Effects of arbuscular mycorrhizal fungi on the growth ...

Journal of Plant Nutrition

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Effects of arbuscular mycorrhizal fungi on the growth and zinc uptake of trifoliate orange (Poncirus trifoliata) seedlings grown in low-zinc soil Ying Y. Chen, Cheng Y. Hu & Jia X. Xiao To cite this article: Ying Y. Chen, Cheng Y. Hu & Jia X. Xiao (2017) Effects of arbuscular mycorrhizal fungi on the growth and zinc uptake of trifoliate orange (Poncirus trifoliata) seedlings grown in low-zinc soil, Journal of Plant Nutrition, 40:3, 324-331, DOI: 10.1080/01904167.2016.1240192 To link to this article: http://dx.doi.org/10.1080/01904167.2016.1240192

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Date: 28 February 2017, At: 02:23

JOURNAL OF PLANT NUTRITION 2017, VOL. 40, NO. 3, 324–331 http://dx.doi.org/10.1080/01904167.2016.1240192

Effects of arbuscular mycorrhizal fungi on the growth and zinc uptake of trifoliate orange (Poncirus trifoliata) seedlings grown in low-zinc soil Ying Y. Chen, Cheng Y. Hu, and Jia X. Xiao Key Laboratory for the Conservation and Utilization of Important Biological Resources, Anhui Province, College of Life Sciences, Anhui Normal University, Wuhu, China

ABSTRACT

ARTICLE HISTORY

The effects of the arbuscular mycorrhizal (AM) fungi, Glomus intraradices and G. versiforme, on growth and zinc (Zn) uptake were investigated in trifoliate orange (Poncirus trifoliata) seedlings exposed to low-Zn soil. Low-Zn decreased growth, levels of leaf chlorophyll, soluble protein and sugar, and soil enzymatic activities, and pH in 0–2 cm rhizosphere soil. Low-Zn soil also decreased mineral nutrients (including Zn) concentrations in the shoots and roots. Glomus intraradices especially, significantly enhanced plant biomass, leaf soluble protein and sugar concentrations, root viability, acid phosphatase, catalase, invertase and urease activities, and easily extractable glomalin content in 0–2 cm and 2–4 cm rhizosphere soil. It also increased concentrations of Zn, phosphorus, potassium and magnesium in the shoots and roots, while decreased the soil pH. Arbuscular mycorrhizal fungi, especially G. intraradices, has the potential to improve growth and Zn uptake of triofoliate orange seedlings grown in low-Zn soil.

Received 7 July 2014 Accepted 16 September 2015 KEYWORDS

arbuscular mycorrhizae; Poncirus trifoliata; low-Zn; mineral nutrient; soil enzyme

Introduction Zinc (Zn) is an essential micronutrient required for the normal growth and development of higher plants. Zn deficiency appears to be the most widespread and frequent micronutrient deficiency problems in crops reviewed by Broadley et al. (2007) and Alloway (2008). In China, it is estimated that 51.1% of farmland is potentially Zn deficient (Liu 1996). Additionally, 58.1% of the soils from 446 citrus orchards in southern Jiangxi province were rated as low-Zn (Ling et al. 2012; Xing et al. 2013). Thus, understanding the mechanism by which plants acquire and use Zn is a high priority. Arbuscular mycorrhizal (AM) symbiosis is a mutualistic association between AM fungi and the roots of most terrestrial plants. It is recognized that AM symbiosis plays an important role in tolerance against environmental stress and improving plant nutrients owing to the uptake of nutrients via the mycorrhizal pathway and to the indirect effects of morphological and physiological changes to the roots (Khalil et al. 2011; Mohandas 2012; Nzanza, Marais, and Soundy 2012; Cavagnaro 2008). AM fungi may also influence nutrient availability via their effects on the soil’s physicochemical properties (Li and Christie 2001), nutrient cycling (Jackson, Burger, and Cavagnaro 2008) and microbial communities in rhizosphere (Cavagnaro et al. 2007). Several studies have clearly shown that Zn uptake via mycorrhizae is important for the alleviation of Zn-deficient symptoms in wheat (Ryan and Angus 2003) and maize (Kothari, Marschner, and Romheld 1991; Subramanian et al. 2011). Nevertheless,

