ISTRO 18th Triennial Conference Proceedings, June 15-19, 2009 Izmir-TURKEY
Impact of Increasing Atmospheric CO2 on Crop Gas Exchange under Different Tillage Practices Stephen A. PRIOR, Francisco J. ARRIAGA, G. Brett RUNION,
Hugo H. ROGERS, H. Allen TORBERT
U.S. Department of Agriculture-Agricultural Research Service National Soil Dynamics Laboratory,
411 South Donahue Drive, Auburn, Alabama 36832 USA,
[email protected]
Abstract: Increasing atmospheric CO2 concentration may impact production agriculture. In the fall of 1997, a study was initiated to examine the response of different tillage systems to changing atmospheric CO2 level. The study used a split-plot design (three replications) with two tillage systems (conventional tillage and no-tillage) as main plots and two atmospheric CO2 levels (ambient and twice ambient) as sub-plots using open top chambers on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional tillage system was a grain sorghum [Sorghum bicolor (L.) Moench.] and soybean [Glycine max (L.) Merr.] rotation with winter fallow and spring tillage practices. In the no-tillage system, sorghum and soybean were rotated and three cover crops were used [crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)] under no-tillage practices. Over multiple growing seasons (three for each crop), the effect of management and CO2 level on leaf level gas exchange during row crop reproductive growth were evaluated. Findings were fairly consistent across years with higher photosynthetic rates being observed under high CO2 (more so with soybean) regardless of management practice. Further, elevated CO2 led to decreased stomatal conductance and transpiration, and increased water use efficiency. Results suggest that better soil moisture conservation and high rates of photosynthesis can occur in both tillage systems in CO2-enriched environments during reproductive growth. Key words: global change, conservation tillage, photosynthesis, transpiration.
INTRODUCTION and LITERATURE REVIEW Over the last decade, numerous studies have
reduced under soil water deficits owing to decreases
demonstrated that elevated atmospheric CO2 often
in photosynthesis, stomatal aperture, and water
enhances
net
potential (Boyer, 1982) during critical reproductive
photosynthesis, and biomass production (Amthor,
stages when demand for water is high. The effect of
1995). The effect of elevated CO2 on crop residue
elevated CO2 in the field may depend on the crop
production
in
species utilized; C3 and C4 crops such as soybean and
agroecosystems (Rogers et al., 1999; Torbert et al.,
sorghum represent two photosynthetic types which
2000). Furthermore, C dynamics can be altered by
are known to respond differentially to elevated CO2
management practices (Kern and Johnson, 1993;
both with regard to carbon metabolism and water use
Potter et al., 1998). There is a lack of information on
(Rogers et al., 1983b; Amthor, 1995).
plant
can
water
influence
use
soil
efficiency,
C
dynamics
how elevated CO2 will interact with management
In the current study, crops were grown in a large
practices, especially the newer ones being used in
outdoor soil bin under two different atmospheric CO2
conservation systems. Systems that maintain high
environments (ambient and twice ambient) and
levels of residue can help mitigate problems by
management conditions (conventional tillage and no-
enhancing soil C storage and soil water holding
tillage). The objective was to investigate the effect of
capacity, reducing evaporative soil water loss, and
management and CO2 level on leaf level gas exchange
improving soil water infiltration. Crop growth is often
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ISTRO 18th Triennial Conference Proceedings, June 15-19, 2009 Izmir-TURKEY
during row crop (sorghum and soybean) reproductive
cm) using time domain reflectometry (Topp et al.,
growth over multiple growing seasons.
1980), but only the 20 cm data are presented.
MATERIAL and METHOD
RESULTS and DISCUSSION
This study was initiated in the fall of 1997 using
The rise in atmospheric CO2 concentration may
an outdoor soil bin (7m x 76 m) at the USDA-ARS
alter future responses. Past work has clearly shown
National
Auburn,
that elevated atmospheric CO2 often enhances plant
Alabama, USA (Batchelor, 1984). A split-plot design
biomass production and subsequently the amount of
replicated three times was used with two cropping
residue returned to the soil surface and belowground
systems (conventional and no-tillage) as main plots
(Torbert et al., 2000). A review of the literature
and two CO2 levels (ambient and twice ambient) as
indicated that the fate of crop residue and soil carbon
subplots using open top field chambers (Rogers et al.,
dynamics are highly influenced by management
1983a) on a Decatur silt loam (clayey, kaolinitic,
practices under current atmospheric CO2 conditions
thermic Rhodic Paleudults).
