Microbial and Hydrological Controls of Nitrogen Losses From Alpine and Chaparral Ecosystems During Seasonal Transitions

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

The project will examine biogeochemical and hydrological mechanisms that influence the extent of N limitation in alpine and chaparral ecosystems of the Sierra Nevada, California. These ecosystems exhibit large, episodic losses of nitrate and their future integrity is threatened by climate change and nearby human activities. The investigators hypothesize that a key factor controlling N-losses in these ecosystems is the effect of transitions between growing and non-growing seasons on microbial populations and biogeochemical processes in soils during non-growing seasons. Seasonal transitions in Mediterranean climates, like those of California, are characterized by abrupt shifts from dry to wet conditions, warm to cold temperatures and from low to high runoff periods. These transitions induce changes in soil moisture and temperature that mediate flushing of nitrate. Over the long-term, nitrate losses during seasonal transitions may be a primary mechanism by which N limitation is maintained in alpine and chaparral ecosystems. The project will take a watershed approach to studying N dynamics in alpine and chaparral ecosystems and will utilize a combination of innovative techniques, including plot-scale studies, isotopic and chemical tracers, watershed mass balances and ecosystem modeling. Results from these investigations will help explain a major question in terrestrial ecology: Why are plant communities N limited? Additionally, the work will provide an understanding of the connections between hydrology and biogeochemistry during seasonal transitions, which is needed to predict how California's montane ecosystems will respond to anticipated global change.