CONTACT Jia X. Xiao [email protected] Key Laboratory for the Conservation and Utilization of Important Biological Resources, Anhui Province, College of Life Sciences, Anhui Normal University, Wuhu 241000, China. © 2017 Taylor & Francis Group, LLC

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very few investigations have addressed the response of woody plants, such as citrus, one of the most important horticultural crops in the world, to AM inoculation under Zn-poor conditions. Trifoliate orange (Poncirus trifoliata) is used as the main rootstock in most citrus producing areas in China, but Poncirus trifoliata has short or even rare root hairs in field systems, and is thus dependent on AM fungi for optimal growth (Wu and Xia 2006; Wang et al. 2012). The potential of AM fungi to enhance citrus growth, plant transpiration, root hydraulic conductivity and photosynthesis has been documented (Wu and Xia 2006; Khalil et al. 2011). Under low-Zn soil, AM fungi can improve Zn nutrition in maize plants (Cavagnaro, Dickson, and Smith 2010). Under high-Zn conditions, colonization of roots by AM fungi can result in reduced accumulation of Zn in maize or citrus plants tissues (Cavagnaro, Dickson, and Smith 2010; Yang et al. 2011). However, under Zn-poor conditions, the effects of AM fungi on the growth and Zn uptake of trifoliate orange plants are not well understood. There is insufficient information on the responses of the citrus rootstock to AM fungal colonization when exposed to a Zn deficiency. Therefore, the aim of this study is to evaluate the effects of mycorrhization by G. intraradices or G. versiforme on the trifoliate orange seedlings under Zn-poor conditions. Comparisons in plant growth, mineral nutrients including Zn in various plant parts, as well as enzymatic activities and pH value in rhizosphere soil, were investigated.

Materials and methods Plant culture and experimental procedure Trifoliate orange (Poncirus trifoliata) seedlings growing in sterile soil with uniform stem diameter (0.20–0.22 cm) and height (0.15–0.17 m) were selected. The seedlings were transplanted into root bags containing autoclaved experiment mixture (0.11 MPa, 121 C, 2 h) of clay loam, quartz sand and vermiculite (3:1:1, v/v/v): pH value 6.85, organic matter 13.8 g¢kg¡1, total nitrogen (N) 0.24 g¢kg¡1, ammonium acetate (NH4OAc)-potassium (K) 17.18 mg¢kg¡1, sodium bicarbonate (NaHCO3)-phosphorus (P) 10.5 mg¢kg¡1, NH4OAc -calcium (Ca) 356.18 mg¢kg¡1, NH4OAc-magnesium (Mg) 11.25 mg¢kg¡1, diethylene triamine pentaacetic acid (DTPA)-Zn 0.32 mg¢kg¡1, DTPA-copper (Cu) 0.112 mg¢kg¡1. The clay loam classified as Carbonati-Udic Argosols was taken from the surface layer (0–30 cm) after removing upper vegetation of the Experimental Sample Garden, Anhui Normal University (Wuhu, China). The root bags were 4 cm in diameter and 14 cm in depth, made with 32 mm nylon mesh screen. The experimental soil mixture range in horizon was separated into 0–2 cm and 2–4 cm away from the citrus taproot by the nylon bags. The mycorrhizal inoculum, provided by Institute of Plant Nutrition and Resources in the Beijing Academy of Agriculture and Forestry Sciences, consisted of spores, soil, hyphae and infected jowar root fragments from a stock culture of Glomus intraradices (No. BGC AH01), and G. versiforme (No. BGC HUN02B), and propagated on maize and white clover plants grown in a sandy soil for 12 weeks. The inoculated dosage was 20 g of inoculum per root bag containing »240 spores. The inocula were placed 5 cm below roots at transplantation time, non-AM treatment received the same weight of autoclaved mixture. According to the standards for classifying the soil nutrient status of citrus orchard (Zhuang 1994; Tang et al. 2013), the experiment soil mixture had extremely low levels of available zinc, copper potassium, magnesium, phosphorus and calcium (Zn, Cu, K, Mg, P and Ca). To maintain the nutrient supply, the seedlings were supplied with 1/2 Hoagland’s No.2 nutrient solution, in which the macronutrients were supplied at half strength, and micronutrients at full strength, except Zn, which supplied at two concentrations (0 and 0.05 mg¢L¡1) every 20 days. Treatments with 0 mg¢L¡1 and 0.05 mg¢L¡1 Zn represented Zn-poor (ZP) and Zn-rich (ZR) conditions, respectively. The modified Zn-free full strength nutrient solution contained 4 mmol¢L¡1 calcium nitrate tetrahydrate (Ca(NO3)2¢4H2O), 6 mmol¢L¡1 potassium nitrate (KNO3), 1 mmol¢L¡1 ammonium phosphate monobasic (NH4H2PO4), 2 mmol¢L¡1 magnesium sulfate heptahydrate (MgSO4¢7H2O), 46 mmol¢L¡1 boric acid (H3BO3), 9 mmol¢L¡1 manganese(ii) chloride tetrahydrate (MnCl2¢4H2O), 0.3 mmol¢L¡1 copper (II) sulfate pentahydrate (CuSO4¢5H2O), 0.1 mmol¢L¡1 molybdic acid (H2MoO4) and 50 mmol¢L¡1 ferric ethylenediaminetetraacetic acid (Fe-EDTA).

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Each pot loaded with three root bags was placed in a greenhouse for 5 months with natural daylight from May to September, the average day/night temperature was 25/20 C, average air relative humidity was 80%. The site is located at 31 200 N latitude, 119 210 E longitude, at a 10 m above sea level.

Plant and soil analyses At harvest time, plant height and taproot length were determined by a measuring tape, leaf area was determined by the Handheld Laser Leaf Area Meter (CI-203). Part fresh plants were oven dried at 75 C for 48 h to record plant dry weight. A fraction of fresh roots were carefully washed and cut into 1 cm root pieces to fix in formalin-acetic acid-alcohol solutions, these roots were cleared with 10% (w/ v) potassium hydroxide (KOH) and stained with 0.05% (w/v) trypan blue in lactophenol for mycorrhizal colonization determination (Phillips and Hayman 1970). Mycorrhizal dependency percentage was calculated as follows: Mycorrhizal dependency percentage (%) D 100£dry weight per AM-infected plant / dry weight per non-AM infected plant (Graham and Syvertsen 1985). Leaf chlorophyll and soluble sugar concentrations and root viability were measured according to Wang (2006). Soluble protein was found out by Bradford’s procedure using bovine serum albumin as the standard (Bradford 1976). Phenol sodium colorimetry was used to determine soil urease, and defined as millgram of ammonium (NH3-N) in 1 g air-dried soil for 24 h, soil acid phosphatase was extracted by the sodium acetate buffer (pH 5.0), and its activity was determined using spectrophotometry, and defined as milligram of phenol consumption in 1 g air-dried soil for 12 h (Zhou 1987). Titration was used to determine invertase, and defined as milligram of Na2S2O3 consumption in 1 g air-dried soil for 24 h under 37 C, soil catalase (CAT) activity was defined as the consumption of potassium permanganate (KMnO4) (0.1 mol¢L¡1) for 1 min in 1 g air-dried soil (Zhou 1987). Easily extractable glomalin (EEG) in soils were determined with the method of Wright and Upadhyay (1996), soil pH was determined in a 1:2.5 (w/v) soil/water suspension (Zhou 1987). The dried shoots and roots were ground to fine powder and wet digested in nitric acid-perchloric acid (HNO3-HClO4) (4:1 v/v) before analysis of zinc, phosphorus, potassium and magnesium (Zn, P, K and Mg) by inductively coupled plasma optical emission spectrometry (ICP-OES, Pekin Elmer Optimal 2100 DV) (Zhuang 1994).

