Table 1. Dry season branch-level water balance for all branches with < 10% missing data. The
first column of data contains the tree number followed by the branch number. FU (L) is the total
amount of water in liters that was recovered during the study period. The σ of FU (L) is the error
term associated with the FU estimate determined using error propagation analysis (see the
Results section). The % FU indicates the percentage of the total positive flow in liters throughout
the study that was recovered via FU. The % time FU is the percentage of hours in the study
period (small gaps in data are excluded) that FU was occurring. NT (L) is the total number of
liters of water that were lost during the nighttime hours in the study while σ of NT (L) was the
error term for each branch calculated with error propagation and the % NT was the percentage of
the total transpiration that occurred at night. The % time NT is the percentage of nighttime hours
in the study period (small gaps in data are excluded) when transpiration was occurring. The r2
(FU) column contains the regression coefficients for branch-level regression analyses between
the number of hours in a fog event and the amount (total L) of FU. The r2 (NT) column contains
the regression coefficients of branch-level regression analyses between the average nighttime
VPD and the total nighttime transpiration (L/night). For a graphical display of the results for the
last two columns, please see figures 5, 6 S2 and S3.
Table 2. Results of a linear, two-source mixing model demonstrating the percent of water
originating from foliar uptake in eight common plant species in the seasonally dry tropical
montane cloud forests of Veracruz, Mexico.
Figure 1a-e. Daily rainfall totals (a), daily mean air temperature (b), mean nightly vapor
pressure deficit (c) fog occurrence (d) and daily sap flow averages (e) over the course of the
study period in 2010 measured on the study trees and at a meteorological station near the study
trees. Arrows in the top panel refer to periods of time shown in Figures 2 and 3. The transition
from the dry season to the wet season occurred in early June. Error bars indicate the standard
error of the mean.
Figure 2a,b. Sap flow for two foggy periods in the dry season. In both panels the dark shading
represents the percent canopy wetness while the light shading represents the percent fog
occurrence. The black line represents the hourly sap flow for Oak1. For the period of time in the
upper panel (March4-5) there was no rainfall and canopy wetness occurred 10 hours after the
percent fog occurrence was 100. In the lower panel (February2-3) there was a rain event shown
with the arrow. In this case, the canopy wetness occurred at the same time as the rain event. In
both panels, sap flow is negative during most of the period when the canopy is wet. Oaks 2 and 3
show a similar pattern.
Figure 3. Sap flow for the three Oak trees for a 2-day dry period (Jan23-24). The shaded area
represents the hourly mean VPD. During this period there was 100% visibility, dry canopies, and
no rainfall until the end of the period where an arrow indicates the time of a small rainfall event.
High nighttime VPD resulted in positive nighttime flow rates on both the 23rd and the 24th. The
VPD dropped with the rainfall event the night of the 24th and the sap flow quickly dropped as
well.
Figure 4. The relationship between the number of hours of a leaf wetness event induced by fog
and/or rain and the FU (L/event). This figure shows the average relationship for all branches in
the three oak canopies. The r2 for this relationship is shown in the lower part of the panel. Values
on the Y-axis are negative to indicate reverse flow.
Figure 5. The relationship between nighttime VPD and NT. Each data point is the total number
of liters transpired in a given night averaged across all branches. The r2 for this relationship is
shown in the lower part of the panel.
Table1.
Branch
1_1
1_3
1_5
1_8
2_1
2_2
2_3
2_5
2_6
2_7
3_1
3_2
3_5
3_6
AVG
FU (L)
-40.9
-7.3
-16.7
-76.2
-5.0
-10.5
-5.7
-42.3
-47.4
-16.5
-21.2
-19.5
-21.4
-6.8
-24.1
σ of FU (L)
14.1
2.9
5.1
28.3
2.0
4.5
2.5
23.4
16.0
5.5
8.0
6.5
5.2
3.2
9.1
% FU
12
11
5
14
4
4
6
16
11
12
11
15
4
5
9.3
%time FU
40
36
30
40
28
23
28
43
39
40
34
37
32
31
34.4
NT (L)
65.8
16.4
57.5
101.4
26.7
48.3
16.6
42.4
62.6
13.9
31.0
21.1
113.6
23.6
45.8
σ of NT (L)
22.7
6.5
17.4
37.6
10.6
20.5
7.3
23.5
21.1
4.7
11.6
7.1
27.4
11.0
16.4
% NT
19
24
16
18
20
19
18
16
14
10
16
16
20
18
17.4
% time NT
53
60
61
51
64
70
63
46
50
49
57
56
61
61
57.4
r 2 (FU) r 2 (NT)
0.93
0.59
0.32
0.92
0.59
0.28
0.44
0.73
0.61
NS
0.61
0.65
0.91
0.72
0.78
NS
0.75
0.71
NS
0.39
0.65
0.58
0.57
0.53
0.62
0.42
0.82
0.81
Table 2.
Species
Leaf H2O originating from tracer (%)
Alchornea latifolia
6.7 - 12.4
Alnus jorullensis
19.9 - 22.2
Clethra macrophylla
6.3 - 13.7
Miconia glaberrima
6.3 - 13.6
Quercus lanceifolia
9.8 - 12.9
Quercus ocoteifolia
8.3 - 15.5
Pinus patula
6.7 - 8.6
Pinus pseudostrobilus
7.1 - 17.0
Rainfall (mm)
60
a.
50
40
Fig3 Fig2b
Fig2a
30
20
10
0
25
b.
T air (C)
20
15
10
5
0
c.
VPD (kPa)
1.5
1.0
0.5
0.0
Fog (%)
100
d.
