DISSERTATION RESEARCH: INCREASED SOIL CARBON WITH NITROGEN ADDITIONS IN NITROGEN-RICH TROPICAL FORESTS: SEARCHING FOR MECHANISMS

人类活动极大地增加了地球上氮的可获得性，热带地区的氮沉积率预计将是未来几十年全球最高的。由于热带森林中的植物生长通常不受氮素的刺激，因此在土壤中，氮素有效性增加对碳积累的影响可能最大。在两个热带森林类型中，土壤碳在施氮3.5年后有所增加。拟议的研究将集中在与这种增加有关的生物学机制上。具体来说，将使用微生物酶分析和分解实验过程中微生物群落组成的测量来确定氮对碳损失的影响。将应用一种将土壤分为不稳定和顽固不化的土壤的分级方案，以探索微生物活动和土壤碳变化之间的联系。这项研究将有助于阐明人类改变全球氮循环可能对热带森林中存在的大型土壤碳库的二氧化碳释放产生积极或消极影响的机制。该项目的信息还将用于加利福尼亚州和波多黎各的本科生和中学生的教育和培训计划，并将成为在加利福尼亚州伯克利为未得到充分服务的学生参加课后计划的学生(6-12年级)进行科学实验的基础。

Human activity has greatly increased the availability of nitrogen on Earth, with nitrogen deposition rates in tropical regions predicted to be the highest globally in coming decades. Because plant growth is not commonly stimulated by nitrogen in tropical forests, the effects of increased nitrogen availability on carbon accumulation are likely to be largest in soils. An increase in soil carbon after 3.5 years of nitrogen fertilization has been observed in two tropical forest types. The proposed study will focus on the biological mechanisms related to this increase. Specifically, microbial enzyme assays and measurements of microbial community composition over the course of a decomposition experiment will be used to determine effects of nitrogen on carbon loss. A fractionation scheme to separate soils into labile and recalcitrant pools will be applied to explore links between microbial activity and changes in soil carbon. This study will help illuminate mechanisms by which human alteration of the global nitrogen cycle might affect, positively or negatively, carbon dioxide releases from the large soil carbon pools that exist in tropical forests. Information from this project also will be used in education and training programs for undergraduate and secondary school students in California and Puerto Rico, and will form the basis for a science experiment conducted with students (grades 6-12) enrolled in an after-school program for under-served students in Berkeley, California.