Babacar Thioye
email: babacarthioye@yahoo.fr

Hervé Sanguin

Aboubacry Kane

Sergio Mania De Faria

Dioumacor Fall

Dioumacor Fall f Yves Prin

Diaminatou Sanogo

Cheikh Ndiaye

Robin Duponnois

Samba Ndao Sylla

Ndao Sylla

Amadou Mustapha Bâ

Impact of mycorrhiza-based inoculation strategies on Ziziphus mauritiana Lam. and its native mycorrhizal communities on the route of the Great Green Wall (Senegal)

Keywords: Arbuscular mycorrhizal fungi community, Rhizophagus irregularis, Inoculation, Illumina sequencing, Rock phosphate, Ziziphus mauritiana

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The jujube tree (Ziziphus mauritiana Lam.) is a multipurpose fruit tree commonly used in Sahelian and Sudanian areas in West Africa [START_REF] Okafor | Amélioration des essences forestières donnant des produits comestibles[END_REF]. It is an important source of income for rural communities and contributes to overcome nutritional problems [START_REF] Arbonnier | Arbres, arbustes et lianes des zones sèches d'Afrique de l'Ouest[END_REF]. For these reasons, the jujube tree is one of tree species selected by the pan-African Great Green Wall (GGW) project to « green » and fight against the poverty, degradation of soils and desertification [START_REF] Dia | Projet Majeur de la Grande Muraille Verte de l'Afrique : Concepts et mise en oeuvre[END_REF]. In Senegal, the GGW project promotes tree planting and economically interesting drought-tolerant plant species, water retention ponds, agricultural production systems and other income-generating activities, as well as basic social infrastructures. However, fruit tree planting programs in such environmental conditions (i.e drought, degraded land) are generally subjected to a low tree growth and high tree mortality rates due to transplant shocks from tree nursery to field (Close et al. 2013). Different strategies were proposed to improve the growth and survival of fruit trees, e.g. inoculation with arbuscular mycorrhizal (AM) fungi, fertilization with rock phosphate (RP), and plant propagation by micrografting [START_REF] Reena | Growth stimulation of Tamarindus indica by selected VA mycorrhizal fungi[END_REF][START_REF] Guissou | Responses of Parkia biglobosa (Jacq.) Benth., Tamarindus indica L. and Ziziphus mauritiana Lam. to arbuscular mycorrhizal fungi in a phosphorus-deficient sandy soil[END_REF][START_REF] Bâ | Functional compatibility of two arbuscular mycorrhizae with thirteen fruit trees in Senegal[END_REF][START_REF] Mathur | Influence of arbuscular mycorrhizae on biomass production, nutrient uptake and physiological changes in Ziziphus mauritiana Lam. under water stress[END_REF][START_REF] Danthu | Propagation végétative d'une variété améliorée de jujubier (Ziziphus mauritiana Lam.) introduite au Sénégal[END_REF][START_REF] Danthu | Vegetative propagation of Ziziphus mauritiana var. Gola by micrografting and its potential for dissemination in the Sahelian Zone[END_REF][START_REF] Bâ | Domestication of jujube fruit trees (Zizyphus mauritiana Lam.)[END_REF][START_REF] Guissou | Contribution of arbuscular mycorrhizal fungi to growth and nutrient uptake by jujube and tamarind seedlings in a phosphate (P)-deficient soil[END_REF][START_REF] Sidibé | The use of mycorrhizal inoculation in the domestication of Ziziphus mauritiana and Tamarindus indica in Mali (West Africa)[END_REF].

The jujube tree is highly dependent on AM symbiosis [START_REF] Bâ | Mycorhization contrôlée et fertilisation phosphatée: Application à la domestication du jujubier[END_REF]Thioye et al. 2007) and it has been suggested than AM fungal root colonization of jujube seedlings in a nursery was an essential prerequisite to limit the mortality of outplanted jujube trees in the field [START_REF] Bâ | Mycorhization contrôlée et fertilisation phosphatée: Application à la domestication du jujubier[END_REF]. AM fungi are known for their ability to improve plant growth and notably to efficiently scavenge for soil phosphorus (P) resources [START_REF] Smith | Mycorrhizal Symbiosis[END_REF], one of most the limiting resources in West African soils for the establishment of tree plantations and agriculture crops [START_REF] Friesen | Phosphorus acquisition and cycling in crop and pasture systems in low fertility tropical soils[END_REF]. Paradoxically, important resources in phosphate rocks (RP) are available in West Africa, and their use could provide an alternative to soluble P fertilizers that are poorly accessible to rural communities due to their high containable [START_REF] Nziguheba | Phosphorus in smallholder farming systems of sub-Sahara Africa: implication for agricultural intensification[END_REF].

Previous studies have demonstrated that jujube trees associated with AM fungi showed a better growth and mineral nutrition than non AM-associated jujube trees [START_REF] Guissou | Responses of Parkia biglobosa (Jacq.) Benth., Tamarindus indica L. and Ziziphus mauritiana Lam. to arbuscular mycorrhizal fungi in a phosphorus-deficient sandy soil[END_REF][START_REF] Bâ | Functional compatibility of two arbuscular mycorrhizae with thirteen fruit trees in Senegal[END_REF][START_REF] Bâ | Mycorhization contrôlée et fertilisation phosphatée: Application à la domestication du jujubier[END_REF][START_REF] Sidibé | The use of mycorrhizal inoculation in the domestication of Ziziphus mauritiana and Tamarindus indica in Mali (West Africa)[END_REF][START_REF] Guissou | Effect of of arbuscular mycorrhizae on growth and mineral nutrition of greenhouse propagated fruit trees from diverse geographic provenances[END_REF], for example by using more efficiently soluble P from RP [START_REF] Bâ | Mycorhization contrôlée et fertilisation phosphatée: Application à la domestication du jujubier[END_REF]. However, the beneficial effects of AM fungal association were dependent on jujube species and AM fungal species [START_REF] Thioye | Growth response of different species of Ziziphus to inoculation with arbuscular mycorrhizal fungi[END_REF].

Rhizophagus irregularis, isolate IR27 (syn. Glomus aggregatum IR27; [START_REF] Bâ | et d'Acacia mangium Willd.: Diversité et abondance relative des champignons mycorhiziens à arbuscules dans deux types de sols de la zone Nord et Sud Soudanienne du Burkina Faso[END_REF] was one of the most efficient AM fungi to promote growth and mineral nutrition of various jujube tree species and provenances of Z. mauritiana (Thioye et al. 2007). This AM fungal species has a worldwide distribution (Öpik et al. 2006), well adapted to competition in natural habitats and disturbed agroecosystems [START_REF] Öpik | Composition of root-colonizing arbuscular mycorrhizal fungal communities in different ecosystems around the globe[END_REF][START_REF] Bouffaud | Regional-scale analysis of arbuscular mycorrhizal fungi: the case of Burgundy vineyards[END_REF]. It represents the most widely used AM fungal species in mycorrhiza-based ecological engineering strategies [START_REF] Ceballos | The in vitro mass-produced model mycorrhizal fungus, Rhizophagus irregularis, significantly increases yields of the globally important food security crop cassava[END_REF], mostly because of its ability to be cultured in an in vitro system [START_REF] Bécard | Early events of vesicular-arbuscular mycorrhiza formation on Ri T-DNA transformed roots[END_REF][START_REF] St-Arnaud | Enhanced hyphal growth and spore production of the arbuscular mycorrhizal fungus Glomus intraradices in an in vitro system in the absence of host roots[END_REF], allowing to set up a large-scale biotechnological production.

However, monitoring of mycorrhiza-based beneficial plant effects from tree nursery to field, and the evaluation of impacts on native microbial community as the mycorrhizal community were poorly assessed [START_REF] Alguacil | A molecular approach to ascertain the success of "in situ" AM fungi inoculation in the revegetation of a semiarid, degraded land[END_REF][START_REF] Pellegrino | Establishment, persistence and effectiveness of arbuscular mycorrhizal fungal inoculants in the field revealed using molecular genetic tracing and measurement of yield components[END_REF], notably regarding fruit trees [START_REF] Raebild | Improved management of fruit trees in West African parklands[END_REF]. Since the development of new generation sequencing technologies, field-based monitoring of microbial biodiversity noted a genuine revolution, providing unprecedented insights into the ecology of AM fungal community in a wide range of climatic zones [START_REF] Davison | Global assessment of arbuscular mycorrhizal fungus diversity reveals very low endemism[END_REF], but Sahelian regions remains poorly represented

