**2. Plant temperature and its simulation model of thermo-sensitive male sterile rice**

The present chapter was performed to investigate the temporal and spatial distribution of Tp and its relationships with microclimate of canopy and irrigated water by using a TGMS line under irrigated and non-irrigated conditions. Two models were established to understand how Tp is regulated by environments.

A TGMS rice line, Peiai64S, was used as plant material. Flowing irrigated water depth of 10- 15 cm was treated, and no irrigated (keeping humid) was treated as control.

Tp and microclimatic factors were determined as below:

Plant Temperature for Sterile Alteration of Rice 163

During 21:00-07:00, Tp20 and Tp40 were lower than TA only by 0.27°C and 0.06°C,

Fig. 1 and its simulation equations (1), (2), (3) showed that, during daytime (06:00-18:00), the variation of both Tp and TA fit the sinusoid curve, but the coefficient showed TA>Tp40>Tp20. During night time (18:00-06:00), the variation of both Tp and TA fit the exponent curve, but the coefficient showed TA>Tp40≈Tp20. The simulation equations and their effects were

 

 

 

20.8 5.3sin ( 5.78) /14.44 06 : 00 18 : 00 19.54 2.3exp ( 6) / 4 /0.94 06 : 00 19.54 2.3exp ( 18) / 4 /0.94 18 : 00

20.7 5.8sin ( 5.78) /14.44 06 : 00 18 : 00 19.38 2.3exp ( 6) / 4 /0.94 06 : 00 19.38 2.3exp ( 18) / 4 /0.94 18 : 00

20.7 6.8sin ( 5.78) /16.44 06 : 00 18 : 00 19.32 4.2exp ( 6) / 4 /0.94 06 : 00 19.32 4.2exp ( 18) / 4 /0.94 18 : 00

*t t*

*t t*

*t t*

*t t*

*t t*

*t t*

Differences (visual temperature difference from thermometer, >0.2°C) were detected in value and time between the maximum Tp and the maximum TA. The daily maximum value was 26.1°C for Tp20, and 26.5°C for Tp40, whereas the maximum value was 27.5°C for TA. The maximum value of Tp occurred at 13:00, 1 h earlier than that of TA. Their minimum values, however, both appeared at 06:00. The fluctuation in daily change also showed significant

Fig. 2 showed Tp and Ta at different heights observed at 06:00 and 13:00 under non-irrigated condition (30 d, same as Fig.1). Although the differences between Tp and Ta were not significant, Tp at 13:00 at heights of 10 cm, 20 cm, 30 cm and 40 cm were all higher than Ta at corresponding heights without exception. Tp40 and Tp20 were higher by 0.24°C and 0.60°C, respectively. The decreased rate of Tp (0.1°C /10 cm) was lower than that of Ta (0.41°C /10 cm). At 06:00, Tp at 30-40 cm was higher than Ta, whereas it showed an opposite difference

Solar radiation and irrigated water were two main heat sources affecting rice Tp. Cloud cover, wind speed and LAI of canopy also affect Tp by regulating heat transmission or radiation intensity. Temperature and flowing speed of irrigated water were two main

*R2*=0.956\*\* (1)

*R2*=0.957\*\* (2)

*R2*=0.972\*\* (3)

 

 

 

difference: TA (6.8°C)>Tp40 (5.8°C)>Tp20 (5.3°C).

**2.1.2 Difference of Tp at vertical height** 

**2.2 Effects of environmental factors on Tp**

*Ttt*

*Tt t*

*Tt t*

respectively.

described as follows:

20

40

*A*

at 10-20 cm.

factors regulating Tp.

*p*

*p*

Tp: PTWD-2A sensors were inserted in stem sheaths at heights of 10 cm, 20 cm, 30 cm and 40 cm, respectively, to measure Tp.

Air, water and soil temperatures: PTWD-2A sensors were placed at 10 cm and 5 cm under the ground, and 5 cm, 20 cm, 40 cm, 60 cm, 100 cm, 150 cm above the ground, respectively, to measure temperatures of soil, water and air.

Wind speed: EC-9S sensors were used to measure wind speed at height of 150 cm.

All above data were obtained using TRM-ZS1, automatically collecting every 10 seconds and storing every 10 minutes.

When 50% of flag leaves appeared perfectly, five plants were sampled and dissected at height of each 10 cm to determine layered LAI. Layered LAI was determined with traditional method, i.e., calculated according to the dry matter of harvested layer and the specific leaf area of each layer from sampled leaves (SLA).

#### **2.1 Change of rice Tp**

#### **2.1.1 Daily change of Tp**

Fig. 1 showed the daily changes of air temperature at height of 150 cm (TA) and Tp at heights of 20 cm and 40 cm (Tp20 and Tp40) under non-irrigated condition. The data were collected from random 30 days, during which 11 d were sunshine, 9 d were cloudy, and 10 d were overcast. Tp showed different value from TA, although they had a similar trend in daily change. TA and Tp could be simulated by using same parameters and a similar equation.

Fig. 1. Daily change of air temperature at 150 cm and plant temperature at 20 cm, 40 cm heights.

Calculated the data of Fig. 1, result showed that, during 08:00-20:00, Tp was significantly lower than TA. Tp20 was lower than TA by an average of 1.44°C and the largest margin of 2.3°C, while Tp40 was lower than TA by an average of 1.25°C and the largest margin of 2.1°C.

Tp: PTWD-2A sensors were inserted in stem sheaths at heights of 10 cm, 20 cm, 30 cm and 40

Air, water and soil temperatures: PTWD-2A sensors were placed at 10 cm and 5 cm under the ground, and 5 cm, 20 cm, 40 cm, 60 cm, 100 cm, 150 cm above the ground, respectively,

All above data were obtained using TRM-ZS1, automatically collecting every 10 seconds

When 50% of flag leaves appeared perfectly, five plants were sampled and dissected at height of each 10 cm to determine layered LAI. Layered LAI was determined with traditional method, i.e., calculated according to the dry matter of harvested layer and the

Fig. 1 showed the daily changes of air temperature at height of 150 cm (TA) and Tp at heights of 20 cm and 40 cm (Tp20 and Tp40) under non-irrigated condition. The data were collected from random 30 days, during which 11 d were sunshine, 9 d were cloudy, and 10 d were overcast. Tp showed different value from TA, although they had a similar trend in daily change. TA and Tp could be simulated by using same parameters and a similar

Fig. 1. Daily change of air temperature at 150 cm and plant temperature at 20 cm, 40 cm

Calculated the data of Fig. 1, result showed that, during 08:00-20:00, Tp was significantly lower than TA. Tp20 was lower than TA by an average of 1.44°C and the largest margin of 2.3°C, while Tp40 was lower than TA by an average of 1.25°C and the largest margin of 2.1°C.

Wind speed: EC-9S sensors were used to measure wind speed at height of 150 cm.

cm, respectively, to measure Tp.

and storing every 10 minutes.

**2.1 Change of rice Tp 2.1.1 Daily change of Tp**

equation.

heights.

to measure temperatures of soil, water and air.

specific leaf area of each layer from sampled leaves (SLA).

During 21:00-07:00, Tp20 and Tp40 were lower than TA only by 0.27°C and 0.06°C, respectively.

Fig. 1 and its simulation equations (1), (2), (3) showed that, during daytime (06:00-18:00), the variation of both Tp and TA fit the sinusoid curve, but the coefficient showed TA>Tp40>Tp20. During night time (18:00-06:00), the variation of both Tp and TA fit the exponent curve, but the coefficient showed TA>Tp40≈Tp20. The simulation equations and their effects were described as follows:

$$T\_{p20} = \begin{cases} 20.8 + 5.3 \sin\left[\pi(t - 5.78) / 14.44\right] & 06:00 \le t \le 18:00\\ \left\{19.54 + 2.3 \exp\left[-\left(t + 6\right) / 4\right]\right\} / 0.94 & t < 06:00 \quad R^2 = 0.956^{\*\*}\\ \left\{19.54 + 2.3 \exp\left[-\left(t - 18\right) / 4\right]\right\} / 0.94 & t > 18:00 \end{cases} \quad \text{(1)}$$

