Growth and Development Growth Rates of Organs

7.5.1 Carbon dioxide

Carbon dioxide affects the partitioning of dry matter to various plant organs. Acock and Allen (1985) summarized growth and development information for

Table 7.6. Plastochron interval and final mainstem node number for soybean in CO2 and air temperature experiments in controlled-environment chambers. (Adapted from Baker et al, 1989.)

CO2 concentration (mmol mol-1)

Day/night temperature (°C)

Plastochron interval (d trifoliolate-1)

Final mainstem node number (no. plant-1)

300

26/19

4.2a*

10.3 ± 0.5

31/24

3.3b

11.5 ± 0.9

36/29

3.2b

12.0 ± 0.5

600

26/19

3.9a

11.2 ± 0.4

31/24

2.7c

11.4 ± 0.3

36/29

2.6c

12.1 ± 0.5

*Numbers followed by the same letter are not significantly different at the 0.05 probability level as determined by t-tests.

*Numbers followed by the same letter are not significantly different at the 0.05 probability level as determined by t-tests.

many species of vegetation, including soybean. In vegetative growth of soybean, Rogers et al. (1983, 1994, 1997) found that elevated [CO2] increased dry matter partitioning in the order of roots > stems > leaves. Similar results were obtained by Allen et al. (1991). After beginning reproductive development, an increasing fraction of the total dry matter was found in the pods (Table 7.7).

The SLW increases with increasing [CO2], probably due to increasing amounts of structural and non-structural carbohydrates (Rogers et al., 1983; Allen et al., 1988, 1991, 1998). Rogers et al. (1984) and Allen et al. (1991) found that SLW increased with elevated [CO2] (Table 7.8).

The LAI generally increases with exposure to elevated [CO2], due both to larger individual leaves and to more leaves produced per plant (Rogers et al., 1983; Jones et al., 1985a,c). Branching may increase with increasing [CO2], so more sites exist for leaves to form (Rogers et al., 1984).

Table 7.7. Soybean plant components as a percentage of total dry matter of plants grown at subambient to superambient concentrations of CO2. (Adapted from Allen et al, 1991.)

(CO2 concentration |mmol mol-1) Component 160 220 280 330 660 990

13 DAPa (V2 Stage)b

Table 7.7. Soybean plant components as a percentage of total dry matter of plants grown at subambient to superambient concentrations of CO2. (Adapted from Allen et al, 1991.)

(CO2 concentration |mmol mol-1) Component 160 220 280 330 660 990

13 DAPa (V2 Stage)b

Root (%)

11

10

9

12

10

10

Cotyledon (%)

20

16

14

14

11

10

Stem (%)

23

25

26

26

26

27

Leaflet (%)

46

49

51

48

53

53

TDMc (g m-2)

14

13

15

16

20

24

34 DAP (V8 Stage)

Root (%)

7

7

7

8

9

8

Stem (%)

23

25

27

26

28

29

Petiole (%)

12

13

15

14

16

16

Leaflet (%)

58

55

51

52

47

47

TDM (g m-2)

65

71

116

129

154

225

66 DAP (R5 Stage)

Stem (%)

17

20

25

22

25

27

Petiole (%)

10

11

13

13

14

14

Leaflet (%)

35

35

35

32

32

30

Pod (%)

38

34

27

33

29

29

TDM (g m-2)

227

282

489

486

794

873

94 DAP (R7 Stage)

Stem (%)

10

13

15

14

16

19

Petiole (%)

6

6

6

7

7

6

Leaflet (%)

17

16

15

14

12

111

Pod (%)

67

65

64

65

65

64

TDM (g m-2)

308

302

634

617

687

838

aDays after planting.

bBased on Fehr and Caviness (1977).

cTDM is total dry matter of the plant components listed at each DAP.

Table 7.8. Specific leaf weighta (g m 2) for soybean grown at subambient to superambient concentrations of CO2. (Adapted from Allen et al.,1991.)

CO2 concentration (mmol mol-1) Days after Developmental -

planting stageb 160 220 280 330 660 990

aLeaf dry weight/leaf area. bBased on Fehr and Caviness (1977).

Allen et al. (1991) developed a simple growth model and fitted it to dry matter data of soybean grown at [CO2] of 160, 220, 280, 330, 660 and 990 |mmol mol-1. The plants were grown at day/night temperatures of 31/23°C under well-watered conditions and with optimum soil nutrients. The model was linear for DAP and a rectangular hyperbola for [CO2]. Leaf area and dry weights of stems, petioles, leaves and the total plant were fitted to the model over the linear phase of growth from 24 to 66 DAP using the SAS non-linear least-squares iterative method (SAS, 1985). The model is:

