Scaling Up of Leaf Transpiration and Stomatal Conductance of Eucalyptus grandis x Eucalyptus urophylla in Response to Environmental Variables - Agricultural Chemistry - page 76

pot and plot, on average were similar, differing from the watershed scale that had mean
lower than 33%, approximately. The energy available for physiological activity was higher
in the pot scale, 100% higher than the watershed scale.

Variable Pot Plot Watershed

Ψ pd (MPa) -0,30 -0,15 -0,21

VPD (kPa) 1,32 1,36 0,88

Qleaf (μmol m -2 s -1 ) 1027 802 505

Table 1. Mean Ψpd and environmental variables for Eucalyptus grandis x Eucalyptus urophylla in the
three scales.

3.1. Relation between E and Gs according to Qleaf and VPD

Figure 2 shows the interactions between gas exchange and environmental variables Qleaf
and VPD. The values of E followed the evolution of Qleaf and VPD being almost
imperceptible the difference between the curves of the plot and watershed scale. The
observed values for the pot and watershed scales were between 0.9 and 11.4 mol m -2 s -1 and
for the plot scale, 1.3 to 13.3mol m -2 s -1 . The Gs also accompanied the increase in Qleaf,
however, the greater tendency was found in the watershed scale. As for the VPD, the Gs
showed smaller response amplitude in the plot and watershed scales, concentrated on the
range of 0.1 to 0.5 mol m -2 s -1 . On the pot scale, it was observed the reduction of Gs with
increasing VPD, with values close to 0.8mol m -2 s -1 in situations of 1.0 kPa to 0.02mol m -2 s -1
in extremes of VPD (3.0 kPa).