SOIL DENITRIFICATION RATES IN 4 SUB-ALPINE PLANT-COMMUNITIES OF THE SIERRA-NEVADA

The acetylene inhibition method was used to determine soil denitrification rates of a riparian, meadow, forest, and barren site in the eastern Sierra Nevada. Data were collected from these four subalpine plant communities during dawn-to-dusk measurement periods in June, August, and October in order to examine denitrification during the dry season. Soil temperature, moisture, organic matter, C, N, C/N ratio, NO3-N, and pH were measured to assess their effects on denitrification rates. At all sites, denitrification rates varied randomly during each measurement period and were not influenced by variation in any other soil parameter investigated. Comparisons among the four communities revealed that no single site consistently exhibited the highest or lowest denitrification rate throughout the study. Denitrification rates and soil temperatures in the riparian, meadow, and forest communities declined concurrently during the October measurement period relative to those measured in June and August. Declining denitrification rates from June through October paralleled a decrease in soil organic matter in the riparian community, and denitrification rate varied with soil N over the three measurement periods at the barren site. These results suggest that denitrification in wildland soils varies both temporally and spatially, and that soil physical and chemical parameters identified here as influencing this process explain long-term but not short-term variations in denitrification rates.