Experimental design and statistical analysis The experiment was a randomized block design with G. intraradices and G. versiforme inoculation or remained non-inoculation under two Zn conditions. Three replications (six plants in each) were designated for each treatment making a total of 36 pots. The data were subjected to an analysis of variance (ANOVA) using the Statistical Analysis System software (SAS Institute Inc., Cary, NC, USA) and differences were compared by the least significant differences test at a 5% level.

Results Plant biomass and physiological indices The Zn-poor conditions decreased mycorrhizal colonization, plant height, taproot length, leaf area and dry weight per plant. Compared with the Zn-rich condition, low-Zn reduced plant height, taproot length, leaf area and dry weight per plant by 11.33%, 22.69%, 51.30% and 34.65%, respectively. Regardless of the Zn condition, AM fungi, especially G. intraradices, significantly improved plant height, taproot length, leaf area and dry weight per plant. Additionally, the mycorrhizal colonization and dependency were higher in seedlings inoculated with G. intraradices than with G. versiforme (Table 1). Leaf chlorophyll aCb and leaf soluble protein and sugar contents were significantly decreased in Zn-poor conditions, but root viability was not significantly affected. Regardless of the Zn condition,


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Table 1. Mycorrhizal colonization, plant height, taproot length, leaf area, dry weight per plant and mycorrhizal dependence of trifoliate orange seedlings under Zn-poor (ZP) and Zn-rich (ZR) conditions with G. intraradices, G. versiforme or without (Non-AMF). Zn condition ZP ZR

AMF status

Non-AMF G. versiforme G. intraradices Non-AMF G. versiforme G. intraradices Significance

ZP AMF ZP£AMF

Mycorrhizal colonization (%)

Plant height (cm)

0d 24.80 § 4.31c 45.57 § 2.78b 0d 25.48 § 2.31c 47.04 § 1.36a

13.31 § 0.29f 14.21 § 1.89e 15.39 § 0.36c 15.01 § 0.36d 16.12 § 0.05b 17.05 § 0.06a

Dry weight per Mycorrhizal Taproot length Leaf area (cm) (cm2¢plant¡1) plant (g¢plant¡1) dependency (%) 16.12 § 0.05f 20.18 § 0.08e 21.22 § 0.42c 20.85 § 0.08d 22.00 § 0.14b 23.30 § 0.05a

Ns

NS

1.88 § 0.06f 3.55 § 0.09e 4.34 § 0.11c 3.86 § 0.10d 4.67 § 0.13b 5.33 § 0.11a

0.66 § 0.01f 1.22 § 0.01d 1.47 § 0.01c 1.01 § 0.04e 1.90 § 0.03b 2.30 § 0.05a

— 184.85 § 0.03d 222.61 § 1.01b — 188.87 § 0.05c 228.33 § 1.05a

NS

NS NS

NS

Mycorrhizal dependency percentage (%) D 100£dry weight per AM-infected plant / dry weight per non-AM infected plant. Values represent the mean § SE of three replicates (n D 3), samples from six plants were collected for each replicate. Different letters indicate significant differences at p < 0.05 in each column.

AM fungi, especially G. intraradices, significantly enhanced leaf chlorophyll aCb, leaf soluble protein and sugar contents and root viability (Table 2). Soil enzymatic activities, EEG and pH The activities of acid phosphatase, CAT, invertase and urease were reduced in 0–2 cm or 2– 4 cm rhizosphere soil (except for invertase in 2–4 cm rhizosphere soil) under Zn-poor conditions. Irrespective of the Zn condition, AM fungi, especially G. intraradices, enhanced acid phosphatase, CAT, invertase and urease activities in 0–2 cm or 2–4 cm rhizosphere soil, and the enzymatic activities were significantly higher in 0–2 cm than in 2–4 cm rhizosphere soil (Figure 1). Easily extractable glomalin (EEG) concentrations were decreased in the rhizosphere of AM inoculated seedlings in low-Zn soil. In contrast, in the 0–2 cm rhizosphere soil of non-AM seedlings, the pH value was increased by the Zn-poor condition, while in 2–4 cm rhizosphere soil it remained stable. Irrespective of the rhizosphere and Zn conditions, the rhizosphere of AM-inoculated seedlings had higher EEG concentrations but lower pH values compared with non-AM seedlings, and higher EEG contents and lower pH values were observed in the rhizosphere of seedlings inoculated with G. intraradices compared with seedlings inoculated with G. versiforme (Figure 2). Table 2. Leaf chlorophyll aCb, leaf soluble protein and sugar contents, and root viability of trifoliate orange seedlings under Zn-poor (ZP) and Zn-rich (ZR) conditions with G. intraradices, G. versiforme or without (Non-AMF). Zn condition ZP ZR