Y = P0 + P1 x [(DAP - D) x (CO2 - G)]/(CO2 + Kc), (Eqn 7.6)

where Y = growth variable (dry weight or leaf area); 0o = intercept on y-axis when second term is zero; 01 = maximum asymptotic value of growth rate when [CO2] is no longer limiting; D = DAP offset parameter to remove time lag of seedling emergence and non-linear early plant growth; CO2 = carbon dioxide concentration (|mmol CO2 mol-1); G = apparent CO2 compensation point; and KC = hyperbolic function shape factor related to the apparent Michaelis constant. The partial derivative with respect to [CO2] is:

5 Y/5CO2 = [01 x (DAP - D) x (KC + GMCO2 + Kc)2, (Eqn 7.7)

and the partial derivative with respect to DAP is:

The fitted parameters of equation 7.6 based on 1984 soybean data are given in Table 7.9 (Allen et al., 1991). These parameters were used to compute growth rates in Table 7.10 during the linear phase of vegetative growth (DAP 24 to 66). From this model, the relative enhancement resulting from [CO2] at 660 vs. 330 |mmol mol-1 was 1.62, 1.56, 1.36 and 1.21 for dry weight of stems, petioles, leaves, and for leaf area, respectively. Growth rate of individual soybean seeds (seed size at maturity) is much less affected by elevated [CO2], except for smaller seeds when plants are grown at low concentrations of 160 |mmol mol-1

Table 7.9. Estimated parameters3 of soybean growth modelb fitted by non-linear regression procedures to CO2 concentration and days after planting (DAP) for the 24-66 DAP linear growth phase. (Adapted from Allen etal., 1991.)

Parameter of growth model

Dependent -

variable b0c (g m-2) b1d (g m-2 d-1) De (DAP) Gf (|mmol mol-1)Kcg (|mmol mol-1)

Total dry weight

4.243

26.881

Stem dry weight

2.951

7.682

Petiole dry weight

0.987

3.930

Leaflet dry weight

4.556

7.206

Leaflet area

0.493h

0.214i

22.96 120.6 214.1

22.14 116.3 183.8

aComputed originally on a per plant basis, and then adjusted to g m 2 based on an average 28 plants m-2 over the 24-66 DAP interval.

cIntercept on y-axis when second term is zero.

dMaximum asymptotic growth rate as CO2 increases.

eDAP offset parameter to remove time lag of seedling emergence and non-linear early plant growth.

fApparent CO2 compensation point. gApparent Michaelis constant. hm2 m-2. im2 m-2 day-1.

Table 7.10. Growth rates3 during the linear phase of soybean vegetative growth at subambient to superambient concentrations of CO2. (Adapted from Allen et al., 1991.)

CO2 concentration (mmol mol 1)

Plant component 160 200 280 330 660 990

Total shoot dry weightb,c

5.0

8.4

10.9

12.5

18.2

20.7

Stem dry weightc

0.8

1.7

2.4

2.9

4.7

5.5

Petiole dry weightc

0.5

1.0

1.4

1.6

2.5

2.9

Leaf dry weightc

1.7

2.7

3.4

3.9

5.3

5.8

Leaf area (m2 m-2 day-1)

0.070

0.116

0.140

0.153

0.185

0.195

aComputed during 24 to 66 days after planting (DAP) from Eqn 7.8 and Table 7.9. bIncludes seed and podwalls, as well as stems, petioles, and leaves. cDry weight g m-2 day-1.

aComputed during 24 to 66 days after planting (DAP) from Eqn 7.8 and Table 7.9. bIncludes seed and podwalls, as well as stems, petioles, and leaves. cDry weight g m-2 day-1.

(Allen et al., 1991). Thus, the biggest factor for increasing seed yield appears to be the number of seeds harvested per plant.

7.5.2 Temperature

Vegetative growth is often stimulated by increasing temperature, as is leaf and canopy photosynthesis (Boote et al., 1997). However, reproductive growth leading to seed yield is often depressed by the same increases of temperature that enhance vegetative growth. For soybean, individual seed growth rates and final mass per seed decline as temperature exceeds a daily average of about 23°C (Egli and Wardlaw, 1980; Baker et al., 1989; Pan, 1996). (See Chapter 5, this volume, for temperature effects on rice.)

7.5.3 Water deficits and nutrient deficits

Available soil water is the primary determinant of plant growth, as was demonstrated by Briggs and Schantz (1914). Growth rates of all plants and all plant organs are decreased when soil water is limiting, as has been shown many times (Allen, 1999).

Boote et al. (1997) reviewed some of the literature regarding nutrient limitations on crop responses to elevated [CO2]. In spite of early speculation that nutrient limitations might override the benefits of elevated [CO2], this has not always been the case. Kimball et al. (1993) reported equal [CO2]-stimulated growth responses of N-limited and adequately fertilized cotton grown in field soil. Elevated [CO2] stimulated growth and yield of non-nodulated soybean plants cultured in either growth-limiting N supply (Cure et al., 1988a) or growth-limiting P supply (Cure et al., 1988b).

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