Influence of water potential and soil type on conventional japonica super rice yield and soil enzyme activities

Journal of Integrative Agriculture 2017, 16(5): 1044–1052 Available online at www.sciencedirect.com

ScienceDirect

RESEARCH ARTICLE

Influence of water potential and soil type on conventional japonica super rice yield and soil enzyme activities ZHANG Jing, WANG Hai-bin, LIU Juan, CHEN Hao, DU Yan-xiu, LI Jun-zhou, SUN Hong-zheng, PENG Ting, ZHAO Quan-zhi College of Agronomy, Henan Agricultural University/Collaborative Innovation Center of Henan Grain Crops/Henan Key Laboratory of Rice Biology, Zhengzhou 450002, P.R.China

Abstract We carried out a pool culture experiment to determine the optimal water treatment depth in loam and clay soils during the late growth stage of super rice. Three controlled water depth treatments of 0–5, 0–10 and 0–15 cm below the soil surface were established using alternate wetting and drying irrigation, and the soil water potential (0 to –25 kPa) was measured at 5, 10 and 15 cm. A 2-cm water layer was used as the control. We measured soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and rice yield. The results showed that the 0–5-cm water depth treatment significantly increased root antioxidant enzyme activities in loam soil compared with the control, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield did not differ from those of the control. The 0–10- and 0–15-cm water depth treatments also increased root antioxidant enzyme activities, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield decreased. In clay soil, the soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and yield did not change with the 0–5-cm water treatment, whereas the 0–10- and 0–15-cm water treatments improved these parameters. Therefore, the appropriate depths for soil water during the late growth period of rice with a 0 to –25 kPa water potential were 5 cm in loam and 15 cm in clay soil. Keywords: rice, yield components, soil type, soil enzyme activity, antioxidant enzyme activity, chlorophyll fluorescence parameters, water potential

1. Introduction Rice is one of the top three food crops worldwide and has

Received 22 August, 2016 Accepted 2 November, 2016 Correspondence PENG Ting, Tel: +86-371-63558122, Fax: +86371-63558126, E-mail: [email protected], ZHAO Quanzhi, Tel: +86-371-63558293, Fax: +86-371-63558126, E-mail: [email protected] © 2017, CAAS. All rights reserved. Published by Elsevier Ltd. doi: 10.1016/S2095-3119(16)61575-7

the largest planting area and total yield in Asia. The rice planting area in China is broad, and includes the area from Heilongjiang Province to Hainan Province. The soil types differ in these areas and include a variety of paddy soils (Li 1992). In recent years, the majority of the region has promoted water-saving cultivation techniques, such as alternate wetting and drying and ridging, and aerobic irrigation technology, due to a water shortage (Luo 2010). Reasonable intermittent irrigation increases soil water use efficiency and maintains stable yields compared to maintaining the water layer in paddy soil (Borrell et al. 1997). Zhang et al. (2008) reported that wetting irrigation at the early stage, shallow irrigation at the booting stage and alternate wetting

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and drying irrigation at the heading stage increase flag leaf chlorophyll content, postpone leaf senescence and improve net photosynthetic rate and peroxidase (POD) and superoxide dismutase (SOD) activities, which are conducive to maintaining normal cell metabolism and increasing production. Qian et al. (2005) discovered that root biomass, absorbing area, and absorbing capacity are significantly better when using ridge culture than flat planting because roots extend deeper. Light alternate wetting and drying irrigation increases the flag leaf photosynthetic rate at the grain filling stage (Zhang et al. 2011), increases 1 000-grain weight (Yang et al. 2005), improves rice quality (Liu et al. 2008), and increases rice yield (Dong et al. 2011; Fu et al. 2014). Ridge and furrow cultivation, aerobic irrigation and alternate wetting and drying irrigation adjust soil moisture, enhance soil permeability and improve soil redox conditions. However, the appropriate depth range to detect soil moisture at the late rice growth stage remains unclear, particularly because there are no moisture criteria for different soil depths in paddy soil. In this study, a soil potential of –25 kPa was selected as the standard soil water condition in loam and clay paddy soil to reveal the suitable depth to regulate soil moisture during the late rice growth stage. Then, we investigated soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and rice yield at different water depths. The results of this study will provide a theoretical basis for cultivating high-yielding rice in different soil types.

