梯度，跨越3000米的海拔高度，从低地雨林到上部山地雨林。2.探索关键环境变量（例如，植物生产力、气候、土壤湿度、碳和氮的可利用性、氧气）影响CH4和N2O排放。3.确定现有的数学模型是否能够模拟热带生态系统的CH4和N2O排放量，必要时调整这些模型，以更好地模拟实地观测。4.确定安第斯山脉的温室气体排放是否能够解释一些“缺失”的热带甲烷和一氧化二氮源，方法是使用数学建模、卫星图像和土地覆盖数据库（即，GIS）。拟议中的研究将大大提高我们的理解甲烷和N2O排放量的一个重要的，但研究不足的地区，并将帮助我们确定安第斯生态系统的相对贡献的甲烷和N2O预算南美洲。安第斯高地生态系统的CH4和N2O通量的排放率和环境控制的知识也将帮助我们评估其他热带高原是否可能是CH4和N2O的来源，并评估其对全球大气CH4和N2O预算的潜在贡献。最后，发展和适应的数学模型，准确地模拟热带CH4和N2O通量将使我们能够预测热带高地的可能响应未来的环境或气候变化。

Tropical ecosystems are major sources of the greenhouse gases (GHGs) methane (CH4) and nitrous oxide (N2O), which are 25 and 298 times more effective than carbon dioxide (CO2), respectively, in trapping long-wave radiation in the atmosphere. Increases in CH4 and N2O concentrations since the start of the Industrial Revolution are responsible for over one-third of global warming, and future changes in the atmospheric budgets of these GHGs have implications for the Earth's climate and environmental conditions. N2O emissions, in particular, are projected to rise in the future due to agricultural expansion and enhanced atmospheric nitrogen deposition. Recent studies of the global budgets of CH4 and N2O using satellite imagery, atmospheric measurements, and modelling suggest that significantly more CH4 and N2O are released from the tropics than previously thought due to unaccounted sources of CH4 and N2O. It is critical for us to identify and characterise these 'missing' sources if we wish to understand the current contribution of the tropics to GHG budgets. Knowledge of these 'missing' sources is also necessary for predicting how tropical GHG emissions are likely to respond to future environmental or climatic change. One strong potential candidate for these 'missing' sources of CH4 and N2O are tropical uplands. Tropical uplands have been conspicuously absent from existing atmospheric budgets, because scientific attention has largely focused on CH4 and N2O emissions from lowland forests, savannas, or wetlands. Studies from tropical uplands suggest that they are potentially large sources of CH4 and N2O, with emissions that are equal to or greater than those from lowland environments. Upland rainforests in Puerto Rico, for example, emit more CH4 than lowland forests, with emission rates that are on par with northern wetlands, the largest natural sources of CH4 worldwide. To address these gaps in knowledge, we will conduct a comprehensive study of CH4 and N2O cycling in the Peruvian Andes, using a mixture of field measurements, controlled environment studies, and mathematical modelling. Specifically, we will: 1. Investigate how CH4 and N2O fluxes vary in space and time along an environmental gradient that spans 3000 m of altitude, from lowland rainforest to upper montane rainforest. 2. Explore how key environmental variables (e.g., plant productivity, climate, soil moisture, carbon and nitrogen availability, oxygen) influence CH4 and N2O emissions. 3. Determine if existing mathematical models are able to simulate CH4 and N2O emissions from tropical ecosystems, adapting these models as necessary to better simulate field observations. 4. Determine if GHG emissions from the Andes are able to account for some of the 'missing' tropical sources of CH4 and N2O by extrapolating our field observations to the regional scale using a combination of mathematical modelling, satellite imagery, and land cover databases (i.e., GIS). The proposed research will greatly advance our understanding of CH4 and N2O emissions for an important but understudied region, and will help us determine the relative contribution of Andean ecosystems to the CH4 and N2O budgets for South America. Knowledge of the emission rates and environmental controls on CH4 and N2O fluxes from upland Andean ecosystems will also help us evaluate whether other tropical uplands are likely to be sources of CH4 and N2O, and assess their potential contributions to the global atmospheric budgets of CH4 and N2O. Lastly, the development and adaptation of mathematical models that accurately simulate tropical CH4 and N2O fluxes will allow us to predict the likely response of tropical uplands to future environmental or climatic change.