CAREER: Development of a proxy for past and present plant photorespiration rates based on 13C-D and D-D clumping in wood methoxyl groups

森林是美国景观的视觉主导部分，是我们建筑业的关键，也是未来二氧化碳排放量被提议封存的重要领域。因此，更好地了解环境因素如何影响陆地生物圈具有内在的社会效益。植物研究的一个基本方面是了解是什么控制着它们的生长-换句话说，是什么决定了植物可以从大气中吸收并转化为生物质的碳的数量？在其他条件相同的情况下，今天通常发现植物生长得更好，二氧化碳（CO2）越多，它们就越好。碳固定率对CO2的依赖性被称为“CO2施肥效应”。它基于这样的想法，即增加二氧化碳将增加全球光合速率，并对未来气候具有重大意义。该提案的重点是地质过去，在过去的6500万年中，二氧化碳浓度从180 ppm的冰川低点变化到数千万年前的约1000 ppm。一个问题是，在现代植物中看到的，古代植物是否对地质时期二氧化碳浓度的变化做出了反应？植物是否在最后一次冰期因低二氧化碳而挨饿，并在数千万年前在富含二氧化碳的大气中茁壮成长？模型预测这是真的，但没有“代理人”可以重建植物生长率如何对地质过去的二氧化碳水平变化做出反应。在这里，研究人员建议开发这样一个代理来测试这些想法，使用木材的稳定同位素组成的基础上，丰富的稀有稳定同位素的碳和氢结合在一起的木材组织。他将在实验和现代植物上校准测量结果，然后研究过去地质学的样本。作为这项工作的一部分，他还将为9-第12届教育工作者通过全球气候变化教育资源的加州大学古生物博物馆，也将被纳入课堂讲授加州大学伯克利分校地球历史模型预测，二氧化碳浓度的变化在中生代已经改变了全球陆地初级生产力，通过改变的相对速率，植物的光呼吸与光合作用。预计这些变化将产生全球范围的后果，包括改变全球硅酸盐风化速率，并导致生态系统在冰川pCO 2低期间处于近乎饥饿的状态。有没有可用的代理过去的光呼吸速率，可以测量化石材料来测试这些假设。该项目提出了一个综合的研究和教育计划，重点是开发基于木质素甲氧基的同位素组成的光呼吸速率的第一个代理，其中两个稀有同位素（称为聚集同位素; 13 CH 2D-O-木质素和12 CH 2D-O-木质素）可以在现代和化石材料上测量。该代理将根据理论、实验和对现代环境样本的调查进行开发和校准。然后，它将被应用到测试长期存在的假设，陆地生态系统的碳饥饿在末次冰期由于光呼吸率升高与低大气CO2。建议采用的方法有：（1）化学提取和纯化木材木质素中的甲氧基，并转化为分析物CH_3Cl。(2)使用高分辨率同位素比质谱仪测量来自CH 3Cl离子碎片的12 CH 3+、12 CH 2D+、13 CH 3+、13 CH 2D+和12 CHD 2+的强度。(3)植物在受控条件下在生长室中的生长。(4)从档案中收集现代和化石木材。(5)同位素配分函数比的理论计算。这项工作将为社区提供一个新的、经过校准的替代物，并允许立即测试一个长期存在的假设，即pCO 2在地质时间尺度上的变化如何影响或不影响陆地生态系统。通过一项综合教育和研究方案，将把研究纳入供公众和教师使用的教材。这些材料将由加州大学古生物学博物馆开发的“了解全球变化”网络资源托管和传播。由UCMP主办的教育网站每月接待数百万访问者，从而达到广泛，多样化的社区，包括公众，学生和教育工作者。最后，研究将被整合到由调查员教授的课程中，包括研究生研讨会课程的开发和新课程和练习的创建。为这些课程开发的教学材料将依次张贴在理解全球变化网站上，以便为使用该网站制定自己的课程计划的教育工作者提供范例、课程和练习。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Forests are a visually dominating part of the U.S. landscape, key to our construction industries, and an important area of where future emissions of CO2 are proposed to be sequestered. Thus, having a better understanding of how environmental factors affect the terrestrial biosphere has inherent societal benefit. A fundamental aspect of the study of plants is understanding what controls how well they grow — put another way, what sets the amount of carbon plants can take up from the atmosphere and convert into biomass? All else being equal, plants are generally found today to grow better the more carbon dioxide (CO2) they have available. The dependence of carbon fixation rates on CO2 is termed the ‘CO2 fertilization effect’. It is based on the idea that increasing CO2 will increase global photosynthetic rates and is of great relevance for future climate. The focus of this proposal is on the geological past where CO2 concentrations have changed over the past 65 million years by ~1000 ppm from glacial lows of 180 ppm to ~1000 ppm tens of millions of years ago. A question is whether, as seen in modern plants, ancient plants responded to changes in CO2 concentrations over geologic time? Did plants starve during the last glacial episodes due to low CO2 and thrive tens of millions of years ago in CO2 rich atmospheres? Models predict that this is true, but there are no ‘proxies’ that can reconstruct how plant growth rates responded to changing CO2 levels in the geologic past. Here the investigator proposes to develop such a proxy to test these ideas using the stable isotopic composition of wood based on the abundance of rare stable isotopes of carbon and hydrogen bound together in wood tissues. He will