at Henan Agricultural University (Zhengzhou, China) in May– November of 2014 and 2015. Conventional japonica super rice Xindao 18 was selected as the test material. Soil physical and chemical properties are shown in Table 1. During the rice growing period, 480 kg ha–1 urea was supplied as base fertilizer, tiller fertilizer and panicle fertilizer at an application ratio of 3:3:4. The ratio of nitrogen, phosphate and potassium was 1:0.5:1.2. Seeds were sown singly on May 5 using a plastic floppy disk. Seedlings were transplanted manually in early June into a 30 cm×13 cm area. The pool experiments (concrete walls on three sides and a glass wall on one side; length×width×height=2 m×1.5 m× 1 m) included three controlled water depth treatments (0–5, 0–10 and 0–15 cm below the soil surface) established by introducing holes in the glass side at 5, 10 and 15 cm (Fig. 1). One pool was maintained at a 2-cm water layer as the control (CK). Water treatments started at the booting stage by opening the holes at different soil depths. Vacuum water potential sensors (Institute of Soil Science, Chinese Academy of Sciences) were buried at 5, 10 and 15 cm corresponding to the treatments. When the soil water potential decreased to –25 kPa as a result of alternate wetting and drying irrigation (Yang et al. 2005; Liu et al. 2008), the pools were irrigated to the 2-cm water layer. Each treatment was repeated three times.

2. Materials and methods

Yield and its components Four representative plants were collected from each pool at maturation, and effective panicle number, grain number, seed setting rate, 1 000-grain weight, and yield per plant were measured. Determining soil enzyme activities Soil samples were

2.2. Measurement and methods

2.1. Experimental design The experiments were carried out in the experimental park Table 1 Soil physical and chemical properties Soil type Loam Clay

Sand Silt (0.05–2 mm) (%) (0.002–0.05 mm) (%) 66.61 16.59 27.77 45.09

Clay Available N Available P Available K (<0.002 mm) (%) (mg kg–1) (mg kg–1) (mg kg–1) 16.80 23.27 18.63 70.64 27.14 16.21 20.15 105.23

Water level Soil surfaces

Soil surfaces

Soil surfaces

5 cm

5 cm

5 cm

5 cm

5 cm

5 cm

5 cm

5 cm

5 cm

5 cm

5 cm

5 cm

CK

0–5 cm

0–10 cm

Fig. 1 Schematic diagram of the cement pool culture experiment.

Soil bulk density (g cm–3) 1.46 1.75

Soil surfaces

Closed hole Opened hole

0–15 cm

pH 6.55 6.91

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collected from depths of 10–15 cm at the early filling stage (7 days after flowering), middle filling stage (14 days after flowering) and late filling stage (21 days after flowering). After air drying, urease, alkaline phosphatase, and catalase (CAT) activities were measured. Urease activity was determined using sodium phenol colorimetry (Wang et al. 2015). Alkaline phosphatase activity was determined according to Dong et al. (2011). Determining the chlorophyll fluorescence parameters of leaves Plants were selected at the early, middle and late filling stages, when the tiller number and growth stage were roughly the same. The top two rice leaves were used to determine the fluorescence parameters using the DUAL-PAM100 instrument (Heiz Walz Co., Germany). Determination of root SOD, POD and CAT activities At the early, middle and late filling stages, uniformly growing plants were selected to measure SOD, POD and CAT activities of rice roots. The SOD, POD and CAT activities were determined by the method of He et al. (2011).

2.3. Data analysis Data were analyzed with the SPSS 19 Software (SPSS Inc., Chicago, IL, USA). The Excel 2007 Software (Microsoft Inc., Redmond, WA, USA) was used for data processing.

