An Experimental Study of Algal Communities on Sphagnum.

Our knowledge of the factors that control the distribution and abundance of bog algae is largely based on observational and correlational studies which have not been designed to isolate single key factors or clarify the role of macronutrients. These studies have often been non-quantitative and performed on a scale irrelevant to microorganisms. This literature is reviewed with a discussion of the role of geographic factors, pH, humic acids, "minerotrophic" gradients, macronutrients, substrates, colonization, desiccation, and algal patchiness. A small-scale experimental field study of the algal epiphytes of Sphagnum was performed on the floating mat of an acid bog. The objectives were to find patterns in the structure of the algal community and to see how nutrient additions affect these patterns. Plots were established on the mat. Some plots were left untreated while others were sprayed semi-weekly with solutions of distilled water, phosphate, ammonium, trace nutrients (including silicate), or all of these. I identified and counted the algae after washing them off Sphagnum plants, and measured the concentrations of phosphate, silicate, ammonium, and nitrate in the water subtending the mosses on these plots. Data from untreated and watered plots revealed that the algal community on low plots (closer to the edge of the bog lake, and dominated by S. cuspidatum and S. recurvum) was more abundant and diverse, and that nutrient concentrations were lower in water from these plots than from high plots (farther from the mat edge and dominated by S. magellanicum). Abundance and diversity were less variable on watered plots than on untreated plots. Data from fertilized plots revealed that any of the nutrient additions increased abundances; however, different algal groups dominated plots receiving different nutrient additions. Untreated, watered, and ammonium-treated plots were dominated by chlorophytan species. Trace nutrients sustained the growth of diatoms, whereas phosphate addition fostered cyanobacterial growth. While species show intense small-scale patchiness, the quality and quantity of macronutrient inputs may strongly influence the ecology of algal communities on Sphagnum.PhDEcologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158846/1/8215015.pd