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Effects of Water Supply and Light Intensity on the Growth of Spring Wheat

Masahiko Tamaki1, Tomio Itani2 and Katsu Imai3

1 School of Bioresources, Hiroshima Prefectural University, Shobara 727-0023, Japan. Email tamakim@bio.hiroshima-pu.ac.jp

2 School of Bioresources, Hiroshima Prefectural University, Shobara 727-0023, Japan. Email itani@bio.hiroshima-pu.ac.jp

3 School of Agriculture, Meiji University, Kawasaki 214-0033, Japan. Email imai@isc.meiji.ac.jp

Abstract

The effects of water supply and light intensity on the growth of spring wheat (Triticum aestivum L.) were studied under carefully controlled conditions. The leaf water potential (LWP) was measured from 5 to 40 d after the initiation of water supply treatments (DAIT). The LWP decreased as DAIT progressed. At higher photosynthetic photon flux densities (PPFDs), the LWP decreased as the water supply decreased. The water supply rate had little impact on tiller initiation and survival under low PPFD. As the PPFD increased, however, tillering responded sharply to water supply. Differences in tiller numbers were mainly due to differences in the number of subtillers from T0, Tl and T2 primary tillers. The water supply rate did not affect plant growth significantly under low PPFD. lncreased PPFD resulted in increased plant growth, except for leaf numbers per main stem, as water supply rate increased. Thus, there was a highly significant interaction of water supply and light intensity on the growth of spring wheat.

Media summary

There was a highly significant interaction of water supply and light intensity on development, tillering and dry matter production of spring wheat.

Key Words

Growth, Leaf water potential, Light intensity, Wheat, Water supply.

Introduction

The objective of this experiment was to study the interaction of water supply and light intensity on the growth of spring wheat under carefully controlled water conditions. To accurately and reproduceably control the water supply to individual plants, we used a water control system (Tamaki et a1. 1999) suggested by Wookey et al. (1991) and originally described by Snow and Tingey (1985).

Methods

The water control system (Tamaki et a1. 1999) consists of a sleeve in which plants are grown in a rooting medium, which fits into a device containing a column of floral foam through which the water flow passes toward the rooting medium. The height differential between the rooting medium and the water table, and the hydraulic conductivity of the pathway through the floral foam are controlled. The roots are prevented from growing into the floral foam column by a nylon screen.

Four seeds of spring wheat (cv. Penawawa) were sown in each plant sleeve, using a rooting medium of a 2:1:1 mixture (by volume) of pumice, sand and peat moss. The plants were grown at 25/15 C day/night temperature and a photosynthetic photon flux density (PPFD) of 100, 200, 300 or 400 μmol/m2/s (I100, I200, I300, I400) with a 14-h photoperiod. Plants were illuminated under VHO ‘cool white’ 110-W fluorescent lamps and 60-W tungsten-filament lamps at different bench heights. The PPFD was measured 4 cm above the top of the canopy using LI-188B quantum sensor (LI-COR, Lincoln, NB, USA).

Table 1. Fertile tiller numbers of primary, secondary, tertiary and quaternary tillers, and of subtillers from T0-T4 primary tillers. Values followed by different letters are significantly different at p<0.05.of water supply

