RUI: Soil carbon sequestration and turnover after twelve years of CO2 fertilization at the Duke Forest FACE experiment

杜克森林自由空气二氧化碳富集（FACE）实验是运行时间最长的实验，在该实验中，一个完整的森林生态系统暴露于高浓度的大气二氧化碳中。该实验解决了人类向大气排放二氧化碳如何影响森林中碳固存和养分循环的基本问题。FACE试验中的土壤将被取样并进行化学分析，以更好地了解土壤氮有效性如何控制碳固存和促进树木生长，以应对二氧化碳浓度上升。迄今为止，实验表明，二氧化碳浓度升高会增加树木和森林地面（即凋落物层）的碳储量。然而，没有观察到矿物土壤中碳含量的增加。很可能是土壤固碳的速度太慢，难以检测。来自进一步土壤化学分析的信息将确定额外氮的来源，以支持所观察到的树木生长的增加。了解树木生长和生产力的氮限制对于预测森林生态系统对大气CO2浓度上升的长期响应至关重要。森林中的碳固存可以潜在地缓解与人类二氧化碳排放相关的气候变化。鲍登学院的本科生将在为期一年的生物和化学荣誉项目中进行大部分研究。此外，这项研究的结果将在环境科学课程和研究研讨会上提出，以使更多的学生了解。

The Duke Forest Free-air CO2 Enrichment (FACE) experiment is the longest running experiment in which an intact forest ecosystem is exposed to elevated concentrations of atmospheric CO2. The experiment addresses fundamental questions about how human emissions of CO2 to the atmosphere affect carbon sequestration and nutrient cycling in forests. The soils in the FACE experiment will be sampled and chemically analyzed to better understand how soil nitrogen availability controls carbon sequestration and enhanced tree growth in response to rising CO2 concentration. To date, the experiment has shown that elevated CO2 increased carbon storage in trees and in the forest floor (i.e., the litter layer). However, increases in the carbon content of the mineral soil were not observed. It is likely that the rates of soil carbon sequestration are too slow to be easily detected. Information from further soil chemical analyses will identify the source of the additional nitrogen required to support the observed increase in tree growth. Understanding nitrogen limitation of tree growth and productivity is vital for predicting the long-term response of forest ecosystems to rising atmospheric CO2 concentrations. Carbon sequestration in forests can potentially mitigate climate change associated with human CO2 emissions. Undergraduate students at Bowdoin College will conduct much of this research during year-long honors projects in biology and chemistry. Additionally the results of this research will be presented in environmental science courses and research seminars to reach a greater number of students.