HR: 14:05h
AN: B23E-02    [Abstracts]
TI: Hydraulic Redistribution of Soil Water in a Drained Loblolly Pine Plantation: Quantifying Patterns and Controls over Soil-to-Root and Canopy-to-Atmosphere Interactions
AU: * Domec, J
EM: jdomec@ncsu.edu
AF: North Carolina State University, Department of Forestry and Environmental Resources, Raleigh, NC 27695, United States
AU: Noormets, A
EM: anoorme@ncsu.edu
AF: North Carolina State University, Department of Forestry and Environmental Resources, Raleigh, NC 27695, United States
AU: King, J S
EM: john_king@ncsu.edu
AF: North Carolina State University, Department of Forestry and Environmental Resources, Raleigh, NC 27695, United States
AU: Sun, G
EM: gesun@fs.fed.us
AF: USDA-Forest Service Southern Research Station, 920 Main Campus Dr. Venture Center 2 Suite 300, Raleigh, NC 27606, United States
AU: McNulty, S G
EM: smcnulty@fs.fed.us
AF: USDA-Forest Service Southern Research Station, 920 Main Campus Dr. Venture Center 2 Suite 300, Raleigh, NC 27606, United States
AU: Gavazzi, M J
EM: mgavazzi@ncsu.edu
AF: USDA-Forest Service Southern Research Station, 920 Main Campus Dr. Venture Center 2 Suite 300, Raleigh, NC 27606, United States
AU: Strickland, S
EM: sstrickland@fs.fed.us
AF: USDA-Forest Service Southern Research Station, 920 Main Campus Dr. Venture Center 2 Suite 300, Raleigh, NC 27606, United States
AU: Boggs, J L
EM: jboggs@fs.fed.us
AF: USDA-Forest Service Southern Research Station, 920 Main Campus Dr. Venture Center 2 Suite 300, Raleigh, NC 27606, United States
AB: The conversion of wetlands to intensively managed forest lands in eastern North Carolina is widespread and the consequences on water and carbon balances are not well studied. Quantification of evapotranspiration (ET), tree transpiration and their biophysical regulation are needed for assessing forest water management options. We characterized vertical variation in the diurnal and seasonal soil volumetric water content at 10 cm intervals to evaluate changes in water availability for root uptake and monitored eddy covariance ET and tree transpiration (sap flux) in a drained Loblolly pine (Pinus taeda L.) plantation. We also quantified the magnitude of hydraulic redistribution (HR), the passive movement of soil water from deep to shallow roots, to identify factors affecting the seasonal dynamics of root water uptake, root and plant water potentials and stomatal conductance. Soil water content varied with soil depth and total water use from the upper 1m peaked between 4 and 6.5 mm/day during the growing season and was strongly correlated and similar to ET (ET represented 90-95% of total water depletion). After periods of more than 10 days without rain, water extraction shifted to the deeper layers, and recharge from HR approached 0.5 mm/day in the upper 60 cm. However, the upper 30cm accounted for 40% of total water depletion from the upper 1m at peak water uptake (>4 mm/day), and increased to 65% during days of low water uptake (<2 mm/day), illustrating the contribution of deeper roots to water uptake during days of high evaporative demand. This result was supported by the fact that deep roots (from 30-50cm) accounted for 65% of the total water redistributed. Because of stomatal regulation to prevent water potentials from reaching critical values that would cause significant loss of tree hydraulic conductivity, maximum tree transpiration during high evaporative demand remained constant at around 3 mm/day. Tree transpiration represented on average 60% of ET. However, it represented only 50% of ET on days following rain events and up to 80% of ET after prolonged periods without rain. We propose that HR prevented predawn water potentials from decreasing during periods of increasing soil water deficit, therefore maintaining a constant driving force for water uptake of around 1.7 MPa. It was thought that HR was an important mechanism for maintaining shallow root function during drought and preventing total stomatal closure but our study shows that even in wet conditions with soil water potentials never dropping below -0.6 MPa, HR may play a role in wetland hydrological balance. This first approximation of the extent of HR in this ecosystem suggests that it is likely to be an important process in wet forests of North Carolina.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0476 Plant ecology (1851)
DE: 1813 Eco-hydrology
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting