PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Nitrogen losses from native perennial and exotic annual grasslands in California.
Parker, Sophie*,1, Schimel, Joshua1, 1 University of California, Santa Barbara, CA, USA
ABSTRACT- Given that the introduction of even a single plant species can have large effects on nitrogen cycling in an ecosystem, the invasion of native perennial grassland communities by exotic species of annual grasses from Europe raises many questions regarding the processing and retention of nitrogen in these systems. To examine the effects of grassland species change on nitrogen cycling, we employed the use of experimental grassland plots with homogeneous initial soils. Plots were seeded with a mix of either native perennial grasses (Nassella pulchra, Bromus carinatus, and Elymus glaucus) or nonnative annuals (Bromus hordeaceus, Bromus madritensis, and Hordeum murinum). Using tension lysimeters, we quantified leaching losses of nitrate, ammonium, and dissolved organic nitrogen. Rates of mineralization, nitrification, and denitrification were measured to examine the relative importance of these different microbial processes in contributing to nitrogen loss from each experimental grassland type. Comparisons of microbial process rates were also made in naturally occurring annual and perennial grasslands. Exotic annual grass stands may be somewhat more leaky with regard to nitrogen than stands of native perennial grasses. Seasonal trends in microbial process rates that correspond with soil moisture indicate that rates of nitrification and denitrification, as well as leaching losses, may be dependent on the amount and timing of rainfall. In dry years, low soil moisture may be more important than species composition in determining nitrogen losses from grasslands, while differences in plant phenology and microbial process rates may drive nitrogen loss in wetter years.
Key words: nitrogen cycling, soil microbial processes, grasslands, invasive species