Land-use change impacts on carbon and nitrogen cycling and greenhouse gas emissions

随着人口的增加，土地利用的变化速度正在加快，陆地生态系统正受到人为压力的威胁。提出的研究探讨了人类干扰如何改变陆地生态系统中碳和氮循环的关键过程。关键问题是：1)森林管理实践如何改变森林结构和与大气的碳交换速率；2)原农业用地和草地的造林如何影响土壤碳储量；3)向森林生态系统添加的氮的命运是什么，土地利用模式如何影响流域尺度的氮保留？本研究将结合实地研究、基于过程的模型以及与遥感专家的合作，探讨森林管理如何改变森林结构，以及森林结构的变异性如何在不同时空尺度上影响森林生长率和净碳储量。不同的方法和模型将在缅因州的豪兰森林和加拿大的两个Fluxnet站点进行测试。利用安大略省已造林的农业用地的时间序列，本研究将量化前农业用地转为森林（造林或再造林）后碳和氮循环过程的变化，以及对净碳储量的影响。这项研究的结果最初基于缅因州豪兰森林的结果，将探索添加到森林冠层的氮在生态系统中移动的过程，以及它对净碳储量的影响。安大略省历史和当前的土地使用和水质数据将用于量化影响外源氮保留的流域尺度因素。这些结果将与其他国家的结果进行比较，这些国家的氮来源和土地利用模式差异很大。这项创新研究为控制陆地生态系统中碳和氮循环的过程提供了新的见解。这些信息将有助于提供创新的政策解决方案，以帮助解决社会面临的关键环境问题。

As human populations increase, rates of land-use change are accelerating, and terrestrial ecosystems are being threatened by anthropogenic stresses.  The proposed research explores how human disturbances alter key processes of carbon and nitrogen cycling in terrestrial ecosystems.  Key questions are 1) How do forest management practices alter forest structure and rates of carbon exchange with the atmosphere 2) How does afforestation of former agricultural land, and grasslands, influence soil carbon storage and 3) What is the fate of nitrogen added to forest ecosystems, and how do patterns of land use influence catchment-scale nitrogen retention? Using a combination of field studies, process-based models, and collaboration with remote sensing specialists, this research will address how forest management alters forest structure, and how variability in forest structure influences forest growth rate and net carbon storage over various spatial and temporal scales.  Different approaches and models will be tested at Howland Forest in Maine and at two Fluxnet Canada sites.  Using a chronosequence of afforested agricultural lands in Ontario, this research will quantify changes in carbon and nitrogen cycling processes following the conversion of former agricultural land to forests (afforestation or reforestation), and the impact on net carbon storage.  Based initially on results from Howland Forest in Maine, results from this research will explore the processes by which nitrogen added to a forest canopy moves through the ecosystem, and it's impact on net carbon storage.  Land-use and water quality data in Ontario, both historical and current, will be used to quantify catchment-scale factors that influence retention of exogenous nitrogen.   These results will be compared to those from other countries with vastly different sources of nitrogen and land-use patterns. This innovative research provides new insights into processes that control carbon and nitrogen cycling in terrestrial ecosystems.  This information will help inform innovative policy solutions to help solve key environmental issues facing society.