$$\begin{cases} 20.7 + 5.8 \sin\left[\pi(t - 5.78) / 14.44\right] & 06:00 \le t \le 18:00 \end{cases}$$

$$T\_{P40} = \begin{cases} 20.7 + 5.8 \sin\left[\pi (t - 5.78) / 14.44\right] & 06:00 \le t \le 18:00\\ \left\{ 19.38 + 2.3 \exp\left[-\left(t + 6\right) / 4\right] \right\} / 0.94 & t < 06:00\\ \left\{ 19.38 + 2.3 \exp\left[-\left(t - 18\right) / 4\right] \right\} / 0.94 & t > 18:00 \end{cases} \quad \text{(2)}$$

$$TA = \begin{cases} 20.7 + 6.8 \sin\left[\pi (t - 5.78) / 16.44\right] & 06:00 \le t \le 18:00\\ \left\{ 19.32 + 4.2 \exp\left[-\left(t + 6\right) / 4\right] \right\} / 0.94 & t < 06:00\\ \left\{ 19.32 + 4.2 \exp\left[-\left(t - 18\right) / 4\right] \right\} / 0.94 & t > 18:00 \end{cases} \quad \text{(3)}$$

Differences (visual temperature difference from thermometer, >0.2°C) were detected in value and time between the maximum Tp and the maximum TA. The daily maximum value was 26.1°C for Tp20, and 26.5°C for Tp40, whereas the maximum value was 27.5°C for TA. The maximum value of Tp occurred at 13:00, 1 h earlier than that of TA. Their minimum values, however, both appeared at 06:00. The fluctuation in daily change also showed significant difference: TA (6.8°C)>Tp40 (5.8°C)>Tp20 (5.3°C).

#### **2.1.2 Difference of Tp at vertical height**

Fig. 2 showed Tp and Ta at different heights observed at 06:00 and 13:00 under non-irrigated condition (30 d, same as Fig.1). Although the differences between Tp and Ta were not significant, Tp at 13:00 at heights of 10 cm, 20 cm, 30 cm and 40 cm were all higher than Ta at corresponding heights without exception. Tp40 and Tp20 were higher by 0.24°C and 0.60°C, respectively. The decreased rate of Tp (0.1°C /10 cm) was lower than that of Ta (0.41°C /10 cm). At 06:00, Tp at 30-40 cm was higher than Ta, whereas it showed an opposite difference at 10-20 cm.

#### **2.2 Effects of environmental factors on Tp**

Solar radiation and irrigated water were two main heat sources affecting rice Tp. Cloud cover, wind speed and LAI of canopy also affect Tp by regulating heat transmission or radiation intensity. Temperature and flowing speed of irrigated water were two main factors regulating Tp.

Plant Temperature for Sterile Alteration of Rice 165

A and B denote sunny day with sunshine time >8 h; C and D denote overcast day with no sunshine

In the present chapter, Tp at 20 cm and 40 cm, and TA at 150 cm observed at 06:00 and 13:00 were used to establish linear regression equations. Results showed that the regression coefficient of Tp40 was lower than that of Tp20, confirming that solar radiation was the key

40 cm: *Tp40* =0.9670 *TA* + 0.8885 *R*² = 0.995\*\*, *n* = 30

40 cm: *Tp40* =0.9199 *TA* + 2.3416 *R*² = 0.982\*\*, *n* = 30

40 cm:*Tp40* =0.9205 *TA* + 1.7991 *R*² = 0.997\*\*, *n* = 30

Fig. 3. Daily change of air and plant temperature at 20 cm and 40 cm heights.

06:00 Tp: 20 cm: *Tp20* =0.9949 *TA* + 0.1741 *R*² = 0.992\*\*, *n* = 30

13:00 Tp: 20 cm: *Tp20* =0.9338 *TA* + 2.3121 *R*² = 0.973\*\*, *n* = 30

Daily average: 20 cm: *Tp20* =0.9338 *TA* + 1.6011 *R*² = 0.996\*\*, *n* = 30

time.

