these saplings is affected by the transpiration rate of the
leaf and not by the photosynthetic rate.
There are some interesting recent studies indicating
that xylem sap flow affects the respiration of non-stomatal
woody organs (Negisi 1979; Levy et al. 1999;
Teskey and McGuire 2002, 2007; Bowman et al. 2005).
Teskey et al. (2008) reported a positive correlation between
the CO2 concentration in xylem sap and stem CO2
efflux and a negative correlation between the stem CO2
efflux and sap flow rates in the daytime. Aubrey and
Teskey (2009) suggested that the respired CO2 in the
root system was dissolved in xylem sap and moved upward
into the stem via the xylem stream. They estimated
that the amount of carbon transported by the xylem flow
is comparable to that diffused as soil CO2 efflux. If so,
the root respiration measured as CO2 efflux from the
root surface would underestimate the real mitochondrial
respiration in the daytime. However, the novelty of the
present study is not lost even if the root respiration rate
in the present study underestimates the actual mitochondrial
respiration. The present study indicates that
the root respiration rate increases with the increasing
transpiration rate in leaves (Figs. 6, 7). If the root respiration
is underestimated in the daytime due to the
large sap flow rate, the actual root respiration rate
should exceed that of the measured root respiration.
This would support our finding more strongly that the
root mitochondrial respiration rate increases when the
leaf transpiration rate is high in the daytime. As a matter
of course, a part of CO2 produced by the mitochondrial
respiration would be transported upward to the aboveground
plant parts by xylem sap flow driven by transpiration
in the leaf. Thus, in order to quantitatively
understand the role of the plant root respiration and its
regulating mechanisms, the internal transport of CO2 by
xylem sap flow must be studied further.
The root respiration rates of the canopy trees and
saplings showed a correlation with the transpiration rate
at 1 h before and 20 min before the measurements,
respectively. This indicates that there may be some delay
in the water flow from the root to the leaf, which is
these saplings is affected by the transpiration rate of the
leaf and not by the photosynthetic rate.
There are some interesting recent studies indicating
that xylem sap flow affects the respiration of non-stomatal
woody organs (Negisi 1979; Levy et al. 1999;
Teskey and McGuire 2002, 2007; Bowman et al. 2005).
Teskey et al. (2008) reported a positive correlation between
the CO2 concentration in xylem sap and stem CO2
efflux and a negative correlation between the stem CO2
efflux and sap flow rates in the daytime. Aubrey and
Teskey (2009) suggested that the respired CO2 in the
root system was dissolved in xylem sap and moved upward
into the stem via the xylem stream. They estimated
that the amount of carbon transported by the xylem flow
is comparable to that diffused as soil CO2 efflux. If so,
the root respiration measured as CO2 efflux from the
root surface would underestimate the real mitochondrial
respiration in the daytime. However, the novelty of the
present study is not lost even if the root respiration rate
in the present study underestimates the actual mitochondrial
respiration. The present study indicates that
the root respiration rate increases with the increasing
transpiration rate in leaves (Figs. 6, 7). If the root respiration
is underestimated in the daytime due to the
large sap flow rate, the actual root respiration rate
should exceed that of the measured root respiration.
This would support our finding more strongly that the
root mitochondrial respiration rate increases when the
leaf transpiration rate is high in the daytime. As a matter
of course, a part of CO2 produced by the mitochondrial
respiration would be transported upward to the aboveground
plant parts by xylem sap flow driven by transpiration
in the leaf. Thus, in order to quantitatively
understand the role of the plant root respiration and its
regulating mechanisms, the internal transport of CO2 by
xylem sap flow must be studied further.
The root respiration rates of the canopy trees and
saplings showed a correlation with the transpiration rate
at 1 h before and 20 min before the measurements,
respectively. This indicates that there may be some delay
in the water flow from the root to the leaf, which is
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