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

森林在视觉上是美国景观的重要组成部分，是我们建筑行业的关键，也是未来二氧化碳排放的重要封存区域。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，是什么决定了植物从大气中吸收并转化为生物量的碳量？在其他条件相同的情况下，如今人们普遍发现，植物吸收的二氧化碳越多，生长得越好。固碳率对二氧化碳的依赖性被称为“二氧化碳施肥效应”。它基于增加二氧化碳会增加全球光合速率的想法，这与未来的气候有很大的关系。这一提议的重点是地质过去，在过去的6500万年里，二氧化碳浓度从冰河时期的180 ppm到数千万年前的1000 ppm，变化了1000 ppm。一个问题是，是否像在现代植物中看到的那样，古代植物对地质时期二氧化碳浓度的变化做出了反应？在最后一次冰河时期，植物是否因为二氧化碳含量低而挨饿，而在数千万年前富含二氧化碳的大气中茁壮成长？模型预测这是正确的，但是没有“代理”可以重建过去地质时期植物生长速度如何响应不断变化的二氧化碳水平。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，基于木材组织中碳和氢结合在一起的稀有稳定同位素的丰度。他将通过实验和现代植物对测量结果进行校准，然后研究过去地质时代的样本。作为这项工作的一部分，他还将通过加州大学古生物博物馆的全球气候变化教育资源，为9-12年级的教育者创建新的在线教学资源，这也将整合到加州大学伯克利分校的课程中。地球历史模型预测，显生宙二氧化碳浓度的变化通过改变植物的光呼吸和光合作用的相对速率而改变了全球陆地初级生产力。据预测，这些变化会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二氧化碳分压低期间几乎处于饥饿状态。对于过去的光呼吸速率，没有可用的替代方法可以用化石材料来测量来检验这些假设。该项目提出了一项综合研究和教育计划，重点是开发一种基于木质素甲氧基基团同位素组成的光呼吸速率的首个代理，该同位素具有两种稀有同位素（称为团块同位素；13ch2d -o -木质素和12ch2d -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来开发和校准。然后，它将被应用于测试一个长期存在的假设，即陆地生态系统在最后一个冰期是由于与低大气二氧化碳相关的光呼吸速率升高而导致的碳饥饿。建议采用的方法是：(1)从木质素中化学提取和纯化甲氧基，并将其转化为分析物CH3Cl。(2)利用高分辨率同位素比质谱仪测定CH3Cl离子碎片中12CH3+、12CH2D+、13CH3+、13CH2D+和12CHD2+的强度。(3)受控条件下植物在生长室内的生长。(4)从档案中收集现代木材和化石木材。(5)同位素配分函数比值理论计算。这项工作将为该社区提供一个新的、校准的代理，并允许立即测试一个长期存在的假设，即二氧化碳分压在地质时间尺度上的变化如何影响陆地生态系统。通过一个综合的教育和研究计划，研究将被纳入一般公众和教师的教育材料。这些材料将由加利福尼亚大学古生物博物馆（UCMP）开发的“了解全球变化”网络资源托管和传播。UCMP主办的教育网站每月接待数百万的访问者，因此覆盖了一个广泛的、多样化的社区，包括普通公众、学生和教育工作者。最后，研究将整合到研究者所教授的课程中，包括开发研究生研讨会课程和创建新的课程和练习。为这些课程开发的教材将被发布在“了解全球变化”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示例课程和练习。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.