HR: 11:35h
AN: B12B-06    [Abstracts]
TI: Seasonal controls on soil respiration fluxes and isotopic content in an African Savanna ecosystem: Implications for site to regional carbon flux estimates
AU: * Neff, J C
EM: jason.c.neff@colorado.edu
AF: University of Colorado, Department of Geological sciences, 2200 Colorado Avenue Benson Earth Science, Boulder, CO 80309-399, United States
AU: Hanan, N
EM: niall@nrel.colostate.edu
AF: Natural Resource Ecology Laboratory, Colorado State University, Natural Resource Ecology Laboratory Colorado State University, Fort Collins, CO 80523-1499, United States
AU: Berry, J A
EM: jberry@globalecology.stanford.edu
AF: Department of Global Ecology, Carnegie Institution of Washington, 260 Panama Street, Stanford, CA 94305, United States
AU: Williams, C A
EM: caw@umbc.edu
AF: UMBC GEST NASA GSFC Biospheric Sciences, NASA GSFC Biospheric Sciences, Greenbelt, MD 20771, United States
AU: Fernandez, D P
EM: daniel.fernandez@colorado.edu
AF: University of Colorado, Department of Geological sciences, 2200 Colorado Avenue Benson Earth Science, Boulder, CO 80309-399, United States
AU: Scholes, R J
EM: bscholes@csir.co.za
AF: Council for Scientific and Industrial Research, Council for Scientific and Industrial Research, Pretoria, 001, South Africa
AB: The savannas of South Africa are characterized by a patchy mosaic vegetation structure comprised of C3 trees and C4 grasses and a strong seasonal precipitation regime. This patchy vegetation structure combined with the strong seasonal precipitation regime potentially leads to substantial variation in both the isotopic content and magnitude of soil respiration. From the perspective of tower-based carbon flux measurements and regional carbon flux studies, the spatial and temporal patterns in soil respiration could present challenges to understanding regional carbon flux controls. In this study, we carried out both low and high frequency measurements of soil respiration using collars and continuous-measurement soil CO₂ probes to understand short and longterm soil respiration dynamics. On a short timescale the continuous measurements of CO₂ flux show soil respiration increases substantially after rainfall; however, a lag time between precipitation and increased soil respiration suggests physical factors affect flux response. Also, following precipitation, soil respiration hysteresis curves occur while soil moisture remains elevated, suggesting substrate limitations may reduce soil CO₂ flux. On an annual timescale fluxes from under tree canopies are 35% greater than interspace grass dominated areas, with the majority of the difference occurring during the wet season. Because of the isotopic SOM differences between under tree canopies (-21.21‰) and interspace grass dominated areas (-16.66‰), the seasonal shifts in flux contributions from these two settings also leads to seasonal variation in site level soil δ¹³CO₂ fluxes. As a consequence, the isotopic content of respiration measured from an eddy covariance tower and interpretation of ecosystem C exchange could be affected by wind direction and plant patch cover heterogeneity.
DE: 0428 Carbon cycling (4806)
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0486 Soils/pedology (1865)
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: 2007 Fall Meeting