HR: 08:30h
AN: B21D-03 INVITED    [Abstracts]
TI: Using the δ¹³C of ecosystem respiration to monitor ecosystem metabolism of entire watersheds in complex terrain.
AU: * Pypker, T G
EM: tgpypker@mtu.edu
AF: Michigan Technological University, School of Forest Resources and Environmental Science, 1400 Townsend Dr., Noblet Building, Houghton, MI 49931, United States
AU: Hauck, M
EM: mjhauck@gmail.com
AF: Oregon State University, Department of Forest Science, Richardson Hall, Corvallis, OR 97331, United States
AU: Sulzman, E W
EM: elizabeth.sulzman@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science, 109 Crop Science Building, Corvallis, OR 97331, United States
AU: Unsworth, M H
EM: unswortm@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, Corvallis, OR 97331, United States
AU: Mix, A C
EM: acmix@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, Corvallis, OR 97331, United States
AU: Kayler, Z
EM: zachary.kayler@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science, 109 Crop Science Building, Corvallis, OR 97331, United States
AU: Conklin, D
EM: david.conklin@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science, 109 Crop Science Building, Corvallis, OR 97331, United States
AU: Kennedy, A
EM: adam.kennedy@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science, 109 Crop Science Building, Corvallis, OR 97331, United States
AU: Barnard, H
EM: holly.barnard@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science, 109 Crop Science Building, Corvallis, OR 97331, United States
AU: Phillips, C
EM: Claire.Phillips@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science, 109 Crop Science Building, Corvallis, OR 97331, United States
AU: Bond, B J
EM: barbara.bond@oregonstate.edu
AF: Oregon State University, Department of Crop and Soil Science, 109 Crop Science Building, Corvallis, OR 97331, United States
AB: Complex terrain presents formidable challenges to ecosystem studies. Valleys, steep slopes, and windswept ridges impose wide variations in microclimate, soil properties, and plant communities; this variability greatly hinders strategies for systematic sampling and up-scaling. Our recent work in a deeply incised watershed (20 to 33° slopes) in Oregon's Cascade Mountains suggested the possibility of using the δ¹³CO₂ of ecosystem respiration (δ¹³C_ER) in mountainous ecosystems as a tool to monitor seasonal and interannual variations in physiological processes in vegetation of entire watersheds. We demonstrated that nocturnal cold air drainage is persistent, occurs on greater than 80% of summer nights and is well mixed. Furthermore, nighttime air samples collected from the base of the watershed contain a representative sample of respired CO₂ from most of the watershed. We also found that on most clear nights the range of CO₂ concentrations over a single night is sufficient for using the Keeling Plot approach to determine the carbon isotopic composition of δ¹³C_ER. The goals of the current study were to determine if variations in δ¹³C_ER were correlated to environmental variables and could be used to predict expected variations in canopy-average stomatal conductance ( g_s). As reported by other researchers, changes in δ¹³C_ER were significantly correlated to measured soil matric potential (ψ_m) and vapor pressure deficit (VPD) measured on the same day and six days earlier, respectively. Midday g_s was estimated using a simple hydraulic model with only ψ_m and VPD as predictive variables. Midday g_s from zero and five days earlier were correlated to δ¹³C_ER. To examine direct relationships between δ¹³C_ER and recent g_s, we used models relating isotope discrimination to stomatal conductance and photosynthetic capacity at the leaf level to estimate values of stomatal conductance ("g_s-I") that would be expected if respired CO₂ were derived entirely from recent photosynthate. We compared these values with g_s estimated from the hydraulic model. The magnitude, range and temporal variation in the two values were surprisingly similar. We conclude that δ¹³C_ER could potentially be used to directly monitor basin-average variations in g_s in complex terrain. If our findings hold to closer scrutiny, this method may be used to monitor leaf physiological properties on the ecosystem scale in complex terrain.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting