title: Nitrogen deposition effects on carbon storage and fungal:bacterial ratios in coastal sage scrub soils of southern California.
abstract: The effects of nitrogen (N) across a deposition gradient on bacterial and fungal degradation pathways were studied in southern California coastal sage scrub soils to determine whether elevated N levels alter microbial community structure and organic matter accumulation. Three sites across an N deposition gradient having low, intermediate, and high levels of atmospheric N deposition were studied for 20 mo. Fungi:bacteria (F:B) biomass ratios were determined by phospholipid fatty acid analysis. Plots at each location included control plots receiving ambient N deposition and treatment plots that were fertilized with an additional 50 kg N ha(-1) yr(-1) of slow-release urea. Results showed that organic carbon (C) levels varied seasonally but that F:B ratios were relatively stable and similar across the three locations and over time. Total organic C decreased in response to N additions only at the low N deposition site. The results suggest that organic matter degradation pathways leading to C storage in soils that have been exposed to high levels of atmospheric N deposition are not responsive to additional increases in N and that N effects on organic C in semiarid soils may be significant only in areas with prior low exposure to N pollution.
authors.affiliation: Department of Environmental Sciences, University of California, Riverside, CA 92521, USA.
authors.forename: Kun
authors.initials: K
authors.lastname: Liu
authors.forename: David
authors.initials: D
authors.lastname: Crowley
mesh_terms: D018533:Biomass; D002140:California; D002244:Carbon / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000737:chemistry*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D002244:Carbon; D009584:Nitrogen