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Chapter 6. Responses of Agricultural Crops to Free-Air CO2 Enrichment

Chapter 6. Responses of Agricultural Crops to Free-Air CO2 Enrichment

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294



KIMBALL et al.

at both ample and low N conditions. Roots were generally stimulated more than

shoots. Woody perennials had larger growth responses to elevated CO2, but their

reductions in stomatal conductance were smaller. Tissue N concentrations went

down, while carbohydrate and some other carbon-based compounds went up, with

leaves being the organs affected most. Phenology was accelerated slightly in most

but not all species. Elevated CO2 affected some soil microbes greatly but not others,

yet overall activity was stimulated. Detection of statistically significant changes in

soil organic carbon in any one study was nearly impossible, yet combining results

from several sites and years, it appeared that elevated CO2 did increase sequestration of soil carbon. Comparisons of the FACE results with those from earlier

chamber-based results were consistent, which gives confidence that conclusions

C 2002 Elsevier Science (USA).

drawn from both types of data are accurate.



I. INTRODUCTION

The increasing CO2 concentration of Earth’s atmosphere and associated predictions of global warming (IPCC, 1996) have stimulated research programs to

determine the likely effects of the future elevated CO2 levels on agricultural productivity and on the functioning of natural ecosystems (e.g., Dahlman et al.,

1985). However, even predating the global change concerns, the effects of atmospheric CO2 enrichment have been studied for more than a century in greenhouses, controlled-environment chambers, open-top chambers, and other enclosures to confine the CO2 gas around the experimental plants (e.g., Drake et al.,

1985; Enoch and Kimball, 1986; Schulze and Mooney, 1993). The results of these

many chamber-based experiments have been reviewed by Kimball (1983, 1986,

1993), Morison (1985), Cure (1985), Cure and Acock (1986), Kimball and Idso

(1983), Poorter (1993), Idso and Idso (1994), Ceulemans and Mousseau (1994),

Wullschleger et al. (1997), Cotrufo et al. (1998), Norby et al. (1999), Nakagawa

and Horie (2000), Curtis and Wang (1998), and Wand et al. (1999) (although the

latter two also included a few observations from recent nonchamber open-field

experiments).

However, the environment inside enclosures is not generally like that outside

(e.g., Kimball et al., 1997; McLeod and Long, 1999); thus, there have been

many concerns that the results from such enclosure-based CO2-enrichment experiments might not be representative of future open fields and forests. Therefore, various attempts were made to develop techniques which could maintain

the CO2 concentrations over open-field plots at elevated levels despite the challenges imposed by open-field winds causing rapid dispersal of the CO2 (Allen,

1992; Norby et al., 2001). Eventually, engineers from Brookhaven National

Laboratory (Upton, New York) working cooperatively with scientists from the



CO2 RESPONSES OF AGRICULTURAL CROPS



295



U.S. Department of Agriculture, Agricultural Research Service, and from Tuskegee

University, as well as others, were able to adapt a “vertical vent pipe” technology

that could adequately maintain the desired high levels of CO2 over open-field

plots all growing-season long (Hendrey, 1993; Norby et al., 2001). The first such

experiment with publishable biological data was conducted on cotton in 1989

at Maricopa, Arizona. After success with cotton, the Brookhaven group moved

their engineering efforts to the forest, and they were able to increase the scale

of the apparatus to accommodate 14-m-tall trees (e.g., Delucia et al., 1999).

Once it was demonstrated that such free-air CO2 enrichment (FACE) experiments were feasible, several other research groups also initiated similar experiments in both managed and natural ecosystems. To date, there are about 30 active

or planned FACE sites (http://cdiac.esd.ornl.gov/programs/FACE/face.html;

http://www.face.bnl.gov/; http://gcte-focus1.org/co2.html).

The purposes of this paper are (i) to compile the available data from the FACE

experiments on agricultural crops; (ii) to determine the relative responses of the

several crops to elevated CO2 with regard to their physiology, growth, yield, water

relations, and soil processes; (iii) to search for similarities and differences among

species and plant functional types; and (iv) to compare these FACE results with

those from prior chamber-based studies.



II. METHODOLOGY

We have extracted data from papers and manuscripts generated by our

agricultural-crop-oriented free-air CO2 enrichment (FACE) projects at Maricopa,

Arizona; Shizukuishi, Iwate, Japan; and Rapolano, Terme, Italy, as well as from

the grassland project at Eschikon, Switzerland. The experimental protocols and

site characteristics for the several experiments are listed in Table I. From the absolute crop response values, we computed the relative increases (or decreases, which

are listed as negative increases) due to the FACE treatment with respect to their

corresponding control treatments at ambient CO2, as listed in Table II. The number

of FACE experiments is relatively small, so conclusions cannot be as definitive

as desired. On the other hand, the relatively large plot size of the FACE projects

produces enough plant material to support the research of a large number of cooperating scientists from several disciplines, so the number of processes for which

measurements were obtained is comparatively large.

The crops include wheat (Triticum aestivum L.), rice (Oryza sativa L.), perennial ryegrass (Lolium perenne), sorghum (Sorghum bicolor (L.) Măoench), potato

(Solanum tuberosum L.), white clover (Trifolium repens), lucerne or alfalfa

(Medicago sativa L.), cotton (Gossypium hirsutum L.), and grape (Vitis vinifera L.).

These crops are representative of several functional types of plants. Specifically, wheat, rice, and ryegrass are all C3 grasses, and sorghum is a C4 grass.



Table I

Experimental Protocols and Site Characteristics for Several Agricultural FACE Experiments

FACE experiment (experiment ID)a

Parameter

Location

Species or ecosystem



Latitude (deg, min)

Longitude (deg, min)

Elevation (m)

Experiment start dateb

296

Experiment end dateb



Growing season startc



Growing season endc



FACE startd



FACE endd

Solar rad.e(MJ m−2 day−1)

Max. air temp.f(◦ C)



MCCot89–91



MCWht93–94



MCWht96–97



Maricopa,

Arizona

Cotton

(Gossypium

hirsutum L.)



Maricopa,

Arizona

Wheat (Triticum

aestivum L.)



Maricopa,

Arizona

Wheat (Triticum

aestivum L.)



33◦ 4 N

111◦ 59 W

358

17-04-1989

23-04-1990

16-04-1991

17-09-1989

17-09-1990

16-09-1991

17-04-1989

17-04-1990

16-04-1991

17-09-1989

17-09-1990

16-09-1991

19-05-1989

04-05-1990s

26-04-1991

17-09-1989

17-09-1990

16-09-1991

Avg. 25.1

Avg. 46.3



33◦ 4 N

111◦ 59 W

358

15-12-1992

08-12-1993



MCSor98–99



Swiss93–98



RiceFACE98–99



Eschikon,

Switzerland

Grassland; ryegrass

(Lolium perenne)

and white clover

(Trifolium repens)

47◦ 27 N

8◦ 41 E

550

31-5-1993



Shizukuishi,

Iwate, Japan

Rice (Oryza sativa L.)



33 4 N

111 59 W

358

15-12-1995

15-12-1996



Maricopa,

Arizona

Sorghum

[Sorghum

bicolor (L.)

Măoench]

33 4 N

111 59 W

358

16-07-1998

15-06-1999



24-05-1993

01-06-1994



29-05-1996

28-05-1997



21-12-1998

26-10-1999



Continuing



29-09-1998

24-09-1999



15-12-1992

08-12-1993



15-12-1995

15-12-1996



16-07-1998

15-06-1999



Temp > 5◦ C



21-05-1998

20-05-1999



24-05-1993

01-06-1994



29-05-1996

28-05-1997



21-12-1998

26-10-1999



Temp < 5◦ C



29-09-1998

24-09-1999



01-01-1993

28-12-1993



01-01-1996

03-01-1997



31-07-1998

01-07-1999



1-6-1993



03-06-1998

20-05-1999



16-05-1993

18-05-1994



15-05-1996

12-05-1997



21-12-1998

26-10-1999



Continuing



29-09-1998

24-09-1999



Avg. 18.7

Avg. 38.5



Avg. 19.9

Avg. 40.9



Avg. 21.6

Avg. 44.2



∼14.2

25



Avg. 13.8

24.5



39◦ , 38 N

140◦ , 57 E

200

21-05-1998

20-05-1999



Min. air temp.f(◦ C)