**2.3.2 Statistical relation of Tp to TA**

resource of heat in plant.

Fig. 2. Plant (▲●■) and air (△○□) temperatures at different heights. a and b lines denotes plant height and layer of maximum leaf density, respectively.

#### **2.3 Effects of Ta on Tp**

#### **2.3.1 Change of Ta and its effects on Tp**

Fig. 3 showed daily changes of Tp and Ta at heights of 20 cm and 40 cm under sunshine (11 d) and cloudy (10 d) days. During 06:00-13:00 in sunshine days, Tp was increased earlier than Ta by 1 h, and Tp was maximized at 13:00 (28.1°C for Tp20, and 28.7°C for Tp40). In contrast, Ta was increased later than Tp by 1 h, and Ta was maximized at 14:00 (27.4°C for Ta20, and 28.5°C for Ta40). Besides, the raising intensity was Tp stronger than Ta by 0.7°C (20 cm) and 0.2°C (40 cm). Tp showed close to or even little lower than Ta during night time (18:00-06:00). The significant difference between Ta and Tp during daytime might be caused by the larger absorption of solar radiation by plant than air. When the heat was absorbed, the plant released its energy in long wave, which resulted in an increase of Ta around the plant. After 13:00, along with the diminishing of solar radiation, Tp began to decrease but Ta was reacted dully (decreased one or two hours later under sunny days). Under cloudy days, Tp was higher than Ta all the day. At heights of 20 cm and 40 cm, Tp was 0.4°C higher on average, and the maximum one by 0.5°C for Tp20 and 0.4°C for Tp40, and the minimum one by 0.3°C for Tp20 and 0.4°C for Tp40, respectively. This suggested that there was a weak exchange between plant and air on cloudy days.

Fig. 2. Plant (▲●■) and air (△○□) temperatures at different heights. a and b lines

Fig. 3 showed daily changes of Tp and Ta at heights of 20 cm and 40 cm under sunshine (11 d) and cloudy (10 d) days. During 06:00-13:00 in sunshine days, Tp was increased earlier than Ta by 1 h, and Tp was maximized at 13:00 (28.1°C for Tp20, and 28.7°C for Tp40). In contrast, Ta was increased later than Tp by 1 h, and Ta was maximized at 14:00 (27.4°C for Ta20, and 28.5°C for Ta40). Besides, the raising intensity was Tp stronger than Ta by 0.7°C (20 cm) and 0.2°C (40 cm). Tp showed close to or even little lower than Ta during night time (18:00-06:00). The significant difference between Ta and Tp during daytime might be caused by the larger absorption of solar radiation by plant than air. When the heat was absorbed, the plant released its energy in long wave, which resulted in an increase of Ta around the plant. After 13:00, along with the diminishing of solar radiation, Tp began to decrease but Ta was reacted dully (decreased one or two hours later under sunny days). Under cloudy days, Tp was higher than Ta all the day. At heights of 20 cm and 40 cm, Tp was 0.4°C higher on average, and the maximum one by 0.5°C for Tp20 and 0.4°C for Tp40, and the minimum one by 0.3°C for Tp20 and 0.4°C for Tp40, respectively. This suggested that there was a weak

denotes plant height and layer of maximum leaf density, respectively.

**2.3 Effects of Ta on Tp** 

**2.3.1 Change of Ta and its effects on Tp**

exchange between plant and air on cloudy days.

A and B denote sunny day with sunshine time >8 h; C and D denote overcast day with no sunshine time.

Fig. 3. Daily change of air and plant temperature at 20 cm and 40 cm heights.

#### **2.3.2 Statistical relation of Tp to TA**

In the present chapter, Tp at 20 cm and 40 cm, and TA at 150 cm observed at 06:00 and 13:00 were used to establish linear regression equations. Results showed that the regression coefficient of Tp40 was lower than that of Tp20, confirming that solar radiation was the key resource of heat in plant.


Plant Temperature for Sterile Alteration of Rice 167

Fig. 5. Daily change of plant temperature at 20 cm and 40 cm under irrigated treatment and

Tp (30 d, same as Fig. 1) at four heights at 06:00 and 13:00 was compared between irrigated and non-irrigated conditions (Table 1). The effect of irrigated water on Tp was decreased lower along with the increase of height. It was a difference by 2.5°C at 10 cm, 0.6°C at 20 cm, 0.5°C at 30 cm, and 0.4°C at 40 cm. At 06:00, irrigated water could increase Tp (increasing rate of 3.7°C at 10 cm), but the increasing rate was lowered along with the increasing of plant height. Around noon, Tp showed 0.7°C increase at 10 cm but a decrease at 20-40 cm. The effect of

irrigated water on Tp was stronger at the lower site than at the higher site in plants.

Item 06:00 13:00 Daily average

Irrigated 10 cm 24.7±9.4 26.9±7.6 25.7±8.3 Non-irrigated 21.2±8.5 26.2±8.0 23.2±7.6 Difference 3.5±3.9 0.7±3.5 2.6±2.2

Irrigated 10 cm 21.9±8.7 25.9±7.9 23.5±8.0 Non-irrigated 20.8±8.4 26.1±8.1 22.9±7.5 Difference 1.1±1.5 -0.2±1.9 0.7±1.0

Irrigated 10 cm 21.8±8.4 26.0±7.4 23.4±7.6 Non-irrigated 20.8±8.3 26.4±8.6 22.9±7.6 Difference 1.0±2.3 -0.3±2.0 0.5±1.0

Irrigated 10 cm 21.4±8.3 26.3±8.3 23.3±7.7 Non-irrigated 20.7±8.4 26.5±8.6 22.9±7.6 Difference 0.8±1.0 -0.2±1.0 0.5±0.5

Note: Difference: difference of plant temperature between irrigated water of 10 cm depth and non-irrigated.

Table 1. Comparison of plant temperature observed at four heights at 06:00 and 13:00

between irrigated and non-irrigated conditions

non-irrigated conditions.

Tp10

Tp20

Tp30

Tp40

**2.5.2 Effects of irrigated water on Tp at vertical height** 

### **2.4 Effect of wind speed**

Fig. 4 showed the relationship between Tp20 and wind speed at 150 cm (V). The equation was: *Tp20* = -14.411*V* +32.622 (*R2*=0.334\*, *n*=39). The result indicated that wind speed on the top of canopy had a significant effect on Tp.

Fig. 4. Relationship between plant temperature at 20 cm and wind speed at 150 cm.

### **2.5 Effects of irrigated water**

Irrigated water was another important effect regulating rice Tp. Water temperature (Tw) and Ta were varying in different manners, which resulted in a remarkable difference in their effects on Tp.

### **2.5.1 Temporal change of effects of irrigated water on Tp**

Fig. 5 showed daily varying curves of Tp (30 d) at 20 cm and 40 cm of plants grown with and without irrigated water. The average temperature of inflow water was 26.9°C (21.5- 34.0°C), and TA was 23.7°C (13.5-36.5°C). Irrigated water increased Tp at 20 cm and 40 cm by 0.7°C and 0.5°C, respectively, or by 0.35°C and 0.25°C, respectively, for per 1°C of water-air temperature margin. The effect of increased Tp by irrigated water was higher at night than at daytime. Tp20 was increased by 1.01°C during 19:00-05:00, and by 0.37°C during 06:00-18:00, but decreased by 0.19°C during 11:00-14:00. At 40 cm, Tp40 was increased by 0.77°C during 19:00-05:00, and by 0.20°C during 06:00-18:00, but decreased by 0.25°C during 11:00-13:00. The results showed that irrigated water had more significant effects on Tp during night than daytime. In daytime, solar radiation partly withstood the effects of water irrigated. At the noon when solar radiation was the maximum, irrigated water decreased Tp.

Fig. 4 showed the relationship between Tp20 and wind speed at 150 cm (V). The equation was: *Tp20* = -14.411*V* +32.622 (*R2*=0.334\*, *n*=39). The result indicated that wind speed on the

Fig. 4. Relationship between plant temperature at 20 cm and wind speed at 150 cm.