The current study aimed the evaluation of different mycorrhiza-based ecological engineering strategies, i.e. using a R. irregularis inoculant combined or not with a RP fertilizer from Senegal, on jujube seedling growth and nutrition in tree nursery and after outplanting in an experimental field. The ecological impact of each practice will be assessed by the monitoring of AM fungal community structure and diversity associated with jujubes trees after one year of plantation by using high throughput Illumina sequencing. The work was carried out on two different jujube tree cultivars from different provenances, a local one adapted to the harsh conditions observed on the route of the GGW and an Indian provenance particularly appreciated by West African farmers because of its precocity in fruiting, the larger size of its fruits and its taste [START_REF] Vashishtha | Ziziphus for drylands -a perennial crop solving perennial problems[END_REF][START_REF] Danthu | Vegetative propagation of Ziziphus mauritiana var. Gola by micrografting and its potential for dissemination in the Sahelian Zone[END_REF]).

Materials and methods

Mycorrhizal inoculum, fertilizer and plant material

The Rhizophagus irregularis isolate IR27 (syn. Glomus aggregatum IR27; [START_REF] Bâ | et d'Acacia mangium Willd.: Diversité et abondance relative des champignons mycorhiziens à arbuscules dans deux types de sols de la zone Nord et Sud Soudanienne du Burkina Faso[END_REF] originated from an Acacia holosericea planting in the North of Burkina Faso, and provided by the LCM laboratory (IRD, Dakar, Senegal, certified ISO 9001, version 2000), was used as AM fungal inoculum. It was propagated on maize (Zea mays L.) for three months on sterilized sandy soil in a tree nursery. The sandy soil used in the experiment was collected from Sangalkam (Senegal). It was a sandy soil with 88.8 % sand, 5.8 % silt, 5.4 % clay, 0.6 % organic matter, 0.3 % total C, 0.02 % total N, ratio C/N = 14, 333.5 ppm total K, 41.4 ppm total P, 2.1 ppm P-Bray 1, 1.03 ppm Ca, 0.3 ppm Mg, pH = 6.0 of a soil/water mixture (ratio 1:2, v/v) and pH = 4.6 of a soil / KCl mixture (ratio 1:2, v/v). The soil was passed through a 2 mm sieve, sterilized for four hours in an autoclave oven system at 180°C to eliminate native AMF, and transferred into plastic bags (1.5 kg of soil per plastic bag). The AM fungal inoculum consisted of sand, spores, fragments of hyphae and maize root segments. The inoculum density of R. irregularis IR27 was calibrated by the most probable number method [START_REF] Adelman | Infectivity of vesicular-arbuscular mycorrhizal fungi: Influence of host-soil diluent combinations on MPN estimates and percentage colonization[END_REF] as 1635 infective propagules per 20 g of inoculum. Noninoculated controls also received 20 g of autoclaved crude AM fungal inoculum. The fertilizer consisted of rock phosphate (RP, 30 % of P 2 O 5 ) provided by the Société d'Etudes et de Réalisation des Phosphates de Matam (Senegal). It was used 0 and 1.73 g P/kg/plant, according to [START_REF] Bâ | Mycorhization contrôlée et fertilisation phosphatée: Application à la domestication du jujubier[END_REF].

Two cultivars of jujube seedlings (Tasset from Senegal and Gola from India) were used in this study and provided by the CNRF / ISRA (Senegal). Seeds of each jujube seedlings were surface-sterilized with 1 % NaOCl for 15 min, washed several times and soaked in sterile distilled water for 30 min before being planted in the soil as three per plastic bag (24 cm × 7.5 cm).

Nursery experimental set up and plant growth measurements

Plants were grown in a tree nursery at research center ISRA / IRD (Bel Air, Dakar, Senegal) (14°44'N, 17°30'W) under natural sunlight (35°C day, 27°C night, relative humidity 75 % and 14 h photoperiod). After emergence, the seedlings were thinned to one plant per plastic bag. The experiment was set up as a 2×2×2 factorial design consisting of two jujube cultivars, with AM fungal inoculation or not, and with or without RP fertilization. Experiment was arranged in a completely randomized design with 20 replicates per treatment combination.

Mycorrhizal inoculation and fertilization with RP were achieved by placing either 20 g portions of AM fungal and /or two different RP doses below the seeds during transplanting.

