NSF Postdoctoral Fellowship in Biology FY 2017: Reconstructing CO2 fertilization with herbaria

这是美国国家科学基金会生物学博士后研究奖学金，隶属于生物馆藏研究项目。该研究员Leander Anderegg正在进行研究并接受培训，以创新的方式利用生物收集，并由两个主办机构的两位赞助科学家指导：Todd Dawson（加州大学伯克利分校）和Joseph Berry（卡内基科学研究所）。这位研究员正在研究过去一个世纪以来，植物对大气中不断增加的二氧化碳（CO2）的反应，以预测未来植物将如何应对人类不断增加的二氧化碳排放。植物就像商人：它们本质上把水交换到大气中，以换取通过光合作用产生糖所需的二氧化碳。通过燃烧化石燃料，人类改变了全球碳水交换速率，使从大气中“购买”二氧化碳的水成本降低，从而有利于植物。从理论上讲，这可以促进世界各地的植物生长，提高作物产量，并增加未来生态系统可以从大气中吸收的二氧化碳排放量。然而，最近的观察表明，这种二氧化碳施肥效应比以前认为的要有限和多变得多。这项研究探讨了为什么二氧化碳施肥反应如此复杂，重点关注干旱胁迫和植物物种之间的差异如何决定植物是否以及如何对大气中二氧化碳的上升做出反应。这位研究员正在使用博物馆植物标本馆收集的百年植物样本，以及从同一地点收集的现代样本，来重建加州各地的树种是如何应对不断上升的二氧化碳的。这位研究员正在比较这些古代和现代树叶的形态、解剖结构和化学成分，以确定树木在过去一个世纪里是如何改变它们的生理的。通过本研究收集的植物对二氧化碳响应的历史和当代记录也揭示了不同物种和气候下二氧化碳施肥的变化。他正在利用这些信息，再加上从树核中重建的树木生长和机械光合作用模型，来了解水分的可用性和物种生理如何决定树木对二氧化碳浓度升高的反应。这项工作有助于调和短期二氧化碳施肥实验的结果和树木年轮对水和二氧化碳交换率的长期观测结果。对导致不同CO2施肥响应的植物性状和环境条件的细致理解将提高我们在加速环境变化下预测陆地生态系统功能的能力。他正在接受植物解剖、同位素和建模技术方面的培训，同时也在开发新方法，从未充分利用的植物标本馆藏品中获取关键信息。

This is an NSF Postdoctoral Research Fellowship in Biology, under the program Research Using Biological Collections. The fellow, Leander Anderegg, is conducting research and receiving training that utilizes biological collections in innovative ways, and is being mentored by two sponsoring scientists at two host institutions: Todd Dawson (University of California-Berkeley) and Joseph Berry (Carnegie Institute for Science). The fellow is investigating how plants have responded to rising amounts of carbon dioxide (CO2) in the atmosphere over the past century, in order to predict how plants will respond to increasing human CO2 emissions in the future. Plants are like merchants: they essentially trade water to the atmosphere in exchange for the CO2 they need to produce sugars through photosynthesis. By burning fossil fuels, humans have changed the global carbon-water exchange rate in plants' favor by making it less water-expensive to 'buy' CO2 from the atmosphere. Theoretically, this could increase plant growth around the world, improving crop yields and increasing how much of our CO2 emissions ecosystems can absorb from the atmosphere in the future. However, recent observations suggest that this CO2 fertilization effect is far more limited and variable than previously thought. This research explores why CO2 fertilization responses are so complex, focusing on how drought stress and differences between plant species determine if and how a plant responds to rising atmospheric CO2.The fellow is using hundred-year-old plant samples from museum herbarium collections along with modern samples collected from the same locations to reconstruct how tree species across California have responded to rising CO2. The fellow is comparing the morphology, anatomy and chemical composition of these historical and modern leaves to determine how trees have changed their physiology over the past century. The historical and contemporary records of plant responses to CO2 collected through this research are also revealing how CO2 fertilization varies across species and climates. The fellow is using this information, along with tree growth reconstructions from tree cores and mechanistic photosynthesis models, to understand how water availability and species physiology dictate tree responses to elevated CO2. This work is helping to reconcile the results of short-term CO2 fertilization experiments and long-term observations from tree rings of the exchange rate between water and CO2. A nuanced understanding of the plant traits and environmental conditions that lead to different CO2 fertilization responses will improve our ability to predict terrestrial ecosystem function under accelerating environmental change. The fellow is being trained in plant anatomical, isotopic and modeling techniques while also developing new methods for unlocking critical information from underused herbarium collections.