(Kern and Johnson, 1993). Currently, there is a lack of
Soil
Dynamics
Laboratory
in
In the conventional system, grain sorghum and
information on how elevated CO2 will interact with no-
soybean were rotated each year with spring tillage
till management practices. Advantages of no-till
after winter fallow. In the no-tillage system, grain
management is that maintaining high levels of residue
sorghum and soybean were also rotated, but with
can help mitigate problems by enhancing soil C
three winter cover crops (crimson clover, sunn hemp,
storage and soil water holding capacity, reducing
and wheat) which were also rotated; all were grown
evaporative soil water loss, and improving soil water
without tillage. The wheat served as cover as well as
infiltration.
being harvested for grain. Cover crops were broadcast
Although previous work has shown that total
planted while row crop seeds were planted on 0.38 m
residue inputs were higher under no-till, especially
row spacing. Extension recommendations were used
under elevated CO2 conditions (Prior et al., 2005), the
in managing the crops.
impact of no-till management on enhancing crop
At final harvest, plants were removed and total
yields was small relative to conventional tillage in our
fresh weights recorded. A subsample of the non-yield
study. Dry matter data across all seasons for both
material (residue) was taken and its fresh weight
crops are shown in Figure 1. In general, benefits of
recorded; the subsample was dried (55 oC) and total
no-till altering yield and stover production was more
residue was calculated using the fresh weight to dry
notable
weight ratios (Prior et al., 2005). The remaining
comparison, the benefits of additional CO2 was clearly
residue material was returned to each plot. For grain
evident in all years of study. Soybean exhibited a
in
sorghum
compared
to
soybean.
In
crops (sorghum, soybean, and wheat), yields were
greater response to elevated CO2 across all growing
determined following correction for moisture. In the
seasons relative to sorghum. The greater response of
conventional system (after fallow period), weed dry
soybean to CO2 are in general agreement with
weight was measured as described above and residue
reviews of the literature (Rogers et al., 1983b; Rogers
was returned to plots prior to tillage.
and Dahlman, 1993; Amthor, 1995). level
Likewise, management had little effect on gas
stomatal
exchange measurements reported here (Figs. 2 and
conductance (data not shown), and transpiration)
3). Response patterns to imposed treatment across
were made twice a week using a LI-6400 Portable
the various years were consistent in that elevated CO2
Photosynthesis System (LI-COR, Inc., Lincoln, NE).
had a greater impact on reported measurement. C3
During
reproductive
measurements
[i.e.,
growth, photosynthesis,
leaf
Measurements were taken at midday on three
and C4 crops such as soybean and sorghum represent
different randomly chosen leaves (fully expanded, sun
two photosynthetic types which are known to respond
exposed leaves at the canopy top) per plot and were
differentially to elevated CO2 both with regard to
initiated at the start of reproductive growth. Soil water
carbon metabolism and water use (Rogers et al.,
status was also monitored at two depths (20 and 40
1983b; Amthor, 1995). Multiple years of observations
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ISTRO 18th Triennial Conference Proceedings, June 15-19, 2009 Izmir-TURKEY
in our study clearly illustrated this pattern of
transpiration for soybean and sorghum in a field study
response. Seasonal averages indicated that elevated
using
stem
flow
gauges.
Overall,
changes
in
CO2 increased soybean photosynthesis approximately
photosynthesis and transpiration led to elevated CO2-
50% regardless of the management system used for
induced increases in water use efficiency of 86% for
all years. In comparison, sorghum photosynthesis
soybean and 51% for sorghum. These shifts in water
increased about 15% across years for both systems.
use efficiency are in general agreement with reviews
The photosynthetic field response of these two crops
of the literature (Rogers et al., 1983b; Rogers and
were in the range previously reported in a review by
Dahlman, 1993; Amthor, 1995).
