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Response of vegetative growth and fruit development to regulated deficit irrigation at different growth stages of pear-jujube tree
Agricultural Water Management 96 (2009) 1237–1246
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Response of vegetative growth and fruit development to regulated deficit irrigation at different growth stages of pear-jujube tree Ningbo Cui a, Taisheng Du b,*, Fusheng Li c, Ling Tong b, Shaozhong Kang a,b,**, Mixia Wang a, Xiaozhi Liu b, Zhijun Li a a b c
Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest A&F University, Yangling, Shaanxi 712100, China Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China Agricultural College, Guangxi University, Nanning, Guangxi 530005, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 30 November 2008 Accepted 22 March 2009 Available online 17 April 2009
In order to investigate the response of vegetative growth, fruit development and water use efficiency to regulated deficit irrigation at different growth stages of pear-jujube tree (Zizyphus jujube Mill.), different water deficit at single-stage were treated on field grown 7-year old pear-jujube trees in 2005 and 2006. Treatments included severe (SD), moderate (MD) and low (LD) water deficit treatments at bud-burst to leafing (I), flowering to fruit set (II), fruit growth (III) and fruit maturation (IV) stages. Compared to the full irrigation (control), different water deficit treatments at different growth stages reduced photosynthesis rate (Pn) slightly and transpiration rate (Tr) significantly, thus it improved leaf water use efficiency (WUEL, defined as the ratio of Pn to Tr) by 2.7–26.1%. After the re-watering, Pn had significant compensatory effect, but Tr was not enhanced significantly, thus WUEL was improved by 31.4–42.2%. I-SD, I-MD, II-SD and II-MD decreased new shoot length, new shoot diameter and panicle length by 8–28%, 13–23% and 10–31%, respectively. Simultaneously, they reduced leaf area index (LAI) and pruning amount significantly. Flowering of pear-jujube tree advanced by 3–8 days in the water deficit treatments at stage I, Furthermore, SD and MD at stage I increased flowers per panicle and final fruit set by 18.9–40.5% and 15.5–36.6%, respectively. After a period of re-watering, different water deficit treatments at different growth stages improved the fruit growth rate by 15–30% without reduction of the final fruit volume. Compared to the control, I-MD, I-SD, I-LD, I-MD and I-SD treatments increased fruit yield by 13.2–31.9%, but reduced water consumption by 9.7–17.5%, therefore, they enhanced water use efficiency at yield level (WUEY, defined as ratio of fruit yield to total water use) by 17.3–41.4%. Therefore, suitable period and degree of water deficit can reduce irrigation water and restrain growth redundancy significantly, and it optimize the relationship between vegetative growth and reproductive growth of pear-jujube trees, which maintained or slightly increased the fruit yield, thus water use efficiency was significantly increased. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Fruit development Pear-jujube tree (Zizyphus jujube Mill.) Regulated deficit irrigation Vegetative growth Water use efficiency
1. Introduction Jujube (Zizyphus jujube Mill.) originated from China and has been planted more than 5000 years. Now the planting area of jujube in China is about 30,000 ha, with total yield of 600 million kg. Jujube is mainly cultivated in northern China where scientific and reasonable irrigation is needed for high yield and quality. However, inappropriate irrigation method may result in waste of water resources and poor fruit quality.
* Corresponding author. Fax: +86 10 62737611. ** Corresponding author at: Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China. Fax: +86 10 62737611. E-mail addresses: [email protected] (T. Du), [email protected] (S. Kang). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.03.015
Regulate deficit irrigation (RDI) is an important physiological water-saving technique since it has been applied on fruit trees by many researchers. Chalmers and Ende (1975) found that water deficit had significant effect on vegetative growth of fruit trees, but slight on fruit growth, which provided the theoretical basis of RDI in saving irrigation water and increasing production. Behboudian and Mills (1997) indicated that RDI limited plant overgrowth and reduced the pruning amount and irrigation water significantly, thus improved water use efficiency. Cheng et al. (2003) indicated that water deficit treatments significantly inhibited the vegetative growth of pear (Pyrus bretsehneideri Rehd CV. Yali) at bud-burst and flowering stages and decreased leaf area, and new shoot length and pruning amount by 15–25% and 18–33% as compared to the control, and the final fruit set was more than 85% for different water deficit treatments. Similar conclusion was also drawn on
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litchi and sweet orange (Zhang and Fu, 2005; Pe´rez-Pe´rez et al., 2008). It was also found that after experiencing moderate water deficit, the re-watering quickly restored the water status of peach tree and maintained the same yield as the level of the control, even if the water deficit was greater than 65% (Girona et al., 2003). At the same time, single-stage and compound-stage water deficit can save irrigation water by 13–24% and 23–35%, and significantly improved water use efficiency. Zegbe-Domı´nguez et al. (2006) and Ferna´ndez et al. (2006) also got the similar results. Robert et al. (1995) indicated that water deficit had less negative impact on fruit tree at the early stage than at the later stage, and the rewatering had compensatory effect on the fruit growth. Xu and Cheng (2003) found that water deficit from the budding to early fruit expansion stages of pear (P. bretsehneideri Rehd CV. Xiangli) had no adverse effect on fruit set, single fruit weight and final fruit yield, and any water deficit treatment did not cause fruit cracking. The similar conclusion on macadamia nut was also got by Liu et al. (2004). Photosynthesis is an important physiological process of plants. Tree photosynthesis is very sensitive to water deficit, which directly affects fruit development and final yield. Villar-Salvador et al. (1999) indicated that the photosynthetic efficiency was the determining factor in the plant productivity and yield level under water deficit conditions. Ma et al. (2006) and Ahmed et al. (2007) showed that water deficit decreased leaf net photosynthetic rate (Pn) of pearjujube and olive slightly, but reduced the transpiration rate (Tr) remarkably, thus resulted in significant improvement of leaf water use efficiency, indicating that fruit trees could adapt to a certain degree of water stress through controlling the stomatal aperture. Wang et al. (2008c) found that re-watering increased leaf Pn of fruit tree significantly after experiencing moderate water deficit, suggesting that super compensatory effect occurred after experiencing water stress. Therefore, crop growth redundancy theory, ‘sink and source’ theory for the transfer of assimilate and water deficit effect on different plant physiological function has provided theoretical basis for the RDI technique (Kang et al., 2000, 2007). At present, there are fewer systematic studies on the effect of different growth stages with different water deficit levels and rewatering on physiological parameters, growth, fruit development and water use, as well as the transfer of photosynthetic product in pear-jujube tree. How to implement the regulated water deficit based on growth characteristics and physiological water requirement of pear-jujube tree and optimize the allocation of the photosynthetic product in the tree has become the urgent question to be resolved so as to obtain the fruit production with watersaving, steady-yield and high-efficiency. Our study aims to provide experimental basis in developing sustainable water-saving, steady-yield, high-efficiency jujube production in arid and semiarid regions after studying the growth, fruit development and water use of pear-jujube tree under RDI in the field. 2. Materials and methods 2.1. Experimental site The field experiments were continuously conducted from early April (leaf exhibition at the initial stage) to late September (leaf