calibrate the measurement experimentally and on modern plants and then study samples from the geological past. As part of this work, he will additionally create new online teaching resources for 9-12th educators through the Global Climate Change educational resources of the University of California Museum of Paleontology and that will also be integrated into classes taught at UC Berkeley.Models of earth history predict that changes in CO2 concentrations over the Phanerozoic have altered global terrestrial primary productivity by changing the relative rates of photorespiration vs. photosynthesis in plants. These changes are predicted to have had global-scale consequences, including changing global silicate weathering rates and causing ecosystems to have been in near starvation during glacial pCO2 lows. There are no available proxies for past photorespiration rates that can be measured on fossil materials to test these hypotheses. This project proposes an integrated research and education plan focused on the development of a first-of-its-kind proxy for photorespiration rates based on the isotopic composition of lignin methoxyl groups with two rare isotopes (termed clumped isotopes; 13CH2D-O-lignin and 12CH2D-O-lignin) that can be measured on modern and fossil material. The proxy will be developed and calibrated based on theory, experiments, and a survey of modern environmental samples. It will then be applied to test the long-standing hypothesis that terrestrial ecosystems were carbon starved in the last glacial period due to elevated photorespiration rates associated with low atmospheric CO2. Proposed methodologies that will be employed are: (1) Chemical extraction and purification of methoxyl groups from wood lignin and conversion to the analyte CH3Cl. (2) Use of a high-resolution isotope-ratio mass spectrometer to measure intensities of 12CH3+, 12CH2D+, 13CH3+, 13CH2D+, and 12CHD2+ from CH3Cl ion fragments. (3) Growth of plants in growth chambers under controlled conditions. (4) Collection of modern and fossil wood from archives. (5) Theoretical calculations of partition function ratios of isotopologues. This work will provide the community with a new, calibrated proxy and allow for the immediate testing of a long-standing hypothesis on how changes in pCO2 on geological timescales has or has not affected terrestrial ecosystems. Through an integrated educational and research program, the research will be incorporated into educational materials for the general public and for teachers. These materials will be hosted and disseminated by the Understanding Global Change web resource developed by the University of California Museum of Paleontology (UCMP). The educational websites hosted by the UCMP receive millions of visitors per month and thus reach a broad, diverse community that includes the general public, students, and educators. Finally, the research will be integrated into the classes taught by the investigator, including development of a graduate seminar course and creation of new lessons and exercises. The teaching materials developed for these classes will in turn be posted onto the Understanding Global Change website in order to provide examples lesson and exercises for educators using this website to develop their own lesson plans.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.