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Supplementary materials
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Plant community composition regulates the responses of Prairie soil respiration to
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experimental warming
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Xia Xu, Zheng Shi, Dejun Li, Xuhui Zhou, Rebecca A. Sherry, Yiqi Luo
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Supplementary references
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McCune B, Grace JB (2002) Analysis of Ecological Communities. MjM Software Design,
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Gleneden Beach, OR, USA.
Palmer MW (1993) Putting things in even better order: the advantages of canonical
correspondence analysis. Ecology, 74, 2215-2230.
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Supplementary Table S1
For Tsoil and Wsoil, values are mean  SE.
Variable
Treatment
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
1007
863
833
647
966
515
744
1307
726
1017
906
549
678
UC
17.90.5
19.40.5
16.40.4
17.10.4
16.70.4
16.90.4
17.30.4
16.80.4
16.10.4
16.70.4
16.60.5
18.90.5
19.80.5
UW
20.00.5
19.10.5
17.80.4
18.50.4
18.40.4
19.00.4
19.50.4
18.20.4
17.20.4
17.30.4
17.90.5
20.20.5
21.10.5
CC
18.80.5
17.9.0.5
16.70.4
17.20.4
17.00.4
17.50.4
17.90.4
17.10.4
16.00.4
17.00.4
16.70.4
20.10.5
21.00.5
CW
21.30.5
20.50.5
18.00.4
19.20.4
19.00.4
20.20.4
20.60.4
19.50.4
18.20.4
19.60.4
19.10.5
22.20.5
23.10.5
UC
22.91.2
29.80.7
27.30.9
22.00.7
27.60.7
24.81.1
23.50.9
29.90.4
27.00.8
26.62.88
30.32.6
22.01.8
19.42.1
UW
19.20.8
28.80.3
26.51.1
21.00.5
27.50.4
21.70.7
22.00.5
28.70.5
25.20.7
24.63.2
28.73.1
21.41.6
18.22.2
CC
21.61.0
28.80.7
27.11.1
22.30.8
27.50.7
24.10.8
23.10.7
29.70.4
26.10.6
26.02.8
29.82.7
21.71.4
18.92.1
CW
17.40.8
28.40.3
26.31.0
20.20.7
26.30.6
20.90.8
20.90.6
28.60.4
24.40.6
24.02.9
28.03.0
21.31.9
18.32.6
AP (mm)
Tsoil (°C)
Wsoil (%)
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Annual precipitation (AP), soil temperature and moisture (Tsoil, Wsoil) under different treatments at the experimental site.
Note: UC: unclipped control temperature; UW: unclipped and warming; CC: clipped and control temperature; CW: clipped and warming.
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Supplementary figure legends
Figure S1 Variation in ANPP under the four treatments (A-B) and warming-induced changes in
ANPP (C-D) and C4 grasses (E-F) from 2000 to 2012. ANPP: aboveground net primary
production. Values are mean ± SE with 6 replicates.
Fig. S2 Variation in ANPP contributed by C3 forbs under the four treatments (A-B) and
warming-induced changes in C3 forbs (C-D) from 2000 to 2012. In 2000, 2001, and 2002, the
biomass C3 forbs is obtained based on the correlation between C3/C4 cover ratio and C3 biomass
in clipped subplots each year (all P<0.01, n=12) because we did not separate ANPP into C3
forbs and C4 grasses when measuring ANPP during those years. C4 biomass is calculated as the
difference between ANPP and C3 (Xu et al., 2012b). Values are mean ± SE with 6 replicates.
Figure S3 Variation in BNPP under the four treatments (A-B), the absolute (C-D) and the
relative (E-F) warming-induced changes in BNPP from 2000 to 2012. BNPP: belowground net
primary production. Values are mean ± SE with 6 replicates.
Figure S4 Seasonal variation in soil respiration under the four treatments (A-B) and
warming-induced changes in soil respiration (C) from 2000 to 2012. Monthly data are used in
this figure and values are mean ± SE with 6 replicates.
Figure S5 Relationships of warming-induced changes in annual soil respiration with
warming-induced changes in soil temperature (A) and soil moisture (B) from 2000 to 2012. The
abnormal point (smaller than 0 based on the X-axis) shown in panel A is from the unclipped
subplot in 2001, which probably resulted from measurement errors. The relationship in panel A
is not statistically significant (P>0.05) even with removal of the abnormal point. Yearly data are
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used in this figure.
Figure S6 Warming-induced changes in soil respiration negatively affected by the proportion of
ANPP contributed by C4 grasses across the 13 years. Yearly data are used in this figure.
