PARENT SESSION
Oral Session # 50: Forest Ecology III: Modeling; Nutrient Cycling.
Presiding: L Comas
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 100.
Tree girdling and soil carbon cycling at the Niwot Ridge Ameriflux Site, Colorado.
Scott-Denton, Laura*,1, Schliemann, Sarah1, Backlund, Brant1, Monson, Russell1, 1 University of Colorado, Boulder, CO
ABSTRACT- The importance of the linkage between recent photosynthesis and below-ground carbon cycling is becoming more clear as ecosystem-level carbon flux datasets become larger and temporally dense. This study attempted to examine this linkage by measuring soil carbon pools and soil respiration in a Colorado subalpine forest after cutting off fresh photosynthate to plots by girdling trees and trenching soil. Ten plots of approximately 10m2 were established. In five of these plots all the trees (2-4) were girdled during the winter while the trees were dormant. After snowmelt, the circumference of the girdled plots was trenched through the organic soil layer to a depth of approximately 30cm. Soil samples were taken from the organic layer throughout the season, including the time before snowmelt. Soil respiration measurements were taken after snowmelt on established arrays of collars. Soil respiration was shown to be similar between the girdled and control plots at the beginning and end of the season but to be reduced in the girdled plots by approximately 50% at the mid-summer maximum. Soil microbial biomass was also depressed in the mid-summer maximum in the girdled plots, but seemed to show an ephemeral peak during snowmelt in the girdled plots that may represent a stimulation of the soil heterotrophs. Soil fungi as measured by soil ergosterol was not significantly effected by girdling, nor did it vary significantly throughout the summer, though it seemed to follow a similar pattern to the total microbial biomass. Soil soluble carbon content showed a large peak during snowmelt in the control plots that was absent from the girdled plots. The magnitude and timing of these results suggest that the influence canopy above-ground processes can have critical short-term effects on soil carbon cycling and the below-ground community structure.
Key words: soil respiration, fungal biomass, soil trenching, microbial biomass