TreatmentsA

Total

Primary

Secondary

Tertiary

Quaternary

Subtillers from primary tiller

T0

T1

T2

T3

T4

WHI100

3.5e

3.4d

0.1e

0.0b

0.0

0.0c

0.0c

0.1c

0.0b

0.0

WMI100

3.4e

3.4d

0.0e

0.0b

0.0

0.0c

0.0c

0.0c

0.0b

0.0

WLI100

3.4e

3.4d

0.0e

0.0b

0.0

0.0c

0.0c

0.0c

0.0b

0.0

WHI200

7.0d

4.9bcd

2.0d

0.1b

0.0

0.0c

0.6c

1.1bc

0.4ab

0.0

WMI200

6.9d

4.9bcd

1.9d

0.1b

0.0

0.0c

1.3c

0.7bc

0.0b

0.0

WLI200

4.3de

3.8d

0.5e

0.0b

0.0

0.0c

0.3c

0.2bc

0.0b

0.0

WHI300

16.3b

5.9ab

7.4b

2.9a

0.1

1.4b

4.6ab

2.9a

1.3a

0.2

WMI300

12.0c

5.4abc

4.8c

1.8ab

0.0

0.6bc

3.8b

1.6b

0.5ab

0.1

WLI300

6.0de

4.1cd

1.8de

0.1b

0.0

0.0c

1.4c

0.5bc

0.0b

0.0

WHI400

21.4a

7.0a

9.8a

4.5a

0.1

4.0a

5.8a

3.0a

1.5a

0.1

WMI400

18.8ab

6.6ab

8.7ab

3.4a

0.1

3.0a

5.0ab

2.8a

1.3a

0.1

WLI400

6.3de

4.1cd

2.2d

0.0b

0.0

0.3bc

1.3c

0.6bc

0.0b

0.0

AWH, WM and WL represent high, medium and low water supplies; I100, I200, I300 and I400 represent 100, 200, 300 400 μmol/m2/s PPFD with a 14-h photoperiod, respectively.

After germination, the plants were thinned to one per sleeve to eliminate population density effects. The plants were irrigated as needed with a modified Long Ashton complete nutrient solution (Hewitt, 1966) until the second leaf was mature. Thereafter, three water supply treatments were imposed:

WH (high water supply): The water table was set at 12 cm below the root screen, with no ceramic disc in the floral foam column.

WM (medium water supply): The water table was set at 12 cm below the root screen, and a ceramic disc of flow rate of 50 mL/h/cm2/atm (Soil Moisture Equipment, Santa Barbara, CA, USA) was installed in the floral foam column.

WL (low water supply): The water table was set at 12 cm below the root screen, and a ceramic disc of flow rate of l mL/h/cm2/atm was installed in the floral foam column.

The LWP was measured every 7 d on the second youngest main stem leaf on each plant, using SC10A multiple chamber thernmocouple psychrometer (Decagon Devices, Pullman,WA, USA), from 5 until 40 d after the initiation of water supply treatments (DAIT) (data not shown). Individual tillers were tagged and labeled as they emerged from the leaf sheaths, using the nomenclature suggested by Klepper et al. (1982). Primary tillers were designated T0 to T5. At anthesis, all plants were harvested and fertile tillers and plant height were recorded. Leaf area was measured using LI-3100 leaf area meter (LI-COR Biosciences, Lincoln, NE, USA). The plants were then separated into shoots and roots and oven-dried for 48 h at 75C and weighed.

Results

Fertile tiller numbers at anthesis are shown in Table 1. Total surviving tiller number increased as light intensity and water supply increased. Differences in the total tiller numbers were mainly due to differences in the number of subtillers from T0, T1 and T2 primary tillers. There were no significant effects of water supply on tillering at I100. Tillers were initiated primarily from the main stem and there were no subtillers except at WH, where a subtiller was produced at T2 on one of eight plants.

At I200, there were fewer tillers produced at WL. At WL, there were no subtillers from T0 and T5 (data not shown), and only the primary tillers and the secondary tillers T1 and T2 were produced.

Table 2. Phyllochron and leaf numbers on the main stem.Values followed by different letters are significantly different at p<0.05.

TreatmentsA

Phyllochron

Leaf number

(degree-d/leaf)

WHI100

133a

8.8b

WMI100

133a

8.5b

WLI100

134a

8.3b

WHI200

127bc

9.6ab

WMI200

126bc

9.6ab

WLI200

128b

9.3b

WHI300

111e

9.9ab

WMI300

114de

10.3ab

WLI300

123c

10.1ab

WHI400

108e

10.6a

WMI400

111e

10.4a

WLI400

116d

10.5a

ASymbols are the same as in Table 1.

At I300 and I400 there were similar effects of water stress. Total tiller numbers decreased significantly at WL. At WL plants initiated significantly fewer primary and secondary tillers and no subtillers from T3 and T4. Furthermore, the PPFD had no significant effects on total tiller numbers at WL. At WH and WM, however, higher PPFD increased tillering.

Plants responded to I100 by failing to produce particular tillers. No T0 tillers were produced at I100 (data not shown). Subtillers from T0 were not found in any treatments of I100 and I200, and in WL at I300. The T0 tillers were produced on only 1 of 24 plants among all treatments at I200, on only 2 of 24 plants in all treatments at I300, and 8, 7 and 5 of 8 plants at WH WM and WL, respectively at I400 (data not shown). All T1 tillers survived in all treatments at I300 and I400 (data not shown). However, T1 survived on only 7 of 24 plants in all treatments at I200, and T1 was absent at I100 (data not shown).