falling at later stage) in 2005 and 2006. The experimental site is situated at Dengzhuang, Dali, Shannxi, northwest China (latitude 348520 N, longitude 1098560 E, altitude 1340 m) which locates in a continental semiarid temperate zone with a mean annual precipitation of 513.6 mm and a mean annual evaporation from a free water surface of 1689.34 mm. The average field capacity in the upper 1.0 m of the soil profile is approximately 22.8% (mass basis) with bulk density of 1.36 g/cm3. The groundwater table is consistently below 5.6 m, without replenishment effect on the designed soil profile. 2.2. Experimental plant and design Twenty-eight healthy and uniform 7-year old pear-jujube (Zizyphus jujuba Mill. cv. Lizao) trees of were selected as experimental trees. Trees were planted in 3 m within-row spacing and 2 m between the rows. The whole growing season of pearjujube tree was divided into bud-burst to leafing stage (stage I, early April–early May), flowering to fruit set stage (stage II, mid May–late June), fruit growth stage (stage III, late June–late July), fruit maturation stage (stage IV, early August–mid September) and dormancy stage (stage V, this October–next March). Thirteen treatments including full irrigation (FI, control), low (LD, 2/3 of full irrigation), moderate (MD, 1/2 of irrigation) and severe (SD, no irrigation) water deficit at the growth stages I–IV were designed and applied. FI, LD, MD and SD treatments received irrigation water of 900 m3/hm2 (90 mm), 600 m3/hm2 (60 mm), 450 m3/hm2 (45 mm) and 0 m3/hm2 (0 mm), respectively during the water deficit treatment stage with irrigation water of 900 m3/ hm2 at the rest three stages. Each treatment was applied to one tree in a plot with the area of 3 m2 (2 m 1.5 m) with four replicates of FI and two repetitions of the other treatments. The other design was the same as the experiment by Cui et al. (2008), the irrigation scheme is shown in Table 1. 2.3. Measurements 2.3.1. Precipitation Precipitation data at different growth stages were provided by Dali County Weather Bureau, Shaanxi (the weather station was 2 km far away from the experimental site, and the topography in this region is planar, so the precipitation data are representative). Total precipitation over the whole growth stage of pear-jujube tree was 250.5 mm and 174.9 mm in 2005 and 2006, respectively. The precipitation at stages I–IV was 24 mm, 72.2 mm, 61.1 mm and 93.2 mm in 2005, and 14.16 mm, 75.14 mm, 74.05 mm and 11.55 mm in 2006, respectively. 2.3.2. Growth measurements Eight shoots were selected in four directions of each tree (avoiding leggy branches) with a tag labeled on each shoot respectively to measure and calculate the new shoot growth from early May. The length and diameter of new shoots were respectively measured using steel ruler and vernier caliper every 10 days, then average length and diameter of the shoot was calculated based on two measurements of a day as the cumulative growth. Eight panicles per tree at the similar location selected from different directions
Table 1 Irrigation water amount for different treatments in Pear-Jujube tree growing season (mm). Growth stage
T1 (CK)
T2 (SD)
T3 (MD)
T4 (LD)
T5 (SD)
T6 (MD)
T7 (LD)
T8 (SD)
T9 (MD)
T10 (LD)
T11 (SD)
T12 (MD)
T13 (LD)
Bud-burst to leafing stage (I) Flowering to fruit set stage (II) Fruit growth stage (III) Fruit maturation stage (IV)
90 90 90 90
0 90 90 90
45 90 90 90
60 90 90 90
90 0 90 90
90 45 90 90
90 60 90 90
90 90 0 90
90 90 45 90
90 90 60 90
90 90 90 0
90 90 90 45
90 90 90 60
Table 2 Transpiration rate (Tr), photosynthetic rate (Pn), stomatal conductance (gs) and water use efficiency (WUEL) of pear-jujube trees leaves under different water deficit treatments in 2006. Treatment
Pn (mmol/m2 s)
Tr (mmol/m2 s)
gs (mmol/m2 s)
WUEL (mmolCO2/molH2O)
5 d after water deficit
Pn (mmol/m2 s)
Tr (mmol/m2 s)
T1 (CK) T2 (SD) T3 (MD) T4 (LD) F value
14.880.93a 8.900.75c 11.42 0.82b 13.43 1.12ab 13.54*
1.400.22a 0.720.20d 0.860.17c 1.050.24b 93.59***
93.008.32a 71.006.02c 69.004.32c 78.007.55b 37.54**
10.63 1.05b 12.36 0.82ab 13.28 0.74a 12.79 1.12ab 4.12*
16.52 1.30a 13.83 1.12ab 15.24 0.88a 15.56 1.35a 6.22*
1.88 0.24a 0.98 0.18c 1.19 0.14c 1.54 0.14b 38.24**
Flowering to fruit set stage (II)
T1 (CK) T5 (SD) T6 (MD) T7 (LD) F value
11.98 0.62a 7.22 0.43b 8.33 0.50b 10.53 0.72a 3.12*
1.410.18a 0.720.20c 0.880.21c 1.28 0.14b 117.60***
52.006.45a 35.004.34d 40.005.30c 45.00 3.38b 26.24**
11.90 0.62b 14.43 0.45a 13.250.86ab 11.52 0.70a 3.99*
12.33 0.90ab 11.25 0.45b 11.98 0.54ab 13.73 1.10a 2.47ns
1.22 0.09a 0.78 0.13c 0.76 0.07c 0.92 0.12b 27.26**
Fruit growth stage (III)
T1 (CK) T8 (SD) T9 (MD) T10 (LD) F value
12.13 0.84a 7.08 0.45c 8.15 0.48c 10.98 0.62b 20.62**
1.70 0.14a 0.78 0.08d 1.17 0.11c 1.43 0.20b 77.23***
121.00 9.02a 57.00 7.10c 61.00 5.50c 91.00 8.10b 36.24**
10.81 0.82c 14.50 0.74a 12.12 0.44b 11.73 0.37b 4.27*
15.78 1.15a 10.13 0.72b 14.56 0.52ab 16.53 1.12a 4.33*
1.34 0.11a 0.85 0.08c 1.04 1.06b 1.12 1.12b 16.24**
1.36 0.15a 0.72 0.14d 1.02 0.08c 1.24 0.14b 38.21**
61.00 8.22a 32.00 4.30c 36.00 5.42c 53.00 7.56b 21.39**
T1 (CK) T11 (SD) T12 (MD) T13 (LD) F value
8.27 0.40a 6.40 0.52c 7.55 0.38b 8.03 0.75ab 9.68*
WUEL (mmolCO2/molH2O)
102.25 9.38a 78.25 7.02b 82.50 6.55b 96.50 5.34a 5.20*
8.79 0.52c 14.11 0.77a 12.81 0.84b 10.10 0.92bc 8.32*
3 d after re-watering
Bud-burst to leafing stage (I)
Fruit maturation stage (IV)
gs (mmol/m2 s)
6.08 0.72b 8.89 0.38a 7.40 0.52ab 6.48 0.46 b 4.29*
71.75 6.38a 48.75 5.12b 54.75 6.34b 69.25 5.52ab 7.68* 103.75 8.52a 74.75 6.37b 96.25 8.10a 98.75 7.30a 6.24*
12.09 1.10b 14.42 0.88ab 15.76 0.72a 14.92 1.10a 1.75ns 11.78 1.14b 11.92 0.72b 14.00 0.65a 14.76 1.10a 5.58*
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Growth stages
Note: Values are means S.E. (n = 8). Field experiment 2006, significant difference marked by different small letter in same column (P < 0.05). P = 0.05; ns: not significant. * F > F0.05. ** F > F0.01. *** F > F0.001.
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were measured every 10 days as the cumulative growth. The flowering time and flowers per panicle and final fruit set were recorded for different water deficit treatments. The fruit volume was measured 20 days after the fruit set using the method of Cui et al. (2008). The measurements were done every 10 days. The volume of eight fruits in the same treatment was averaged as final fruit volume. The difference between two measurements during the period was taken as the volume growth rate (Vf, cm3/d). Leaf areas for different water deficit treatments were measured with a LAI-2000 canopy analyzer every 30 days, and then leaf area index (LAI) was calculated using Hemiview software. 2.3.3. Measurement of physiological parameters Physiological parameters such as leaf photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs), and intercellular CO2 concentration (Ci) were measured with a LI-6400 portable photosynthesis system (LI-COR, Nebrasaka, USA) during 9:30– 10:30 a.m. in the morning 5 days after deficit water treatment and 3 days after re-watering at each growth stage. In each treatment, three to four sunlit healthy leaves were randomly selected in different directions and labeled, each leaf was measured three times, and the same leaves were measured at each growth stage, then the leaf water use efficiency (WUEL, Pn/Tr) was calculated.
2.4. Data analysis Analysis of variance (ANOVA) was done using GLM processes of Statistical Analysis Software (SAS 6.12, SAS Institute Ltd., USA). All treatment means were compared for any significant differences using the Duncan’s multiple range tests at significant level of P0.05. 3. Results 3.1. Effect of water deficit at different stages on physiological parameters of pear-jujube tree Water deficit and re-watering had significant effect on leaf Tr, Pn, gs and WUEL of pear-jujube tree (Table 2). Tr, Pn and gs were significantly reduced 5 d after water stress, and their percentage reduction increased with the degree of water deficit. Tr and gs were more sensitive to water deficit than Pn, and their percentage reduction was also greater. Compared to the control, SD, MD, LD at different growth stages improved average WUEL by 26.1%, 17.2% and 2.7% although Pn had no significant difference (P > 0.05). Rewatering after 3 days can slightly restore Tr, Pn and gs in the water deficit treated at stages I–III. Moreover, compared to the control, Pn in the other water deficit treatments at different growth stages had no significant difference (P > 0.05), but Tr and gs had significant
Fig. 1. Accumulated length of new shoot under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 8). I, II, III and IV stand for bud-burst to leafing stage, flowering to fruit set stage, fruit growth stage and fruit maturation stage of pear-jujube tree, respectively.
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difference (P < 0.05) with exception for SD treatment, and LD treatment at stages II and III also increased Pn and WUEL significantly. In addition, SD, MD and LD treatments at different growth stages changed average Pn by 13.2%, 1.1% and 11.6%, and increased average WUEL by 37.1%, 42.2% and 31.4%. Simultaneously, the MD and LD treatments at different growth stages decreased gs significantly, which can prevent CO2 into leaf cells, which resulted in decreasing of leaf Ci (intercellular CO2 concentration) and Pn, indicating that the decline of photosynthesis was mainly due to strong reversible stomatal limitation, but the photosynthetic rate can effectively be resumed after the re-watering. The SD treatment reduced leaf gs and Pn and damaged the membrane system and increased lipid peroxidation into superoxide radical, thus the Ci remained unchanged or even increased (data not shown), indicating that the decline of photosynthesis was mainly due to poor reversible non-stomatal limitation, i.e. due to lower photosynthetic activity of leaf cells. Since SD treatment severely damaged photosynthetic system, the re-watering cannot restore photosynthetic capacity. Therefore, after experiencing moderate water deficit treatments, photosynthetic ability recovered when re-watered, and this resulted in higher WUE, furthermore, stimulated the nutrition accumulation and life activity of the tree.
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3.2. Effect of water deficit at different stages on vegetative growth of pear-jujube tree 3.2.1. New shoot and panicle It was showed that water deficit treatments at different growth stages of pear-jujube tree had significant effect on the growth of new shoot, compared to the control, the length and diameter of new shoot at each water deficit treatment were significantly decreased by 6–28% and 13–22% at stages I and II, respectively (Figs. 1a, b and 2a, b). Furthermore, III-MD treatment reduced new shoot length slightly, III-LD and MD treatments decreased the new shoot diameter significantly by 12% and 28% (Figs. 1c and 2c). However, water deficit treatments at stage IV had no significant effect on the growth of new shoot. In addition, after early July, since the fruit growth had entered into the second period of rapid growth, water deficit at stages II and III decreased the diameter of new shoot, but did not increase the length significantly. As shown in Fig. 3, compared to the control, water deficit at stage I reduced panicle length by 10–31% (P < 0.05), but increased panicle diameter. Water deficit treatments at stage II reduced panicle length slightly. Since the peak of vegetative growth have
Fig. 2. Accumulated diameter of new shoot under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 8). I, II, III and IV stand for bud-burst to leafing stage, flowering to fruit set stage, fruit growth stage and fruit maturation stage of pear-jujube tree, respectively.
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Fig. 3. Accumulated length of panicle under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 8). I and II stand for bud-burst to leafing stage and fruit maturation stage of pear-jujube tree, respectively.
already completed, water deficit at stages III and IV had no significant impact on panicle growth (data not shown). 3.2.2. Leaf area index and pruning amounts As compared to the control, water deficit treatments reduced leaf area index of pear-jujube tree significantly at stages I and II (P < 0.05), but insignificantly at stages III and IV (Fig. 4). Because the growth of branches and leaves had reached its peak in the early stage III, the second period of shoot growth in this stage had little impact on LAI. As shown in Fig. 5, water deficit significantly reduced the pruning amounts of pear-jujube tree (P < 0.01) at stages I and II, by 40% and 22% in 2005, and 37% and 23% in 2006, respectively. Water deficit also significantly reduced the pruning amounts at stage III by 17% and 13% in both years, respectively. But water deficit at stage IV did not reduce the pruning amounts. Since the stages I and II are the vigorous vegetative growth period of pear-jujube tree, water deficit can effectively inhibited the overgrowth of vegetative organ, thus water deficit reduced pruning amounts significantly. Although main vegetative growth of the tree was stagnant at stage III, the water deficit treatments can effectively restrain the growth of autumn branches, so water deficit reduced pruning amounts slightly. 3.3. Effect of water deficit at different stages on fruit development of pear-jujube Water deficit at stage I and II had some effect on flowering time, flowers per panicle and final fruit set in both years (Table 3). Compared to the control, the water deficit treatments at stage I brought forward the flowering by 3–8 days and increased the
flowers per panicle by 12.2–40.5%. I-SD and MD treatments also significantly improved final fruit set (P < 0.05), whereas I-LD treatment maintained the control level. Water deficit treatments at stage II reduced the flowers per panicle and final fruit set by 4.2– 22.1% and 12.0–26.7%, respectively. Fig. 6 shows that the change of growth rate of fruit volume (Vf) had similar trend in different water deficit treatments, which had two peaks of fruit growth (about July 3 and August 1). And water deficit at different growth stages had effect on Vf to some extent. The vegetative growth of the tree at stage I was the priority when water deficit treatments were implemented (April 16), but Vf in the water deficit treatments was significantly higher than control in the early of fruits growth (Fig. 6a). The fruit began to grow shortly after the second irrigation (June 10). Compared to the control, water deficit treatments at stage II lowered Vf significantly (Fig. 6b), but the re-watering enhanced Vf significantly. Thus, the re-watering at stages I and II increased Vf in water deficit treatments by 15–30% as compared to the control. The stage III is in the second peak of fruit growth and the transition period from cell division to cell enlargement of fruit, and cell expansion has higher sensitivity to water deficit, thus Vf in the water deficit treatments (July 15) was significantly lower than that of control (P < 0.01, Fig. 6c), but the Vf was recovered slightly after the re-watering. However, Vf in the water deficit treatments (August 12) had no significant difference from that of the control at stage IV (Fig. 6d). Therefore, water deficit had no significant effect on fruit growth at stages I and IV, but had negative impact at stages II and III. Water deficit treatments at different growth stages had some effect on fruit volume (Cui et al., 2008). Moderate and severe water deficit at stages I and IV increased the fruit volume, but water deficit treatments at stage II reduced the fruit volume because of lower bud growth and Vf. But water deficit had little effect on Vf at stage III. Moreover, Vf in 2005 was significantly greater than that in 2006 since more precipitation in 2005 (250.5 mm) than in 2006 (174.9 mm) during the growth stages of pear-jujube tree (from April to August). In the same study, Cui et al. (2008) indicated that different water deficit treatments in different growth stages reduced water consumption of pear-jujube tree significantly, LD, MD and SD treatments at different growth stages decreased water consumption by 5–7%, 8–14% and 15–18%, respectively. In addition, moderate water deficit in right period can improve WUEY. Compared to the control, different water deficit treatments increased WUEY by 14.0–41.4% and 75.9–4.7% in 2005 and 2006, respectively. MD and SD treatments at stages I and IV improved WUEY significantly in both years. Thus, MD and SD treatments at the bud-burst to leafing stages, any water deficit treatments at the fruit maturation stage and LD treatment at the fruit growth stage can be applied, however, any water deficit treatments cannot be applied at the flowering to fruit set stage. 4. Discussion 4.1. Effect of water deficit on physiological parameters of pear-jujube tree In general, the light use efficiency by plants is only 1%. And it is a primary mean to increase light use efficiency by improving photosynthetic efficiency. Therefore, research on photosynthetic parameters under water deficit condition is helpful to accurately understand the change of physiological characteristics of fruit trees in adverse circumstances, which provided scientific basis in improving photosynthetic efficiency and WUEL effectively. Leaf photosynthesis was sensitive to water deficit. Slight water deficit had no significant on Pn, with the increscent water deficit degree, Pn began to decline greatly after the leaf water potential
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Fig. 4. Leaf area index (LAI) under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 2). I, II, III and IV stand for budburst to leafing, flowering to fruit set, fruit growth and fruit maturation stages of pear-jujube tree, respectively. * represents significantly difference at P = 0.05 by Duncan’s multiple range test.
dropped to a certain threshold, which may reduce the accumulation of photosynthetic products (Kang et al., 2007). Our study found that leaf photosynthesis parameters of pear-jujube tree reduced with the increasing water deficit. Such reduction was mainly due to the photosynthesis controlled by the stomatal limitation to the non-stomatal limitation, which was consistent with the result on apricot-plum (Liu et al., 2007). Our study also found that the re-watering significantly recovered the photosynthetic parameters of pear-jujube tree treated with water deficit treatments. The re-watering significantly improved Pn and WUEL with exception of III-SD treatment. Similar results were also found in sweet orange (Pe´rez-Pe´rez et al., 2008) and grapevine (Tiago et al., 2007). Pe´rez-Pe´rez et al. (2008) indicated that gs of the water deficit treatments after the re-watering were significantly lower than that of the control, which resulted in the increased WUEL. Therefore, moderate water deficit can effectively regulate photosynthetic capacity of fruit trees and reduce transpiration, and the re-watering can increase photosynthetic rate and WUEL significantly. The main reason is that moderate water deficit treatment can effectively enhance the activity of leaf superoxide dismutase (SOD) and solar energy capturing capacity of leaves (Lu et al., 1996), then it improved photochemical efficiency and photosynthesis, which increased WUEL significantly (Wang et al., 2008a).
It was also showed that water deficit decreased leaf net photosynthetic rate (Pn) of pear-jujube (Ma et al., 2007) and olive (Ahmed et al., 2007) slightly, but reduced the transpiration rate (Tr) significantly, thus water deficit increased leaf water use efficiency significantly, which is in agreement with our study. 4.2. Effect of water deficit on vegetative growth of pear-jujube tree This study shows that water deficit at early growth stage can inhibit the vegetative growth, reduce ‘‘luxury’’ shoot and leaf area growth of pear-jujube tree. Since water deficit can alter the allocation ratio of photosynthetic product between root and canopy, the root system may obtain more assimilates for its growth, but water deficit inhibits the canopy growth, thus it reduced leaf area and transpiration. However, leaf growth was gradually recovered after relieving water deficit. Olien and Flore (1990) showed that the re-watering could recover leaf growth of 1year old potted peach to normal growth firstly in the vegetative organs. Li et al. (1989) also indicated that water deficit firstly inhibited new shoot diameter in the vegetative growth of peach, strong inhibitory effect was found in 1–3 months after relieving water deficit, our study also had similar conclusion. Moreover, Han et al. (2005) found that controlling redundant of vegetative growth
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hormone balance in the plant (Cuevas et al., 2007), which increased fruit set and established an important foundation for pre-maturity and yield increase. 4.3. Effect of water deficit on fruit development of pear-jujube
Fig. 5. Pruning amount under different water deficit levels at different growth stages of pear-jujube tree in 2005–2006. I, II, III and IV stand for bud-burst to leafing stage, flowering to fruit set stage, fruit growth stage and fruit maturation stage of pear-jujube tree, respectively. Each column is mean of two or four replicates, error bar is S.E.
is an effective way to increase fruit yield. In our study, water deficit at stages II and III decreased the diameter of new shoot after early July. Because tree vegetative growth was the lowest at stage III, water deficit made the growth of new shoot more slowly, but the activity of fruit cells was less sensitive to water deficit, and a high gradient of osmotic pressure between the branches and leaves was maintained, thus most of the nutrients, water and the photosynthesis product stored in the source organs (branches, leaves) can flow into the sink organs (fruit) within the tree body, then the photosynthetic product was transferred from the vegetative growth to the reproductive growth (Wang et al., 2008b), which resulted in lower new shoot diameter growth. Early water deficit treatments advanced the flowering time of loquat and increased flowers per panicle, flower dry weight and fruit set significantly (Cuevas et al., 2007), but reduced the quantity and quality of flower at the flowering stage significantly (Cuevas et al., 2007; Rodrı´guez et al., 2006), which was similar to our result. This is because water deficit at the early growth stage can regulate
Our results showed that Vf after experienced water deficit at stage I was relatively higher because the water deficit inhibited the vegetative growth, after the re-watering, the stored photosynthesis products and nutrition substances in leaves and branches transferred to the bud and fruit organs, stronger compensatory effect on photosynthesis and full water supply at the fruit growth stage were benefit for fruit development and final fruit volume. The re-watering had significant compensatory effect on fruit growth at stages II and III, because the water deficit at stage II caused a number of flower buds fell off, which declined the fruited set by 30%, thus the competition of nutrients, water and other energy substances between the fruits was reduced, which resulted in significant compensatory effect. Since the reproductive growth of pear-jujube peaked at stage III, the vegetative growth was more sensitive to water deficit than the reproductive growth, thus water deficit made more photosynthetic products and other energy substances transfer into reproductive growth. Such phenomenon was more significant after the re-watering. Therefore, the re-watering after water deficit had the compensatory effect on fruit development. Caspari et al. (1994) and Li (1993) also found that water deficit treatment at fruit cell division stage had such compensatory effect on fruit development, which could open up an important channel to transfer more photosynthetic product into fruits. The peak growth stage of roots, branches and leaves and fruits alternately appeared, which can avoid the competition on photosynthetic products between fruits and other organs during the fruit growth stages (Abrisqueta et al., 2008), thus it is favorable to transfer more photosynthetic product and energy substances into fruit organs. The yield of fruit trees is dependent on fruit set and single fruit volume. In the same study, moderate water deficit increased the yield at stages I and IV, which was respectively caused by the increasing fruit set at stage I and single fruit volume at stage IV (Cui et al., 2008). Water deficit at the early stage increased the yield of peach and pear slightly (Li, 1993) and water deficit at fruit growth and maturation stages had no significant effect on dry matter accumulation of fruits (Girona et al., 2003). And Cui et al. (2008) also indicated that water deficit treatment improved WUEY significantly. Furthermore, it was found that the water deficit treatment during the whole growth stages of loquat tree increased WUEY by 40%, but did not reduce fruit yield and quality (Hueso and Cuevas, 2008). Similar conclusion was also obtained in many references (Costa et al., 2007; Cuevas et al., 2007; Iniesta et al., 2008; Tiago et al., 2007).
Table 3 Effect of water deficit on flowering time, flowers number and fruits number per panicle of Pear-Jujube tree in 2005–2006. Growth stage
Treatment
2005
2006
Flowering time month-day
Flowers per panicle
Fruits per panicle
Flowering time month-day
Flowers per panicle
Fruits per panicle
Bud-burst to leafing stage (I)
T1 T2 T3 T4
(CK) (SD) (MD) (LD)
15-May 7-May 10-May 11-May
32.4c 46.5a 42.6b 34.4c
13.4b 15.5a 14.2a 12.5b
13-May 6-May 9-May 10-May
34.3c 48.2a 40.7b 38.5bc
12.7c 16.6a 14.5b 12.4c
Flowering to fruit set stage (II)
T5 (SD) T6 (MD) T7 (LD)
15-May 16-May 15-May
26.6d 27.4d 31.5c
9.8c 10.6c 11.3b
14-May 13-May 13-May
25.3d 28.4d 32.4c
9.2e 10.4d 10.5d
Note: Significant difference marked by different small letter in same column (P < 0.05).
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Fig. 6. Growth rate of fruit volume under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 6). For a given date, statistically significant differences (P < 0.05 or 0.01) between control and stressed seedlings are indicated: * and ** represent P < 0.05 and P < 0.01, respectively.
5. Conclusions Regulated deficit irrigation with varying degree at different growth stages of pear-jujube tree indicated that the moderate water deficit reduced stomatal conductance and transpiration; the re-watering improved the water use efficiency because of the compensatory effect on photosynthesis and more photosynthesis product and nutrition substances transferred into the reproductive organs. Water deficit treatment at the bud-burst to leafing stage obviously suppressed the vegetative growth of pear-jujube tree and was advantageous to transfer more stored photosynthesis product and nutrition substances to the reproductive organ after the flowering stage. Water deficit reduced the fruit growth rate of pear-jujube slightly, but the re-watering had overcompensatory effect to reduce the negative influence on fruit growth. And water deficit treatments reduced water consumption and improved the WUEY of pear-jujube tree at different growth stages, especially severe water deficit at the bud-burst to leafing stage and moderate and severe water deficit at the fruit maturation stage. However, this study only investigated the effect of different water deficit treatments at different single growth stages on tree growth, fruit development and water use, but has not involved in the effect of water deficit treatments at the compound-stages and the multi-stages, more research need to be carried out in the future. Acknowledgments We are grateful to the research grants from the National Key Basic Research Program of China (973 Program, 2006CB403406); Program for Changjiang Scholars and Innovative Research Team in University in China (IRT0657) and China National Natural Science Fund (50709038, 50679081, 50869001).
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Robert, C.E., Edwatd, I.P., Tobert, G.E., 1995. Deficit irrigation to control vegetable growth in apple and monitoring fruit growth to schedule irrigation. Hortic. Sci. 30, 1229–1232. Rodrı´guez, M.C., Hueso, J.J., Cuevas, J., 2006. Flower development in ‘Algerie’ loquat under scanning electron microscopy. In: II International Symposium on Loquat. Guangzhou, China. Tiago, P.S., Carlos, M.L., Rodrigues, M.L., Claudia, R.S., Jorge, M.R., Joaˇo, P.M., Pereira, J.S., Chave, M.M., 2007. Effect of deficit irrigation strategies on cluster microclimate for improving fruit composition of Moscatel field-grown grapevines. Sci. Hortic. 112, 321–330. Villar-Salvador, P., Oca¯na, L., Pe¯nuelas, Carrasco, I., 1999. Effect of water stress conditioning on the water relations, root growth capacity, and the nitrogen and non-structural carbohydrate concentration of Pinus halepensis Mill. (Aleppo pine) seedlings. Ann. Forest Sci. 56, 459–465. Wang, Y., Yao, Y., Lu, J., Li, J., Ding, Z., Li, S., Zhang, J., 2008a. Effect of regulated deficit irrigation on photosynthetic characteristics & water use efficiency of winter wheat. Agric. Res. Arid Areas 26, 59–60. Wang, L., Zhang, T., Ding, S., 2008b. Effect of drought and rewatering on photosynthetic physioecology of wheat of differing ploidy. Acta Ecol. Sinica 28 (4), 1593–1599. Wang, Y., Wu, B., Zhao, J., Jiang, Q., Li, S., 2008c. Soluble sugar contents in fruits and leaves during fruit development and their relationship in peach cultivars of difference in fruit glucose/fructose. Sci. Agric. Sinica 41, 2063–2069. Xu, S., Cheng, X., 2003. Effect of regulated deficit irrigation on yield and quality of Xiangli Pear. Xinjiang Agric. Sci. 40, 6–9. Zegbe-Domı´nguez, J.A., Behboudian, M.H., Clothier, B.E., 2006. Responses of ‘Petopride’ processing tomato to partial rootzone drying at different phenological stages. Irrig. Sci. 24, 203–210. Zhang, C., Fu, Z., 2005. Impact of water stress on the root and shoot growth of litchi seedlings. J. Fruit Sci. 22, 339–342.
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Response of vegetative growth and fruit development to regulated deficit irrigation at different growth stages of pear-jujube tree Ningbo Cui a, Taisheng Du b,*, Fusheng Li c, Ling Tong b, Shaozhong Kang a,b,**, Mixia Wang a, Xiaozhi Liu b, Zhijun Li a a b c
Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest A&F University, Yangling, Shaanxi 712100, China Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China Agricultural College, Guangxi University, Nanning, Guangxi 530005, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 30 November 2008 Accepted 22 March 2009 Available online 17 April 2009
In order to investigate the response of vegetative growth, fruit development and water use efficiency to regulated deficit irrigation at different growth stages of pear-jujube tree (Zizyphus jujube Mill.), different water deficit at single-stage were treated on field grown 7-year old pear-jujube trees in 2005 and 2006. Treatments included severe (SD), moderate (MD) and low (LD) water deficit treatments at bud-burst to leafing (I), flowering to fruit set (II), fruit growth (III) and fruit maturation (IV) stages. Compared to the full irrigation (control), different water deficit treatments at different growth stages reduced photosynthesis rate (Pn) slightly and transpiration rate (Tr) significantly, thus it improved leaf water use efficiency (WUEL, defined as the ratio of Pn to Tr) by 2.7–26.1%. After the re-watering, Pn had significant compensatory effect, but Tr was not enhanced significantly, thus WUEL was improved by 31.4–42.2%. I-SD, I-MD, II-SD and II-MD decreased new shoot length, new shoot diameter and panicle length by 8–28%, 13–23% and 10–31%, respectively. Simultaneously, they reduced leaf area index (LAI) and pruning amount significantly. Flowering of pear-jujube tree advanced by 3–8 days in the water deficit treatments at stage I, Furthermore, SD and MD at stage I increased flowers per panicle and final fruit set by 18.9–40.5% and 15.5–36.6%, respectively. After a period of re-watering, different water deficit treatments at different growth stages improved the fruit growth rate by 15–30% without reduction of the final fruit volume. Compared to the control, I-MD, I-SD, I-LD, I-MD and I-SD treatments increased fruit yield by 13.2–31.9%, but reduced water consumption by 9.7–17.5%, therefore, they enhanced water use efficiency at yield level (WUEY, defined as ratio of fruit yield to total water use) by 17.3–41.4%. Therefore, suitable period and degree of water deficit can reduce irrigation water and restrain growth redundancy significantly, and it optimize the relationship between vegetative growth and reproductive growth of pear-jujube trees, which maintained or slightly increased the fruit yield, thus water use efficiency was significantly increased. ß 2009 Elsevier B.V. All rights reserved.
Keywords: Fruit development Pear-jujube tree (Zizyphus jujube Mill.) Regulated deficit irrigation Vegetative growth Water use efficiency
1. Introduction Jujube (Zizyphus jujube Mill.) originated from China and has been planted more than 5000 years. Now the planting area of jujube in China is about 30,000 ha, with total yield of 600 million kg. Jujube is mainly cultivated in northern China where scientific and reasonable irrigation is needed for high yield and quality. However, inappropriate irrigation method may result in waste of water resources and poor fruit quality.
* Corresponding author. Fax: +86 10 62737611. ** Corresponding author at: Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China. Fax: +86 10 62737611. E-mail addresses: [email protected] (T. Du), [email protected] (S. Kang). 0378-3774/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2009.03.015
Regulate deficit irrigation (RDI) is an important physiological water-saving technique since it has been applied on fruit trees by many researchers. Chalmers and Ende (1975) found that water deficit had significant effect on vegetative growth of fruit trees, but slight on fruit growth, which provided the theoretical basis of RDI in saving irrigation water and increasing production. Behboudian and Mills (1997) indicated that RDI limited plant overgrowth and reduced the pruning amount and irrigation water significantly, thus improved water use efficiency. Cheng et al. (2003) indicated that water deficit treatments significantly inhibited the vegetative growth of pear (Pyrus bretsehneideri Rehd CV. Yali) at bud-burst and flowering stages and decreased leaf area, and new shoot length and pruning amount by 15–25% and 18–33% as compared to the control, and the final fruit set was more than 85% for different water deficit treatments. Similar conclusion was also drawn on
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litchi and sweet orange (Zhang and Fu, 2005; Pe´rez-Pe´rez et al., 2008). It was also found that after experiencing moderate water deficit, the re-watering quickly restored the water status of peach tree and maintained the same yield as the level of the control, even if the water deficit was greater than 65% (Girona et al., 2003). At the same time, single-stage and compound-stage water deficit can save irrigation water by 13–24% and 23–35%, and significantly improved water use efficiency. Zegbe-Domı´nguez et al. (2006) and Ferna´ndez et al. (2006) also got the similar results. Robert et al. (1995) indicated that water deficit had less negative impact on fruit tree at the early stage than at the later stage, and the rewatering had compensatory effect on the fruit growth. Xu and Cheng (2003) found that water deficit from the budding to early fruit expansion stages of pear (P. bretsehneideri Rehd CV. Xiangli) had no adverse effect on fruit set, single fruit weight and final fruit yield, and any water deficit treatment did not cause fruit cracking. The similar conclusion on macadamia nut was also got by Liu et al. (2004). Photosynthesis is an important physiological process of plants. Tree photosynthesis is very sensitive to water deficit, which directly affects fruit development and final yield. Villar-Salvador et al. (1999) indicated that the photosynthetic efficiency was the determining factor in the plant productivity and yield level under water deficit conditions. Ma et al. (2006) and Ahmed et al. (2007) showed that water deficit decreased leaf net photosynthetic rate (Pn) of pearjujube and olive slightly, but reduced the transpiration rate (Tr) remarkably, thus resulted in significant improvement of leaf water use efficiency, indicating that fruit trees could adapt to a certain degree of water stress through controlling the stomatal aperture. Wang et al. (2008c) found that re-watering increased leaf Pn of fruit tree significantly after experiencing moderate water deficit, suggesting that super compensatory effect occurred after experiencing water stress. Therefore, crop growth redundancy theory, ‘sink and source’ theory for the transfer of assimilate and water deficit effect on different plant physiological function has provided theoretical basis for the RDI technique (Kang et al., 2000, 2007). At present, there are fewer systematic studies on the effect of different growth stages with different water deficit levels and rewatering on physiological parameters, growth, fruit development and water use, as well as the transfer of photosynthetic product in pear-jujube tree. How to implement the regulated water deficit based on growth characteristics and physiological water requirement of pear-jujube tree and optimize the allocation of the photosynthetic product in the tree has become the urgent question to be resolved so as to obtain the fruit production with watersaving, steady-yield and high-efficiency. Our study aims to provide experimental basis in developing sustainable water-saving, steady-yield, high-efficiency jujube production in arid and semiarid regions after studying the growth, fruit development and water use of pear-jujube tree under RDI in the field. 2. Materials and methods 2.1. Experimental site The field experiments were continuously conducted from early April (leaf exhibition at the initial stage) to late September (leaf
falling at later stage) in 2005 and 2006. The experimental site is situated at Dengzhuang, Dali, Shannxi, northwest China (latitude 348520 N, longitude 1098560 E, altitude 1340 m) which locates in a continental semiarid temperate zone with a mean annual precipitation of 513.6 mm and a mean annual evaporation from a free water surface of 1689.34 mm. The average field capacity in the upper 1.0 m of the soil profile is approximately 22.8% (mass basis) with bulk density of 1.36 g/cm3. The groundwater table is consistently below 5.6 m, without replenishment effect on the designed soil profile. 2.2. Experimental plant and design Twenty-eight healthy and uniform 7-year old pear-jujube (Zizyphus jujuba Mill. cv. Lizao) trees of were selected as experimental trees. Trees were planted in 3 m within-row spacing and 2 m between the rows. The whole growing season of pearjujube tree was divided into bud-burst to leafing stage (stage I, early April–early May), flowering to fruit set stage (stage II, mid May–late June), fruit growth stage (stage III, late June–late July), fruit maturation stage (stage IV, early August–mid September) and dormancy stage (stage V, this October–next March). Thirteen treatments including full irrigation (FI, control), low (LD, 2/3 of full irrigation), moderate (MD, 1/2 of irrigation) and severe (SD, no irrigation) water deficit at the growth stages I–IV were designed and applied. FI, LD, MD and SD treatments received irrigation water of 900 m3/hm2 (90 mm), 600 m3/hm2 (60 mm), 450 m3/hm2 (45 mm) and 0 m3/hm2 (0 mm), respectively during the water deficit treatment stage with irrigation water of 900 m3/ hm2 at the rest three stages. Each treatment was applied to one tree in a plot with the area of 3 m2 (2 m 1.5 m) with four replicates of FI and two repetitions of the other treatments. The other design was the same as the experiment by Cui et al. (2008), the irrigation scheme is shown in Table 1. 2.3. Measurements 2.3.1. Precipitation Precipitation data at different growth stages were provided by Dali County Weather Bureau, Shaanxi (the weather station was 2 km far away from the experimental site, and the topography in this region is planar, so the precipitation data are representative). Total precipitation over the whole growth stage of pear-jujube tree was 250.5 mm and 174.9 mm in 2005 and 2006, respectively. The precipitation at stages I–IV was 24 mm, 72.2 mm, 61.1 mm and 93.2 mm in 2005, and 14.16 mm, 75.14 mm, 74.05 mm and 11.55 mm in 2006, respectively. 2.3.2. Growth measurements Eight shoots were selected in four directions of each tree (avoiding leggy branches) with a tag labeled on each shoot respectively to measure and calculate the new shoot growth from early May. The length and diameter of new shoots were respectively measured using steel ruler and vernier caliper every 10 days, then average length and diameter of the shoot was calculated based on two measurements of a day as the cumulative growth. Eight panicles per tree at the similar location selected from different directions
Table 1 Irrigation water amount for different treatments in Pear-Jujube tree growing season (mm). Growth stage
T1 (CK)
T2 (SD)
T3 (MD)
T4 (LD)
T5 (SD)
T6 (MD)
T7 (LD)
T8 (SD)
T9 (MD)
T10 (LD)
T11 (SD)
T12 (MD)
T13 (LD)
Bud-burst to leafing stage (I) Flowering to fruit set stage (II) Fruit growth stage (III) Fruit maturation stage (IV)
90 90 90 90
0 90 90 90
45 90 90 90
60 90 90 90
90 0 90 90
90 45 90 90
90 60 90 90
90 90 0 90
90 90 45 90
90 90 60 90
90 90 90 0
90 90 90 45
90 90 90 60
Table 2 Transpiration rate (Tr), photosynthetic rate (Pn), stomatal conductance (gs) and water use efficiency (WUEL) of pear-jujube trees leaves under different water deficit treatments in 2006. Treatment
Pn (mmol/m2 s)
Tr (mmol/m2 s)
gs (mmol/m2 s)
WUEL (mmolCO2/molH2O)
5 d after water deficit
Pn (mmol/m2 s)
Tr (mmol/m2 s)
T1 (CK) T2 (SD) T3 (MD) T4 (LD) F value
14.880.93a 8.900.75c 11.42 0.82b 13.43 1.12ab 13.54*
1.400.22a 0.720.20d 0.860.17c 1.050.24b 93.59***
93.008.32a 71.006.02c 69.004.32c 78.007.55b 37.54**
10.63 1.05b 12.36 0.82ab 13.28 0.74a 12.79 1.12ab 4.12*
16.52 1.30a 13.83 1.12ab 15.24 0.88a 15.56 1.35a 6.22*
1.88 0.24a 0.98 0.18c 1.19 0.14c 1.54 0.14b 38.24**
Flowering to fruit set stage (II)
T1 (CK) T5 (SD) T6 (MD) T7 (LD) F value
11.98 0.62a 7.22 0.43b 8.33 0.50b 10.53 0.72a 3.12*
1.410.18a 0.720.20c 0.880.21c 1.28 0.14b 117.60***
52.006.45a 35.004.34d 40.005.30c 45.00 3.38b 26.24**
11.90 0.62b 14.43 0.45a 13.250.86ab 11.52 0.70a 3.99*
12.33 0.90ab 11.25 0.45b 11.98 0.54ab 13.73 1.10a 2.47ns
1.22 0.09a 0.78 0.13c 0.76 0.07c 0.92 0.12b 27.26**
Fruit growth stage (III)
T1 (CK) T8 (SD) T9 (MD) T10 (LD) F value
12.13 0.84a 7.08 0.45c 8.15 0.48c 10.98 0.62b 20.62**
1.70 0.14a 0.78 0.08d 1.17 0.11c 1.43 0.20b 77.23***
121.00 9.02a 57.00 7.10c 61.00 5.50c 91.00 8.10b 36.24**
10.81 0.82c 14.50 0.74a 12.12 0.44b 11.73 0.37b 4.27*
15.78 1.15a 10.13 0.72b 14.56 0.52ab 16.53 1.12a 4.33*
1.34 0.11a 0.85 0.08c 1.04 1.06b 1.12 1.12b 16.24**
1.36 0.15a 0.72 0.14d 1.02 0.08c 1.24 0.14b 38.21**
61.00 8.22a 32.00 4.30c 36.00 5.42c 53.00 7.56b 21.39**
T1 (CK) T11 (SD) T12 (MD) T13 (LD) F value
8.27 0.40a 6.40 0.52c 7.55 0.38b 8.03 0.75ab 9.68*
WUEL (mmolCO2/molH2O)
102.25 9.38a 78.25 7.02b 82.50 6.55b 96.50 5.34a 5.20*
8.79 0.52c 14.11 0.77a 12.81 0.84b 10.10 0.92bc 8.32*
3 d after re-watering
Bud-burst to leafing stage (I)
Fruit maturation stage (IV)
gs (mmol/m2 s)
6.08 0.72b 8.89 0.38a 7.40 0.52ab 6.48 0.46 b 4.29*
71.75 6.38a 48.75 5.12b 54.75 6.34b 69.25 5.52ab 7.68* 103.75 8.52a 74.75 6.37b 96.25 8.10a 98.75 7.30a 6.24*
12.09 1.10b 14.42 0.88ab 15.76 0.72a 14.92 1.10a 1.75ns 11.78 1.14b 11.92 0.72b 14.00 0.65a 14.76 1.10a 5.58*
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Growth stages
Note: Values are means S.E. (n = 8). Field experiment 2006, significant difference marked by different small letter in same column (P < 0.05). P = 0.05; ns: not significant. * F > F0.05. ** F > F0.01. *** F > F0.001.
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were measured every 10 days as the cumulative growth. The flowering time and flowers per panicle and final fruit set were recorded for different water deficit treatments. The fruit volume was measured 20 days after the fruit set using the method of Cui et al. (2008). The measurements were done every 10 days. The volume of eight fruits in the same treatment was averaged as final fruit volume. The difference between two measurements during the period was taken as the volume growth rate (Vf, cm3/d). Leaf areas for different water deficit treatments were measured with a LAI-2000 canopy analyzer every 30 days, and then leaf area index (LAI) was calculated using Hemiview software. 2.3.3. Measurement of physiological parameters Physiological parameters such as leaf photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs), and intercellular CO2 concentration (Ci) were measured with a LI-6400 portable photosynthesis system (LI-COR, Nebrasaka, USA) during 9:30– 10:30 a.m. in the morning 5 days after deficit water treatment and 3 days after re-watering at each growth stage. In each treatment, three to four sunlit healthy leaves were randomly selected in different directions and labeled, each leaf was measured three times, and the same leaves were measured at each growth stage, then the leaf water use efficiency (WUEL, Pn/Tr) was calculated.
2.4. Data analysis Analysis of variance (ANOVA) was done using GLM processes of Statistical Analysis Software (SAS 6.12, SAS Institute Ltd., USA). All treatment means were compared for any significant differences using the Duncan’s multiple range tests at significant level of P0.05. 3. Results 3.1. Effect of water deficit at different stages on physiological parameters of pear-jujube tree Water deficit and re-watering had significant effect on leaf Tr, Pn, gs and WUEL of pear-jujube tree (Table 2). Tr, Pn and gs were significantly reduced 5 d after water stress, and their percentage reduction increased with the degree of water deficit. Tr and gs were more sensitive to water deficit than Pn, and their percentage reduction was also greater. Compared to the control, SD, MD, LD at different growth stages improved average WUEL by 26.1%, 17.2% and 2.7% although Pn had no significant difference (P > 0.05). Rewatering after 3 days can slightly restore Tr, Pn and gs in the water deficit treated at stages I–III. Moreover, compared to the control, Pn in the other water deficit treatments at different growth stages had no significant difference (P > 0.05), but Tr and gs had significant
Fig. 1. Accumulated length of new shoot under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 8). I, II, III and IV stand for bud-burst to leafing stage, flowering to fruit set stage, fruit growth stage and fruit maturation stage of pear-jujube tree, respectively.
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difference (P < 0.05) with exception for SD treatment, and LD treatment at stages II and III also increased Pn and WUEL significantly. In addition, SD, MD and LD treatments at different growth stages changed average Pn by 13.2%, 1.1% and 11.6%, and increased average WUEL by 37.1%, 42.2% and 31.4%. Simultaneously, the MD and LD treatments at different growth stages decreased gs significantly, which can prevent CO2 into leaf cells, which resulted in decreasing of leaf Ci (intercellular CO2 concentration) and Pn, indicating that the decline of photosynthesis was mainly due to strong reversible stomatal limitation, but the photosynthetic rate can effectively be resumed after the re-watering. The SD treatment reduced leaf gs and Pn and damaged the membrane system and increased lipid peroxidation into superoxide radical, thus the Ci remained unchanged or even increased (data not shown), indicating that the decline of photosynthesis was mainly due to poor reversible non-stomatal limitation, i.e. due to lower photosynthetic activity of leaf cells. Since SD treatment severely damaged photosynthetic system, the re-watering cannot restore photosynthetic capacity. Therefore, after experiencing moderate water deficit treatments, photosynthetic ability recovered when re-watered, and this resulted in higher WUE, furthermore, stimulated the nutrition accumulation and life activity of the tree.
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3.2. Effect of water deficit at different stages on vegetative growth of pear-jujube tree 3.2.1. New shoot and panicle It was showed that water deficit treatments at different growth stages of pear-jujube tree had significant effect on the growth of new shoot, compared to the control, the length and diameter of new shoot at each water deficit treatment were significantly decreased by 6–28% and 13–22% at stages I and II, respectively (Figs. 1a, b and 2a, b). Furthermore, III-MD treatment reduced new shoot length slightly, III-LD and MD treatments decreased the new shoot diameter significantly by 12% and 28% (Figs. 1c and 2c). However, water deficit treatments at stage IV had no significant effect on the growth of new shoot. In addition, after early July, since the fruit growth had entered into the second period of rapid growth, water deficit at stages II and III decreased the diameter of new shoot, but did not increase the length significantly. As shown in Fig. 3, compared to the control, water deficit at stage I reduced panicle length by 10–31% (P < 0.05), but increased panicle diameter. Water deficit treatments at stage II reduced panicle length slightly. Since the peak of vegetative growth have
Fig. 2. Accumulated diameter of new shoot under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 8). I, II, III and IV stand for bud-burst to leafing stage, flowering to fruit set stage, fruit growth stage and fruit maturation stage of pear-jujube tree, respectively.
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Fig. 3. Accumulated length of panicle under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 8). I and II stand for bud-burst to leafing stage and fruit maturation stage of pear-jujube tree, respectively.
already completed, water deficit at stages III and IV had no significant impact on panicle growth (data not shown). 3.2.2. Leaf area index and pruning amounts As compared to the control, water deficit treatments reduced leaf area index of pear-jujube tree significantly at stages I and II (P < 0.05), but insignificantly at stages III and IV (Fig. 4). Because the growth of branches and leaves had reached its peak in the early stage III, the second period of shoot growth in this stage had little impact on LAI. As shown in Fig. 5, water deficit significantly reduced the pruning amounts of pear-jujube tree (P < 0.01) at stages I and II, by 40% and 22% in 2005, and 37% and 23% in 2006, respectively. Water deficit also significantly reduced the pruning amounts at stage III by 17% and 13% in both years, respectively. But water deficit at stage IV did not reduce the pruning amounts. Since the stages I and II are the vigorous vegetative growth period of pear-jujube tree, water deficit can effectively inhibited the overgrowth of vegetative organ, thus water deficit reduced pruning amounts significantly. Although main vegetative growth of the tree was stagnant at stage III, the water deficit treatments can effectively restrain the growth of autumn branches, so water deficit reduced pruning amounts slightly. 3.3. Effect of water deficit at different stages on fruit development of pear-jujube Water deficit at stage I and II had some effect on flowering time, flowers per panicle and final fruit set in both years (Table 3). Compared to the control, the water deficit treatments at stage I brought forward the flowering by 3–8 days and increased the
flowers per panicle by 12.2–40.5%. I-SD and MD treatments also significantly improved final fruit set (P < 0.05), whereas I-LD treatment maintained the control level. Water deficit treatments at stage II reduced the flowers per panicle and final fruit set by 4.2– 22.1% and 12.0–26.7%, respectively. Fig. 6 shows that the change of growth rate of fruit volume (Vf) had similar trend in different water deficit treatments, which had two peaks of fruit growth (about July 3 and August 1). And water deficit at different growth stages had effect on Vf to some extent. The vegetative growth of the tree at stage I was the priority when water deficit treatments were implemented (April 16), but Vf in the water deficit treatments was significantly higher than control in the early of fruits growth (Fig. 6a). The fruit began to grow shortly after the second irrigation (June 10). Compared to the control, water deficit treatments at stage II lowered Vf significantly (Fig. 6b), but the re-watering enhanced Vf significantly. Thus, the re-watering at stages I and II increased Vf in water deficit treatments by 15–30% as compared to the control. The stage III is in the second peak of fruit growth and the transition period from cell division to cell enlargement of fruit, and cell expansion has higher sensitivity to water deficit, thus Vf in the water deficit treatments (July 15) was significantly lower than that of control (P < 0.01, Fig. 6c), but the Vf was recovered slightly after the re-watering. However, Vf in the water deficit treatments (August 12) had no significant difference from that of the control at stage IV (Fig. 6d). Therefore, water deficit had no significant effect on fruit growth at stages I and IV, but had negative impact at stages II and III. Water deficit treatments at different growth stages had some effect on fruit volume (Cui et al., 2008). Moderate and severe water deficit at stages I and IV increased the fruit volume, but water deficit treatments at stage II reduced the fruit volume because of lower bud growth and Vf. But water deficit had little effect on Vf at stage III. Moreover, Vf in 2005 was significantly greater than that in 2006 since more precipitation in 2005 (250.5 mm) than in 2006 (174.9 mm) during the growth stages of pear-jujube tree (from April to August). In the same study, Cui et al. (2008) indicated that different water deficit treatments in different growth stages reduced water consumption of pear-jujube tree significantly, LD, MD and SD treatments at different growth stages decreased water consumption by 5–7%, 8–14% and 15–18%, respectively. In addition, moderate water deficit in right period can improve WUEY. Compared to the control, different water deficit treatments increased WUEY by 14.0–41.4% and 75.9–4.7% in 2005 and 2006, respectively. MD and SD treatments at stages I and IV improved WUEY significantly in both years. Thus, MD and SD treatments at the bud-burst to leafing stages, any water deficit treatments at the fruit maturation stage and LD treatment at the fruit growth stage can be applied, however, any water deficit treatments cannot be applied at the flowering to fruit set stage. 4. Discussion 4.1. Effect of water deficit on physiological parameters of pear-jujube tree In general, the light use efficiency by plants is only 1%. And it is a primary mean to increase light use efficiency by improving photosynthetic efficiency. Therefore, research on photosynthetic parameters under water deficit condition is helpful to accurately understand the change of physiological characteristics of fruit trees in adverse circumstances, which provided scientific basis in improving photosynthetic efficiency and WUEL effectively. Leaf photosynthesis was sensitive to water deficit. Slight water deficit had no significant on Pn, with the increscent water deficit degree, Pn began to decline greatly after the leaf water potential
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Fig. 4. Leaf area index (LAI) under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 2). I, II, III and IV stand for budburst to leafing, flowering to fruit set, fruit growth and fruit maturation stages of pear-jujube tree, respectively. * represents significantly difference at P = 0.05 by Duncan’s multiple range test.
dropped to a certain threshold, which may reduce the accumulation of photosynthetic products (Kang et al., 2007). Our study found that leaf photosynthesis parameters of pear-jujube tree reduced with the increasing water deficit. Such reduction was mainly due to the photosynthesis controlled by the stomatal limitation to the non-stomatal limitation, which was consistent with the result on apricot-plum (Liu et al., 2007). Our study also found that the re-watering significantly recovered the photosynthetic parameters of pear-jujube tree treated with water deficit treatments. The re-watering significantly improved Pn and WUEL with exception of III-SD treatment. Similar results were also found in sweet orange (Pe´rez-Pe´rez et al., 2008) and grapevine (Tiago et al., 2007). Pe´rez-Pe´rez et al. (2008) indicated that gs of the water deficit treatments after the re-watering were significantly lower than that of the control, which resulted in the increased WUEL. Therefore, moderate water deficit can effectively regulate photosynthetic capacity of fruit trees and reduce transpiration, and the re-watering can increase photosynthetic rate and WUEL significantly. The main reason is that moderate water deficit treatment can effectively enhance the activity of leaf superoxide dismutase (SOD) and solar energy capturing capacity of leaves (Lu et al., 1996), then it improved photochemical efficiency and photosynthesis, which increased WUEL significantly (Wang et al., 2008a).
It was also showed that water deficit decreased leaf net photosynthetic rate (Pn) of pear-jujube (Ma et al., 2007) and olive (Ahmed et al., 2007) slightly, but reduced the transpiration rate (Tr) significantly, thus water deficit increased leaf water use efficiency significantly, which is in agreement with our study. 4.2. Effect of water deficit on vegetative growth of pear-jujube tree This study shows that water deficit at early growth stage can inhibit the vegetative growth, reduce ‘‘luxury’’ shoot and leaf area growth of pear-jujube tree. Since water deficit can alter the allocation ratio of photosynthetic product between root and canopy, the root system may obtain more assimilates for its growth, but water deficit inhibits the canopy growth, thus it reduced leaf area and transpiration. However, leaf growth was gradually recovered after relieving water deficit. Olien and Flore (1990) showed that the re-watering could recover leaf growth of 1year old potted peach to normal growth firstly in the vegetative organs. Li et al. (1989) also indicated that water deficit firstly inhibited new shoot diameter in the vegetative growth of peach, strong inhibitory effect was found in 1–3 months after relieving water deficit, our study also had similar conclusion. Moreover, Han et al. (2005) found that controlling redundant of vegetative growth
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hormone balance in the plant (Cuevas et al., 2007), which increased fruit set and established an important foundation for pre-maturity and yield increase. 4.3. Effect of water deficit on fruit development of pear-jujube
Fig. 5. Pruning amount under different water deficit levels at different growth stages of pear-jujube tree in 2005–2006. I, II, III and IV stand for bud-burst to leafing stage, flowering to fruit set stage, fruit growth stage and fruit maturation stage of pear-jujube tree, respectively. Each column is mean of two or four replicates, error bar is S.E.
is an effective way to increase fruit yield. In our study, water deficit at stages II and III decreased the diameter of new shoot after early July. Because tree vegetative growth was the lowest at stage III, water deficit made the growth of new shoot more slowly, but the activity of fruit cells was less sensitive to water deficit, and a high gradient of osmotic pressure between the branches and leaves was maintained, thus most of the nutrients, water and the photosynthesis product stored in the source organs (branches, leaves) can flow into the sink organs (fruit) within the tree body, then the photosynthetic product was transferred from the vegetative growth to the reproductive growth (Wang et al., 2008b), which resulted in lower new shoot diameter growth. Early water deficit treatments advanced the flowering time of loquat and increased flowers per panicle, flower dry weight and fruit set significantly (Cuevas et al., 2007), but reduced the quantity and quality of flower at the flowering stage significantly (Cuevas et al., 2007; Rodrı´guez et al., 2006), which was similar to our result. This is because water deficit at the early growth stage can regulate
Our results showed that Vf after experienced water deficit at stage I was relatively higher because the water deficit inhibited the vegetative growth, after the re-watering, the stored photosynthesis products and nutrition substances in leaves and branches transferred to the bud and fruit organs, stronger compensatory effect on photosynthesis and full water supply at the fruit growth stage were benefit for fruit development and final fruit volume. The re-watering had significant compensatory effect on fruit growth at stages II and III, because the water deficit at stage II caused a number of flower buds fell off, which declined the fruited set by 30%, thus the competition of nutrients, water and other energy substances between the fruits was reduced, which resulted in significant compensatory effect. Since the reproductive growth of pear-jujube peaked at stage III, the vegetative growth was more sensitive to water deficit than the reproductive growth, thus water deficit made more photosynthetic products and other energy substances transfer into reproductive growth. Such phenomenon was more significant after the re-watering. Therefore, the re-watering after water deficit had the compensatory effect on fruit development. Caspari et al. (1994) and Li (1993) also found that water deficit treatment at fruit cell division stage had such compensatory effect on fruit development, which could open up an important channel to transfer more photosynthetic product into fruits. The peak growth stage of roots, branches and leaves and fruits alternately appeared, which can avoid the competition on photosynthetic products between fruits and other organs during the fruit growth stages (Abrisqueta et al., 2008), thus it is favorable to transfer more photosynthetic product and energy substances into fruit organs. The yield of fruit trees is dependent on fruit set and single fruit volume. In the same study, moderate water deficit increased the yield at stages I and IV, which was respectively caused by the increasing fruit set at stage I and single fruit volume at stage IV (Cui et al., 2008). Water deficit at the early stage increased the yield of peach and pear slightly (Li, 1993) and water deficit at fruit growth and maturation stages had no significant effect on dry matter accumulation of fruits (Girona et al., 2003). And Cui et al. (2008) also indicated that water deficit treatment improved WUEY significantly. Furthermore, it was found that the water deficit treatment during the whole growth stages of loquat tree increased WUEY by 40%, but did not reduce fruit yield and quality (Hueso and Cuevas, 2008). Similar conclusion was also obtained in many references (Costa et al., 2007; Cuevas et al., 2007; Iniesta et al., 2008; Tiago et al., 2007).
Table 3 Effect of water deficit on flowering time, flowers number and fruits number per panicle of Pear-Jujube tree in 2005–2006. Growth stage
Treatment
2005
2006
Flowering time month-day
Flowers per panicle
Fruits per panicle
Flowering time month-day
Flowers per panicle
Fruits per panicle
Bud-burst to leafing stage (I)
T1 T2 T3 T4
(CK) (SD) (MD) (LD)
15-May 7-May 10-May 11-May
32.4c 46.5a 42.6b 34.4c
13.4b 15.5a 14.2a 12.5b
13-May 6-May 9-May 10-May
34.3c 48.2a 40.7b 38.5bc
12.7c 16.6a 14.5b 12.4c
Flowering to fruit set stage (II)
T5 (SD) T6 (MD) T7 (LD)
15-May 16-May 15-May
26.6d 27.4d 31.5c
9.8c 10.6c 11.3b
14-May 13-May 13-May
25.3d 28.4d 32.4c
9.2e 10.4d 10.5d
Note: Significant difference marked by different small letter in same column (P < 0.05).
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Fig. 6. Growth rate of fruit volume under different water deficit levels at different growth stages of pear-jujube tree in 2006. Points are means S.E. (n = 6). For a given date, statistically significant differences (P < 0.05 or 0.01) between control and stressed seedlings are indicated: * and ** represent P < 0.05 and P < 0.01, respectively.
5. Conclusions Regulated deficit irrigation with varying degree at different growth stages of pear-jujube tree indicated that the moderate water deficit reduced stomatal conductance and transpiration; the re-watering improved the water use efficiency because of the compensatory effect on photosynthesis and more photosynthesis product and nutrition substances transferred into the reproductive organs. Water deficit treatment at the bud-burst to leafing stage obviously suppressed the vegetative growth of pear-jujube tree and was advantageous to transfer more stored photosynthesis product and nutrition substances to the reproductive organ after the flowering stage. Water deficit reduced the fruit growth rate of pear-jujube slightly, but the re-watering had overcompensatory effect to reduce the negative influence on fruit growth. And water deficit treatments reduced water consumption and improved the WUEY of pear-jujube tree at different growth stages, especially severe water deficit at the bud-burst to leafing stage and moderate and severe water deficit at the fruit maturation stage. However, this study only investigated the effect of different water deficit treatments at different single growth stages on tree growth, fruit development and water use, but has not involved in the effect of water deficit treatments at the compound-stages and the multi-stages, more research need to be carried out in the future. Acknowledgments We are grateful to the research grants from the National Key Basic Research Program of China (973 Program, 2006CB403406); Program for Changjiang Scholars and Innovative Research Team in University in China (IRT0657) and China National Natural Science Fund (50709038, 50679081, 50869001).
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