Plot diameterg(m)

No. of replicatesh

No. of CO2 levelsi

Predilution of the CO2? j

Set point or increment?k

FACE CO2 conc.(s)l

Daily enrichment timem

“No-enrichment” criterian

Add’nal treat. #1 nameo



297



Avg. −2.8

20

4

2

Yes

Set point

550

24 h day− 1

None

Water



Avg. −3.7

20

4

2 + Ambient

Yes

increment

+200

24 h day− 1

None

Nitrogen



Avg. 2.0

21

4

2

Yes

increment

+200

24 h day− 1

None

Water



−5

18

3

2

Yes

Set point

600

Daylight

Winter

Nitrogen



15.9

10

4

2

No

200 ppm increment

589 (at the ring center)

24 h

na

Nitrogen



Main or split?p

Level 1q (dry or low-N)



Avg. 7.6

18

4

2

Yes

Set point

550

Daylight

None

Water in 1990

and 1991

Split

Avg. 1009 mm



Split

Avg. 335 mm



Split

Avg. 483 mm



Split

140 kg ha− 1 y− 1



Split

Low (40 kg N/ha)



Level 2q (wet or high-N)



Avg. 1202 mm



Avg. 679 mm



Split

70 kg N ha− 1 in

1996; 15 kg

N ha− 1 in 1997

350 kg N ha− 1



Avg.1133 mm



560 kg ha− 1 y− 1



Standard [80 (1998) or

90 (1999) kg N/ha]

High [120 (1998) or 150

(1999) kg N/ha]



1120 kg ha− 1 y− 1



Level 3q (very high-N)

Add’nal treat. #2 nameo

Main or split?p

Level 1q

Level 2q

Add’nal treat. #3

Main or Split?p

Level 1q

Level 2q

Level 3q

Reference(s)r



Pinter et al.

(1994),

Mauney et al.

(1994),

Lewin et al.

(1994)



Hunsaker et al.

(1996),

Kimball et al.

(1999),

GCTE (1996)



Kimball et al.

(1999)



Ottman et al.

(2001)



Cutting frequency

Split

4 cuts y− 1

8 cuts y− 1, then 5

Sward type

Split

Lolium perenne

Trifolium repens

Mixture

Jongen et al.

(1995),

Hebeisen et al.

(1997),

Daepp et al. (2000)



Kim et al. (2001),

Kobayashi et al.

(2001)



continues



Table I—continued

FACE experiment (experiment ID)a

Parameter



CLAIRE 94–95



CLIVARA 96–97



Location

Species or ecosystem



Rapolano, Terme, Italy

Grape (Vitis vinifera cv.

Sangiovese)



Rapolano, Terme, Italy

Grape (Vitis vinifera cv.

Sangiovese)



Latitude (deg, min)

Longitude (deg, min)

Elevation (m)

Experiment start dateb



50◦ 32 N

8◦ 41.3 E

172

01-05-1994

19-4-1995

04-10-1994

17-10-1995

01-05-1994

19-04-1995

04-10-1994

17-10-1995

01-15-1994

02-05-1995

04-10-1994

17-10-1995

Avg. 21.3

35.8

0.9

8 × 1.5

3

2

Yes

Set point

700

Daylight



50◦ 32 N

8◦ 41.3 E

172

22-04-1996

20-04-1997

30-09-1996

07-10-1997

22-04-1996

20-04-1997

30-09-1996

07-10-1997

06-05-1996

11-05-1997

01-10-1996

07-10-1997

Avg. 20.9

Avg. 32.4

Avg. −1.3

8 × 1.5

2

3

Yes

Set point

550, 700

Daylight



Experiment end dateb

298



Growing season startc

Growing season endc

FACE startd

FACE endd

Solar rad.e(MJ m− 2 day− 1)

Max. air temp.f(◦ C)

Min. air temp.f(◦ C)

Plot diameter g(m)

No. of replicatesh

No. of CO2levelsi

Predilution of the CO2? j

Set point or increment?k

FACE CO2conc.(s)l

Daily enrichment timem



POTATO95

Rapolano, Terme, Italy

Potato (Solanum

tuberosum cv.

