PARENT SESSION
Oral Session # 38: Forest Ecology II: Soils, Carbon, and Nutrient Cycling.
Presiding: B Clinton
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 100.
Nitrogen fertilization alters fungal and bacterial biomass and microbial community structure in three long-term experiments.
Wallenstein, Matthew*,1, 2, Schlesinger, William2, S.K., Rhee3, Zhou, Jizhong3, 1 Duke University, Durham, NC2 Duke University, Durham, NC3 Oak Ridge National Laboratory, Oak Ridge, TN
ABSTRACT- We collected soil samples throughout the 2002 growing season in three long-term nitrogen fertilization experiments in New England, USA (Harvard Forest, Bear Brook Watershed, Mt. Ascutney). Fungal and bacterial biomass were assessed using the chloroform fumigation-extraction technique and by substrate induced respiration coupled with selective inhibitors. At two of the sites, we found a large and significant decrease in total biomass with increasing nitrogen inputs. The ratio of fungal:bacterial biomass also decreased with increasing N. Across all 3 sites, there was a negative correlation between microbial biomass and annual net N mineralization, and a positive correlation with pH. We also used functional gene microarrays to assess long-term changes in the functional diversity and gene abundance in DNA extracted from these soils. These microarrays provide abundance data for over 5000 genes important in nitrogen, carbon, phosphorus, and sulfur cycling. These analyses revealed consistent shifts in the diversity and abundance of several nitrogen cycling genes with fertilization treatments. These results suggest that long-term changes in nitrogen inputs to forest soils result in fundamental changes in microbial community structure that are likely to alter nitrogen cycling.
Key words: microbial biomass, functional gene, microarray, nitrogen fertilization