**2.5.1 Temporal change of effects of irrigated water on Tp**

Irrigated water was another important effect regulating rice Tp. Water temperature (Tw) and Ta were varying in different manners, which resulted in a remarkable difference in their

Fig. 5 showed daily varying curves of Tp (30 d) at 20 cm and 40 cm of plants grown with and without irrigated water. The average temperature of inflow water was 26.9°C (21.5- 34.0°C), and TA was 23.7°C (13.5-36.5°C). Irrigated water increased Tp at 20 cm and 40 cm by 0.7°C and 0.5°C, respectively, or by 0.35°C and 0.25°C, respectively, for per 1°C of water-air temperature margin. The effect of increased Tp by irrigated water was higher at night than at daytime. Tp20 was increased by 1.01°C during 19:00-05:00, and by 0.37°C during 06:00-18:00, but decreased by 0.19°C during 11:00-14:00. At 40 cm, Tp40 was increased by 0.77°C during 19:00-05:00, and by 0.20°C during 06:00-18:00, but decreased by 0.25°C during 11:00-13:00. The results showed that irrigated water had more significant effects on Tp during night than daytime. In daytime, solar radiation partly withstood the effects of water irrigated. At the noon when solar radiation was the maximum, irrigated

**2.4 Effect of wind speed** 

**2.5 Effects of irrigated water** 

effects on Tp.

water decreased Tp.

top of canopy had a significant effect on Tp.

Fig. 5. Daily change of plant temperature at 20 cm and 40 cm under irrigated treatment and non-irrigated conditions.

#### **2.5.2 Effects of irrigated water on Tp at vertical height**

Tp (30 d, same as Fig. 1) at four heights at 06:00 and 13:00 was compared between irrigated and non-irrigated conditions (Table 1). The effect of irrigated water on Tp was decreased lower along with the increase of height. It was a difference by 2.5°C at 10 cm, 0.6°C at 20 cm, 0.5°C at 30 cm, and 0.4°C at 40 cm. At 06:00, irrigated water could increase Tp (increasing rate of 3.7°C at 10 cm), but the increasing rate was lowered along with the increasing of plant height. Around noon, Tp showed 0.7°C increase at 10 cm but a decrease at 20-40 cm. The effect of irrigated water on Tp was stronger at the lower site than at the higher site in plants.


Note: Difference: difference of plant temperature between irrigated water of 10 cm depth and non-irrigated.

Table 1. Comparison of plant temperature observed at four heights at 06:00 and 13:00 between irrigated and non-irrigated conditions

Plant Temperature for Sterile Alteration of Rice 169

Flowing speed of irrigated water was also an important factor affecting Tp. The margin of Tw between inflow and outflow (50 m between them) denotes the flowing speed of irrigated water. The equation of Tp established by margin of Tw between inflow and outflow of 13 days (with TA=17.4-22.5°C) showed that Tp was affected significantly by flowing speed of

Fig. 7. Relationship between plant temperature and temperature difference of water inflow-

Rice layered LAI was decreased along with the increase of plant height. The relationship between Tp at 06:00 and 13:00 and their corresponding LAI at 5 heights was shown in Fig. 8. At 13:00, Tp was increased (actual value was increased from 26.9°C to 28.4°C) along with the decrease of the accumulated LAI. At 06:00, Tp was decreased (actual value was decreased from 20.6°C to 19.7°C) along with the decrease of the accumulated LAI. It indicated that the canopy absorbed solar radiation at daytime and released the heat energy during night,

Fig. 8. Relationship between plant temperature (Tp) and LAI (*x*) at 06:00 and 13:00.

**2.5.4 Effects of flowing speed of irrigated water on Tp**

irrigated water (Fig.7).

outflow.

which regulated Tp.

