HR: 16:25h
AN: B24C-02    [Abstracts]
TI: Coupled hydraulic and photosynthetic feedbacks on forest transpiration throughout the growing season
AU: * Mackay, D S
EM: dsmackay@buffalo.edu
AF: Department of Geography, SUNY at Buffalo, 105 Wilkeson Quadrangle, Buffalo, NY 14261, United States
AU: Ewers, B E
EM: beewers@uwyo.edu
AF: Department of Botany, University of Wyoming, 1000 E. University Avenue, Laramie, WY 82071, United States
AB: Ecosystem models account for vegetative controls on water fluxes using environmental drivers and hydraulic and/or biochemical limits on canopy stomatal conductance (Gs), variations in space and time of leaf area index (L), and species or biome specific parameters. However, some parameters, such as maximum stomatal conductance or its reference proxy at vapor pressure deficit of 1 kPa (Gsref), may not be strictly time-independent suggesting as yet undefined mechanisms in the models. We developed a model of coupled canopy water and carbon exchange, which allowed us to examine photosynthetic and hydraulic feedbacks on Gsref spanning the whole growing season for several dominant tree species in wetland and upland positions that collectively account for most a 1600 square km region centered on the WLEF AmeriFlux tower in Wisconsin, USA. The model assimilated half-hourly sap flux and micrometeorological data to quantify and explain temporal variations in Gsref for trembling aspen, sugar maple, and red pine in upland sites, and speckled alder and white cedar in wetland sites. Results show (1) phenological effects on photosynthetic activity with feedback on Gsref in all species, and (2) lags of up to two months between maximum per unit leaf area photosynthetic rates for conifer versus deciduous species. These results show that for given environmental conditions canopy transpiration depends on both L and timing of biochemical activation, both of which have implications for regional ecosystem water cycling.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0466 Modeling
DE: 1852 Plant uptake
SC: Biogeosciences [B]
MN: 2007 Fall Meeting