Figure S7 Negative impact of the proportion of ANPP contributed by C4 grasses on
aboveground net primary production (ANPP, A) and belowground net primary production
(BNPP, B) under warming. Yearly data are used in this figure.
Figure S8 Effects of warming and clipping on plant community structure. Blocked canonical
correspondence analysis (CCA) ordination showed similar community structure in the control
and warmed plots in 2000-2004 (A) but different structure in 2005-2012 (B). Canonical
correspondence analysis (CCA) is a multivariate ordination technique with constraints added
from a matrix of environmental variables (McCune & Grace, 2002). All ordination techniques
attempt to order or cluster data characterized by multiple variables by collapsing multiple
variables into a few axis. Canonical ordination techniques limit the structure the ordinations can
take on based on environmental variables. CCA maximizes differences that correlate to the
measured environmental variables (and may ignore differences in community structure that are
unrelated to the environmental variables). For an experimental design with only 2 levels of each
environmental factor (such as this experiment), dummy variables (i.e. 0 or 1) can be used in the
environmental matrix. CCA assumes a hump-shaped distribution of species responses (unlike
principle component analysis (PCA) and redundancy analysis (RDA) which assume linear
responses). CCA performs well with skewed distributions, correlated environmental variables,
and missing factors (Palmer, 1993). Yearly data are used in the CCA
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Year
Fig. S1
6
20
20
12
10
08
UW-UC
20
0
-1
(d)
06
100
(c)
20
200
UC (b)
UW
04
300
(a)
20
02
00
(e) C4-ANPP
20
20
12
10
08
06
-2
ANPP (g m yr )
400
20
20
20
20
04
02
00
-1
120
20
20
20
-2
Warming-induced chages in ANPP (g m yr )
500
CC
CW
CW-CC
80
40
0
(f) C4-ANPP
120
80
40
0
Year
Fig. S2
7
12
(b)
20
10
08
06
04
UW-UC
20
20
20
20
(c)
02
00
UC
UW
20
20
-1
(a)
12
10
08
06
04
-2
C3-ANPP (g m yr )
150
20
20
20
20
20
02
00
0
80
20
20
Warming-induced chages
-2
-1
in C3-ANPP (g m yr )
180
CC
CW
120
90
60
30
(d)
40
0
-40
-80
CW-CC
Year
Fig. S3
8
20
20
12
10
08
UW-UC
20
-1
(d)
06
0
(c)
20
200
UC (b)
UW
04
400
(a)
20
02
00
(e)
20
20
12
10
08
06
-2
600
20
20
20
20
04
-1
350
20
02
00
0
120
20
20
-2
Warming-induced changes in BNPP (g m yr , C, D) and (%, E, F) BNPP (g m yr )
800
CC
CW
CW-CC
280
210
140
70
(f)
90
60
30
0
-2
-1
Rs (umol m s )
9
(a)
UC
UW
6
3
0
CC
CW
6
-2
-1
Rs (umol m s )
(b)
4
2
Warming-induced
-2 -1
changes in Rs (umol m s )
0
3
(c)
UW-UC
CW-CC
2
1
0
-1
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
Year
Fig. S4
9
20
08
20
09
20
10
20
11
20
12
20
13
Warming-induced
-2 -1
increases in R s (gC m y )
350
(a)
(b)
280
210
140
70
0
0
1
2
3 -4
-3
o
-2
-1
Warming-induced changes in Tsoil ( C, A) and Wsoil (%, B)
Fig. S5
10
0
Warming-induced
-2 -1
increases in Rs (gC m y )
450
y=-6.65x+155.19
2
r =0.24, P=0.017
360
270
180
90
0
-10
-5
0
5
10
Warming-induced changes in the
proportion of ANPP from C4 grasses (%)
Fig. S6
11
160
y=-2.94x+58.69
2
r =0.20, P=0.023
(a)
Warming-induced changes in
-2 -1
ANPP (A) and BNPP (B) (g m y )
120
80
40
0
(b)
300
200
100
0
-100
-10
y=-5.57x+123.68
2
r =0.14, P=0.057
-5
0
5
10
Warming-induced changes in the
proportion of ANPP from C 4 grasses (%)
Fig. S7
12
UC
UW
CC
CW
0.2
0.0
-0.4
0.4
0.0
-0.4
0.8
0.4
0.0
-0.8
2005-2012
-0.4
0.4 0.0
-0.8
-0.4
-0.8
Axis2
0.8
0.4
0.0
2000-2004 -0.4
0.0
-0.8
-0.3
-0.6
Axis2
Ax
is1
-0.2
Ax
is1
Axis3
0.4
(b)
Axis3
(a)
Fig. S8
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