PARENT SESSION
Poster Session #27: Nutrient Cycling I.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Changes in soil nitrogen cycling processes and microbial communities across a meadow-forest gradient.

Waterstripe, Kirk^*,1, Rich, Jeremy¹, Mintie, Ann¹, Heichen, Rachel¹, Ritchie-Posavatz, Nancy¹, Bottomley, Peter¹, Cromack, Kermit¹, Myrold, David¹, ¹ Oregon State University, Corvallis, OR

ABSTRACT- Differences in vegetation can influence microbial community composition and nutrient cycling. To investigate the linkage between vegetation type and microbial communities and N cycling processes, we compared N cycling parameters, microbial biomass and functional diversity in soils from adjacent meadows and forests. Soil samples were taken along transects that crossed meadow-forest ecotones at two sites in the H.J. Andrews Experimental Forest, in the Cascade Mountains of Oregon, USA. We measured rates and potential rates of several N cycle processes, and microbial biomass and functional diversity. The results indicate functional differences exist between the meadow and forest soil with respect to the nitrogen cycle, fungal biomass, and functional diversity. Mean rates for net N mineralization, potential denitrification and nitrification were higher in meadow soil than in forest soil. N₂ fixation, and fungal biomass measured by direct microscopic counts were higher in forest soil. No difference in bacterial biomass or chloroform fumigation biomass was detected. Analysis of LH-PCR patterns using PCA showed differences between forest and meadow soils. N mineralization and fungal biomass shifted nonlinearly across the meadow-forest boundary, while the population of nitrifying bacteria showed a linear trend. At these sites, net nitrification and denitrification are dominant N cycling processes in meadow soil, while ammonification is dominant in forest soil. Certain process rates and community parameters change linearly across the meadow-forest edge while others change in a nonlinear fashion.

KEY WORDS: nitrogen cycle, microbial diversity, forest, meadow