Primura)

50◦ 32 N

8◦ 41.3 E

172

27-05-1995

05-09-1995

10-06-1995

05-09-1995

10-06-1995

04-05-1995

21.5

35.8

2.9

8

1

4

Yes

Set point

460,560,660

Daylight



CHIP98–99

Rapolano, Terme, Italy

Potato ( Solanum

tuberosum cv. Bintje)

50◦ 32 N

8◦ 41.3 E

172

20-05-1998

05-05-1999

18-08-1998

17-08-1999

28-05-1998

26-05-1999

18-08-1998

17-08-1999

28-05-1998

27-05-1999

18-08-1998

17-08-1999

Avg. 21.4

Avg. 37.8

Avg. 5.1

8

3

2 + Ambient

Yes

Set point

560

Daylight



“No-enrichment” criterian

Reference(s)r



a



None

Bindi et al. (1995a,

1995b),

Raschi et al. (1996),

Giuntoli (2000)



None

Bindi et al. (2000),

Bindi, Fibbi et al. (2001)

Bindi, Fibbi, and

Miglietta (2001)

Giuntoli (2000)



None

Miglietta et al. (1997,

1998),

Vaccari et al. (2000)



None

Bindi et al. (1998, 1999)



Experiment identification names.

Dates for the start and end of the experiments.

c

Calendar year dates or criteria for the start and stop of the growing seasons.

d

Start and stop dates of the FACE treatment(s). (For most experiments, these dates are the same as the growing season dates.).

e

Mean daily solar radiation obtained during growing season(s), expressed in MJ m−2 day−1.

f

Maximum and minimum air temperatures during growing season(s) in ◦ C.

g

Diameter of useable plot area in m, or for rectangular plots, length and width.

h

Number of replicate CO2 and other treatment plots.

i

Number of treatment CO2 levels. A “2” means experiments with FACE and Control treatments or with FACE and ambient treatments. “Control” means plots with

air flow near identical to that of the FACE plots but without added CO2. “Ambient” means plots with no forced air flow and no added CO2. “2 + ambient” means

experiments with FACE, control, and ambient treatments. For experiments with multiple levels of FACE concentrations, a list of the several CO2 levels is given.

j

A “yes” means a blower system in the FACE apparatus prediluted CO2 with air, or a “no” means pure CO2 was released.

k

“Set point” or “increment” indicates whether a constant target CO2 set point was used or whether a target increment in concentration above normal air CO2 levels

was used.

l

The set point CO2 concentration(s) or the increment(s) in CO2 concentration preceded by a “+”. Units of μmol mol−1.

m

Portion of day CO2 enrichment was done such as “24 h” or “daylight” or other amount.

n

Constraints that were put on the enrichment, such high-wind cutoff or low-temperature cutoff.

o

Name(s) of any other additional factorial treatments in the experiment such as low water or low nitrogen.

p

“Split” or “main” indicates whether the CO2 main plots were split or whether additional full-size main plots of the other factor(s) were added.

q

Levels of the additional treatment factors with units.

r

Reference(s) that best describe the experimental conditions.

b



299



Table II

Percentage Increases in Several Plant Response Parameters to Elevated CO2 of Various Agricultural Crops Grown in Monoculture Relative to

Their Responses at Ambient CO2a

Percentage increases due to elevated CO2

Ample water

Very high N

Experiment ID



Crop; condition



%



+SE



Low water



Ample N

%



+SE



Low N

%



+SE



Ample N

%



+SE



References



Net photosynthesis



300



C3 grasses

MCWht93

Wheat upper leaf

MCWht93

Wheat flag leaf

MCWht93

Wheat 8th leaf

MCWht93

Wheat 7th leaf

(Daily integral of net CO2 uptake)

MCWht96

Wheat upper leaf

MCWht97

Wheat upper leaf

(Seasonal carbon assimilated)

