Doctoral Dissertation Research: Reconstructing How Ecosystems Develop in High Northern Latitudes Using Genetic Markers and Temperature Signals in Lake Sediments

这项博士论文研究项目将重建过去7000年来一个湖泊流域的植物群落，以更好地了解冻土带生态系统如何对不断变化的环境条件做出反应。随着北极变暖，植被范围预计将向北扩展；高纬度木本植被的增加对全球和北纬生态系统都有重要影响。通过确定过去的植物群落是如何变化的，并通过使用两种分析湖泊沉积物的新技术来重建温度，这位博士生将加强对过去和潜在变暖的未来高纬度气候和生物地理之间相互作用的复杂性的理解。该项目将为本科生提供研究、教育和培训机会。作为博士论文研究改进奖，该奖项还将为有前途的博士生建立强大的独立研究生涯提供支持。博士生将结合相对较新的技术来分析过去的环境。一种是对以前的湖泊沉积物进行沉积古DNA的分析，这是在大量沉积物中发现的降解DNA的复杂混合物，以确定全新世时期湖泊集水区内生活的植物。学生将使用的第二种技术是最近开发的一种生化工具，使用一种称为“支链甘油二烷基甘油四醚”(BrGDGTS)的细菌细胞膜脂的分布，它能够估计过去的温度。使用这些技术，学生将寻求以下几组研究问题的答案：1)随着冰川的消退，矮灌木需要多长时间才能在湖泊集水区形成？2)植物多样性是如何对早期全新世的温暖和晚期全新世的降温做出反应的？3)白桦树是什么时候形成的，它是否在全新世的温度波动中保持存在？通过结合使用这些新技术，该项目的结果将为影响北方高纬度地区植物向北迁移的气候和时间因素提供新的视角。

This doctoral dissertation research project will reconstruct the plant community of a lake catchment over the last 7,000 years in order to better understand how tundra ecosystems respond to changing environmental conditions. As the Arctic warms and vegetation ranges are expected to expand northward; the increase in woody vegetation at high latitudes has important implications for both global and northern latitude ecosystems. By identifying how past plant community shifted and by reconstructing temperatures using two new techniques that analyze lake sediments, the doctoral student will enhance understanding about the complexities of the interplay between climate and biogeography at high latitudes both in the past and in a potentially warmer future. The project will provide research education and training opportunities for undergraduate students. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising doctoral student to establish a strong independent research career.The doctoral student will use a combination of relatively new techniques to analyze past environments. One is the analysis of previously dated lake sediments for sedimentary ancient DNA, the complex mixture of degraded DNA found within bulk sediment, in order to identify the plants that lived within the lake catchment during the Holocene Epoch. The second technique the student will employ is a recently developed biochemical tool, the use of a distribution of a class of bacterial cell membrane lipids called "branched glycerol dialkyl glycerol tetraethers" (brGDGTs) which is able to estimate past temperature. Using these techniques, the student will seek answers to the following sets of research questions: 1) Following the retreat of glaciers, how long did it take for dwarf shrubs to become established in the lake catchment? 2) How did plant diversity respond to the warmth of the early Holocene and cooling during the Late Holocene? 3) When did Betula (dwarf birch), a shrub that likes warmer temperatures currently near its northern limit in this field area, become established, and did it remain present through Holocene temperature fluctuations? Through the use of these new techniques in combination, the project's results will offer new perspectives about the climatic and temporal factors influencing northward plant migration in high northern latitudes.