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Contribution of competition for light to within‐species variability in stomatal conductance
Author(s) -
Loranty Michael M.,
Mackay D. Scott,
Ewers Brent E.,
Traver Elizabeth,
Kruger Eric L.
Publication year - 2010
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2009wr008125
Subject(s) - vapour pressure deficit , photosynthetically active radiation , transpiration , stomatal conductance , canopy , canopy conductance , atmospheric sciences , environmental science , maple , leaf area index , throughfall , water content , conductance , hydrology (agriculture) , soil water , botany , soil science , mathematics , biology , photosynthesis , geology , geotechnical engineering , combinatorics
Sap flux ( J S ) measurements were collected across two stands dominated by either trembling aspen or sugar maple in northern Wisconsin. Observed canopy transpiration ( E C ‐ obs ) values derived from J S were used to parameterize the Terrestrial Regional Ecosystem Exchange Simulator ecosystem model. Modeled values of stomatal conductance ( G S ) were used to determine reference stomatal conductance ( G Sref ), a proxy for G S that removes the effects of temporal responses to vapor pressure deficit ( D ) on spatial patterns of G S . Values of G Sref were compared to observations of soil moisture, several physiological variables, and a competition index ( C I ) derived from a stand inventory, to determine the underlying cause of observed variability. Considerable variability in G Sref between individual trees was found, with values ranging from 20 to 200 mmol m −2 s −1 and 20 to 100 mmol m −2 s −1 at the aspen and maple stands, respectively. Model‐derived values of G Sref and a sensitivity to D parameter ( m ) showed good agreement with a known empirical relationship for both stands. At both sites, G Sref did not vary with topographic position, as indicated by surface soil moisture. No relationships were observed between G Sref and tree height ( H T ), and a weak correlation with sapwood area ( A S ) was only significant for aspen. Significant nonlinear inverse relationships between G Sref and C I were observed at both stands. Simulations with uniform reductions in incident photosynthetically active radiation ( Q 0 ) resulted in better agreement between observed and simulated E C . Our results suggest a link between photosynthesis and plant hydraulics whereby individual trees subject to photosynthetic limitation as a result of competitive shading exhibit a dynamic stomatal response resulting in a more conservative strategy for managing hydrologic resources.