MCWht93,96

Wheat ears

MCWht97

Wheat canopy

Swiss94

Ryegrass 7-day cut

Swiss94

Ryegrass uncut

C4 grasses

MCSor98,99



Sorghum upper leaf



C3 woody perennials

MCCot89

Cotton upper leaf

MCCot90

Cotton canopy



31.5

25.6

68.6



32.8

21.6



Garcia et al. (1998)

Osborne et al. (1998)

Osborne et al. (1998)

Osborne et al. (1998)

5.0

7.3



25.9

19.7



10.0

9.2



Wall, Adam et al. (2001)

Wall, Adam et al. (2001)



58.0

19.2

32.5

43.5



19.0

24.1



32.0

8.7

45.2

45.8



8.5



13.5



23.3



21.2



Wall, Brooks et al. (2001)



28.2

32.1



13.0

38.9



17.8



23.3



Hileman et al. (1994)

Hileman et al. (1994)



58.0



Wechsung et al. (2000)

Brooks et al. (2001)

Rogers et al. (1998)

Rogers et al. (1998)



20.8

22.4



Water relations: stomatal conductance

MCWht93

MCWht96–97



C4 grasses

MCSor98–99



301



Wheat

Wheat

C3 grass means

SE



−32.7

−36.0

−34.4

1.7



Sorghum



−37.3



13.8



−32.4



22.6



Wall, Brooks et al. (2001)



−18.2

−12.3

−14.7

3.7

−19.6

−12

−18

−15

−8

−32

−23.0

−6

4

−21.3

−16.0



8.9

3.2



−22.2



14.3



Hileman et al. (1994)

Raschi et al. (1996)



C3 woody perennials

MCCot90

Cotton

CLAIRE95

Grape

C3 woody means

SE

Literature

Literature

Wheat

Literature

Rice

Literature

Sorghum

Literature

Cotton

Literature

Potato

Literature

Literature

Woody

SE

Literature

Wild C3 grass

Literature

Wild C4 grass



Garcia et al. (1998)

Wall, Adam et al. (2001)



−44.0



Kimball and Idso (1983)

Cure (1985)

Cure (1985)

Cure (1985)

Cure (1985)

Cure (1985)

Morison (1985)

Curtis and Wang (1998)



−14.5



−12.8



Wand et al. (1999)

Wand et al. (1999)



Water relations: canopy temperature (◦ C, not %)

C3 grasses

MCWht93

MCWht96



Wheat

Wheat



0.6

0.6



0.1



1.1



0.1



Kimball et al. (1995)

Kimball et al. (1999)

continues



Table II—continued

Percentage increases due to elevated CO2

Ample water

Very high N

Experiment ID



Crop; condition



C3 woody perennials

MCCot89

Cotton



%



+SE



Low water



Ample N

%



0.8



+SE



Low N

%



+SE



Ample N

%



+SE



0.1



References



Kimball et al. (1992)



Water relations: evapotranspiration or water use



302



C3 grasses

MCWht93

MCWht94

MCWht96

MCWht97

MCWht93–97

MCWht96–97



Wheat; water bal.

Wheat; water bal.

Wheat; water bal.

Wheat; water bal.

Wheat; energy bal.

Wheat; energy bal.



−3.6

−3.3

−3.5

−3.9

−6.7



C4 grasses

MCSor98

MCSor99



Sorghum; water bal.

Sorghum; water bal.



−11.1

−8.7



C3 woody perennials

MCCot90

Cotton; water bal.

MCCot91

Cotton; water bal.

MCCot91

Cotton; stem flow



−0.7

−1.3



4.5

−2.2



Hunsaker et al. (1996)

Hunsaker et al. (1996)

Hunsaker et al. (2000)

Hunsaker et al. (2000)

Kimball et al. (1999)

Kimball et al. (1999)



−19.5

3.0

2.6



−1.1

−1.9

0.0



0.0

−6.5



6.2

4.0



−1.6

−1.6



Conley et al. (2001)

Conley et al. (2001)

Hunsaker et al. (1994)

Hunsaker et al. (1994)

Dugas et al. (1994)



Water relations: leaf water potential

[Negative % increase values indicate FACE plants had higher (i.e., less negative and less stressful) water potentials]

C4 grasses

MCSor98–99



Sorghum



C3 woody perennials

CLAIRE95

Grape



−2.8



5.5



−2.9



1.2



−8.8



4.2



Wall, Brooks et al. (2001)

Raschi et al. (1996)



Peak leaf area index

C3 grasses

MCWht96

MCWht97

Swiss96-97

Swiss96-97



Wheat

Wheat

Ryegrass, vege.

