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

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

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.