COS 79-6 - Canopy stomatal conductance under drought, disturbance and death

Wednesday, August 10, 2011: 3:20 PM
12B, Austin Convention Center
Karina VR Schafer, Biological Sciences, Rutgers University Newark, Newark, NJ

Stomatal conductance controls carbon and water fluxes in forest ecosystems, therefore its accurate characterization in land surface flux models are necessary. Sap-flux scaled canopy conductance (GC) was used to evaluate the effect of drought, disturbance and mortality on three oak species in an upland oak/pine stand in the New Jersey Pine Barrens from 2005 to 2008. Canopy conductance was analyzed by performing boundary line analysis, selecting for the highest value under a given light condition.


Regressing GC with the driving force vapor pressure deficit (VPD) resulted in reference canopy conductance at 1 kPa VPD (GCref). Predictably, drought in 2006 caused GCref to decline.  Quercus prinus was least affected, followed by Q. coccina with Q. velutina having the highest reductions. A defoliation event in 2007 caused GCref to increase due to reduced leaf area and possible increased water availability.  Q. prinus quadrupled in GCref, doubled in Q. velutina and increased by 50% in Q. coccina. Canopy mortality in 2008 led to higher GCref in Q. prinus but not Q. velutina or Q. coccina. Comparing light response curves of canopy conductance (GCref) and stomatal conductance (gS) derived from gas-exchange measurements showed marked differences in behavior. Canopy GCref failed to saturate under ambient light conditions whereas leaf level gS saturated at 1200 µmol m-2 s-1. The results presented here emphasize the differential responses of leaf and canopy level conductance to saturating light conditions and the effects of various disturbances (drought, defoliation and mortality) on the carbon and water balance of an oak-dominated forest.

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