Effect of different drip irrigation methods and fertilization on growth, physiology and water use of young apple tree

Scientia Horticulturae 129 (2011) 119–126

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Effect of different drip irrigation methods and fertilization on growth, physiology and water use of young apple tree Qiliang Yang a,b , Fucang Zhang b,∗ , Fusheng Li c,∗∗ a b c

Faculty of Modern Agricultural Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650224, China Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of Ministry of Education, Northwest A&F University, Yangling, Shaanxi 712100, China College of Agriculture, Guangxi University, Nanning, Guangxi 530005, China

a r t i c l e

i n f o

Article history: Received 8 December 2010 Received in revised form 12 March 2011 Accepted 14 March 2011 Keywords: Alternate drip irrigation Nitrogen Phosphorus Water use efficiency Root hydraulic conductance Young apple tree

a b s t r a c t A pot experiment was conducted to investigate the effect of three drip irrigation methods (i.e. conventional drip irrigation (CDI), both sides of the root-zone irrigated with full watering, alternate drip irrigation (ADI), both sides of the root-zone irrigated alternatively with half of the full watering, and fixed drip irrigation (FDI), only one side of the root-zone irrigated with half of the full watering) on growth, physiology, root hydraulic conductance and water use of young apple tree under different nitrogen (N) or phosphorus (P) fertilization (i.e. CK (no fertilization), N1 (0.2 g N/kg), N2 (0.4 g N/kg), P1 (0.2 g P2 O5 /kg) and P2 (0.4 g P2 O5 /kg)). Results show that compared to CDI, ADI and FDI reduced mean root dry mass, daily transpiration, root hydraulic conductance (Kr ), leaf photosynthesis rate, transpiration rate and stomatal conductance of young apple tree by 6.9 and 27.7, 29.3 and 45.0, 6.8 and 37.9, 2.5 and 4.8, 32.6 and 33.0, 22.1 and 22.3%, but increased leaf water use efficiency (WUE) by 31.3 and 29.8%, respectively when they saved irrigation water by 50%. Compared to the CK, N or P fertilization significantly increased Kr , and Kr was increased with the increased N or P fertilization level. There were parabolic correlations between Kr and root dry mass, daily transpiration and stomatal conductance. Our results indicate that ADI reduced transpiration rate significantly, but it did not reduce photosynthesis rate and Kr significantly, thus alternate drip irrigation improved WUE and the regulation ability of water balance in plants. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Water and nutrient stresses are two major constraints in agriculture production and lower yield in the northwest China, but there is a large cultivation area of apple tree due to ample sunlight. In recent years, irrigation demand for apple orchard is increasing to enhance yield and profit in the region (Kang and Zhang, 2004). However, irrigated fruit orchard faces with the challenge of shortage of water resources. Therefore, new irrigation methods are required to reduce both water consumption and the detrimental environmental effects of agricultural practices. Partial root-zone irrigation (PRI), including alternate PRI (APRI) and fixed PRI (FPRI) or partial root-zone drying (PRD), has been received considerable attention as a water-saving irrigation technique. APRI involves approximately half of the root system exposed to drying soil, while the remaining half is irrigated as conventional irrigation, and the wetting and drying sides of the root system are

∗ Corresponding author. Tel.: +86 29 87091151; fax: +86 29 87091151. ∗∗ Corresponding author. Tel.: +86 771 3235314 806; fax: +86 771 3235314 802. E-mail addresses: [email protected], [email protected] (F. Zhang), [email protected], [email protected] (F. Li). 0304-4238/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2011.03.019

repeatedly alternated with certain frequency. So far APRI has been tested and used in some fruit crops, e.g. pear (Kang et al., 2003), peach (Goldhamer et al., 2002), grapevine (Du et al., 2008; Loveys et al., 1998) and apple (Leib et al., 2006). Many studies indicate that APRI reduces transpiration rate significantly and maintained higher level of photosynthesis rate, which leads to the increase of leaf water use efficiency (WUE) (Kang et al., 2002; Kirda et al., 2004), and also reduces excessive vegetative growth of crops (Graterol et al., 1993). Kang et al. (2003) indicate that APRI reduces transpiration loss without significant reduction of pear yield, then increases WUE, and has a compensatory water uptake effect in the wet part of the root-zone. Goldhamer et al. (2002) indicate no significant difference between PRD and regulated deficit irrigation (RDI) in young peach trees. PRD saves irrigation water of more than 50% with significant reduction in shoot growth and improves fruit quality without significant reduction of grapevine yield (Loveys et al., 1998). Du et al. (2008) indicate that compared to conventional drip irrigation, alternate drip irrigation improves WUE by 26.7–46.4% and fruit quality of table grape without detrimental effect on the fruit yield in arid region. Caspari et al. (2004) indicate that seasonal irrigation input is reduced by 30–50% without loss in fruit size or yield after applying PRD to ‘Gala’, ‘Fuji’, and ‘Braeburn’ apples. Leib et al. (2006) show that RDI and PRD saves approximately 45–50%

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Q. Yang et al. / Scientia Horticulturae 129 (2011) 119–126

Fig. 1. Layout of three drip irrigation methods.

of irrigation water and improves without any significant impact on fruit yield and size in PRD. However, RDI reduces apple yield compared to normal irrigation in the second year. There are some reports about the effect of APRI on nutrient uptakes by root system. Skinner et al. (1999) indicate that alternate furrow irrigation successfully increases N uptake and reduces the potential for NO3 − leaching. Compared to the conventional irrigation, APRI increases total N and P uptakes and N and P use efficiencies (Hu et al., 2009; Li et al., 2007). Furthermore, root absorbing capacity in the nutrientsupplied zone is significantly increased, which may compensate nutrient uptake in the whole (Robinson, 1994). Root hydraulic conductance (Kr ) decreases with the reduced soil water content when plants suffered from water stress in soil. Kang and Zhang (1997) show that soil hydraulic conductance (Ks ), hydraulic conductance of soil–root interface (Ksr ) and Kr are reduced when soil water potential is decreased, their relationship is Ks > Ksr > Kr . Lo Gullo et al. (1998) also indicate that soil water potential, the difference of soil–root interface water potential, Ks , Ksr and Kr decrease with the reduced soil water content. North and Nobel (1991) indicate that soil drought reduces Kr due to the increase of cavitation and embolism in the xylem. Kramer and Boy (1995) indicate that poor aeration in soil decreases water uptake by root system. This is because poor aeration increases root radial hydraulic resistance, but reduces root respiration intensity and oxygen concentration in the root-zone, which leads to higher CO2 concentration in the root-zone. However, higher CO2 concentration reduces more Kr than hypoxia. North and Nobel (1991) find that soil drought reduces Kr greatly, however, at 3d after rewatering, lots of new roots are appeared, and Kr is higher than that of full watering. In recent years, Hu and Kang (2007) find that the hydraulic conductivity of maize in the non-irrigated root-zone of APRI is significantly higher than that of FPRI. However, there are few reports about effect of APRI on root hydraulic conductivity under different fertilization treatments. Nitrogen (N) and phosphorus (P) stresses lead to the change of growth, physiology and water use of plants (Lovelock et al., 2006; Radin and Matthews, 1989). Both N- and P-deficiencies restricte leaf expansion, reduced stomatal conductance, transpiration, photosynthesis and the hydraulic conductivity of the plants, but there is no significant effect on leaf water potential (Radin and Matthews, 1989). However, applying N and P fertilizers increases Kr (Lovelock et al., 2006). There are few studies about the change of root hydraulic conductivity and its relationship with the growth, photosynthesis and transpiration loss under the partial rootzone irrigation and different fertilization treatments. Therefore,

the objective of this study was to investigate the effect of partial root-zone irrigation on growth, photosynthetic physiology, root hydraulic conductivity and water use efficiency of pot-grown young apple trees under different N or P fertilization, so as to provide scientific basis in applying PRI in the orchard. 2. Materials and methods 2.1. Experimental site and materials The experiment was conducted in a greenhouse without temperature controlling equipment in Northwest A&F University in Yangling, Shaanxi, China (latitude 34◦ 18 N, longitude 108◦ 24 E, 521 m altitude) under natural light condition from March to September in 2008. During the experimental period, the photon flux density ranged from 450 to 800 ␮mol m−2 s−1 . Mean day and night temperatures were 27–15 ◦ C and relative humidity ranged from 35 to 70%. Experimental soil is alluvial soil (Fluvisols), soil pH was 8.15, organic matter content 16.9 g/kg, total N content 0.98 g/kg, total P content 0.76 g/kg, total K content 14.9 g/kg, available N content 69.8 mg/kg, available P content 10.07 mg/kg and available K content 163.30 mg/kg. Two-year-old grafted young apple trees (Malus pumila Mill, Fuji), which is the major cultivar in China, was used as experimental tree, and its rootstock is XiFu hitom (Mal us micromal us Mak). 2.2. Experimental design Three drip irrigation methods and five fertilization treatments were designed in pot experiment. This experimental plan yielded 15 treatments (i.e. 3 × 5) and each treatment was replicated nine times. The layout of three drip irrigation methods was shown in Fig. 1. Three drip irrigation methods included conventional drip irrigation (CDI, both sides of the pot respectively laying one drip line, both sides of the root-zone irrigated simultaneously at each watering), alternate drip irrigation (ADI, both sides of the pot respectively laying one drip line and repeating alternate watering, only one side of the root-zone irrigated at each watering, the other side of the root-zone irrigated at next watering) and fixed drip irrigation (FDI, fixed side of the pot laying one drip line, only one side of the root-zone irrigated at each watering). The drip system was used by the gravity (Qinchuan Irrigation, Inc., Yangling, Shanxi, China), and the emitters were pressure-compensated with flow rate of 0.5 L/h, the emitters were spaced at 40 cm down the row with polyethylene (PE) tubes (1.6 cm in external diameter). Due to smaller flow

Q. Yang et al. / Scientia Horticulturae 129 (2011) 119–126

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Table 1 Effect of different drip irrigation methods and fertilization on root hydraulic conductance (Kr ) of young apple tree. ADI, FDI and CDI represent alternate, fixed and conventional drip irrigation, respectively. Values are means ± standard errors (n = 3). Different letters in the same column indicate significant difference (P < 0.05). Analysis of variance (ANOVA) P values were shown (P < 0.05, significance; P < 0.01, markedly significance; P > 0.05, no significance). Fertilization

N1

N2

P1

P2

CK

Drip irrigation method

ADI FDI CDI ADI FDI CDI ADI FDI CDI ADI FDI CDI ADI FDI CDI

Significance test (P value) Drip irrigation method Fertilization Drip irrigation method × fertilization

rate, the lasting time was about 5 h per irrigation and the lateral water exchange was less. Five fertilization treatments included, i.e. CK (without N and P added), N1 (0.2 g N/kg), N2 (0.4 g N/kg), P1 (0.2 g P2 O5 /kg) and P2 (0.4 g P2 O5 /kg). N was supplied as urea and P applied in KH2 PO4 form. All chemical fertilizers were applied with analytical regents. The amount of KH2 PO4 was calculated based on the needed P. N and P solutions were applied to the pots assuming that fertilizers were evenly distributed in soil using watering amount according to the field capacity. This study did not consider the difference of K amount for different P treatments due to higher soil available K content. Young apple trees were transplanted to the experimental pots (30 cm in diameter at the top edge, 25 cm in diameter at the bottom, 30 cm in depth) on March 20, 2008. Each pot was filled with 15 kg soil with mean bulk density of 1.2 kg/m3 and had one young apple tree that root system was soaked in rooting powder (IBA, Indole butyric acid, Zhengzhou Sun Rain Biological Products Co., Ltd.) solution for 30 min to promote the growth of new roots before transplanting. Six holes were punched at the bottom and paved with fine sand to provide better aeration. Soil surface was paved with 1 cm thick vermiculite to prevent soil hardening from the irrigation. After 35 d for nursery, young apple trees with homogeneous growth were selected to do fertilization treatment on April 24. After fertilization treatment, three drip irrigation methods were done on May 4. Irrigation quota was 22.64 mm for CDI and 11.32 mm for ADI and FDI treatments. Irrigation date is May 4, 11, 18 and 25, June 2, 9, 14, 19, 24 and 29, July 4, 9, 14, 19 and 29, August 4 and 9. Before June 10, total irrigation times were 6, and total irrigation amount in CDI, ADI and FDI was 135.84, 67.92 and 67.92 mm, respectively. Before July 10, total irrigation times were 12, and total irrigation amount in CDI, ADI and FDI was 271.68, 135.84 and 135.84 mm, respectively. Before August 10, total irrigation times were 17, and total irrigation amount in CDI, ADI and FDI was 384.88, 192.44 and 192.44 mm, respectively.

Measurement time/yy-mm-dd (Kr × 10−6 kg s−1 Mpa−1 ) 2008-06-10

2008-07-10

2008-08-10

Mean

0.85 ± 0.03defg 0.68 ± 0.05efgh 0.98 ± 0.05cdef 1.11 ± 0.09abcde 0.81 ± 0.03fg 1.22 ± 0.07abc 1.04 ± 0.03bcdef 0.82 ± 0.01efg 1.12 ± 0.14abcd 1.29 ± 0.04ab 0.93 ± 0.02defg 1.33 ± 0.25a 0.48 ± 0.1hi 0.31 ± 0.05i 0.50 ± 0.05hi

4.29 ± 0.71efg 2.53 ± 0.71fgh 4.68 ± 0.54def 5.64 ± 0.86cde 4.24 ± 0.43efg 6.03 ± 0.43cde 7.03 ± 0.8bcde 4.45 ± 0.71defg 7.68 ± 1.14bc 9.64 ± 2.01ab 7.29 ± 0.76bcd 10.84 ± 1.62a 1.25 ± 0.24h 0.95 ± 0.26h 1.59 ± 0.09gh

6.05 ± 0.66de 2.86 ± 0.64f 6.08 ± 0.48de 7.67 ± 0.8cd 4.53 ± 0.3ef 7.89 ± 0.51cd 9.55 ± 0.16bc 5.78 ± 0.64de 10.74 ± 0.83ab 12.72 ± 0.2a 9.07 ± 0.19bc 12.95 ± 1.62a 2.38 ± 0.55f 2.05 ± 0.48f 2.52 ± 0.73f

3.73 2.02 3.92 4.81 3.19 5.04 5.88 3.69 6.51 7.88 5.76 8.38 1.37 1.10 1.54

<0.001 <0.001 0.928

0.001 <0.001 0.870

<0.001 <0.001 0.490

sure flow meter (HPFM, Dynamax) according to the method of quasi-steady state (Tyree et al., 1998). The shoots were excised at about 30 mm above the soil, and excised part was levelled with a knife. The HPFM was connected with an Omnifit connector to the base of the excised root system. In this case, the pressure applied to the stem is maintained constant at P = 0.4 MPa till a stable flow is recorded. Kr was measured on June 10, July 10 and August 10, i.e. 47th, 57th and 67th days after the fertilization treatment. Each treatment was replicated three times. 2.3.2. Leaf photosynthetic rate, transpiration rate and stomatal conductance On the 22th, 40th and 62th day after different treatments, leaf photosynthetic rate (Pn ), transpiration rate (Tr ) and stomatal conductance (Gs ) were measured using a LI-6400 portable photosynthesis device (LI-6400, Li-Cor, Lincoln, Nebraska, USA). Each treatment was replicated three times. 2.3.3. Dry mass After measuring the root hydraulic conductance, roots and shoots were harvested separately. Plant material was firstly dried at 105 ◦ C for 30 min, and then dried at 70 ◦ C to constant weight. Each treatment was replicated three times. 2.3.4. Daily transpiration and evapotranspiration Daily transpiration and evapotranspiration of young apple tree were determined by weighting. At 7:00 a.m. the pots were weighted every day during the experimental period. Experimental pots were sealed using plastic sheet and adhesive tape on July 19–25 to measure daily transpiration, only the daily transpiration on 24 July, i.e. the 15th day after watering was shown. 2.4. Statistical analysis

2.3. Measurements 2.3.1. Root hydraulic conductance In order to maintain the same environment condition, all young apple trees were moved to the laboratory before measuring root hydraulic conductance (Kr ). The Kr was measured using high pres-

Analysis of variance (ANOVA) was performed using two-way ANOVA from SAS software. All the treatment means were compared for any significant differences using the Duncan’s multiple range tests at significant level of P0.05 with the SAS for Windows software package.

<0.001 0.902 0.989 0.996 0.543 0.999 <0.001 0.124 <0.001 0.898 <0.001 0.427 0.046 0.999 0.005 0.998

0.013 0.999 <0.001 0.840 <0.001 0.832

<0.001

<0.001 0.13 0.281

<0.001

<0.001

<0.001

<0.001

<0.001

<0.001

<0.001

3.72 ± 0.32ab 3.49 ± 0.16bc 2.67 ± 0.1de 4.32 ± 0.23a 4.18 ± 0.25a 2.92 ± 0.07cd 3.09 ± 0.15bcd 3.1 ± 0.15bcd 2.12 ± 0.17ef 4.25 ± 0.46a 4.27 ± 0.11a 2.89 ± 0.21cd 2.88 ± 0.33cd 3.03 ± 0.03bcd 1.96 ± 0.11f 2.81 ± 0.24a 2.89 ± 0.17a 1.98 ± 0.13b 2.81 ± 0.21a 2.77 ± 0.21a 2.01 ± 0.15b 3.0 ± 0.32a 2.82 ± 0.23a 1.89 ± 0.15b 2.86 ± 0.19a 2.75 ± 0.19a 2.03 ± 0.11b 2.85 ± 0.19a 2.75 ± 0.34a 1.86 ± 0.14b

2009-6-3 2009-5-16

1.77 ± 0.13abc 1.72 ± 0.17abcd 1.23 ± 0.1d 1.96 ± 0.09a 1.92 ± 0.14a 1.47 ± 0.15abcd 2.0 ± 0.21a 1.9 ± 0.24a 1.36 ± 0.18bcd 1.97 ± 0.08a 1.86 ± 0.04ab 1.37 ± 0.13bcd 1.99 ± 0.08a 1.95 ± 0.31aa 1.3 ± 0.08cd 93.67 ± 0.88e 95.0 ± 1.53e 136.67 ± 2.40abc 111.67 ± 2.60d 107.33 ± 5.84d 141.67 ± 0.88a 86.67 ± 3.53ef 88.67 ± 2.33e 130.33 ± 4.10bc 108.33 ± 2.33d 105.67 ± 3.28d 140.33 ± 3.18ab 75.0 ± 2.65g 77.0 ± 4.93fg 126.67 ± 6.33c

2009-6-25 2009-6-3

78.33 ± 0.67cd 74.33 ± 2.60d 90.0 ± 2.65a 80.33 ± 0.88cd 80.67 ± 1.76cd 93.67 ± 1.20a 75.0 ± 1.73d 74.33 ± 2.33d 88.0 ± 3.06ab 83.33 ± 0.88bc 79.33 ± 2.03cd 93.67 ± 2.91a 65.0 ± 1.00e 64.67 ± 0.33e 80.67 ± 2.73cd 63.0 ± 1.15ef 63.0 ± 1.15ef 80.0 ± 4.04ab 67.33 ± 1.76de 72.0 ± 2.53bcd 83.67 ± 2.91a 61.67 ± 2.33ef 62.67 ± 1.20ef 76.0 ± 2.08abc 67.33 ± 1.76de 69.67 ± 1.45cde 83.0 ± 6.43a 57.67 ± 1.76f 57.0 ± 2.31f 63.0 ± 1.15ef

2009-5-16 2009-6-25 2009-6-3

2.68 ± 0.25b 2.67 ± 0.09b 4.05 ± 0.22a 2.78 ± 0.16b 2.79 ± 0.14b 4.09 ± 0.09a 2.57 ± 0.20b 2.53 ± 0.08b 3.85 ± 0.22a 2.66 ± 0.23b 2.58 ± 0.09b 3.87 ± 0.1a 2.47 ± 0.22b 2.26 ± 0.01b 3.77 ± 0.17a 9.8 ± 0.1bc 9.33 ± 0.55c 10.8 ± 0.65ab 11.97 ± 0.27a 11.6 ± 0.46a 11.93 ± 0.28a 7.9 ± 0.35d 7.87 ± 0.5d 8.07 ± 0.23d 11.1 ± 0.38a 11.03 ± 0.33ab 11.17 ± 0.62a 6.97 ± 0.18d 6.87 ± 0.09d 7.4 ± 0.53d

2.51 ± 0.12bc 2.53 ± 0.18bc 3.59 ± 0.21a 2.6 ± 0.16b 2.6 ± 0.17b 3.84 ± 0.19a 2.44 ± 0.16bc 2.46 ± 0.14bc 3.6 ± 0.22a 2.55 ± 0.11bc 2.62 ± 0.2b 3.75 ± 0.2a 2.06 ± 0.16bc 2.0 ± 0.19c 3.33 ± 0.19a

2009-5-16

7.23 ± 0.33ab 7.27 ± 0.2ab 7.13 ± 0.12ab 7.57 ± 0.19ab 7.43 ± 0.28ab 7.77 ± 0.19a 7.07 ± 0.09b 7.07 ± 0.3b 7.0 ± 0.23b 7.67 ± 0.15ab 7.3 ± 0.12ab 7.77 ± 0.07a 6.03 ± 0.17c 5.8 ± 0.21c 6.2 ± 0.15c

2009-6-25 2009-6-3

4.43 ± 0.34bcd 4.3 ± 0.12bcd 4.37 ± 0.12bcd 5.07 ± 0.09ab 4.93 ± 0.03abc 5.6 ± 0.49a 4.8 ± 0.21abc 4.67 ± 0.57bcd 4.83 ± 0.37abc 5.0 ± 0.12ab 4.87 ± 0.29abc 5.1 ± 0.21ab 4.07 ± 0.15cd 3.8 ± 0.25d 4.3 ± 0.10bcd

2.6 ± 0.19b 2.53 ± 0.17b 3.63 ± 0.19a 2.72 ± 0.18b 2.71 ± 0.21b 3.89 ± 0.22a 2.4 ± 0.22b 2.53 ± 0.18b 3.73 ± 0.2a 2.71 ± 0.21b 2.68 ± 0.21b 3.85 ± 0.22a 2.14 ± 0.19b 2.15 ± 0.18b 3.37 ± 0.18a

WUE (␮mol mmol−1 )

2009-5-16

ADI FDI CDI ADI N2 FDI CDI ADI P1 FDI CDI ADI P2 FDI CDI ADI CK FDI CDI Significance test (P values) Drip irrigation 0.189 method Fertilization <0.001 0.937 Drip irrigation method × fertilization

As shown in Fig. 2, there was significant effect of drip irrigation method and fertilization treatment on root and total dry masses of young apple tree (P < 0.05), and the interaction of drip irrigation method and fertilization treatment had significant effect on root dry mass (P < 0.05). Under the same fertilization treatment, compared to the CDI, ADI and FDI reduced mean root and total dry masses by 6.9 and 27.7, 21.8 and 34.8%, respectively. Under the same drip irrigation method, compared to CK, P and N fertilization increased mean root dry mass by 19.0–47.0 and 14.8–42.9%, and total dry masses by 17.2–30.3 and 18.0–40.9%, respectively, showing that P or N fertilization increased root and total dry masses, and P fertilization had higher effect on root dry mass than N fertilization, but N fertilization had higher effect on total dry mass than P fertilization. Compared to CK treatment, P1 and P2 increased root dry mass by 10.0–40.0 and 28.0–55.0%, and total dry mass by 8.0–19.0 and 26.0–41.0%, N1 and N2 increased

N1

3.3. Effect of different drip irrigation methods and fertilization on dry mass accumulation of young apple tree

Gs (m mol m−2 s−1 )

There are no significant effect of drip irrigation method on photosynthesis rate (Pn ), fertilization treatment on leaf water use efficiency (WUE) on May 16 and June 3, and the interaction of drip irrigation method and fertilization treatment on leaf Pn , transpiration rate (Tr ), stomatal conductance (Gs ) and WUE, however, there were significant effects of others treatments on leaf Pn , transpiration rate (Tr ), stomatal conductance (Gs ) and WUE (Table 2). Under the same fertilization treatment, compared to the CDI, ADI and FDI reduced mean Pn , Tr , Gs by 2.5 and 4.8, 32.6 and 33, 22.1 and 22.3%, but increased mean WUE by 31.3 and 29.8%, respectively. Under the same drip irrigation method, compared to CK, P and N fertilization increased mean Pn , Tr , Gs and WUE by times of 1.23–1.30 and 1.33–1.36, 1.08–1.20 and 1.10–1.23, 1.13–1.22 and 1.16–1.25, 1.09–1.14 and 1.11–1.19, respectively, indicating that P and N fertilization increased leaf Pn , Tr , Gs and WUE, and N fertilization had higher effect than P fertilization. Compared to CK, P1 and P2 increased leaf Pn , Tr , Gs and WUE by times of 1.11–1.19 and 1.34–1.41, 1.07–1.17 and 1.09–1.23, 1.09–1.14 and 1.17–1.31, 1.01–1.05 and 1.15–1.23, respectively; N1 and N2 by times of 1.24–1.27 and 1.41–1.45, 1.08–1.21 and 1.13–1.26, 1.13–1.19 and 1.18–1.31, 1.05–1.15 and 1.15–1.25, respectively, illustrating that leaf Pn , Tr , Gs and WUE were increased with the increased P or N level.

Tr (m mol m−2 s−1 )

3.2. Effect of different drip irrigation methods and fertilization on leaf physiology of young apple tree

Pn (␮mol m−2 s−1 )

As shown in Table 1, there was a significant effect of drip irrigation method and fertilization treatment on root hydraulic conductance (Kr ) of young apple tree. Under the same fertilization treatment, compared to the CDI, ADI and FDI reduced Kr by 6.8 and 37.9%, respectively, when they reduced irrigation water by 50%. Under the same drip irrigation method, compared to CK (no fertilization), P and N fertilization increased mean Kr by times of 4.27–5.02 and 2.36–3.11, respectively, indicating that P and N fertilization increased Kr , and P fertilization had higher effect than N fertilization. Compared to CK, P1 and P2 increased mean Kr by times of 3.34–4.29 and 5.22–5.76, and N1 and N2 by times of 1.83–2.73 and 2.89–3.51, respectively, indicating that Kr was increased with increased P or N level.

Drip irrigation method

3.1. Effect of different drip irrigation methods and fertilization on root hydraulic conductance of young apple tree

Fertilization

3. Results

2009-6-25

Q. Yang et al. / Scientia Horticulturae 129 (2011) 119–126 Table 2 Effect of different drip irrigation methods and fertilization on leaf photosynthetic rate (Pn ), transpiration rate (Tr ), stomatal conductance (Gs ) and water use efficiency (WUE) of young apple tree. ADI, FDI and CDI represent alternate, fixed and conventional drip irrigation, respectively. Values are means ± standard errors (n = 3). Different letters in the same column indicate significant difference (P < 0.05). Analysis of variance (ANOVA) P values were shown (P < 0.05, significance; P < 0.01, markedly significance; P > 0.05, no significance).

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Q. Yang et al. / Scientia Horticulturae 129 (2011) 119–126

123

Fig. 2. Effect of different drip irrigation methods and fertilization on roots (a) and total dry masses (b) of young apple tree. ADI, FDI and CDI represent alternate, fixed and conventional drip irrigation, respectively. Values are means ± standard errors (n = 3). Different letters in the same column indicate significant difference (P < 0.05). Analysis of variance (ANOVA) P values were shown (P < 0.05, significance; P < 0.01, markedly significance; P > 0.05, no significance).

root dry mass by 6.0–37.0 and 24.0–50.0%, and total dry mass by 9.0–34.0 and 23.0–48.0%, respectively, indicating that root and total dry masses were increased with the increased P or N level. 3.4. Effect of different drip irrigation methods and fertilization on water use of young apple tree There was significant effect of drip irrigation method and fertilization treatment on daily transpiration and evapotranspiration of young apple tree (Fig. 3). Under the same fertilization treatment, compared to the CDI, ADI and FDI reduced daily transpiration by 29.3 and 45.0%, and evapotranspiration by 22.6 and 35.8%, respectively. Under the same drip irrigation method, compared to CK, P and N fertilization increased daily transpiration by 21.3–61 and 31.8–87.7%, and daily evapotranspiration by 7.2–20.4 and 13.8–25.8%, respectively, indicating that P and N fertilization increased daily transpiration and evapotranspiration of young apple tree, and N fertilization had higher effect on daily transpiration and evapotranspiration than P fertilization. Compared to CK, P1 and P2 increased daily transpiration by 7.0–45.0 and 35.0–77.0%, and daily evapotranspiration by 3.0–18.0 and 12.0–27.0%, respectively. N1 and N2 increased daily transpiration by 17.0–83.0 and 47.0–93.0%, and daily evapotranspiration by 16.0–23.0% and 11.0–29.0%, respectively, indicating that daily transpiration and evapotranspiration were increased with the increasing of P or N level.

3.5. Correlations between root hydraulic conductance and root dry mass, daily transpiration and stomatal conductance Fig. 4 shows the correlations between Kr and root dry mass (Fig. 4a-P and a-N), daily transpiration (Fig. 4b-P and b-N) and stomatal conductance (Fig. 4c-P and c-N) under N or P fertilization. As shown in Fig. 4, the Kr was increased with increasing root dry mass, daily transpiration and stomatal conductance, and there were parabolic correlations between Kr and root dry mass, daily transpiration and stomatal conductance under different drip irrigation methods and fertilization treatments. 4. Discussion 4.1. Effect of different drip irrigation methods and fertilization on root hydraulic conductance Root hydraulic conductivity (Kr ) is an index to indicate the capacity of water uptake and transmission and is affected by soil water content. In this study, compared to CDI, ADI did not decrease Kr significantly, but FDI reduced it markedly (Table 1). There are several reasons about insignificant reduction of Kr for ADI. (1) Partial root-zone irrigation has compensatory effect of water uptake from the wetting part of the root-zone (Hu and Kang, 2007; Kang et al., 2003). As the wetting and drying sides of the root system in ADI treatment were repeatedly alternated in a frequency, rewetting after soil drought for some days increased the growth of new lateral

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Fig. 3. Daily transpiration (a) and evapotranspiration (b) of young apple tree under different drip irrigation methods and fertilization treatments. ADI, FDI and CDI represent alternate, fixed and conventional drip irrigation, respectively. Values are means ± standard errors (n = 3). Different letters in the same column indicate significant difference (P < 0.05). Analysis of variance (ANOVA) P values were shown (P < 0.05, significance; P < 0.01, markedly significance; P > 0.05, no significance).

roots, which increased the radial conductivity of the tissues outside the vascular cylinder (North and Nobel, 1996) and aquaporin activity in the immature distal region (where an endodermis is present) in favour of increased root hydraulic conductivity (Martre et al., 2001). Other studies also suggest that aquaporin activity is often up-regulated under the conditions of moderate water stress, which may regulate root hydraulic conductivity (Kirch et al., 2000). The root aquaporins as a valve may help limit water loss when the soil water potential is lower than that of the root, and then it may help take up more water under adverse conditions (Steudle, 2000). Martre et al. (2001) find that it may help take up more water under the conditions of heterogeneous soil moisture prevailing in its native habitat. Thus the rewetting after drought may help take up more water (Häussling et al., 1988), and its root hydraulic conductance is higher than that of full watering (Hu and Kang, 2007; North and Nobel, 1991). (2) Water moves from root surface to root xylem through a series of tissues, then enters the connection part of lateral and main roots, thus it promotes water uptake (McCully and Canny, 1988). Ekanayake et al. (1985) indicate that the relationship between root numbers and Kr was positive. Due to increased root numbers (Liang et al., 2000; Sepaskhah and Kamgar-Haghighi, 1997) and the nodes between lateral and main roots (McCully and Canny, 1988), thus ADI treatment also did not decrease Kr of young apple tree significantly. (3) The drying side of the root system in ADI yielding ABA enhanced Kr (Hose et al., 2000). Additionally, higher soil aeration (Kang and Cai, 2002) and temperature in the root-zone of ADI treatment (Monteith and Unsworth, 2007) also may help enhance Kr (Clarkson et al., 2000a; Kramer and Boy, 1995), as a result, ADI treatment did not markedly reduce the Kr of young apple tree.

Although FDI treatment also enhanced soil temperature in the root-zone and ABA content resulted from the drying side of the root system, FDI treatment reduced the Kr of young apple tree markedly. Because FDI treatment constantly kept half of the root system exposed to drying soil, the hydraulic resistance of soil–root interface increased and roots started shrinking. As a result, on the one hand, the root density of drying root-zone is reduced and root growth slows down, senesces and even dies (Kang and Cai, 2002), on the other hand, the hydraulic resistance of xylem and xylem embolism is increased (North and Nobel, 1991), meanwhile, soil drought increases the cavitation of xylem that decreases axial hydraulic conductivity (Sperry et al., 2002), thus FDI treatment decreases the Kr of young apple tree markedly. In addition, in this study, the Kr decreased with the advance of the growth (June, July and August) under three drip irrigation methods, which is in agreement with the result of Quercus pubescens in May and August (Nardini et al., 1998). N and P deficiencies reduce the Kr , and then decrease transpiration rate, stomatal conductance and photosynthetic rate (Clarkson et al., 2000b; Trubat et al., 2006). Our study also shows that applied N and P fertilizers increased the Kr when compared to no fertilization treatment. On the one hand, when a plant is subjected to nutrient stress, alteration in the aquaporins slows the movement of water through the plant, resulting in the reduction of Kr (Shaw et al., 2002). On the other hand, mineral nutrient deficiency (e.g. N or P) may inhibit the aquaporine activity that reduced the Kr (Clarkson et al., 2000b). In this study, P fertilization increased more Kr of young apple tree than N fertilization, which is similar to some previous reports (Lovelock et al., 2006; Trubat et al., 2006).

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Fig. 4. Relationship between root hydraulic conductance (Kr ) and root dry mass (a), daily transpiration (b), and leaf stomatal conductance (Gs ) (c). P and N mean P and P fertilization, respectively.

4.2. Effect of different drip irrigation methods and fertilization on leaf physiology, dry mass accumulation and water use Partial root-zone irrigation may substantially reduce water loss but has little effect on photosynthesis rate (Kang and Zhang, 2004). Our study shows that ADI and FDI did not significantly reduce leaf photosynthetic rate (Pn ) (Table 2), but had significant effect on stomatal conductance (Gs ) and transpiration rate (Tr ) (Table 2 and Fig. 3a) at 22th, 40th and 60th days after different fertilization treatments. Additionally, because ADI and FDI only kept half of the root system exposed to wetting soil, they significantly reduced soil surface evaporation and the evapotranspiration (Fig. 3b), which led to the increased water use efficiency (WUE) (Table 2). Our results are in agreement with previous findings from PRD experiments on fruit trees (Kang et al., 2002; Spreer et al., 2007). Compared to no fertilization, applied N and P fertilizers increased leaf Pn , Tr and Gs . Due to higher increase of Pn than Tr under N and P fertilization, leaf WUE was increased, which is in agreement with previous findings (Radin and Matthews, 1989; Xue and Chen, 1990; Zhang and Li, 1996).

This study shows that compared to CDI, ADI reduced root and total dry masses of young apple tree by 6.9% and 21.8%, respectively, when ADI saved irrigation water by 50%, so ADI increased WUE, which is in agreement with previous findings (Kang and Cai, 2002; Li et al., 2007). ADI and FDI had the same irrigation quota, but FDI significantly reduced root and total dry masses when compared to ADI. The possible reason is that FDI constantly kept half of the root system exposed to drying soil, thus it significantly affects the growth of roots and canopy (Kang et al., 2002). 4.3. Correlations between root hydraulic conductance and root dry mass, daily transpiration and stomatal conductance This study shows that the Kr increased with the increasing root dry mass, daily transpiration and stomatal conductance under different drip irrigation methods and fertilization treatments, but the Kr decreased when root dry mass, daily transpiration and stomatal conductance increased to a certain value (Fig. 4a–c), which is related to daily and seasonal changes of root growth, root hydraulic conductivity and stomata (Clarkson et al., 2000b; Hubbard et al.,

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1999; Yang and Tyree, 1993). The Kr changed with root development and increased with aquaporin activity in the immature roots (Martre et al., 2001; Melchior and Steudle, 1993). During the root vigorous growth stage, higher growth rate of new roots increased Kr . Although the root dry mass increased with the growth stage, the Kr firstly increased, then decreased. Running (1980) indicates that the greatest water uptake rate by root system does not occur during the maximum transpiration rate and stomatal conductance but during the reducing process of transpiration rate and stomatal conductance, which may be the lagging effect (hysteresis) caused by the roots. Kramer and Boy (1995) indicates that the lagging effect is caused by water capacity resulted from root parenchyma cells. 5. Conclusions Compared to conventional drip irrigation, alternate drip irrigation (ADI) reduced root hydraulic conductance, root dry mass and daily transpiration of young apple tree by 6.8, 6.9 and 29.3%, but increased water use efficiency by 31.3% when it saved irrigation water by 50%. Thus ADI improved root water uptake and transport efficiency of young apple tree and the regulation ability of water balance in plants. Acknowledgments We are grateful for the grant support from financial support from the Chinese National Natural Science Fund (50579066, 50879073, 50869001, 51009073) and Yunnan Province Natural Science Fund (2010ZC042). References Caspari, H., Neal, S., Alspach, P., 2004. Partial rootzone drying—a new deficit irrigation strategy for apple? Acta Hort. 646, 93–100. Clarkson, D., Carvajal, M., Henzler, T., Waterhouse, R., Smyth, A., Cooke, D., Cochard, H., Martin, R., Gross, P., 2000a. Temperature effects on hydraulic conductance and water relation of Quercus robur L. J. Exp. Bot. 51, 1255–1259. Clarkson, D., Carvajal, M., Henzler, T., Waterhouse, R., Smyth, A., Cooke, D., 2000b. Root hydraulic conductance: daily aquaporin expression and the effects of nutrient stress. J. Exp. Bot. 51, 61–70. Du, T., Kang, S., Zhang, J., Li, F., Yan, B., 2008. Water use efficiency and fruit quality of table grape under alternate partial root-zone drip irrigation. Agric. Water Manage. 95 (6), 659–668. Ekanayake, I., O’ Toole, J., Garrity, D., 1985. Inheritance of root characters and their relations to drought resistance in rice. Crop Sci. 25, 927–933. Goldhamer, D., Salinas, M., Crisosto, C., Day, K., Soler, M., Moriana, A., 2002. Effects of regulated deficit irrigation and partial root zone drying on late harvest peach tree performance. Acta Hort. 592, 345–350. Graterol, Y., van, E., Eisenhauer, D., Elmore, R., 1993. Alternate-furrow irrigation for soybean production. Agric. Water Manage. 24, 133–145. Häussling, M., Jorns, C., Lehmbecker, G., Hecht-Buchholz, C., Marschner, H., 1988. Ion and water uptake in relation to root development in Norway spruce (Picea abies (L.) Karst.). J. Plant Physiol. 133, 486–491. Hose, E., Steudle, E., Hartung, W., 2000. Abscisic acid and hydraulic conductivity of maize roots: a study using cell- and root-pressure probes. Planta 211, 874– 882. Hu, T., Kang, S., Li, F., Zhang, J., 2009. Effects of partial root-zone irrigation on the nitrogen absorption and utilization of maize. Agric. Water Manage. 96, 208–214. Hu, T., Kang, S., 2007. Effects of localized irrigation model on hydraulic conductivity in soil–root system for different root-zones of maize. Trans. CSAE 23 (2), 11–16 (in Chinese with English abstract). Hubbard, R., Bond, B., Ryan, M., 1999. Evidence that hydraulic conductance limits photosynthesis in old Pinus ponderosa trees. Tree Physiol. 111, 413–417. Kang, S., Zhang, J., 2004. Controlled alternate partial rootzone irrigation: its physiological consequences and impact on water use efficiency. J. Exp. Bot. 55 (407), 2437–2446. Kang, S., Hu, X., Jerie, P., Zhang, J., 2003. The effects of partial rootzone drying on root, trunk sap flow and water balance in an irrigated pear (Pyrus communis L.) orchard. J. Hydrol. 280, 192–206. Kang, S., Zhang, J., 1997. Hydraulic conductivities in soil–root system and relative importance at different soil water potential and temperature. Trans. CSAE 2, 76–81 (in Chinese with English abstract).

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