AMF status

Non-AMF G. versiforme G. intraradices Non-AMF G. versiforme G. intraradices Significance

ZP AMF ZP£AMF

Chlorophyll aCb content Soluble protein content (mg¢g¡1FW) (mg¢g¡1FW) 2.61 § 0.02f 4.18 § 0.16e 5.03 § 0.10d 5.22 § 0.02c 6.16 § 0.04b 6.86 § 0.05a

13.06 § 0.02f 13.39 § 0.20e 14.63 § 0.03d 15.21 § 0.04c 15.71 § 0.03b 16.21 § 0.04a

NS

NS

Soluble sugar content (mg¢g¡1FW)

Root viability (mg¢g¡1FW h¡1)

11.71 § 0.03f 15.26 § 0.04e 16.42 § 0.04d 17.82 § 0.03c 18.86 § 0.03b 19.86 § 0.03a

1.06 § 0.02e 1.35 § 0.01d 1.90 § 0.14c 1.21 § 0.04de 2.12 § 0.05b 2.40 § 0.14a

NS NS

Values represent the mean § SE of three replicates (n D 3), samples from six plants were collected for each replicate. Bars with the same letter are not significantly different at p < 0.05.

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Figure 1. Acid phosphatase, catalase (CAT), invertase and urease activities in 0–2 cm and 2–4 cm rhizosphere soil under Zn-poor (ZP) and Zn-rich (ZR) conditions with G. intraradices, G. versiforme or without (Non-AMF). Values represent the mean § SE of three replicates (n D 3), samples from six plants were collected for each replicate. Bars with the same letter are not significantly different at p < 0.05.

Zinc, P, K and Mg concentrations Compared with the Zn-rich soil, Zn concentrations in the shoots and roots of trifoliate orange seedlings grown in the Zn-poor soil were reduced by 37.14% and 20.65%, respectively, and the P, K and Mg concentrations in the shoots were reduced by 47.33%, 54.14% and 20.00%, respectively. In the roots, the corresponding values were reduced by 43.99%, 14.58% and 22.83%. Irrespective of the Zn condition, AM fungi, especially G. intraradices, significantly enhanced Zn, P, K, and Mg concentrations in the shoots and roots (Figure 3).

Figure 2. Easily extractable glomalin (EEG) concentrations and pH values in 0–2 cm and 2–4 cm rhizosphere soil under Zn-poor (ZP) and Zn-rich (ZR) conditions with G. intraradices, G. versiforme or without (Non-AMF). Values represent the mean § SE of three replicates (n D 3), samples from six plants were collected for each replicate. Bars with the same letter are not significantly different at p < 0.05.


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Figure 3. Zinc, P, K and Mg concentrations in the shoots and roots of trifoliate orange seedlings under Zn-poor (ZP) and Zn-rich (ZR) conditions with G. intraradices, G. versiforme or without (Non-AMF). Values represent the mean § SE of three replicates (n D 3), samples from six plants were collected for each replicate. Bars with the same letter are not significantly different at p < 0.05.

