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<p>This dissertation examines issues concerning sap flux scaled estimates of the canopy-averaged
transpiration rate of trees per unit leaf area (E<sub>L</sub>) and stomatal conductance
(G<sub>S</sub>), as well as their implications in the water and carbon balance of
individuals and stands, with the final goal of an integrated assessment of 11 years
of such data from two species (<italic>Pinus taeda</italic> and <italic>Liquidambar
styraciflua</italic>) at the Duke Free Air Carbon dioxide Enrichment (Duke FACE) facility.
These issues include (1) the effects of allometric relationships and xylem characteristics
on the gas phase transport of water from leaves and the hydraulic supply of it, (2)
consideration of the hydraulic capacitance in the inference of stomatal behavior from
sap flux data and (3) the dynamic modeling of stomatal conductance to environmental
drivers using Bayesian techniques. It is shown that a) for resolution of sap flux
in conifers at the scale of minutes under dynamic conditions, time constants for both
stomatal responses and hydraulic capacitance of sapwood must be considered, (b) nighttime
conductance can lead to large errors in rates of sap flux measured under some conditions,
(c) variation in allometry between <italic>P. taeda</italic> individuals can lead
to different rates of transpiration and carbon assimilation per unit leaf area and
that (d) hydraulic time constants for the stems of mature <italic>P. taeda</italic>
at Duke FACE trees varied by the stem length considered and were on the order of 30-45
minutes for a 10-m segment. An analysis incorporating all these elements leads to
the conclusions that (e) both elevated CO<sub>2</sub> (eCO<sub>2</sub>) and fertilization
(FR) resulted in proportionally larger reductions in the E<sub>L</sub> and G<sub>S</sub>
of P. taeda as soil moisture decreased with (f) eCO<sub>2</sub> having little to no
effect in months of high soil moisture and (g) FR leading to ~14% reduction of GS
under high soil moisture in absence of eCO<sub>2</sub>, while (h) both eCO<sub>2</sub>
and FR led to reduced E<sub>L</sub> and G<sub>S</sub> of <italic>L. styraciflua</italic>
across soil moisture conditions.</p>
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