3. Results 3.1. Yield and its components Table 2 shows that rice yield differed significantly between the two soil types under different water depth treatments. Rice yield decreased as the controlled water depth increased

in loam. No differences in yield in 2014 or 2015 were observed between the 0–5-cm treatments and the control; the yield with the 0–10-cm treatment was significantly less than the control, which decreased 7.3% in 2014 and 14.7% in 2015, and the yield with the 0–15-cm treatment decreased by 16.4 and 14.7% in 2014 and 2015, respectively. Rice yield increased in clay soil with controlled water depth. The yield with the 0–5-cm treatment in 2014 and 2015 did not differ from that of the control. The yield with the 0–10-cm treatment increased 4.54 and 6.63% and the yield of the 0–15-cm treatment increased 14.42 and 13.43% in 2014 and 2015, respectively. No differences in effective panicle number, seed setting rate or 1 000-grain weight were detected among the three water treatments in the same year. The decreased yields with the 0–10- and 0–15-cm treatments may have been caused by the decreased number of grains per panicle in the two years. In addition, compared with the yield per plant in 2014, higher yield was observed in 2015 in the both soil types, and the increase of the yield may be resulted from the higher seed setting rate and 1 000-grain weight contributed by the suitable rice growth condition in 2015.

3.2. Soil urease activity As shown in Fig. 2, soil urease activity tended to change in opposing directions in the two paddy soil types. Urease activity showed a gradual decreasing trend as the controlled water depth increased in loam. Urease activity with the 0–5-cm treatment was significantly higher than that in the control at the 2014 middle grain-filling stage and at the 2015 late grain-filling stage. Urease activity of the 0–10-cm layer was significantly less than that of the control at the 2014

Table 2 Yield and its components in the different water treatments in the two types of soil Year

Soil type

Treatment

2014

Loam

0–5 cm 0–10 cm 0–15 cm CK 0–5 cm 0–10 cm 0–15 cm CK 0–5 cm 0–10 cm 0–15 cm CK 0–5 cm 0–10 cm 0–15 cm CK

Clay

2015

Loam

Clay

No. of panicles per plant 13.50±0.75 a 13.81±0.10 a 12.47±0.24 a 13.22±1.11 a 13.40±0.39 a 13.33±0.39 a 13.89±0.46 a 13.00±0.43 a 12.05±0.15 a 11.57±0.12 a 11.67±0.18 a 11.50±0.76 a 11.82±0.39 a 12.50±0.48 a 12.44±0.24 a 11.55±0.43 a

No. of grains per panicle 158.34±2.97 a 144.21±2.94 b 143.95±2.34 b 155.52±2.34 a 154.31±3.25 a 160.18±3.58 a 165.06±3.27 a 156.76±4.33 a 152.17±3.52 a 138.17±3.63 b 135.87±3.52 b 152.52±3.85 a 156.68±5.67 a 158.17±4.06 a 164.33±2.55 a 157.40±8.64 a

Seed setting rate (%) 93.97±1.01 a 93.04±0.95 a 93.84±1.11 a 91.02±2.80 a 92.77±0.65 a 90.78±1.63 a 93.46±0.24 a 90.35±1.39 a 98.02±0.13 a 97.78±0.28 a 97.90±0.26 a 97.91±0.17 a 98.05±0.30 a 97.75±0.20 a 98.15±0.18 a 96.73±0.68 a

1 000-grain weight (g) 22.08±0.65 a 21.31±0.60 a 22.28±0.39 a 21.80±0.87 a 21.53±0.47 a 21.52±0.34 a 21.13±0.14 a 21.50±0.45 a 25.19±0.24 a 25.14±0.21 a 24.76±0.25 a 25.40±0.14 a 26.22±0.21 a 26.17±0.26 a 25.73±0.27 a 25.93±0.55 a

Grain yield per plant (g) 48.85±1.00 a 45.05±0.86 ab 40.05±1.38 b 48.58±1.42 a 38.70±0.90 b 39.57±1.36 ab 43.31±1.19 a 37.85±1.46 b 46.73±1.27 a 40.06±1.37 b 40.04±0.77 b 46.98±2.18 a 47.57±2.33 b 50.31±1.84 ab 53.52±1.11 a 47.18±2.80 b

Different letters in the same column of the same year indicate a significant difference at the 0.05 level. Values are means±SE.