Rogers and Dahlman (1993). Soybean transpiration
In general, management had little effect on gas
was more variable than photosynthesis. Elevated CO2
exchange measurements. These results suggest that
decreased transpiration around 17% across years for
in a future CO2-enriched environment better soil
both systems. Sorghum transpiration decreased more
moisture
consistently—approximately 26%. Dugas et al. (1997)
photosynthesis can lead to increased productivity in
conservation
and
high
rates
of
reported a CO2-induced decrease in whole plant both conventional and conservation tillage systems. 2. 0
2.0
1999 SOYBEAN Dry Matter (kg m -2)
Dry Matter (kg m -2)
1. 6
Stover
1. 2 0. 8 0. 4 0. 0 E
2. 0
0.8 0.4
A
E
2.0 2. 0
1. 2 0. 8 0. 4
1.6 1. 6
A
E
2002 SORGHUM
Grain
Stover
0. 0
Stover
1.2 1. 2 0.8 0. 8 0.4 0. 4 0.0 0. 0
A
E
2.0 2. 0
A
E
A
E
2.0 2. 0
2003 SOYBEAN
Grain
1.2 1. 2 0.8 0. 8 0.4 0. 4 0.0 0. 0
1.6 1. 6
A
E
2004 SORGHUM
Grain
Stover
Dr Dry y Matter (kg m -2)
Dry Dry Matter tter (kg (kg m -2)
Stover
1.2
E
Dry Matter (kg m -2) Dry
Dry Matter (kg m -2)
A 2001 SOYBEAN
Grain
1.6 1. 6
1.6
0.0 A
1. 6
2000 SORGHUM
Grain
Grain
Stover
1.2 1. 2 0.8 0. 8 0.4 0. 4 0.0 0. 0
A
E
Conve onventi tiona onal onal Till Tillag illag age e
A
E
No-Tillag -Tillag age e
A
E
Conventiona entional tional Ti Tillag llage
A
E
No-T -Tilla illag illa ge
Figure 1. Dry production (stover and grain) for soybean (1999, 2001, 2003) and sorghum (2000, 2002, 2004) under ambient (A) and elevated (E) atmospheric CO2 conditions and two management systems (conventional tillage and no-tillage) are shown.
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ISTRO 18th Triennial Conference Proceedings, June 15-19, 2009 Izmir-TURKEY
.2 1
SOYBEAN1999 1999
100
0.5
80
0.4
N TE 0.20
.2 0 .2 1
60
0.2 0.2
40
0.1 0.1
20
0.0 0.0
Pn((μmol molCCO2m m-2ss-1)
205
215
225
235
24 245 5
255
26 265 5
0.5
80
0.4
CTE 0 .17 CTA 0 .16
60
195
205
215
225
235
245
255
265
CTA 0. 0.26 26
60 40
0.1
20
0
0.0
0.1 0
80
CTE 0. 0.23 23
0.3
20
40
40
100 Rainf inf all
NTA 0. 0.22 22
0.2
0.2
275
SOYBEA YBEAN EAN22003
NTE 0. 0.24 24 Irrrigati Ir tio on
N TE 19 .0 0
0
195
275
40
205
21 215 5
225
235
24 245 5
255
NT NTA A 11.5 .52 2
C TE 18 .5 9
30
30 30
.39 9 CT CTE E116.3
CTA 11.5 6
CT CTA A 11.5 .59 9
20
20
20
10
10
10
0
0
Tr((mmol mmol H2O m -2s -1)
195
15
205
215
225
235
245
255
265
21 215 5
225
2 35
24 5
255
265
2 75
195
15
NTE5. 5. 47
NTE 4.80 4.80
NTA 6.98
NTA 6. 6. 09 CTE 4.76 4.76
10
CTA 6. 6.56
0 215
225 25
235
245
255
265
275
205
215
225
235 235
245
255
265 265
275
19 195 5
8
NTA NTA 11.95
6
205
265
275
21 215 5
225
235
245
255
265
275
22 5
23 5
2 45
2 55
26 5
27 5
NT NTA A 1.8 9
6
C TE 3.21 3.21
CTE 3.68
CT CTA A 1.9 6
CTA 2. 2. 00
4
4
2
2
2
0
0 2 15
255
N TE 3.44 3.44
4
2 05
245
N TE 6. 80 6. N TA 7. 85 7. C TE 7. 27 7. C TA 8. 32 8.
