XVI International Botanical Congess

Coastal sage shrublands are undergoing vegetation type conversion to annual grassland in southern California due to anthropogenic impacts, including high N deposition and frequent fire. This type of conversion may be associated with potential changes in the soil microflora. We measured changes in bacteria and saprophytic fungi under native shrubs and exotic annual grasses on a nitrogen pollution gradient. Bacterial and fungal biomass were no different in rhizospheres of grasses and Artemisia on any collection date. Bacterial number was not different among sites in 1996. However, in 1997 there were significant differences in hyphal lengths as well as in bacterial counts between the low N compared with the high N sites. The most polluted area is more bacterial dominated, while the opposite occurs in the sites with lower pollution.