Comparison of Microbial Enzymatic Activity of Slope Aspect and Shrub Species in CSUSM Chaparral

Abstract

Soil microbial extracellular enzymes facilitate key nutrient cycling processes in terrestrial ecosystems. In Mediterranean-type shrublands, factors such as slope aspect and dominant plant species influence soil moisture, organic matter inputs, and microbial activity. This study investigated how slope orientation and shrub species affect the activity of three microbial enzymes: phosphatase, β-glucosidase, and N-acetylglucosaminidase (NAGase). Soil samples were collected beneath both shrub species on opposing slope aspects at a CSUSM chaparral site in southern California. Enzyme activities were measured using colorimetric microplate assays. Two-way ANOVA revealed that phosphatase activity was significantly higher in soils beneath Ceanothus tomentosus compared to Salvia mellifera. No significant differences were found for NAGase. β-glucosidase, showed a trend toward higher activity under Ceanothus. Phosphatase and β-glucosidase activities were positively correlated with soil organic matter and dissolved organic carbon, suggesting microbial function is closely linked to carbon availability. These results show the influence of plant identity on microbial nutrient cycling in semi-arid ecosystems and suggest that nitrogen-fixing shrubs like Ceanothus may alter belowground microbial activity through changes in litter quality and available nutrients.