Discussion According to these results, reductions in plant growth (plant height, taproot length, leaf area and dry weight) were found in trifoliate orange seedlings in response to Zn-poor conditions (Table 1). The shorter taproot length in response to low-Zn affected the plant height, leaf area and dry weight by restricting the uptake of water and nutrients from the soil. Additionally, low-Zn decreased the root viability, leaf chlorophyll and leaf soluble protein and sugar contents (Table 2), which inhibited the root functions and shoot growth. However, the two AM fungi, especially G. intraradices, significantly enhanced the dry weight per plant, as well as the plant height, taproot length and leaf area in the Znpoor soil. The mycorrhizal colonization and dependency of seedlings inoculated with G. intraradices were higher than those of seedlings inoculated with G. versiforme (Table 1). This suggests that the two AM fungi, which were inoculated to trifoliate orange seedlings, displayed different responses to low-Zn stress, and that G. intraradices was more efficient for optimal growth under the Zn-poor conditions. The data also revealed increases in acid phosphatase, CAT, invertase and urease activities and EEG content appeared in the soil with AM-inoculated seedlings compared with non-AM seedlings under Zn-poor conditions (Figure 1). It has been demonstrated that AM inoculation or fertilizer treatment increases enzymatic activities in the rhizophere of many plant species (Kandeler et al. 2002; Subramanian et al. 2009). The high acid phosphatase and urease activities in AM soil make P and N available, and the increases in invertase and CAT may be associated with the carbon cycle and hydrogen peroxide (H2O2) elimination, respectively (Zhou 1987). The intense enzymatic activities may also be associated with the pH reduction in rhizosphere soil and the enhanced availability of mineral nutrients including Zn, which may be attributed to the secretion of root exudates by the mycorrhizal colonized seedlings. This may also explain why the enzymatic activities were higher in 0–2 cm than in 2–4 rhizosphere soil (Figure 1). Additionally, the organic acids, phenols and carbohydrates secreted by mycorrhizal roots may affect glomalin stability in soil. On the other hand, the higher root length of mycorrhizal plants could have favored extensive hyphal length, and, in turn, the production and accumulation of glomalin in soil which leads to the formation of a sticky string-bag of hyphae. These act as an adsorptive site for metallic cations and may result in enhanced Zn availability under Zn-poor conditions.

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The current study showed that low-Zn soil reduced the Zn, P, K and Mg concentrations in the shoots and roots, as well as soil enzymatic activities (Figures 1 and 3). Auxin (IAA), which could be affected by Zn deficiency, is a key leaf-derived regulator of xylem cell differentiation and division within the cambial zone and an initiator of vascular re-differentiation (Savidge 1988). Thus, it is proposed that the differential Zn and other nutrient distribution in seedlings between the Zn-poor and Zn-rich conditions may be influenced by the IAA in plants and soil enzymes. According to the present results, Zn concentrations in the shoots and roots were significantly improved by the two AM fungi, especially G. intraradices (Figure 3), which indicates that mycorrhizal roots have an enhanced ability to take up Zn from soil and to translocate it to shoots compared with non-AM inoculated roots. This is different from the results in Zn-excess conditions. According to Yang et al. (2011) and Xiao, Yang, and Zhang (2012), the exotic AM fungi could enhance Zn accumulation in the roots, but reduce Zn translocation to the shoots of trifoliate orange seedlings under Zn-excess conditions. Additionally, Zn availability in the soil is highly restricted owing to fixation of a major portion of the available form of Zn. Mycorrhizal symbiosis appears to facilitate the release of Zn from unavailable forms and therefore enhance the availability of Zn. Additionally, AM-inoculated seedlings also showed higher levels of P, K and Mg compared with non-AM seedlings (Figure 3) in this study. This is in agreement with other research, such as that by Abdel Latef and He (2011), who found that the concentrations of P and K were higher in AM tomato plants compared with in non-AM plants. Similarly, citrus (Khalil et al. 2011) or wheat (Abdel-Fattah and Asrar 2012) plants inoculated with AM fungi tended to increase the levels of Zn, P, K and Mg in saline soil. Linderman (1992) also found that the extraradical hyphae of AM fungi can bridge the zone of nutrient depletion adjacent to the root, and thus increase availability of immobile soil elements such as Zn by translocating them from more remote sites through the hyphae to the roots. This would explain why mycorrhizal trifoliate orange seedlings had higher concentrations of mineral nutrients, including Zn, in the roots and shoots under the Zn-poor condition, and consequently improved plant growth. In summary, low-Zn soil inhibited the growth of triofoliate orange seedlings, which was accompanied by decreases in growth parameters, soil enzymatic activities and mineral nutrients including Zn concentrations in the shoots and roots. However, under the Zn-poor condition, AM fungi, especially G. intraradices, improved the growth, enzymatic activities and EEG content in rhizosphere soil and the concentrations of Zn, P, K and Mg in the shoots and roots, but decreased the soil pH value. These results indicate that G. intraradices has the potential to enhance the growth and Zn uptake of triofoliate orange seedlings grown in low-Zn soil in a greenhouse.

