Ozone impacts on tropical vegetation; implications for forest productivity (Trop-Oz)

在低层大气中，臭氧（O3）是一种重要的人为温室气体，是一种空气污染物，每年造成数十亿欧元的植物生产力损失。自1850年以来，由于车辆、工业过程和森林燃烧的化学排放，地表O3增加了一倍。虽然土地生态系统（主要是森林）目前通过储存约四分之一的人类释放的二氧化碳（CO2）排放来减缓全球变暖，但这可能会受到影响森林生长的O3浓度上升的破坏。这反过来又会导致更多的二氧化碳留在大气中，加剧全球气候变化。热带雨林负责全球植物生产力的近一半，正是在这些热带地区，我们可能会看到本世纪人类人口的最大扩张。例如，位于亚马逊雨林中心的马瑙斯在过去25年中人口激增，居民人数翻了一番，达到200多万人。随着人口的增长，我们看到城市化和高密度农业地区的O3前体排放量增加。不断变化的空气污染对热带森林的全球影响可能是深远的。在他2007年的开创性工作中，PI Sitch和他在英国气象局和生态与水文中心的同事们第一个确定了O3污染对热带森林的巨大潜在风险，以及这如何反过来加速全球变暖。然而，他们的研究为研究界提出了两个主要挑战：1）这种影响的规模是高度不确定的;因为他们的全球建模研究是基于从温带和北方物种推断植物O3敏感性数据。该项目将通过提供第一套全面的测量O3对热带树木植物功能和生长的影响来解决这个问题。此外，由于O3、CO2和H2O通过植物气孔在大气和叶片之间交换，较高水平的CO2为植物提供了减少气孔开放的机会，这反过来又导致O3吸收减少和损害。该项目将首次调查气候变化（CO2和温度）对热带森林物种O3响应的潜在协同或拮抗影响。2)所有全球植被建模的一个基本挑战是准确地表示高度生物多样性生态系统的结构和功能;全球模型通常只能表示有限的一组广义植物功能类型（例如万年青树、C4草等）。然而，最近收集和合成的植物功能性状数据（如叶片养分浓度，叶片大小和形状），使全球模型中的生态和植物功能的代表性得到改善。包括项目合作伙伴Johan Udling在内的一组科学家最近提出了一个基于叶功能性状的温带和北方树种对O3敏感性的统一理论。我们处于一个独特的位置，可以将这项工作向前推进，以测试热带森林物种的理论，并测试其在区域和全球范围内的影响。在我们的全球植被模型，JULES（联合英国陆地环境模拟器），包括O3的敏感性和基本植物功能性状之间的关系，将导致我们的能力，以评估空气质量对热带森林生产力和碳固存的后果的影响的一个步骤的变化。该模型将被应用在热带森林中的O3热点位置，并与观察到的植物性状信息和O3浓度一起，我们将能够超越单一植物功能类型（PFT）范式进行外推。全球运行的JULES还将使我们能够调查未来O3浓度，土地利用变化和气候变化情景对热带森林生产力和全球碳汇的影响。

In the lower atmosphere ozone (O3) is an important anthropogenic greenhouse gas and is an air pollutant responsible for several billion euros in lost plant productivity each year. Surface O3 has doubled since 1850 due to chemical emissions from vehicles, industrial processes, and the burning of forests. While land ecosystems (primarily forests) are currently slowing down global warming by storing about a quarter of human-released carbon dioxide (CO2) emissions, this could be undermined by rising O3 concentrations impacting forest growth. This in turn would result in more CO2 left in the atmosphere adding to global climate change. Tropical rainforests are responsible for nearly half of global plant productivity and it is in these tropical regions that we are likely to see the greatest expansion of human populations this century. For example, Manaus, in the centre of the Amazon rainforest has seen a population boom in the last 25 years, with the number of residents doubling to just over 2 million people. Alongside this growing population, we see the expansion of O3 precursor emissions from urbanization and high-intensity agricultural areas. The global impacts of changing air pollution on tropical forests are potentially profound. In his seminal work in 2007, PI Sitch and colleagues at the Met Office and Centre for Ecology and Hydrology, were the first to identify the large potential risk to tropical forests from O3 pollution, and how that could in turn accelerate global warming. However, their study presented two major challenges for the research community: 1) the scale of this effect is highly uncertain; as their global modelling study was based on extrapolating plant O3 sensitivity data from temperate and boreal species. This project will address this by providing the first comprehensive set of measurements of O3 effects on plant functioning and growth in tropical trees. Also, as both O3, CO2 and H2O are exchanged between the atmosphere and leaves through a plants stoma, higher levels of CO2 provide plants the opportunity to reduce their stomatal opening, which in turn leads to reduced O3 uptake and damage. This project will for the first time investigate the potential synergistic or antagonistic impacts of climate change (CO2 and Temperature) on O3 responses in tropical forest species. 2) a fundamental challenge in all global vegetation modelling is to accurately represent the structure and function of highly biodiverse ecosystems; global models are generally only able to represent a limited set of generalized plant functional types (e.g. evergreen trees, C4-grasses etc). However, recent collection and synthesis of plant functional trait data (e.g. leaf nutrient concentrations, leaf size and shape) have enabled improved representation of ecology and plant function in global models. A group of scientists, including project partner Johan Uddling, have very recently proposed a unifying theory for O3 sensitivity in temperate and boreal tree species based upon leaf-functional traits. We are in a unique position to take this work forward to test the theory in tropical forest species, and to test the implications of this at the regional and global scale. The inclusion of the relationship between O3 sensitivity and basic plant functional traits in our global vegetation model, JULES (Joint UK Land Environmental Simulator), will lead to a step-change in our ability to assess the impact of air quality on tropical forest productivity and consequences for carbon sequestration. The model will be applied at O3 hotspot locations in tropical forests and together with observed plant trait information and O3 concentrations we will be able to extrapolate beyond the single plant functional type (PFT) paradigm. Global runs of JULES will also enable us to investigate the implications of future O3 concentrations, changes in land-use, and climate change scenarios on the tropical forest productivity and the global carbon sink.