HR: 1340h
AN: B33D-1571 [WITHDRAWN]    [Abstracts]
TI: Leaf Gas Exchange in Relict Spruce-Fir Cloud Forests of the Southern Appalachian Mountains, USA.
AU: * Reinhardt, K
EM: reinhaks@wfu.edu
AF: Wake Forest University, Dept Biology, Winston Hall, Winston-Salem, NC 27109,
AU: Smith, W K
EM: smithwk@wfu.edu
AF: Wake Forest University, Dept Biology, Winston Hall, Winston-Salem, NC 27109,
AB: The relict spruce-fir (Picea rubens Sarg. - Abies fraseri (Pursh) Poir.) forests of the southern Appalachian mountains are found only on high altitude mountain tops that receive copious precipitation (>2000 mm annually) and experience frequent cloud immersion (~65% of the total growth season days). Cloud deposition accounts for up to 50% of the annual water budget for these high-elevation forests. Two sites in North Carolina were established to investigate the influences of cloudiness and cloud immersion on leaf gas exchange and water relations of Fraser fir: Mt. Mitchell (2028 m elevation) and Roan Mtn., NC (1890 m elevation). It was hypothesized that the cool, moist, and cloudy conditions at these sites would exert a strong influence on leaf carbon and water fluxes. Water status was high throughout all hours on measurement days, with xylem water potential always >-1.75 MPa and soil water content always >0.1 m3 m-3. Leaves were wet frequently (>60% of all hours) due to cloud immersion and nightly dewfall, which did not appear to limit photosynthesis, but may influence stomatal response and transpiration. Maximum photosynthesis (Amax) was about 15 umol CO2 m-2 s-1, and saturated at sunlight levels between 400-500 umol m-2 s-1. Maximum leaf conductance (gmax) and transpiration (Emax) were 0.31 mol m-2 s-1 and 3.9 mmol m-2 s-1, respectively, and were strongly associated with LAVD. At both sites, conductance and transpiration decreased exponentially as LAVD increased, with 50-75% reduction between 0-0.5 kPa. Mean instantaneous water use efficiency on clear days was 3.5 umol CO2 m-2 s-1/mmol H2O m-2 s-1 across all transpiration fluxes, but increased on cloudy and cloud-immersed days (range of 2.3 – 6.0 umol CO2 m-2 s-1/mmol H2O m-2 s-1) as transpiration increased. Leaf gas exchange appeared tightly coupled to the response of conductance to LAVD which maintained high water status, even at the relatively low LAVD of these cloud forests. Thus, the cloudy, humid environment of these refugial forests appears to exert a strong influence on leaf gas exchange and water relations of these montane species. Because global climate change is predicted to increase regional cloud ceiling levels, more research on cloud impacts on carbon gain and water relations is needed to predict the future survival of these relic forests.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0476 Plant ecology (1851)
DE: 1813 Eco-hydrology
DE: 1833 Hydroclimatology
DE: 1842 Irrigation
SC: Biogeosciences [B]
MN: 2007 Fall Meeting