Are tropical uplands regional hotspots for methane and nitrous oxide?

热带生态系统是温室气体(GHGs)、甲烷(CH4)和一氧化二氮(N2O)的主要来源，在捕获大气中的长波辐射方面，这两种气体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，这些温室气体大气预算的未来变化对地球的气候和环境条件产生了影响。特别是，由于农业扩张和大气氮沉积增加，预计未来N2O排放量将会上升。最近利用卫星图像、大气测量和模型对全球CH4和N2O预算的研究表明，由于CH4和N2O的来源不明，热带地区释放的CH4和N2O比之前认为的要多得多。如果我们想要了解热带地区目前对温室气体预算的贡献，识别和描述这些“缺失”的来源是至关重要的。要预测热带温室气体排放可能如何应对未来的环境或气候变化，了解这些“缺失”的来源也是必要的。热带高地是甲烷和N2O“失踪”来源的一个强有力的潜在候选者。热带高地显然没有出现在现有的大气预算中，因为科学关注主要集中在低地森林、稀树草原或湿地的CH4和N2O排放上。来自热带高地的研究表明，它们可能是CH4和N2O的大量来源，其排放量等于或超过低地环境的排放量。例如，波多黎各的高地雨林比低地森林排放更多的甲烷，其排放量与世界上最大的甲烷自然来源北方湿地持平。为了解决这些知识上的差距，我们将使用现场测量、受控环境研究和数学模型相结合的方法，对秘鲁安第斯山脉的CH4和N2O循环进行全面研究。具体来说，我们将：1.研究CH4和N2O通量如何随海拔3000米的环境梯度(从低地雨林到高山雨林)在空间和时间上发生变化。2.探索关键环境变量(例如，植物生产力、气候、土壤湿度、碳和氮有效性、氧气)如何影响CH4和N2O的排放。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，根据需要对这些模型进行调整，以更好地模拟野外观测。4.结合数学模型、卫星图像和土地覆盖数据库(即地理信息系统)，通过将我们的实地观测外推到区域尺度，确定安第斯山脉的温室气体排放是否能够解释某些“缺失的”热带CH4和N2O来源。拟议的研究将极大地促进我们对这一重要但研究不足的地区的CH4和N2O排放的了解，并将帮助我们确定安第斯生态系统对南美洲CH4和N2O预算的相对贡献。了解高地安第斯生态系统CH4和N2O通量的排放速率和环境控制也将有助于我们评估其他热带高地是否可能是CH4和N2O的来源，并评估它们对全球大气CH4和N2O预算的潜在贡献。最后，精确模拟热带CH4和N2O通量的数学模型的发展和适应将使我们能够预测热带高地对未来环境或气候变化的可能反应。

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.