Drought responses of C4 plants: resolving the effects of physiological pathway from phylogenetic history

在温暖气候中，使用C4光合途径的植物主导草原生态系统和谷物生产。这一群体生态优势的多重进化起源和突然的地质变化都与大气CO2和气候的变化有关。因此，C4植物对全球变化的响应对于人为气候变化下的生态系统资源管理和理解地球系统具有根本重要性，这两者都是NERC的关键科学目标。近年来，人们的注意力已经从大气CO2转移到水的可用性作为C4植物对过去和未来大气变化的反应的关键驱动力，恢复C4植物干旱关系的主要未回答的问题作为研究重点。至关重要的是，如果C4光合作用是更有效地利用水比C3型，为什么部分的物种NADP-ME C4亚型下降，随着降雨量的减少，而物种NADP-ME亚型表现出相反的模式？C4光合作用的某些亚型赋予耐旱性，而其他亚型与干旱敏感性有关吗？或者这些相关性与C4光合作用的固有特性无关，而是与C4途径起源的独立植物谱系的特征有关？拟议的项目旨在解决这些生理和系统发育的C4植物水关系的组成部分，通过连接实验，模型和新的分子遗传分类的框架内的实地调查。我们的第一个假设，有一个直接的影响C4生理植物耐旱性，将进行测试，利用同源的C3/C4物种对，每个代表独立的C4光合起源在单子叶植物和真双子叶植物组的植物遗传控制实验。受控环境实验已被设计在一个新的机械模型的气孔控制的框架内，开发一个综合的图片C4生理本身如何影响植物水分关系在干旱下。我们的第二个假设，有一个重要的系统发育组成部分耐旱性的C4草，将在PACCAD进化枝，其中包括所有的世界上的C4草和至少四个独立的起源C4途径进行测试。将通过将筛选分析扩展到嵌套在同一进化枝内的C3组来量化生理和系统发育假设的相互作用。实验将针对决定水分吸收、运输和损失以及耐干燥性的关键植物性状，以测试C3和C4类型、NADP-ME和NAD-ME亚型、独立的草分支及其相互作用之间的对比。在南非进行的一项多因素共同花园实验将研究这些相互作用对自然气候和土壤条件下生产力和用水的影响，使用NADP-ME C4和C3物种的子样本，这些物种共同构成南部非洲草植物群的主要部分。

Plants using the C4 photosynthetic pathway dominate grassland ecosystems and cereal production in warm climates. Both the multiple evolutionary origins and abrupt geological shifts in the ecological dominance of this group have been linked with changes in atmospheric CO2 and climate. C4 plant responses to global change are therefore of fundamental importance for ecosystem resource management under anthropogenic climate change and for understanding the Earth System, both key scientific objectives for NERC. In recent years, attention has shifted from atmospheric CO2 towards water availability as a key driver of C4 plant responses to past and future atmospheric change, reinstating major unanswered questions about C4 plant-aridity relationships as research priorities. Crucially, if C4 photosynthesis is more efficient in its use of water than the C3 type, why does the fraction of species with the NADP-ME C4 sub-type decline in grass floras as rainfall decreases, whereas species with the NAD-ME sub-type show the opposite pattern? Do some sub-types of C4 photosynthesis confer drought tolerance, whilst others are linked with drought sensitivity? Or are these correlations unrelated to the inherent properties of C4 photosynthesis, but instead linked with the traits characterising the independent plant lineages where the C4 pathway originated? The proposed project aims to resolve these physiological and phylogenetic components of C4 plant water relations by linking experimental, model and field investigations within the framework of new molecular genetic classifications. Our first hypothesis, that there is a direct effect of C4 physiology on plant drought tolerance, will be tested with phylogenetically controlled experiments using congeneric C3/C4 species pairs, each representing independent C4 photosynthetic origins across monocot and eudicot groups. Controlled environment experiments have been designed within the framework of a new mechanistic model of stomatal control to develop an integrated picture of how C4 physiology per se influences plant water relations under drought. Our second hypothesis, that there is an important phylogenetic component to drought tolerance in the C4 grasses, will be tested within the PACCAD Clade, which encompasses all of the world's C4 grasses and at least four independent origins for the C4 pathway. The interaction of physiological and phylogenetic hypotheses will be quantified by extending the screening analysis to C3 groups nested within the same clade. Experiments will target key plant traits determining water uptake, transport and loss, and desiccation tolerance to test the contrasts between C3 and C4 types, NADP-ME and NAD-ME sub-types, independent grass clades, and their interactions. A multi-factorial common garden experiment in South Africa will examine the implications of these interactions for productivity and water-use in natural climate and soil conditions, using a sub-sample of the NADP-ME C4 and C3 species which together comprise a major part of the southern African grass flora.