2014-05-15_REVISION - M1987064

• Permit No: M1987064
• IBM Index Class Name: REVISION
• Doc Date: 5/15/2014
• Doc Name: Response to adequacy review comments TR04
• From: Elam Construction, Inc.
• To: DRMS
• Type & Sequence: TR4
• Email Name: KAP
• Media Type: D
• Archive: No

182 WFswR,,4 N( ri1 AMERICAN NATURALIST [Volume 65
Tnat.a 1. Selected characteristics of trees monitored in this muiy: Clone rates serve as markers for individual geno-
types but otherwise have no relation to cross type: Cross types are .1(Pnpulres ur►gushfolia), B (backcross hybrids), and
F1 (Ft hybrids).
Clone
Status
Diameter at
base of live
crown (cm)
Cress type
Leaf area (mr
Sapwood
area (cm2)
Leaf area:
sapwood, area
(M2 trn-s)
WC-5
Vnwatered
13.9
A
75.2
149.1
0.50
WO-5
watered
176
A
125.1
167.5
0.75
1008
Unw•atered
21.9
A
187:7
203
0.92
1008
waterer]
16.4
A
107.5
105.6
1.02
t -15
Unw•atm -d
19.3
A
152.3
161.8
0.91
t -15
watered
20.8
A
173.1
173
1100
996
Unwatered
225
B
210.7
225.9
0.93
W6
Watered
17.7
8
126.6
105.8
1.20
11
Unwatered
18.3
B
136
99.9
1.36
11
Watered
22.9
B
218.7
221.7
0.99
1994
Unwatered
34.2
bF')
505.2
704.9
0.72
1994
Watered
30:7
F1
403.8
775.2
0.52
r..
0.30
0.25
0.20
Oe 0.15
0.10
W
0.05
ai
ai
0.008
0.006
0.004
0.002
0.0W
• A rx = 0.23
p =0.12
•
• i
•
•
•
•B r' =0.43
p = 0.02
i
l
0,4 0.6 0.6 1.0 12 1.4 1.6
t A:SA (rtt2 ore)
Fiz 4. Architectural controls of whole -tree physiology,
A. leaf-specific transpiration (?t) versus leaf area to sap-
wood area ratio (LA:SA); % whole -tree hydraulic conduc-
tance (Kh) versus LA:SA.
et al. 2001a; but see Fischer et al. 2004), but
hydraulic conductance was not exceptionally
low compared with other angiosperms (Becker
et al. 1999). Dickmann et al. (1994) also found
no difference in net photosynthesis rates be-
tween irrigated and nonirrigated cottonwood
saplings, and our results are consistent with
responses of Fopulus clones to a 40% reduc-
tion in soil moisture in a study by Braatne et
al. (1992). We conclude that during the height
of summer drought, any uptake of increased
soil moisture was insufficient to influence im-
portant physiological variables such as hydraulic
conductance, canopy conductance, or transpi-
ration. This may be consistent with factors
other than water limiting both photosynthesis
and, by default, water use as has been found in
at least 1 other species in our region (Snyder
et A. 2004).
We speculate there are several other possi-
ble explanations for the lack of response to
uvater additions in our study trees. First, greater
loss of Ieaf area in unwatered trees relative to
watered trees may have partially compensated
for lower water availability to the trees, reduc-
ing any differences in leaf- specific transpira-
tion rates. However, we found no difference in
leaf area loss between watered and nnwatered
trees, suggesting that this potential mechanism
cannot account for the lack of physiological
responsiveness to water additions in our study
trees. Nevertheless, we reconixe that our mea-
sure of leaf area lost due to drought was some-
what coarse, and so we cannot entirely rule out
this possible mechanism for the lack in physi-
ological response of the cottonwood trees to
water additions.
Second, xylem dysfunction in the roots of
study trees might have impaired uptake of
water supplied to the trees by irrigation treat-
ments. Cottonwoods are mostly drought intol-
erant, limited to riparian corridors, and depen-
dent on groundwater, and they typically have