HR: 1340h
AN: GC13A-0928    [Abstracts]
TI: Do Extreme Climatic Events Drive Ecosystem Water Flux Under Elevated CO2 in a Temperate Forest?
AU: * Warren, J M
EM: warrenjm@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN 37831, United States
AU: Norby, R J
EM: rjn@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN 37831, United States
AU: Wullschleger, S D
EM: wullschlegsd@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN 37831, United States
AB: In 2007, much of the Southeastern US experienced a combination of extreme weather events that visibly damaged plant communities across entire landscapes; including a Liquidambar styraciflua (sweetgum) plantation in eastern Tennessee concurrently exposed to elevated CO₂ treatments. At the Oak Ridge National Lab's FACE facility there was a late spring freeze event (-6.5 °C) as leaves were emerging, followed by a record summer drought with forest understory temperatures reaching 38.5 °C. Trees exposed to elevated CO2 often have lower rates of evapotranspiration (ET) which can reduce total site water use, thereby buffering trees against droughty conditions. Sap flux density was monitored in 16 trees using Granier- style sensors to access the potential of a CO₂ treatment-mitigated buffering of perceived plant water stress, and thereby productivity. While up to 60% of young expanding foliage was visibly damaged across treatments following the freeze event, it represented a minor component of subsequent canopy leaf area with no distinguishable impact on sap flux. Trees exposed to elevated CO₂ initially had lower ET than ambient trees, but differences diminished as soil water potential dropped below -0.5 MPa reflecting the increasing water limitations. Sap flux density declined more readily in ambient CO₂ trees during droughty periods, but subsequently recovered following significant rain events. This research suggests that plant response to seasonal dynamics in water availability may be modulated (less responsive) under a projected future CO₂ scenario.
DE: 1630 Impacts of global change (1225)
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology (0476)
DE: 1852 Plant uptake
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting