AUTHOR=Schäfer Karina V.R. 

TITLE=Canopy Stomatal Conductance Following Drought, Disturbance, and Death in an Upland Oak/Pine Forest of the New Jersey Pine Barrens, USA

JOURNAL=Frontiers in Plant Science

VOLUME=2

YEAR=2011

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2011.00015

DOI=10.3389/fpls.2011.00015

ISSN=1664-462X

ABSTRACT=<p>Stomatal conductance controls carbon and water fluxes in forest ecosystems. Therefore, its accurate characterization in land-surface flux models is necessary. Sap-flux scaled canopy conductance was used to evaluate the effect of drought, disturbance, and mortality of three oak species (<italic>Quercus prinus</italic>, <italic>Q. velutina</italic>, and <italic>Q. coccinea</italic>) in an upland oak/pine stand in the New Jersey Pine Barrens from 2005 to 2008. Canopy conductance (<italic>G</italic><sub>C</sub>) was analyzed by performing boundary line analysis and selecting for the highest value under a given light condition. Regressing <italic>G</italic><sub>C</sub> with the driving force vapor pressure deficit (VPD) resulted in reference canopy conductance at 1 kPa VPD (<italic>G</italic><sub>Cref</sub>). Predictably, drought in 2006 caused <italic>G</italic><sub>Cref</sub> to decline. <italic>Q. prinus</italic><italic>G</italic><sub>Cref</sub> was least affected, followed by <italic>Q. coccinea</italic>, with <italic>Q. velutina</italic> having the highest reductions in <italic>G</italic><sub>Cref</sub>. A defoliation event in 2007 caused <italic>G</italic><sub>Cref</sub> to increase due to reduced leaf area and a possible increase in water availability. In <italic>Q. prinus</italic>, <italic>G</italic><sub>Cref</sub> quadrupled, while doubling in <italic>Q. velutina</italic>, and increasing by 50% in <italic>Q. coccinea</italic>. Tree mortality in 2008 led to higher <italic>G</italic><sub>Cref</sub> in the remaining <italic>Q. prinus</italic> but not in <italic>Q. velutina</italic> or <italic>Q. coccinea</italic>. Comparing light response curves of canopy conductance (<italic>G</italic><sub>Cref</sub>) and stomatal conductance (<italic>g</italic><sub>S</sub>) derived from gas-exchange measurements showed marked differences in behavior. Canopy <italic>G</italic><sub>Cref</sub> failed to saturate under ambient light conditions whereas leaf-level <italic>g</italic><sub>S</sub> saturated at 1,200 μmol m<sup>−2</sup> s<sup>−1</sup>. 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.</p>