PARENT SESSION
Wednesday, August 9, 5:00-6:30 pm
Poster Session 16 - Urban ecology
Exhibit Hall, Ballroom Level, Cook Convention Center
Desert crusts in an urban landscape: responses of N2 fixation to anthropogenic C and N deposition.
Wong, Christina*,1, Grimm, Nancy2, Sponseller, Ryan 3, 1 Occidental College, Los Angeles, CA, USA2 Arizona State University, Tempe, AZ, USA3 Arizona State University, Tempe, AZ, USA
ABSTRACT- Atmospheric pollution from urban expansion is significantly increasing the amount of biologically available inorganic carbon (iC), organic carbon (oC), and inorganic nitrogen (iN). Urbanization of desert habitats is among the fastest in the world, thus minimizing damage to arid ecosystems is contingent upon understanding how cities are affecting their ecological structure and function. Elevated emissions may change traditional biogeochemical cycles by altering the role of biological soil crust (BSC) (lichens, moss, cyanobacteria and algae living on the soil surface) as important N2 fixers in the desert. Taking advantage of a depositional gradient in rapidly urbanizing central Arizona, this study will determine if elevated levels of iC, oC and iN change N2- fixation rates by BSC. We will quantify N2-fixation rates, as acetylene reduction activity (ARA), of cyanolichens (Collema sp. and Peltulasp.), Nostoc sp. (dark cyanobacteria) and Microcoleus sp. (light cyanobacteria) at desert and remnant desert sites along the anthropogenic C and N gradient. We predict that urban/downwind sites will have lower ARA than upwind sites. We will test for physiological responses to elevated C and N by experimentally exposing urban/downwind BSCs to upwind C and N levels and upwind BSCs to urban levels. We predict that, compared to unmanipulated controls, urban/downwind BSCs will exhibit reduced ARA whereas upwind BSCs show increased ARA. Prolonged exposure to elevated iN, iC, and oC may cause BSCs to develop new, competitive, physiological mechanisms that significantly alter their biogeochemical function.
Key words: Urban Ecosystem, Biogeochemistry, Biological soil crust