the tree below and seemed more stable than water loss from the
lower crown. In addition, the uppermost foliage always tran-
spired disproportionately more water (> 2.5× in relation to
needle area) than that of the middle and lower crown. Similar
results were noted by Èermák and Kuèera (1990) in large Nor-
way spruce trees.
Diurnal course and time lag
The diurnal course of sap flow closely followed foliar transpi-
ration and thus started first in branch tips, then in branches,
somewhat later in the stem near branches and with the most
pronounced delay in the stem furthest from the foliage. The
top 6 m of the crown and the whole crown appear to begin tran-
spiring almost at the same time; integrated sap flow in
branches of the upper crown showed no significant time shift
compared with the crown total (see Figure 3; maximum lag
was less than 15 min), or with stem sap flow at 51 m. In con-
trast, a pronounced time shift was noted between stem sap
flow at 51 m and at 4 m. Sap flow at the stem base lagged that
of the whole crown by 1 to 2 h. The time lags were even more
pronounced after sunset. Transpiration from the upper crown
or total crown ceased about 2030 h, almost 4 h before sap flow
approached zero at 51 m and 4.5 h before it approached zero at
4 m. During the morning hours, the water balance of the tree
stem between 4 and 51 m was negative. For about 2 h, outflow
to the upper stem was greater than inflow from the lowermost
stem (below 4m). The balance became positive again at about
1000 h when input into the stem at 4 m was greater than output
at 51 m. Depleted water storage was recharged in the afternoon
and at night until the early morning hours of the next day when
transpiration resumed.
Similar to the timing of sap flow lags, temporal variation in
sap flow decreased from the individual branch to the whole
crown (data not shown) and from the upper stem to the lower
stem. Sap flow variation was higher in small, foliated branches
and decreased in the main stem with increasing distance from
the foliage. As the distance from the transpiring surface in-
creased, more transpiring surfaces were integrated and more
tissue buffering capacity was involved, thus the diurnal curves
in the lower stem appeared quite smooth (see Figure 3).
Diurnal courses of sap flow and changes of stored water
Diurnal changes in water storage were varied over the growing
season, but had the same general pattern. Stored water was de-
186
ÈERMÁK, KUÈERA, BAUERLE,
PHILLIPS AND HINCKLEY
TREE PHYSIOLOGY VOLUME 27, 2007
Figure 2. Seasonal course of daily sap flow in the old-growth Doug-
las-fir sample tree (Psme 1373) and daily global radiation in the Wind
River experimental plot. Short lines indicate 10 individual days with
fine weather selected for detailed analysis of water storage, arrows in-
dicate days shown in following figures.
Table 1. Volumes and amounts of free water in parts of the Douglas-fir sample tree, Psme 1373.
Volume (dm
3
)
Free water (dm
3
)
Upper
Mid-
Lower
Bare
Tree
Upper
Mid-
Lower
Bare
Tree
crown
crown
crown
stem
total
crown
crown
crown
stem
total
> 51m
46–51m 23–46m < 23m
> 51m
46–51m 23–46m < 23m
Stem sapwood
92
186
1931
2912
5122 = 81.0%
21
42
438
661
1163 = 81.6%
Stem phloem
13
21
204
316
554 = 8.8%
4
7
58
76
145 = 10.2%
Stem sapw + phl
105
207
2135
3229
5676 = 89.7%
25
49
497
737
1308 = 91.8%
Branch sapwood
29
77
135
0
242 = 3.8%
7
17
31
0
55 = 3.8%
Branch phloem
6
16
29
0
51 = 0.8%
2
5
9
0
16 = 1.1%
Branch sapw + phl
35
93
164
0
293 = 4.6%
8
23
40
0
71 = 5.0%
Sapwood total
121
263
2067
2912
5363 = 84.8%
28
60
469
661
1217 = 85.4%
Phloem total
19
38
233
316
606 = 9.6%
6
12
67
76
161 = 11.3%
Sapwood + phl total
140
301
2299
3229
5969 = 94.4%
34
71
536
737
1379 = 96.7%
Needles total
54
105
198
****
357 = 5.6%
7
14
26
****
47 = 3.3%
Wet tissues total
194
405
2497
3229
6326 = 100%
41
86
562
737
1426 = 100%
3.1%
6.4%
39.5%
51.0%
****
2.9%
6.0%
39.4%
51.7%
****
Stem total
237
608
5948
10200
16993 = 100%
****
****
*****
*****
****
1.4%
3.6%
35.0%
60.0%
****
****
****
*****
*****
****
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