%0 Journal Article
%A Dang, Q.L.
%A Margolis, H.A.
%A Collatz, G.J.
%T Parameterization and testing of a coupled photosynthesis stomatal conductance model for boreal trees
%B Tree Physiology
%D 1998
%V 18
%P 141-153
%N 3
%Z Times Cited: 32; timestamp=(2007.12.05)
%X A coupled photosynthesis-stomatal conductance model was parameterized
and tested with branches of black spruce (Picea mariana (Mill.)
B.S.P.) and jack pine (Pinus banksiana Lamb.) trees growing in the
Northern Study Area of the Boreal Ecosystem-Atmosphere Study (BOREAS)
in Manitoba, Canada. Branch samples containing foliage of all age-classes
were harvested from a lowland old black spruce (OBS) and an old
jack pine (OJP) stand and the responses of photosynthesis (A(n))
and stomatal conductance (g(s)) to temperature, CO2, light, and
leaf-to-air vapor pressure difference (VPD) were determined under
controlled laboratory conditions at the beginning, middle, and end
of the growing season (Intensive Field Campaigns (IFC) 1, 2, and
3, respectively). The parameterized model was then tested against
in situ field gas-exchange measurements in a young jack pine (YJP)
and an upland black spruce (UBS) stand as well as in the OBS and
OJP stands. Parameterization showed that Rubisco capacity (V-max),
apparent quantum yield (alpha') and Q(10) for sink limitation were
the most crucial parameters for the photosynthesis sub-model and
that V-max varied among different measurement series in the laboratory.
Verification of the model against the data used to parameterize
it yielded correlation coefficients (r) of 0.97 and 0.93 for black
spruce and jack pine, respectively, when IFC-specific parameters
were used, and 0.77 and 0.87 when IFC-2 parameters were applied
to all IFCs. For both measured and modeled g(s), the stomatal conductance
sub-model, which linearly relates g(s) to (A(n)h(s))/c(s) (where
h(s) and c(s) are relative humidity and CO2 mole fraction at the
leaf surface, respectively), had significantly steeper slopes and
higher r values when only the VPD response data were used for parameterization
than when all of the response data were used for parameterization.
Testing the photosynthesis sub-model against upper canopy field
data yielded poor results when laboratory estimates of V-max, were
used. Use of the mean V-max, estimated for all upper canopy branches
measured on a given day improved model performance for jack pine
(from a nonsignificant correlation between measured and modeled
A(n) to r = 0.45), but not for black spruce (r = 0.45 for both cases).
However, when V-max, was estimated for each branch sample individually,
the model accurately predicted the 23 to 137% diurnal variation
in A(n) for all stands for both the upper and lower canopy. This
was true both when all of the other parameters were IFC-specific
(r = 0.93 and 0.92 for black spruce and jack pine, respectively)
and when only mid-growing season (IFC-2) values were used (r = 0.92
for both species). Branch-specific V-max estimates also permitted
accurate prediction of field g(s) (r = 0.75 and 0.89 for black spruce
and jack pine, respectively), although parameterization with all
of the response data overestimated g(s) in the field, whereas parameterization
with only the VPD response data provided unbiased predictions. Thus,
after parameterization with the laboratory data, accurately modeling
the range of A(n) and g(s) encountered in the field for both black
spruce and jack pine was reduced to a single unknown parameter,
V-max.
%K black spruce; environmental controls on gas exchange; jack pine GENERAL-CIRCULATION
MODEL; SIMPLE BIOSPHERE MODEL; ATMOSPHERIC CO2; TRANSPIRATION; FOREST;
PRODUCTIVITY; EXCHANGE; CANOPY; SPRUCE
%# brugerolles
%F DangMargolisCollatz1998
%3 BibTeX type = ARTICLE