X Data
80
60
40
20
Mean Vs ( L hr-1 )
0
8
e.
6
4
2
0
JAN
Figure 1a-e.
FEB
MAR
APR
MAY
JUN
Figure 2a,b.
VPD
OAK1
OAK2
OAK3
0.8
2.5
2.0
1.5
0.4
1.0
Rain event
0.5
0.2
0.0
0.0
4am
Figure 3.
12pm
8pm
4am
12pm
8pm
VPD (kPa)
1
Sap flow (L hr- )
0.6
-1
FU (L event )
0.0
-0.4
-0.8
-1.2
-1.6
2
r =0.93
0
20
40
60
80
# Hours of a fog/leaf wetness event
Figure 4.
-1
Sap flow (L night )
1.0
0.8
0.6
0.4
0.2
0.0
r2=0.87
0.0
0.5
1.0
VPD (kPa)
Figure 5.
1.5
Supplemental Figures
18
Oak 2 branch 5
16
Sap flux velocity (cm/hr)
14
12
10
8
6
xylem severing
4
2
0
June 19
June 20
June 21
June 22
June 23
June 24
Figure S1. Zero flow calibration example for Oak2 branch 5. Towards the end of the experiment
a hole was drilled above and below the sensor sets to physically restrict flow. This average flow
was taken as the “true zero” and all sap flow values were calibrated to this true zero which was
performed on each sensor set.
1_1
r2=0.93
-1
-1
1_3
2
r =0.59
0.0
FU (L event )
-1
FU (L event )
0
-0.2
-0.4
-2
-0.6
a.
b.
1_5
2
r =0.32
FU (L event )
-1
-1
FU (L event )
0.0
-0.4
-0.8
-1
-2
-3
-4
-1.2
c.
d.
2_1
2
r =0.61
-1
-1
2_3
2
r =0.61
0.0
FU (L event )
0.0
FU (L event )
1_8
2
r =0.92
0
-0.2
-0.4
-0.6
-0.4
-0.6
e.
0
-0.2
20
40
60
Hours of Fog/LWS Event
80
100
f.
0
20
40
60
Hours of Fog/LWS Event
80
100
2_5
2
r =0.65
-1
FU (L event )
0
-1
FU (L event )
0
-1
-2
-3
2_7
2
r =0.72
-2
h.
3_1
2
r =0.59
0.0
-1
FU (L event )
-1
FU (L event )
-1
-3
g.
0.0
-0.2
-0.4
-0.2
-0.4
-0.6
-0.8
-0.6
j.
i.
3_2
2
r =0.28
FU (L event-1)
-1
-1
-0.4
-0.8
-1
-2
-1.2
l.
k.
0
3_6
r =0.73
2
0.0
-0.1
-0.2
-0.3
m.
0
20
40
60
Hours of Fog/LWS Event
80
20
40
60
Hours of Fog/LWS Event
-1
FU (L event )
3_5
2
r =0.44
0
FU (L event )
0.0
FU (L event )
2_6
r2=0.72
100
80
100
Figure S2 (a-m). The relationship between the number of hours of fog and leaf wetness events
and the FU (L event-1) for branches of the three oak trees. The values on the Y-axis are negative
to indicate reverse flow. The number on the upper right corner of each figure refers to the tree
number followed by the branch number. Below this identification number is the r2 value.
Analyses were completed using square-root transformations. Raw data are shown here for ease
of viewing since the relationships were similar. Branch 2_2 was not plotted since there was no
significant relationship in this branch. For all other branches the relationship was significant at P
<0.0001.
1_1
r2=0.78
1.2
0.8
-1
F(L night )
-1
F (L night )
1.2
0.4
0.0
1-5
2
r =0.75
0.8
0.4
0.0
a.
3_2
2
r =0.4
1_8
r =0.71
2
0.8
-1
F (L night )
-1
F (L night )
2.0
b.
1.5
1.0
0.5
0.0
0.0
c.
2.5
0.4
3_5
r2=0.65
0.6
d.
3_6
r =0.58
2
F (L night )
-1
-1
F (L night )
2.0
1.5
1.0
0.5
0.4
0.2
0.0
0.0
e.
0.0
0.5
1.0
VPD (kPa)
1.5
f.
0.0
0.5
1.0
VPD (kPa)
1.5
2_1
r2=0.57
0.8
F (L night )
0.6
-1
-1
F (L night )
0.8
0.4
0.2
0.0
2_2
r =0.53
2
0.6
0.4
0.2
0.0
g.
2_3
r2=0.62
1.2
F (L night )
0.3
0.2
0.1
0.8
0.4
0.0
0.0
i.
i.
j.
2_6
r =0.82
2
2_7
r2=0.81
-1
F (L night )
1.5
-1
F (L night )
1.5
2_5
r2=0.42
-1
-1
F (L night )
0.4
h.
1.0
0.5
1.0
0.5
0.0
0.0
k.
0.0
0.5
1.0
VPD (kPa)
1.5
l.
0.0
0.5
1.0
1.5
VPD (kPa)
Figure S3 (a-l). The relationship between nighttime VPD (kPa) and nighttime volumetric branch
sap flow (L night-1). Each dot represents a nightly total of water loss (L). The number on the
upper left corner of each figure refers to the tree number followed by the branch number. Below
the identification number is the r2 value for that branch. Analyses were completed using the
square-root transformation of nighttime sap flow data. Raw data are shown here for ease of
viewing. Branches 1_3 and 3_1 were not plotted since there was no significant relationship for
these branches. For all other branches the relationship was significant at P <0.0001.