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late grain-filling stage. Urease activity of the 0–15-cm layer

than that of the control at the 2014 early grain-filling stage.

was also significantly lower than that of the control at the

Soil alkaline phosphatase activity with the 0–15-cm treat-

early, middle and late grain-filling stages in 2014 and at the

ment was also lower than that of the control at early and late

early grain-filling stage in 2015. Urease activity increased in

grain-filling stages in 2014 and middle grain-filling stage in

clay with the increased controlled water depth. The urease

2015. In contrast, alkaline phosphatase activity increased

activity of the 0–5-cm layer was higher at the 2014 early

gradually as controlled water depth increased in clay soil.

and middle grain-filling stages compared with the control.

Alkaline phosphatase activity with the 0–5-cm treatment was

Urease activity of the 0–10-cm layer was higher at the 2014

higher than that of the control at early and late grain-filling

early, middle and late grain-filling stages than that of control.

stages in 2014 and the late grain-filling stage in 2015. Al-

Urease activity of the 0–15-cm layer was higher at the 2014

kaline phosphatase activity with the 0–10-cm treatment was

early, middle, and late grain-filling stages and at the 2015

higher than that of the control at the late grain-filling stage

late grain-filling stage than that of control.

in 2014. Alkaline phosphatase activity with the 0–15-cm treatment was higher than that of the control in 2015.

3.3. Soil alkaline phosphatase activity 3.4. Rice root antioxidant activities The changes in soil alkaline phosphatase activity during the rice grain-filling stage in the two paddy soil types were also

The controlled water depth treatments increased the antioxi-

opposed (Fig. 3). Phosphatase activity decreased gradu-

dant enzyme activities in the two soil types compared with

ally with increasing controlled water depth in loam, and no

the control, and differences between the two soil types were

difference in soil alkaline phosphatase activity was detected

detected (Fig. 4). SOD, POD and CAT activities decreased

between the 0–5-cm treatment and the control. Soil alkaline

in loam with increasing controlled water depth. SOD activity

phosphatase activity with the 0–10-cm treatment was lower

with the 0–5-cm treatment was higher than that of the con-

0–5 cm

Urease activity (NH3-N mg g–1 d–1)

C

0–10 cm

250 a

150

a ab

b c

100

a

b

b

a b c

c

50 0

Early

Middle

Late

D

300 250 200 150 100

a a

ab

a

bb

ab

a

b bb

c

50 0

Urease activity (NH3-N mg g–1 d–1)

300

200

0–15 cm B

Early

Middle

Late

Urease activity (NH3-N mg g–1 d–1)

Urease activity (NH3-N mg g–1 d–1)

A

300 250

a

CK

200

a

aba

aa

ab

b

b

b c

b

150 100 50 0

Early

Middle

Late

300 250 200 150 100

aa

aa

ab b

a ab b

a

a b

50 0

Early

Middle

Late

Fig. 2 Urease activity under different water treatments in loam soil (A, 2014; C, 2015) and clay soil (B, 2014; D, 2015). Different small letters at the same stage indicate a significant difference among treatments at the 5% level. Values are means±SE.

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0–5 cm

0–15 cm

CK

180 160 140 120

a a

a

80

bc

b

60

ab ab ab c

b

a b

40 20 0

Early

Middle

Phosphatase activity (phenol mg g–1 d–1)

C 90 80 70

a

160 140

ab

a

120

b

100 80

a

b

b

b bc

b

c

60

c

40 20 Early

Middle

Late

D a b b

60 50

ab

a

ab

a

a b

ab ab

b

40 30 20 10 0

180

0

Late

Early

Middle

Late

Phosphatase activity (phenol mg g–1 d–1)

100

Phosphatase activity (phenol mg g–1 d–1)

B

Phosphatase activity (phenol mg g–1 d–1)

A

0–10 cm

45

a

ab

40 35 30 25

a

ab

ab ab

a

b b

b c

20

c

15 10 5 0

Early

Middle

Late

Fig. 3 Phosphatase activity under different water treatments in loam soil (A, 2014; C, 2015) and clay soil (B, 2014; D, 2015). Different small letters at the same stage indicate a significant difference among treatments at the 5% level. Values are means±SE.

trol except at the middle grain-filling stage in 2015; SOD activity with the 0–10-cm treatment was higher than that of the control at middle grain-filling stage during the 2014 and 2015. POD activity with the 0–5-cm water controlled treatment was higher than that of the control. SOD, POD and CAT activities increased with increasing controlled water depth in clay (Fig. 4).