Increasing PPFD and water supply resulted in an increase in the rate of leaf emergence on the main stem and, therefore, a decrease in phyllochron value (Table 2). Phyllochron was significantly higher in WL at I300 and I400 but not at I100 and I200. Leaf numbers were not affected significantly by water supply rate, but were affected significantly by PPFD (Table 2).

Water supply had no effect on plant growth under low PPFD (Table 3). Plant height was not significantly affected by water deficiency at I100 and I200, but at I300 and I400 plants were significantly shorter at WL. Both increased water supply and PPFD increased shoot and root weights. At I100 and I200, shoot and root weights were not affected by water supply, but at I300 and I400, they were affected significantly. The dry weight of plants grown at WL was not affected significantly by PPFD, but WH increased it significantly as PPFD increased. With the decrease in water supply, the shoot/root ratio decreased at I200, I300 and I400, but increased at I100. Leaves grown at I100 had larger areas but lower specific leaf weights than leaves grown at higher PPFDs. Wheat plants grown at I100 allocated relatively more dry weight to the production of leaf area and less to the roots than did plants grown at higher PPFDs. Although the plants grown at I100 had low dry matter, they had a higher shoot/root ratio and higher leaf area than plants grown at higher PPFD. This indicates a morphological adjustment to compensate for low PPFD. The larger leaf size at I100 was reflected by increased duration of leaf elongation. However, the with the longer duration of leaf expansion there was a reduction in the number of leaves produced and, consequently, fewer available sites for tiller production

Table 3. Plant growth responses under different water supply rates and PPFD. Values followed by different letters are significantly different at p<0.05.

TreatmentsA

Plant height

Biomass

Leaf area

Specific leaf weight

Shoot dry weight

Root dry weight

Shoot/root

(cm)

(g/plant)

(cm2/leaf)

(mg/cm2)

(g/plant)

(g/plant)

ratio

WHI100

71.6cy

21.3d

18.2a

4.5c

4.8d

0.3d

17.1

WMI100

73.6c

20.3d

17.4a

4.7c

4.6d

0.2d

20.0

WLI100

68.6cd

17.3d

16.1a

4.6c

4.2d

0.2d

26.3

WHI200

70.2cd

36.7d

10.0bc

7.6cab

8.2d

0.8bc

10.8

WMI200

72.8c

36.1d

9.4bc

7.7ab

7.8d

0.8bc

10.4

WLI200

68.7cd

20.4d

9.2bc

7.8bc

5.0d

0.7bc

7.1

WHI300

80.2b

100.5b

9.4bc

9.3a

21.5bc

1.6b

13.8

WMI300

81.8ab

74.2c

10.3b

8.9a

17.3c

1.3b

13.5

WLI300

63.7d

28.7d

9.0bc

7.6ab

7.2d

0.7bc

9.7

WHI400

86.0a

152.3a

9.6bc

8.7a

31.0a

2.5a

12.5

WMI400

82.4ab

120.9b

9.1cbc

8.0ab

24.1b

2.5a

9.5

WLI400

71.3 c

23.0 d

7.4 c

6.5 b

6.7 d

1.2b

5.8

ASymbols are the same as in Table 1.

Conclusion

The present experiment showed a significant interaction of water supply and PPFD on development, tillering and dry matter production of spring wheat. At low PPFD few tillers were produced, the dry matter production was small, and the water supply rate had little impact on plants. As the PPFD increased, the water supply rate affected the production of tiller and dry matter significantly. In other words, as the water supply increased, the growth was largely affected by PPFD. Since higher PPFDs increased transpiration, the plant growth was promoted under increased water supply. Further studies under much higher PPFDs would be worthy to suite the field conditions.

References

Hewitt EJ (I966). Sand and water culture methods in plant nutrition. Commonwealth Agric. Bureaux, Buckinghamshire, pp 547

Klepper B, Rickman RW and Peterson CM (1982). Quantitative characterization of vegetative development in small cereal grains. Agonomy Journal 74, 789-792.

Snow MD and Tingey DT (1985). Evaluation of a system for the imposition of plant water stress. Plant Physiolology 77, 602-607.

Tamaki M, Ashraf M, Imai K and Moss DN (1999). Water and nitrogen stresses on the growth and yield of spring wheat. Environment Control in Biology. 37, 143-151.

Wookey PA, Atkinson CJ, Mansfield TA and Wilkinson JR (1991). Control of plant water deficits using the ’Snow and Tingey system' and their influence on the water relations and growth of sunflower. Journal of Experimental Botany 42, 589-595.

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