Ryegrass, repro.



16.4

16.5



13.0

24.0

11.1

8.1



6.7

−6.2

−5.6

12.2



1.0



3.5



0.4



Rice



10.8



6.3



2.0



C3 grass means

SE



11.0

3.8



10.8

2.9



1.4

2.9



(Vegetative and reproductive stages in pots)

RiceFACE98

Rice

RiceFACE99



303



C4 grasses

MCSor98

MCSor99



−0.7

−9.8

−5.4

4.7



16.6

14.2



C3 broadleaf forb with tuber storage

POTATO95

Potato; 460 ppmv

POTATO95

Potato; 560 ppmv

POTATO95

Potato; 660 ppmv

Chip98

Potato

Chip99

Potato

Potato means

SE



−12.9

5.8

−1.6

−9.8

−11.0

−6.2

3.5



37.7

22.6

11.2

19.0

4.7



C3 woody perennials

MCCot89

Cotton

MCCot91

Cotton

Cotton means

SE



3.8

−15.6

−6.4

10.2



23.5

14.2



Sorghum

Sorghum

C4 grass means

SE



Brooks et al. (2001)

Brooks et al. (2001)

Daepp et al. (2001)

Daepp et al. (2001)

Kobayashi et al.

(unpublished)

Kobayashi et al.

(unpublished)



−0.3

3.1

1.4

1.7



22.5

14.8



Ottman et al. (2001)

Ottman et al. (2001)



Miglietta et al. (1998)

Miglietta et al. (1998)

Miglietta et al. (1998)

Bindi et al. (1998)

Bindi et al. (1999)



20.8



22.6



Mauney et al. (1992)

Mauney et al. (1994)



continues



Table II—continued

Percentage increases due to elevated CO2

Ample water

Very high N

Experiment ID



Crop; condition



%



+SE



Low water



Ample N

%



+SE



Low N

%



+SE



Ample N

%



+SE



References



12.3

16.6



9.1

20.6



Pinter et al. (2002)

Pinter et al. (2002)



Biomass accumulation: shoots



304



C3 grasses

MCWht93

MCWht94



Wheat

Wheat



9.3

7.7



12.2

14.4



[Note: blower effect may have reduced response in 1993 and 1994 (Pinter et al., 2000)]

MCWht96

Wheat

4.8

5.8

8.1

MCWht97

Wheat

11.7

15.8

2.8

RiceFACE98

Rice

16.9

7.6

RiceFACE99

Rice

13.9

10.8

8.1

Swiss93

Ryegrass

5.8

3.0

3.7

Swiss94

Ryegrass

8.0

11.0

−8.6

Swiss95

Ryegrass

10.9

9.7

1.6

Swiss96

Ryegrass

18.6

3.0

−6.2

Swiss97

Ryegrass

10.5

5.6

−0.3

Swiss98

Ryegrass

20.1

4.9

6.9

Swiss96–97

Ryegrass, vegetative

20.2

5.1

16.6

5.7

−2.2

Swiss96–97

Ryegrass, reproduc.

25.4

9.6

20.2

9.7

24.2

(Vegetative and reproductive stages in pots)

19.0

C3 grass means

SE

2.5



11.5

1.4



3.1

2.6



13.8

15.4



Pinter et al. (2002)

Pinter et al. (2002)

Kim et al. (unpublished)

Kim et al. (2001)

Hebeisen et al. (1997)

Hebeisen et al. (1997)

Hebeisen et al. (1997)

Daepp et al. (2000)

Daepp et al. (2000)

Daepp et al. (2000)

Daepp et al. (2001)

Daepp et al. (2001)



6.1

20.2

20.5

4.6

10.5

8.5

11.3

17.5

14.4

2.2



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Chapter 6. Responses of Agricultural Crops to Free-Air CO2 Enrichment

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