3.5. Chlorophyll fluorescence parameters The photosynthetic parameters of leaves in the two soil types showed different trends. The quantum yield (Y(II)), apparent electron transport rate in Photosystem II (ETR(II)), and photochemical quenching (qP) tended to decrease in loam as the controlled water depth increased. In particular, these parameters were significantly lower with the 0–10- and 0–15-cm water treatments than with the 0–5-cm treatment and control in the late grain-filling stage (Table 3). Photo-

synthetic performance of the leaves decreased in response to deeper water in loam. Y(II), ETR(II) and qP tended to increase as the controlled water depth increased in the clay, particularly with the 0–10- and 0–15-cm treatments for which the values were higher than for the 0–5-cm treatment at the late grain-filling stage (Table 3). This result shows that photosynthetic performance of the leaves was improved in the deeper water treatments in clay.

4. Discussion The soil types used in this study were sandy loam and silty clay according to the International System of Soil Classification (USDA 1996; Lu 1999). Soil permeability and water leakage of sandy loam are higher than those of silty clay. Zhu et al. (1994) reported that a –25 kPa water potential detected 10 cm below the soil surface at the tillering and germ cell formation stages causes rice yield to decrease in loam

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0–5 cm

50 40

b

30 20 10

CAT activity (U g–1 FW min–1)

Early

100 90 a 80 ab 70 60 ab b 50 40 30 20 10 0 Early

140 a 120

Middle

E

aa

b

a b

b

b

b

Middle

a bb b

a

a

ab

bb

b

100

c

80 60 40 20 Early

200 180 160 140 ab a ab 120 b 100 80 60 40 20 0 Early

Middle

a

a aa

b b

Middle

b

Late

b

b

40 30 20 10 Early

Middle

Late F

160 140 120 100

a

80

bb

a c

60

ab ab b

a

aa

b

40 20 Early

Middle

160 140 120 a 100 80

a

a a

aa

aa b

b

a

b

60 40 20 Early

Middle

Late L

200 180 160 a 140 ab 120 a bb bc 100 c 80 c 60 40 20 0 Early Middle

a b

bc c

Late

100 90 80 70 60 50 40 30 20 10 0

a

ab ab

a

ab a b

Early

ab b

Middle

ab ab b

Late

160 140 120 100

a a ab a

a b

80

b

aa ab

b

60

b

40 20 0

Late I

0

Late K

a

50

0

Late

b

b

0

Late

H

160

0 J

aba

POD activity (U g–1 FW min–1)

SOD activity (U g–1 FW) POD activity (U g–1 FW min–1)

G

a

b

0 D

a

60

SOD activity (U g–1 FW)

60

a ab

a

a

POD activity (U g–1 FW min–1)

b

a ab a

a

CAT activity (U g–1 FW min–1)

70

aa

80 70

CK C

100 90

abab

80

0–15 cm

CAT activity (U g–1 FW min–1)

a

POD activity (U g–1 FW min–1)

SOD activity (U g–1 FW)

90

B

SOD activity (U g–1 FW)

100

CAT activity (U g–1 FW min–1)

A

0–10 cm

200 180 160 140 120 100 80 60 40 20 0

Early

Middle

Late

a ab bc c

a

aaa

ab

b

Early

b

Middle

200 180 160 140 120 a 100 b 80 ab c 60 ab a b c 40 20 0 Early Middle

a

Late

ab

a

a

b

Late

Fig. 4 Antioxidant activities of rice roots under different water treatments in loam (A, E and I, 2014; C, G and K, 2015) and clay soil (B, F and J, 2014; D, H and L, 2015). SOD, superoxide dismutase; POD, peroxidase; CAT, catalase. Different small letters at the same stage indicate a significant difference among treatments at the 5% level. Values are means±SE.