Funding This work was supported by the National Natural Science Foundation of China (31372014), Anhui Provincial Natural Science Foundation (1308085MC37) and the Provincial Natural Science Research Program of Higher Education of Anhui Province (KJ2012A128 and KJ2016SD24).

References Abdel Laterf, A. A. H., and C. X. He. 2011. Effects of arbuscular mycorrhizal fungi on growth, mineral nutrition, antioxidant enzymes activity and fruit yield of tomato grown under salinity stress. Scientia Horticulturae 127: 228–233. Abdel-Fattah, G. M., and A. A. Asrar. 2012. Arbuscular mycorrhizal fungal application to improve growth and tolerance of wheat (Triticum aestivum L.) plants grown in saline soil. Acta Physiologiae Plantarum 34: 267–277. Alloway, B. J. 2008. Zinc in soils and crop nutrition. 2nd ed. Belgium and Paris: IZA and IFA Brussels. Bradford, M. M. 1976. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Analytical Biochemistry 72: 248–254. Broadley, M. R., P. J. White, J. P. Hammond, I. Zelko, and A. Lux. 2007. Zinc in plants. New Phytologist 173: 677–702. Cavagnaro, T. R., L. E. Jackson, K. M. Scow, and K. R. Hristova. 2007. Effects of arbuscular mycorrhizas on ammonia oxidizing bacteria in an organic farm soil. Microbial Ecology 54: 618–626. Cavagnaro, T. R. 2008. The role of arbuscular mycorrhizas in improving plant zinc nutrition under low soil zinc concentrations: A review. Plant and Soil 304: 315–325.


