Soil nutrient cycling and storage in semi-arid shrubland ecosystems exposed to high N deposition in Southern California

Southern California's geography and expanding population have caused an\ud increasing amount of atmospheric nitrogen (N) deposition into semi-arid\ud shrubland ecosystems. However, the effects of N deposition on semi-arid\ud shrublands of Southern California are still poorly known and must be\ud addressed. This research investigated soil nitrogen storage in several areas\ud of Southern California, which received different levels of exposure to\ud atmospheric nitrogen pollution. Soil samples from five sites of varying\ud atmospheric deposition were analyzed for available and total N, and C, pH\ud and soil organic matter content. The results indicate that soil derived from\ud sites with high pollution exposure had correspondingly higher total N and\ud extractable N, lower pH, and lower C:N ratios than sites with lower pollution\ud exposure. Analysis of resin bags buried below the soil surface (0-1 0 em)\ud showed that accumulation rates of both NH4 and N03 were 1-2 orders of\ud magnitude higher at polluted air sites than at clean air sites, and that soil pH\ud was 0.5 pH point lower in high N pollution sites. These data suggest that\ud atmospheric N deposition can significantly increase soil N storage and rates\ud of N cycling in southern California shrublands.\ud Key words: Nitrogen, carbon, storage, cycling, deposition, C:N, chaparral,\ud coastal sage scrub