**2.6 Effects of LAI of canopy on Tp**

#### **2.5.3 Effects of irrigated water temperature on Tp**

Irrigated water temperature also regulated Tp, due to the difference between water and air temperature. The simulated equation between water-air temperature difference (Tw-A) and

average TA of 117 days was: 0.5 10.6 0.048 25.8 1 ( ) 19.0 *A w A <sup>T</sup> <sup>T</sup>* (*R2*=0.422\*\*, *n*=117), based on the weather record (TA from 17.4-30.5°C with the average of 23.7±8.6°C, Tw from 22.2- 31.9°C with the average of 26.9±6.7°C). It implied that, when TA=29.6°C, then Tw-A=0°C;when TA>29.6°C, Tw-A was lower than TA, irrigated water decreased Tp. Conversely, when TA<29.6°C, irrigated water increased Tp. When TA decreased from 29.6°C, Tw-A would be decreased in power. When TA decreased from 27.4°C to 22.0°C (decreased by 5.4°C), Tw-A was enlarged from 2°C to 4°C. When TA decreased from 16.5°C to 12.9°C (decreased only by 3.6°C), Tw-A was enlarged from 6°C to 8°C. Obviously, the regulatory effect would be enlarged under a lower TA.

Fig. 6 showed the relationship in Tp difference (at 20 cm and 40 cm) between irrigated and non-irrigated (ΔTp) and the difference between water-air temperature (Tw-A, average value of 720 samples) (equation 4 and 5). The results showed that, in a range of (-5.45°C)– (+10.32°C) for Tw-A, ΔTp and Tw-A showed a significant conic relationship. When Tw-A= -5°C, ΔTp at 20 cm and 40 cm was -1.10°C and -0.71°C, respectively. When Tw-A=5°C , ΔTp at 20 cm and 40 cm was 0.84°C and 0.66°C, respectively. When Tw-A=10°C, ΔTp at 20 cm and 40 cm was 1.42°C and 1.26°C, respectively.

Fig. 6. Relationship between plant temperature difference of irrigated-non-irrigated (ΔTp) and temperature difference of water-air (Tw-A).

20 cm:Δ*Tp20* = -0.0051 *Tw-A*2 + 0.1934 *Tw-A R2* = 0.870\*\*, *n* = 17 (4)

$$40\text{ cm} : \Delta T\_{p40} = -0.0011\text{ T}\_{w\cdot A}2 + 0.1368\text{ T}\_{w\cdot A} \quad R^2 = 0.950^{\ast\ast},\ n = 17\tag{5}$$

Irrigated water temperature also regulated Tp, due to the difference between water and air temperature. The simulated equation between water-air temperature difference (Tw-A) and

on the weather record (TA from 17.4-30.5°C with the average of 23.7±8.6°C, Tw from 22.2- 31.9°C with the average of 26.9±6.7°C). It implied that, when TA=29.6°C, then Tw-A=0°C;when TA>29.6°C, Tw-A was lower than TA, irrigated water decreased Tp. Conversely, when TA<29.6°C, irrigated water increased Tp. When TA decreased from 29.6°C, Tw-A would be decreased in power. When TA decreased from 27.4°C to 22.0°C (decreased by 5.4°C), Tw-A was enlarged from 2°C to 4°C. When TA decreased from 16.5°C to 12.9°C (decreased only by 3.6°C), Tw-A was enlarged from 6°C to 8°C. Obviously, the

Fig. 6 showed the relationship in Tp difference (at 20 cm and 40 cm) between irrigated and non-irrigated (ΔTp) and the difference between water-air temperature (Tw-A, average value of 720 samples) (equation 4 and 5). The results showed that, in a range of (-5.45°C)– (+10.32°C) for Tw-A, ΔTp and Tw-A showed a significant conic relationship. When Tw-A= -5°C, ΔTp at 20 cm and 40 cm was -1.10°C and -0.71°C, respectively. When Tw-A=5°C , ΔTp at 20 cm and 40 cm was 0.84°C and 0.66°C, respectively. When Tw-A=10°C, ΔTp at 20 cm and 40 cm

Fig. 6. Relationship between plant temperature difference of irrigated-non-irrigated (ΔTp)

20 cm:Δ*Tp20* = -0.0051 *Tw-A*2 + 0.1934 *Tw-A R2* = 0.870\*\*, *n* = 17 (4)

40 cm:Δ*Tp40* = -0.0011 *Tw-A*2 + 0.1368 *Tw-A R2* = 0.950\*\*, *n* = 17 (5)

0.5 10.6 0.048 25.8 1 ( ) 19.0 *A*

(*R2*=0.422\*\*, *n*=117), based

**2.5.3 Effects of irrigated water temperature on Tp**

regulatory effect would be enlarged under a lower TA.