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Table 3 Chlorophyll fluorescence parameters of rice under different water treatments in two types of soil1) Year 2014

Soil type Loam

Clay

2015

Loam

Clay

Sampling Treatment Y(II) period Early filling 0–5 cm 0.3240±0.0024 ab stage 0–10 cm 0.3233±0.0033 b 0–15 cm 0.3362±0.0025 a CK 0.3353±0.0038 ab Middle filling 0–5 cm 0.2332±0.0080 a stage 0–10 cm 0.2010±0.0097 b 0–15 cm 0.2235±0.0036 ab CK 0.2390±0.0081 a Late filling 0–5 cm 0.1483±0.0043 a stage 0–10 cm 0.1077±0.0048 b 0–15 cm 0.0912±0.0101 b CK 0.1480±0.0047 a Early filling 0–5 cm 0.3190±0.0032 ab stage 0–10 cm 0.3137±0.0051 ab 0–15 cm 0.3010±0.0029 b CK 0.3320±0.0019 a Middle filling 0–5 cm 0.2322±0.0061 ab stage 0–10 cm 0.2462±0.0111 a 0–15 cm 0.2394±0.0059 a CK 0.2207±0.0029 b Late filling 0–5 cm 0.1602±0.0131 ab stage 0–10 cm 0.1632±0.0085 a 0–15 cm 0.1641±0.0029 a CK 0.1301±0.0039 b Early filling 0–5 cm 0.4764±0.0024 a stage 0–10 cm 0.4753±0.0040 a 0–15 cm 0.4762±0.0033 a CK 0.4870±0.0028 a Middle filling 0–5 cm 0.4175±0.0050 b stage 0–10 cm 0.4027±0.0059 bc 0–15 cm 0.3820±0.0094 c CK 0.4437±0.0035 a Late filling 0–5 cm 0.4225±0.0139 ab stage 0–10 cm 0.3970±0.0082 bc 0–15 cm 0.3809±0.0064 c CK 0.4428±0.0032 a Early filling 0–5 cm 0.5238±0.0040 a stage 0–10 cm 0.5532±0.0078 a 0–15 cm 0.5247±0.0061 a CK 0.5317±0.0036 a Middle filling 0–5 cm 0.3928±0.0118 b stage 0–10 cm 0.4501±0.0068 a 0–15 cm 0.4519±0.0084 a CK 0.4143±0.0037 b Late filling 0–5 cm 0.3963±0.0070 bc stage 0–10 cm 0.4360±0.0074 a 0–15 cm 0.4131±0.0040 b CK 0.3991±0.0119 c

ETR(II)

qN

qP

Fv/Fm

44.65±0.32 a 44.68±0.47 a 46.32±0.36 a 46.20±0.52 a 32.16±1.08 a 27.71±1.33 b 30.82±0.50 ab 32.94±1.11 a 20.46±0.58 a 14.86±0.67 b 12.56±1.39 b 20.42±0.64 a 44.02±0.45 a 43.28±0.69 ab 41.50±0.39 b 45.75±0.26 a 32.02±0.83 ab 33.98±1.54 a 33.00±0.82 a 30.37±0.41 b 23.46±1.81 a 22.52±1.19 a 22.61±0.40 a 17.91±0.54 b 65.82±0.33 ab 65.67±0.56 b 65.83±0.45 ab 67.30±0.39 b 57.52±0.69 b 55.53±0.81 bc 52.63±1.29 c 61.12±0.48 a 58.38±1.92 ab 54.88±1.92 bc 52.62±0.89 c 61.18±0.43 a 73.03±0.55 a 73.67±1.08 a 72.53±0.83 a 73.43±0.50 a 54.11±1.60 b 62.03±0.93 a 62.24±1.15 a 57.10±0.52 b 54.77±0.97 b 60.27±1.02 a 57.09±0.56 ab 55.14±1.65 b