331

Cavagnaro, T. R., S. Dickson, and F. A. Smith. 2010. Arbuscular mycorrhizas modify plant responses to soil zinc addition. Plant and Soil 329: 307–313. Graham, J. H., and J. P. Syvertsen. 1985. Host determinants of mycorrhizal dependency of citrus rootstock seedlings. New Phytologist 101: 667–676. Jackson, L.E., M. Burger, and T. R. Cavagnaro. 2008. Roots, nitrogen transformations, and ecosystem services. Annual Review of Plant Biology 59: 341–363. Kandeler, E., P. Marschner, D. Tscherko, T. S. Gahoonia, and N E. Nielsen. 2002. Microbial community composition and functional diversity in the rhizosphere of maize. Plant and Soil 238: 301–312. Khalil, H. A., A. M. Eissa, S. M. El-Shazly, and A. M. Aboul Nasr. 2011. Improved growth of salinity-stressed citrus after inoculation with mycorrhizal fungi. Scientia Horticulturae 130: 624–632. Kothari, S. K., H. Marschner, and V. Romheld. 1991. Contribution of the VA mycorrhizal hyphae in acquisition of phosphorus and zinc by maize grown in calcareous soil. Plant and Soil 131: 177–185. Li, X. L., and P. Christie. 2001. Changes in soil solution Zn and pH and uptake of Zn by arbuscular mycorrhizal red clover in Zn-contaminated soil. Chemosphere 42: 201–207. Linderman, R. G. 1992. Vesicular arbuscular mycorrhizae and soil microbial interaction. In Mycorrhizae in sustainable agriculture, ed. G. J. Bethlenfalvay, and R. G. Linderman. ASA54, Madison, USA. Ling, L. L., L. Z. Peng, C. P. Chun, C. L. Jiang, and L. Cao. 2012. The relationship between leaf nutrient and fruit quality of navel orange in southern Jiangxi province of China. Plant Nutrition and Fertilizer Science 18: 947–954. Liu, Z. 1996. Microelements in soils of China. Nanjing: Jiangsu Science and Technology Publishing House. Mohandas, S. 2012. Arbuscular mycorrhizal fungi benefit mango (Mangifera indica L.) plant growth in the field. Scientia Horticulturae 143: 43–48. Nzanza, B., D. Marais, and P. Soundy. 2012. Yield and nutrient content of tomato (Solanum lycopersicum L.) as influenced by Trichoderma harzianum and Glomus mosseae inoculation. Scientia Horticulturae 144: 55–59. Phillips, J. M., and D. S. Hayman. 1970. Improve procedures for clearing roots and staining parasitic and vesicular arbuscular mycorrhizal fungi for rapid assessment of infection. Transactions of the British Mycological Society 55: 158–161. Ryan, M. H., and J. F. Angus. 2003. Arbuscular mycorrhizae in wheat and field pea crops on a low P soil: increased Zn uptake but no increase in P uptake or yield. Plant and Soil 250: 225–239. Savidge, R. A. 1988. Auxin and ethylene regulation of diameter growth in trees. Tree Physiology 4: 401–414. Subramanian, K. S., J. S. Virgine Tenshia, K. Jayalakshmi, and V. Ramachandran. 2011. Antioxidant enzyme activities in arbuscular mycorrhizal (Glomus intraradices) fungus inoculated and non-inoculated maize plants under zinc deficiency. Indian Journal of Microbiology 51: 37–43. Subramanian, K. S., V. Tenshia, K. Jayalakshmi, and V. Ramachandran. 2009. Biochemical changes and zinc fractions in arbuscular mycorrhizal fungus (Glomus intraradices) inoculated and uninoculated soils under differential zinc fertilization. Applied Soil Ecology 43: 32–39. Tang, Y. Q., L. Z. Peng, C. P. Chun, L. L. Ling, Y. W. Fang, and X. Yan. 2013. Correlation analysis on nutrient element contents in orchard soils and sweet orange leaves in southern Jiangxi province of China. Acta Horticlturae Sinica 40: 623–632. Wang, P., J. J. Zhang, B. Shu, and R. X. Xia. 2012. Arbuscular mycorrhizal fungi associated with citrus orchards under different types of soil management, southern China. Plant, Soil and Environment 58: 302–308. Wang, X. K. 2006. Experimental principle and technique for plant physiology and biochemistry. Beijing: Higher Education Press. Wright, S. F., and A. Upadhyaya. 1996. Extraction of an abundant and unusual protein from soil and comparison with hyphal protein of arbuscular mycorrhizal fungi. Soil Science 161: 575–586. Wu, Q. S., and R.X. Xia. 2006. Arbuscular mycorrhizal fungi influence growth, osmotic adjustment and photosynthesis of citrus under well-watered and water stress conditions. Journal of Plant Physiology 163: 417–425. Xiao, J. X., H. Yang, and S. L. Zhang. 2012. Effects of arbuscular mycorrhizal fungus on net ion fluxes in the roots of trifoliate orange (Poncirus trifoliata) and mineral nutrition in seedlings under zinc contamination. Acta Ecologica Sinica 32: 2127–2134. Xing, F., X. Z. Fu, L. Z. Peng, C. P. Chun, L. L. Ling, X. Li, J. Xue, Y. L. Fan, B. L. Zhong, and L. H. Diao. 2013. Survey of soil available zinc content in naval orange orchards in southern Jiangxi province. Journal of Fruit Science 30: 597–601. Yang, H., J. X. Xiao, A. N. Yang, Y. Shen, S. L. Zhang, J. An, and X. J. Wu. 2011. Effects of five arbuscular mycorrhizal fungi on the tolerance of trifoliate orange (Poncirus trifoliata(L.) Raf.) seedlings against zinc contamination. Chinese Journal of Ecology 30: 93–97. Zhou, L. K. 1987. Soil enzyme. Beijing: Science Press. Zhuang, Y. M. 1994. Citrus nutrition and fertilizer. Beijing: Chinese Agriculture Press.