Effects of Nitrogen Deposition on the Carbon Allocation and Nutrient Concentration of Southern California Vegetation.

Coastal sage scrub and chaparral vegetation of Southern California have become fragmented due to a loss of habitat over the past several decades, which has been caused by several contributing factors such as agriculture, urbanization, increased fire frequency and intensity. Although nitrogen deposition has also been found to be a contributing factor to the loss of coastal sage scrub (CSS) and chaparral habitats in previous studies, the mechanism for these effects not been examined. Leaf tissue from existing field plots, fertilized with nitrogen since 2003, was analyzed for carbon allocation patterns and nutrient retention on a seasonal and annual basis from 2006, 2008 and 2010. Nitrogen fertilization did not have an effect on carbon allocation to cellulose, holocellulose or lignin fractions of leaf tissue in CSS California sagebrush (Artemisia californica) or chaparral chamise (Adenostoma fasciculatum) shrubs. However, it was found that seasonal and interannual variation in soluble carbon were highest in both species, but without any N treatment interaction. It was also found that year and season did have a significant effect on carbon allocation, and these temporal variations were correlated with precipitation rates and nutrient availability. The lack of nitrogen effect in the soluble carbon, holocellulose and lignin fractions suggests these avenues of carbon allocation are linked to life history traits that are specific to each species such as drought tolerance, woodiness, and maturation.