Does physiological innovation change the fundamental relationships between growth and survival?

“活得快，死得早”是摇滚明星和好莱坞演员疯狂放纵的著名描述，但也概括了一个重要的生物学原则。快速生长和繁殖的动植物更容易被天敌或极端环境杀死。我们通常用能量来解释这种生物学上的权衡：花在生长上的能量越多，就意味着花在防御敌人、捕获必要资源或储存逆境生存所需的能量越少。这一解释的一个合乎逻辑的延伸是，如果同样的增长可以用更少的能源实现，那么就可以有更多的能源用于防御、资源捕获和储存，从而提高生存率。然而，这一预测仍然未经检验，尽管它的生物学的核心重要性。C4光合作用在七十多个植物谱系的进化增加了光合作用的能量转换效率在高光和高温下，相比祖先的C3类型的光合作用。为了了解光合效率的提高如何影响生长，我们开发了一种实验方法，能够在相同的环境条件下比较数百种植物的生长。我们已经发现，除了C4光合作用在促进更快生长方面的直接生理效应之外，C4叶片出乎意料地比C3叶片更不密集，进一步提高了生长效率。这使得C4植物更大，更多的生长投资于根部，这使我们假设它们可能能够积累更多的储存，并且在干旱期间比C3植物更容易获得水。总之，这些假设的影响，预计将增加植物生存反复落叶和干旱事件。如果得到实验证据的支持，这些C3和C4植物之间的生态差异将有重要的全球尺度的植物群落对环境变化和土地管理的影响，我们建议使用三个大型的比较实验来测试这些假设，利用我们最近在发展高通量实验筛选方法的进展。我们能够在相同的实验装置中测量数千种植物的生长、根与芽的分配、储存和存活，并开发了新的统计方法来分析大型数据集。我们也是第一个成功应用代谢组学方法来识别和量化多个野生植物物种中的储存化合物的小组。我们的战略，拟议的工作将是联合收割机这些方法，调查生存实验施加的干旱或反复落叶在70个生态重要的草种，代表7个独立的进化起源的C4光合作用和它们的C3姐妹类群。替代假设的生存机制将通过使用不同年龄的植物来操纵大小进行测试。由于C4光合作用对植物水分利用也有直接的生理影响，通过减少气孔孔径，我们将在干旱实验期间对植物水力学进行详细的测量。从三个实验的结果将使我们能够测试的相对重要性，以生存更大的存储，更深的生根，较低的植物用水量，更大的植物尺寸在C4然后C4物种，并获得一个整体的了解系统。这项工作将增强我们对重大生理创新如何改变生长-生存关系并使植物能够探索新的表型空间的机械理解。在整个项目中，我们将与数学建模人员合作，以确保实验将产生有助于开发全球植被如何储存碳和影响气候的改进模型的数据。

"Live fast, die young" famously describes the wild excesses of rock stars and Hollywood actors, but also encapsulates an important biological principle. Animals and plants that grow and reproduce quickly are more likely to be killed by natural enemies or environmental extremes. We usually explain this biological trade-off in terms of energy: more energy spent on growth means less energy invested in defence against enemies, the capture of essential resources, or into stores for surviving adverse conditions. A logical extension of this explanation is that, if the same growth could be achieved using less energy, more would be available for defence, resource capture and storage, thereby increasing survival. However, this prediction remains untested, despite its central importance for biology.The evolution of C4 photosynthesis in more than seventy plant lineages has increased the efficiency of photosynthetic energy conversion at high light and hot temperatures, in comparison with the ancestral C3 type of photosynthesis. To understand how this increase in photosynthetic efficiency influences growth, we have developed an experimental approach capable of comparing growth among hundreds of plant species in the same environmental conditions. We have discovered that, as well as a direct physiological effect of C4 photosynthesis in promoting faster growth, C4 leaves are unexpectedly less dense than C3 ones, further increasing growth efficiency. This allows C4 plants to be larger, with more growth invested in roots, which leads us to hypothesize that they may be able to accumulate greater storage, and have better access to water during drought than their C3 counterparts. Together, these hypothesized effects are expected to increase plant survival following repeated defoliation and drought events. If supported by experimental evidence, these ecological differences between C3 and C4 plants would have important global scale implications for the responses of plant communities to environmental change and land management.We propose to test these hypothesis using three large comparative experiments, capitalizing on our recent advances in developing high-throughput experimental screening methods. We are able to measure growth, allocation to roots verses shoots, storage and survival on thousands of plants in the same experimental set-up, and have developed novel statistical methods to analyze the large resultant datasets. We are also the first group to successfully apply metabolomic methods to identify and quantify storage compounds across multiple wild plant species. Our strategy for the proposed work will be to combine these approaches, investigating survival of experimentally imposed drought or repeated defoliation in seventy ecologically important grass species, representing seven independent evolutionary origins of C4 photosynthesis and their C3 sister taxa. Alternative hypothesized survival mechanisms will be tested by using plants of different ages to manipulate size. Since C4 photosynthesis also has a direct physiological effect on plant water use, by reducing stomatal aperture, we will make detailed measurements of plant hydraulics during the drought experiment. Findings from the three experiments will allow us to test the relative importance to survival of greater storage, deeper rooting, lower plant water use, and greater plant size in C4 then C4 species, and to gain a holistic understanding of the system. The work will enhance our mechanistic understanding of how a major physiological innovation changed growth-survival relationships and enabled plants to explore new phenotypic space. Throughout the project, we will work with mathematical modelers to ensure that the experiments will generate data that are useful for developing improved models of how global vegetation stores carbon and influences climate.