PARENT SESSION
Oral Session # 24: Photosynthesis and Respiration.
Presiding: A Leakey
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 203.
Comparison between potential and actual net assimilation of hybrid poplar in eastern Washington.
Kim, Hyun-Seok1, 2, Oren, Ram1, Hinckley, Thomas2, 1 Duke University, Durham, NC, USA2 University of Washington, Seattle, WA, USA
ABSTRACT- Potential and actual net carbon assimilation of 3-year-old, 8.5 m tall Populus trichocarpa x P. deltoides hybrids was estimated at an irrigated plantation in Eastern Washington. A Conductance-Constrained Carbon Assimilation (4C-A) model was employed based on sapflux-scaled conductance. Although trees were irrigated 24 hours a day, there was clear evidence of a significant soil water potential decrease below optimum levels as indicated from predawn leaf water potential. By assuming a constant non-limiting soil water potential (-0.2 MPa) throughout the season, we estimated potential stomatal conductance based on relationships with photosynthetically active radiation, vapor pressure deficit and boundary layer conductance. Actual net assimilation (June 14th - October 16th, 125 days) was estimated at 1688 g C m-2, 49% of which was used for above ground biomass production (woody biomass: 768 g C m-2; foliage biomass: 55 g C m-2). Potential net assimilation was estimated at ∼16% more than actual (1953 g C m-2). Assuming that partitioning to wood production remains the same without soil moisture limitation, this would add 252 g m-2 ground. Considering the allometrics of this poplar hybrid, its average height at age 4 would have increased from an actual of 10.8 m to a potential of 11 m.
Key words: Populus trichocarpa x P. deltoides, soil water potential, net assimilation, stomatal conductance