Effects of Dry-Season N Input on the Productivity and N Storage of Mediterranean-Type Shrublands

• Published in: Ecosystems (New York) 2009-04, Vol.12 (3), p.473-488
• Main Authors: Vourlitis, George L, Pasquini, Sarah C, Mustard, Robert
• Format: Article
• Language: English
• Subjects: Ammonium nitrate; Animal and plant ecology; Animal, plant and microbial ecology; Anthropogenic factors; Biogeochemistry; Biological and medical sciences; Biomedical and Life Sciences; Chaparral; Chaparral soils; Climatology. Bioclimatology. Climate change; Dry deposition; Dry season; Earth, ocean, space; Ecology; Ecosystem studies; Ecosystems; Environmental Management; Exact sciences and technology; External geophysics; Fertilization; Fundamental and applied biological sciences. Psychology; General aspects; Geoecology/Natural Processes; Hydrology/Water Resources; Ion exchange; Leaching; Life Sciences; Litter; Meteorology; Mineralization; Nitrogen; Plant litter; Plant Sciences; Population growth; Productivity; Rainfall; Resins; Seasons; Semiarid environments; Shrublands; Shrubs; Soil; Soil ecology; Soil surfaces; Storage; Summer; Synecology; Vegetation; Winter; Zoology
• ISSN: 1432-9840; 1435-0629
• DOI: 10.1007/s10021-009-9236-6

Anthropogenic nitrogen (N) deposition is a globally important source of N that is expected to increase with population growth. In southern California, N input from dry deposition accumulates on vegetation and soil surfaces of chaparral and coastal sage scrub (CSS) ecosystems during the summer and fall and becomes available as a pulse following winter rainfall. Presumably, N input will act to stimulate the productivity and N storage of these Mediterranean-type, semi-arid shrublands because these ecosystems are thought to be N limited. To assess whether dry-season N inputs alter ecosystem productivity and N storage, a field experiment was conducted over a 4-year period where plots were exposed to either ambient N deposition (control) or ambient + 50 kgN ha⁻¹ y⁻¹ (added N) that was added as NH₄NO₃ during the fall dry-season of each year. Plots exposed to added N had significantly higher accumulation of NH₄ and NO₃ on ion exchange resins that was due in part to direct fertilization and N mineralization, and the increase in N availability lead to a significant increase in NO₃ leaching in chaparral but not CSS. Nitrogen addition also lead to an increase in litter and tissue N concentration and a decline in the C:N ratio, but failed to alter the ecosystem productivity and N storage of the chaparral and CSS shrublands over the 4-year study period. The reasons for the lack of a treatment response are unknown; however, it is possible that these semi-arid shrublands are not N limited, cannot respond rapidly enough to capture the ephemeral N pulse, are limited by other nutrients, or the N response is dependent on the amount and/or distribution of rainfall. These results have important implications for understanding the potential effects of anthropogenic N deposition on the C and N cycling and storage of Mediterranean-type, semi-arid shrublands.