Fire, Atmospheric pCO2, and Climate as Alternative Primary Controls of C4-Grass Abundance: The Late-Quaternary Perspective

以草为主的生态系统覆盖了地球约三分之一的陆地表面，影响着全球生物地球化学过程(如水、碳和养分循环)，是人类和草食动物的主要食物来源。这些生态系统对未来气候和大气化学变化最敏感。这种敏感性可以部分归因于C3和C4植物两个主要功能基团的差异反应。C4植物在某些环境条件下(如火灾、高温、干旱和低二氧化碳)获得竞争优势。C3和C4植物反过来又对主要的生物地球化学过程产生不同的影响；例如，C4植物在全球净初级生产量中的作用不成比例地大。尽管有这些众所周知的差异，但哪些环境因素直接控制C3和C4植物的相对丰度仍然存在争议。古生态研究可以帮助破译C3和C4植物对各种环境条件的反应，从而为预测未来的变化提供信息。该项目将评估火、气候和大气二氧化碳浓度对过去25,000年来东非和澳大利亚C4草丰度变化的影响。研究人员将分析沉积物岩心以获得一套生态替代指标，并开发一种新技术来估计地质记录中C4植物的丰度。该项目为教育公众了解气候变化和草原生态提供了良好的环境。研究人员将组织针对初中和高中教师以及土地管理人员的暑期课程。

Grass-dominated ecosystems cover about one-third of Earth's land surface, influence global biogeochemical processes (e.g. water, carbon, and nutrient cycling), and serve as major food sources for humans and herbivores. These ecosystems are among the most sensitive to future changes in climate and atmospheric chemistry. This sensitivity can be partially attributed to the differential responses of two major functional groups, C3 and C4 plants. C4 plants gain competitive advantages under certain environmental conditions (e.g. fire, heat, drought, and low pCO2). C3 and C4 plants in turn have distinct influences on major biogeochemical processes; for example, the role of C4 plants in global net primary production is disproportionately large. Despite these well-known differences, it remains controversial what environmental factors directly control the relative abundances of C3 and C4 plants. Paleoecological studies can help decipher the responses of C3 and C4 plants to a wide range of environmental conditions, thereby offering information for anticipating future changes. This project will evaluate the effects of fire, climate, and atmospheric CO2 concentration on the variation of C4-grass abundance over the past 25,000 years in East Africa and Australia. The researchers will analyze sediment cores for a suite of ecological proxy indicators and develop a novel technique to estimate the abundance of C4 plants in geological records. This project provides an excellent context for educating the general public on climate change and grassland ecology. The researchers will organize summer courses targeting middle and high school teachers as well as land managers.