NTE 3.80
N TE 3. 72 3. NT NTA A 1 .8 8 1 C TE 3. 49 49
3. CT CTA A 1 .8 0 1
19 5
235
0
195 8
8
6
225
5
0 205
215
10
5
195
205 205
CTA 6. 6. 08
5
WUE((mmolC CO2//m mol H2O)
2 05
15 15
CTE5. 5. 74
10
275
0
19 5
275
265 N TE 22. 5 1 22. N TA 1 4 .7 1 1 C TE 22. 8 0 22. C TA 1 5 .9 8 1
.81 1 NT NTE E116.8
N TA 12 .8 2
30
100 Ra Raiinf al l
NTA 0 .16
0.3
0
195
40
SOYBE SOYBE YBEAN AN22001
Ra Raii nf all Irrigati gation
.2 0
Wa Watter((mm)
0.3 0.3
NTE 0 0 NTA 0 0 CTE 0 0 CTA 0 0
Water (mm (mm)
0.4 0.4
Wa Watter((mm)
SoilW Water ter(m (m 3m m-3)
0.5 0.5
225
23 5
2 45
25 5
265
275
19 5
2 05
215 215
225
235 23 5
2 45
255 25 5
2 65
0
0 19 5
27 5
2 05
215
Figure 2. Three seasons (1999, 2001, 2003) of gas exchange measures (Pn=photosynthesis; Tr=Transpiration; WUE= water use efficiency) during reproductive growth for soybean grown under conventional tillage (CT) or no-tillage (NT) and exposed to ambient (A) or elevated (E) atmospheric CO2; means within graphs are seasonal averages. Corresponding seasonal rainfall and volumetric soil water measurements are also shown. 0.5 0. 5
80
0.4 0. 4
60
0.2 0.2
40
0.1 0.1
20
0.0 0.0 195
200
205
210
215
Wa Watter (mm)
0.3 0.3
220
80 60
0.2 0. 2
40
0.1 0. 1
20
200
205 20 5
210
215
220
30
CTE CTE 21.42
20
10
NTA NT A 22. 80 CTE CT E 24. 03
2 00 20
2 05
2 10 21
2 15
22 0 22
22 5
T r ( ( m m o l H 2 O m -2 s -1 )
195
T r ( ( m m o l HH 2 O m -2 ss -1 )
10
NTE NT E 3. 3.552 NT NTA A 4.48
8
CTE CT E 4. 4.000 CT CTA A 4.83
6 4 2
200
205
210
215 215
220
225
5
200
205
210
215
220
225
200 20
2 05
2 10 21
2 15
22 0 22
2 00
205
2 10
215 215
0 225
2 20
NT A5.5. 66 CT E4.4. 32 CT A5.5. 63
6 4 2
200
205
210
215
220
NT NTE E 21.60
CT CTE E 21.54 CT CTA A 118.06
200
205
21 2100
215
220
225 NT NTE E33 . 26 NT NTA A33 . 84
8
CT CTE E33 . 22 CT CTA A44 . 14
6 4 2 0 195
225
NT NTA A 116.86
10
0 195 10
225
8
200
205
210
215 215
220
225
15 NTE 6. 6.22 22 NTA NT A44 .10 CTE 6. 6.05 05 CTA 4. 4.21 21
10
5
0 195
20
19 5
15 NTE55 .52 NTA33 .67 CTE55 .59 CTA33 .75
10
0 195
CTA CT A 22. 76
NT E4.4. 29
0 195
WUE ((m mmol C CO O2//m mol H2O
0 195 15
40
0.1 0.1
T r (( m m o l H 2 O m -2 s -1 )
00 19 5 10 10
60
0.2 0.2
20
NTE NT E 24. 62
10
80
CT CTE E 0 .14 CTA 0.20 0.20
0.3 0.3
30
CTA CTA 118.01
20
Rainf inf all
NT NTA A 0 .19
40
NTA NTA 116.45
30
10 100 0
SOGH OGHUM UM22004
NTE 0.20 0.20
0.4 0.4
0.0 0.0
0 225
NTE NTE 18.73
0
WUE((mmol CO2//m mol H2O)
NT NTE E00 .15 NT NTA A00 .16 CT CTE E00 .14 CT CTA A00 .15
WUE((mmo mmoll CO2// molHH20
m -2 s -1 ) P n ((μ m o oll CC O 2 m
40
SOGH OGHUM UM22002
0.3 0. 3
0.0 0. 0 195 40 40
0 225
0.5 0.5
100 100 Rai Rain nf all
Wat Water((mm)
100 100
Wat Wa r(r(m m)3 m -3) S oilW W atete ter (m m (m
NT NTE E 0 .14 0 NT NTA A 0 .15 0 CT CTE E 0 .13 0 CT CTA A 0 .12 0
m-3) SoilW Water te(r (m 3m
SOGH OGHUM UM22000
3
-3
SoilW Water((m m m)
Rainf inf all
0.4 0.4
P n ( ( μ m o l CC O 2 mm -2 ss -1 )
0.5 0.5
200
205
210
215
220
22 225 5
NTE66 .85 NTA44 .41 CTE66 .94 CTA44 .46
10
5
0 195
200
205
210
215
220
225
Figure 3. Three seasons (2000, 2002, 2004) of gas exchange measures (Pn=photosynthesis; Tr=Transpiration; WUE= water use efficiency) during reproductive growth for sorghum grown under conventional tillage (CT) or no-tillage (NT) and exposed to ambient (A) or elevated (E) atmospheric CO2; means within graphs are seasonal averages. Corresponding seasonal rainfall and volumetric soil water measurements are also shown.
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ISTRO 18th Triennial Conference Proceedings, June 15-19, 2009 Izmir-TURKEY
ACKNOWLEDGMENTSThe authors thank B.G. Dorman and J.W. Carrington for technical assistance. This research was supported by the Biological and Environmental Research Program (BER), U.S. Department of Energy, Interagency Agreement No. DE-AI02-95ER62088. REFERENCES
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