0.7385±0.0079 ab 0.7443±0.0015 a 0.7192±0.0055 ab 0.7185±0.0074 b 0.7899±0.0065 a 0.7443±0.0087 c 0.7763±0.0055 ab 0.7589±0.0019 bc 0.7057±0.0081 a 0.7086±0.0089 a 0.6817±0.0236 a 0.6827±0.0231 a 0.7880±0.0073 a 0.7808±0.0049 a 0.7856±0.0041 a 0.7425±0.0002 b 0.7666±0.0133 a 0.7033±0.0241 b 0.7466±0.0120 a 0.7830±0.0016 a 0.7636±0.0163 a 0.7587±0.0114 a 0.7418±0.0076 a 0.7654±0.0092 a 0.5152±0.0077 a 0.4900±0.0028 ab 0.4593±0.0152 b 0.4825±0.0068 ab 0.6493±0.0017 ab 0.5920±0.0042 c 0.6588±0.0114 a 0.6228±0.0099 bc 0.5740±0.0182 b 0.6431±0.0101 a 0.6789±0.0057 a 0.6558±0.0104 a 0.2890±0.0138 b 0.2808±0.0175 b 0.2718±0.0180 b 0.3600±0.0116 a 0.6133±0.0284 a 0.5729±0.0124 b 0.5772±0.0200 b 0.7033±0.0017 a 0.6680±0.0015 a 0.6532±0.0169 a 0.6542±0.0040 a 0.6774±0.0118 a

0.5078±0.0062 a 0.5195±0.0066 a 0.5272±0.0054 a 0.5193±0.0059 a 0.4049±0.0135 a 0.3268±0.0189 b 0.3755±0.0076 a 0.3991±0.141 a 0.2396±0.0086 a 0.1740±0.0097 b 0.1504±0.0194 b 0.2314±0.0102 a 0.5265±0.0040 ab 0.5248±0.0069 ab 0.5064±0.0058 b 0.5340±0.0028 a 0.3854±0.0147 a 0.3840±0.0232 a 0.3962±0.0138 a 0.3807±0.0063 a 0.2858±0.0277 a 0.2742±0.0193 a 0.2673±0.0057 a 0.2160±0.0085 b 0.6444±0.0027 a 0.6380±0.0075 ab 0.6245±0.0027 b 0.6443±0.0027 a 0.6040±0.0099 ab 0.5683±0.0093 b 0.5602±0.0193 b 0.6389±0.0065 a 0.6073±0.0136 b 0.5929±0.0154 b 0.5847±0.0128 b 0.6658±0.0096 a 0.6808±0.0060 a 0.6773±0.0085 a 0.6648±0.0108 a 0.6870±0.0074 a 0.5662±0.0230 b 0.6350±0.0079 ab 0.6373±0.0086 ab 0.6533±0.0049 a 0.5933±0.0110 b 0.6498±0.0054 a 0.6183±0.0072 b 0.6144±0.0091 b

0.8153±0.0088 a 0.8271±0.0010 a 0.8174±0.0055 a 0.8226±0.0050 a 0.8179±0.0031 a 0.8246±0.0023 a 0.8242±0.0020 a 0.8176±0.0013 a 0.8089±0.0055 ab 0.8119±0.0020 a 0.7987±0.0039 b 0.8182±0.0026 a 0.8378±0.0007 a 0.8272±0.0013 a 0.7941±0.0176 a 0.8258±0.0011 a 0.8275±0.0016 a 0.8290±0.0025 a 0.8180±0.0046 a 0.8167±0.0039 b 0.8264±0.0024 a 0.8202±0.0022 c 0.8210±0.0012 bc 0.8257±0.0010 ab 0.8356±0.0019 a 0.8346±0.0019 a 0.8396±0.0008 a 0.8414±0.0006 a 0.8385±0.0022 a 0.8335±0.0005 a 0.8370±0.0013 a 0.8332±0.0020 a 0.8185±0.0011 a 0.8216±0.0019 a 0.8206±0.0016 a 0.8224±0.0018 a 0.8199±0.0013 b 0.8278±0.0016 a 0.8292±0.0009 a 0.8310±0.0011 a 0.8337±0.0016 a 0.8292±0.0009 b 0.8304±0.0007 b 0.8177±0.0005 c 0.8283±0.0007 a 0.8256±0.0011 a 0.8232±0.0007 ab 0.8176±0.0040 b