*w A*

*<sup>T</sup> <sup>T</sup>*

average TA of 117 days was:

was 1.42°C and 1.26°C, respectively.

and temperature difference of water-air (Tw-A).

#### **2.5.4 Effects of flowing speed of irrigated water on Tp**

Flowing speed of irrigated water was also an important factor affecting Tp. The margin of Tw between inflow and outflow (50 m between them) denotes the flowing speed of irrigated water. The equation of Tp established by margin of Tw between inflow and outflow of 13 days (with TA=17.4-22.5°C) showed that Tp was affected significantly by flowing speed of irrigated water (Fig.7).

Fig. 7. Relationship between plant temperature and temperature difference of water inflowoutflow.

#### **2.6 Effects of LAI of canopy on Tp**

Rice layered LAI was decreased along with the increase of plant height. The relationship between Tp at 06:00 and 13:00 and their corresponding LAI at 5 heights was shown in Fig. 8. At 13:00, Tp was increased (actual value was increased from 26.9°C to 28.4°C) along with the decrease of the accumulated LAI. At 06:00, Tp was decreased (actual value was decreased from 20.6°C to 19.7°C) along with the decrease of the accumulated LAI. It indicated that the canopy absorbed solar radiation at daytime and released the heat energy during night, which regulated Tp.

Fig. 8. Relationship between plant temperature (Tp) and LAI (*x*) at 06:00 and 13:00.

Plant Temperature for Sterile Alteration of Rice 171

Fig. 9. Simulation effect of daily plant temperature at 20 cm and 40 cm heights.

3.93% and 2.95%, respectively.

**2.8 Function for rice plant temperature** 

Tp of 20 cm:

Tp of 40 cm:

Validation test showed that, the theoretical and practical values of Tp20 and Tp40 had significant correlations, and the slopes of the linear equation were 1.0183 and 0.9995, close to 1 (Fig. 9). The relative error [(∑︱practical-theoretical︱/practical)/*n*] of Tp20 and Tp40 were

*<sup>p</sup>*<sup>20</sup> 0.964( ) / 2 0.803( ) 0.085(12 ) *T TT in out T TV S in A R2* = 0.993\*\*, *n* = 61 (6)

*<sup>p</sup>*<sup>40</sup> 0.937( ) / 2 0.595( ) 0.063(12 ) *T TT in out T TV S in A R2* = 0.998\*\*, *n* = 15 (7)

It could be traced root as early as 1960's when field microclimate regulated by irrigated water was researched. The detailed procedure, however, was not described until two-line hybrid rice was applied (Xiao *et al* 2000, Zhou *et al* 1993). The sterility of rice TGMS line was controlled by temperature. A credible alteration point in temperature was important not only for selection and identification of TGMS lines, but for monitoring sterility alteration, determining effective methods to keep sterility of such TGMS, and increasing seed production of two-line hybrid rice (Lu *et al* 2004, 2007). In the practice of past two decades, techniques commonly used temperatures from thermometer-screen which was located in a 25×25 m2 green plot and 150 cm height in local weather station (TA). The sensitive part of rice plant to temperature, however, was in its canopy (Lu *et al* 2004, 2007, Zou *et al* 2005). We have noticed that the sterility of rice TGMS lines was affected directly by Tp rather than TA. Therefore, it would be more accurate to monitor sterility of TGMS by using Tp in sensitive organs (Lu *et al* 2007). Tp was the final consequence of various environmental factors including air, water, soil, and the heat exchange among them. When attacked by low temperature during sensitive stage, how does the plant response, and how are agronomical methods used for safeguarding the sterility of rice TGMS? Such issues should be addressed by further studies. It will be too late to guarantee seed
