Structure, Photosynthesis and Light In Canopy Environments (SPLICE)

Splice项目(树冠环境中的结构、光合作用和光)旨在通过考虑植物的三维结构与光相互作用的方式以及这反过来如何影响碳的吸收，来提高我们对全球光合作用的理解，从而提高我们模拟气候变化的能力。我们将使用最先进的技术来测量森林的三维结构和光合作用，并构建详细的计算机模拟来创建一个虚拟实验室，我们可以用它来改进气候模型的模拟。光合作用的过程是地球上生命的基础。在这个项目中，我们关注的是它在陆地碳循环中的作用，这反过来对理解气候变化也很重要。陆地表面吸收了大约25%的人为二氧化碳排放，尽管排放量增加，但这一比例保持了显著的稳定。这种情况是否会继续下去还不得而知。地球系统模型(ESM)本质上是气候模型，包括与气候相关的生物过程，包括植物通过光合作用吸收碳，以便能够模拟(A)该过程对大气二氧化碳浓度的影响和(B)气候变化对全球植被的影响。近几十年来，这些模型在光合作用的模拟方面取得了重大进展，例如与氮循环的相互作用，但它们仍然包括一些非常简单的假设。我们认为，其中最主要的是植被三维结构的表现方式--这一点近40年来一直没有得到改善。ESMS中管理植物截获光线的方程，反过来又驱动光合作用，做出了简化的假设，即叶子在空间中随机排列，而不是聚集到树冠或树枝周围。这使得物理学中的相关方程可以以一种产生计算效率高的计算机代码的方式来求解，但不能很好地代表现实。雷丁大学最近的研究表明，即使是将这些影响的简单表示纳入ESM，也可能对全球碳循环产生重大影响。特别是，我们显示了对全球光合作用的模型估计的增强，即每年50亿吨碳，或燃烧化石燃料释放的二氧化碳的一半以上。其中大部分发生在热带地区，这一地区很可能特别容易受到气候变化的影响。SPLICE将结合地面激光雷达扫描和机载激光雷达测量来测量全球26个森林的3D结构。激光雷达使用散射激光来推断森林的结构，从中获得的信息可以用来重建森林的逐个树枝模拟。我们将利用这些数据，建立森林光环境和由此产生的光合作用的详细3D模型。光合作用通量将使用各种技术来测量，包括观测无人机的太阳诱导荧光(SIF)。这些观测将被用来测试我们的3D模型。SIF是光合作用的一部分，虽然人们知道它已经有一段时间了，但远程观测它的技术相对较新。它提供了光合作用吸收碳量的密切指标。我们的最后一步将是使用详细的3D模型来开发用于ESM的计算机代码的修改版本，以表示光与植被树冠的相互作用。这些修改后的代码将用于英国新的地球系统模型UKESM的陆地表面部分，以评估这些变化在全球范围内的影响，以及它们对碳循环和气候变化的影响程度。

The SPLICE project (Structure, Photosynthesis and Light In Canopy Environments) seeks to improve our understanding of global photosynthesis and hence our ability to model climate change, by considering the way in which the three-dimensional structure of plants interacts with light and how this in turn impacts on the uptake of carbon. We will employ state-of-the-art techniques to measure the three dimensional structure and photosynthesis of forests and construct detailed computer simulations to create a virtual laboratory that we can use to improve simulations from climate models. The process of photosynthesis is fundamental to life on Earth. In this project we are concerned with its role in the terrestrial carbon cycle, which in turn is important for understanding climate change. The land surface absorbs around 25% of anthropogenic CO2 emissions and this proportion has remained remarkably constant despite increasing emissions. Whether or not this will continue is unknown. Earth System Models (ESMs), which are essentially climate models that include climate-relevant biological process, include the uptake of carbon by plants via photosynthesis so that they can model (a) the influence of this process on atmospheric carbon dioxide concentrations and (b) the impact of climate change on global vegetation. There have been significant advances made in the modelling of photosynthesis inside these models in recent decades, for example the interaction with the nitrogen cycle, but they still include some very simple assumptions. We argue that chief amongst these is the way in which the three dimensional structure of vegetation is represented - something that has not been improved for nearly four decades.The equations in ESMs that govern the interception of light by plants, which in turn drives photosynthesis, make the simplifying assumption that leaves are randomly arranged in space, not clustered into tree crowns or around branches. This allows relevant equations in physics to be solved in such a way that results in computationally efficient computer code, but does not represent reality very closely. Recent research from the University of Reading has shown that the impact of including even a simple representation of these effects into an ESM can have large impacts on the global carbon cycle. In particular we showed an enhancement in the modelled estimates of global photosynthesis of 5 billion tonnes of carbon per year, or more than half of CO2 released from burning fossil fuels. Most of this occurs in the tropics, an area of the Earth likely to be especially vulnerable to the impacts of climate change.SPLICE will measure the 3D structure of 26 forests around the world using a combination of terrestrial Lidar scanning and airborne Lidar surveys. Lidar uses scattered laser light to infer structure of forests and information from it can be used to reconstruct a branch-by-branch simulation of the forest. We will take these data and build detailed 3D models of the forest light environment and resulting photosynthesis. The photosynthetic flux will be measured using a variety of techniques, including observations of solar induced fluorescence (SIF) from drones. These observations will be used to test our 3D models. SIF occurs as part of photosynthesis and although it has been known about for some time the technology to observe it remotely is relatively new. It provides a close proxy for the amount of carbon being taken up by photosynthesis.Our final step will be to use the detailed 3D models to develop a modified version of the computer codes used in ESMs to represent the interaction of light with vegetation canopies. These modified codes will be used in the land surface component of UKESM - the UK's new Earth System Model - to assess the impact of these changes globally and the magnitude of their impact on the carbon cycle and hence climate change.