1)

Y(II), quantum yield; ETR(II), apparent electron transport rate in Photosystem II; qN, non-photochemical quenching; qp, photochemical quenching; Fv, variable fluorescence; Fm, the maximal fluorescence. The same stage of the same year in the same column with different letters indicates a significant difference at the 0.05 level. Values are means±SE.

paddy soil. Alternate wetting and mild drying irrigation (0 to –15 kPa) 10 d after transplant enhances rice yield and quality in sandy loam compared with rice grown under traditional irrigation (Dong et al. 2011). Alternate wetting and drying

irrigation can increase rice yield in loam paddy soil (Belder et al. 2004, Lampayan et al. 2015). In this study, we found that controlling the water potential at –25 kPa in the 0–10and 0–15-cm treatments decreased rice yield in loam soil,

ZHANG Jing et al. Journal of Integrative Agriculture 2017, 16(5): 1044–1052

but increased yield in clay soil. These differing results may have been caused by differences in soil moisture conditions and irrigation methods as well as the time of application (Fu et al. 2014). Water stress at the booting stage affects the establishment of rice storage capacity, resulting in a decrease in yield due to small spikelets, decreased grain numbers and lower 1 000-grain weight (Shao et al. 2007; Wang et al. 2016). The effect of controlled water depth on rice yield was better in clay soil than in loam soil due to the poor permeability of clay. In addition, controlling the water potential at –25 kPa in the 0–10- and 0–15-cm treatments may have induced water stress in rice growing on loam soil. Soil enzymes play important roles in the soil ecosystem, which involve all biochemical processes in soil, and are related to decomposition of organic matter, nutrient cycling, energy transfer, and environmental quality (Zhang et al. 2015). Wan et al. (2008) investigated the effect of water gradient on soil enzyme activities in a Carex lasiocarpa marsh and found that urease and phosphatase activities were higher under alternate wetting and drying irrigation and relatively dry conditions than under continuous flooding. Therefore, the increased urease and phosphatase activities in clay with increasing controlled water depth in this study were consistent with Wan et al. (2008). However, the decrease in urease and phosphatase activities in loam suggest that a water potential of –25 kPa at 0–10 and 0–15 cm might impose water stress on microorganisms in loose soil. SOD, POD and CAT are key enzymes for removing reactive oxygen species in plants. Drought stress can induce SOD, POD and CAT activities, and their activities increase gradually under drought conditions within a certain range. However, severe drought decreases POD activity (Pei et al. 2013). Han et al. (2007) found that supplying oxygen to rice roots slows and then maintains decreased root SOD activity. The higher SOD activity in loam suggests that –25 kPa in the 0–10- and 0–15-cm controlled water depth treatments caused oxidative stress to rice roots. Change in chlorophyll fluorescence is a rapid response by plants reflecting photosynthetic activity, which has been widely used as the basis for a sensitive and non-invasive method to evaluate the mechanism of the drought stress response in plants (Efeoğlu et al. 2009). Photosynthetic rate increased under alternate wetting and moderate soil drying (0 to –15 kPa at 15–20 cm) and decreased under alternate wetting and severe soil drying (0 to –30 kPa at 15–20 cm) in sandy loam (Fu et al. 2014).

5. Conclusion In summary, the different soil types were the main cause of the differences in rice yield, soil enzyme activities, root antioxidant enzyme activities, and chlorophyll fluorescence

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parameters measured in this study. The –25 kPa water potential detected at the 15-cm soil depth was suitable for controlled water depth in clay, but caused drought stress in loam. Using a water potential of –25 kPa 15 cm under the soil surface as the irrigation standard could significantly improve soil microbial activities, leaf photosynthetic performance, and rice yield in clay paddy soil.

Acknowledgements This work was supported by the National Natural Science Foundation of China (31271651), the Major Science and Technology Project of Henan Province, China (141100110600), the Special Fund for Agro-scientific Research in the Public Interest of China (201303102), and the Innovation Scientists and Technicians Troop Construction Projects of Henan Province, China (94200510003).

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