PARENT SESSION
Contributed Oral Session 110: Biogeochemistry: Nitrogen Dynamics
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 513 C, Level 5, Palais des congrès de Montréal
N storage and cycling in chaparral and coastal sage scrub ecosystems in response to experimental N deposition: Preliminary results.
Vourlitis, George*,1, Zorba, Gypsi1, Pasquini, Sarah1, Mustard, Robert1, Davis, Kim1, 1 Bioological Sciences Department, San Marcos, CA, USA
ABSTRACT- Anthropogenic N-deposition represents a significant input of N into many southern Californian semi-arid ecosystems, and given that the productivity of chaparral and coastal sage scrub (CSS) is reportedly N-limited, N deposition may cause an increase in C and N storage and cycling of chaparral and CSS. However, most of the N deposited to chaparral and CSS shrublands is in the form of dry deposition that accumulates during the summer and early fall when evergreen and/or drought-deciduous shrubs are physiologically inactive because of drought. Thus, it is unknown how much N deposition is retained by southern California shrublands and whether this added N actually stimulates ecosystem C and N storage. To reduce this uncertainty, in situ N-deposition experiments were initiated in October 2003 in chaparral (post fire) and CSS and continue to date. Plots (100 m2, n = 4 per site) were exposed to 50 kg NH4NO3 during the late-summer of 2003 to simulate the anthropogenic N deposition regime of the South Coast Air Basin. Preliminary results indicate that accumulated inorganic N (NH4 and NO3) in the upper 10 cm of soil increased significantly following N addition. Re-sprouting Adenostoma fasciculatum shrubs exposed to added N had significantly higher tissue N and P concentrations, but not mature CSS shrubs (Artemesia californica and Salvia mellifera). These results suggest that N-deposition may cause available N to increase in chaparral and CSS shrublands and that the initial response of shrubs to added N may be a function of ecosystem type or recovery from fire.
Key words: Fire