Four months after sowing, plants were harvested to measure height, collar diameter and dry weight of shoots and roots (48 h at 70° C). For mycorrhizal root infection measurement, a part of fresh fine roots was collected from the root system of each seedling. Root were gently washed under tap water, bleached (KOH, 10 %) at 80°C during 30 min, and stained in 0.05 % Trypan blue at 80°C during 35 min following the method of [START_REF] Phillips | Improved procedures for clearing roots and staining parasitic and Vesicular-Arbuscular Mycorrhizal fungi for rapid assessment of infection[END_REF].

Percentage of root length colonized by AMF was assessed at ×40 magnification using 100 fragments of lateral roots (approximately 1 cm length) on microscopic slides. Mycorrhizal root colonization was evaluated by using the method of [START_REF] Trouvelot | Mesure du taux de mycorhization VA d'un système radiculaire. Recherche de méthodes d'estimation ayant une signification fonctionnelle[END_REF]. P, N and K contents in jujube leaves were quantified at the LAMA laboratory (IRD, Dakar, Senegal, certified ISO 9001, version 2000) as follows: leaf tissues of each plant were dried, ground, mineralized through heating at 500 °C, digested in 2 ml HCl (6N) and 10 ml HNO 3 . Total P and N contents were determined by the molybdate blue method and Kjeldahl method, respectively. Total K contents were determined by means of an atomic absorption spectrophotometer.

Field experimental set up and plant growth measurements

The orchard (5 ha) was located near the village of Amally in the rural community of Tessekere (15°59'N, 15°19'W) on the route of GGW in the Ferlo region in the Sahelian zone of North, Senegal. The climate is arid with low and erratic mean annual rainfall varying from 100 to 400 mm. The predominant vegetation consists of low trees (i.e Ziziphus mauritiana, Balanites aegyptica and Acacia senegal), open shrub steppes and grasslands growing in sandy soil (Vincke et al. 2009). Physical and chemical analyses of soil were performed in the Agricultural Chemistry Laboratory in Rio de Janeiro (Brazil) with means as following: pH: 6.41; C: 0.12 %; Al: 0 mg; Ca: 160.32 mg; K: 69.84 mg.L -1 ; Mg: 41.33 mg; N: 0.02 %; P: 1974.7 mg. The mycorrhizal soil infectivity determined by the MPN method was very low reaching 4.47 propagules per 100 g of soil. After four months, pre-inoculated and preuninoculated plants were transplanted to field (eight treatments). Rate of survival, height and collar diameter were recorded at 3, 8 and 13 months after transplanting and mycorrhizal root infection was only recorded at 13 months.

DNA extraction, PCR and MiSeq Illumina sequencing

Thirteen months after plantation, three jujube tree root systems for each treatment per replicated block were sampled and pooled (a total of 32 root samples). Each composite root sample was wrapped in tissue paper and placed in a plastic bag containing silica gel and stored air-tight at room temperature. DNA was extracted from 40-50 mg of dried fine roots using a FastPrep-24 homogenizer (MP biomedicals Europe, Illkirch, France) and the FastDNA® SPIN kit (MP biomedicals, Europe) according to manufacturer's instructions.

DNA extracts were then loaded onto PVPP (polyvinylpolypyrrolidone) Micro Bio-Spin® Columns (Bio-Rad, Marnes-la-Coquette, France) and eluted by centrifugation to improve DNA purity and avoid PCR inhibitors. Two replicates were done per composite root sample.

The same approach was used to extract DNA from the AM fungal inoculum (20 g). DNA integrity was checked on 1.5 % agarose gel and stored at -20°C until used in the steps of gene amplification.

Molecular diversity of AM fungi (Glomeromycota) from plant DNA was assessed by 18S rRNA gene amplification with the primers NS31 and AML2 [START_REF] Simon | Specific amplification of 18S fungal ribosomal genes from VA endomycorrhizal fungi colonizing roots[END_REF][START_REF] Lee | Improved PCR primers for the detection and identification of arbuscular mycorrhizal fungi[END_REF]) according to [START_REF] Davison | Communities of arbuscular mycorrhizal fungi detected in forest soil are spatially heterogeneous but do not vary throughout the growing season[END_REF]. PCR round was carried out in a final volume of 50 µl with NS31 and AML2 primers (0.6 µM each), 2 µl DNA (2 extracted DNA replicates per sample), 200 µM of each dNTP, 200 ng/ml BSA, GoTaq® DNA Polymerase (2 units) and 1X Green GoTaq® Reaction Buffer (Promega, Charbonnieres, France), with the following cycling conditions: 94°C for 3min; 30 cycles of 94°C for 30 s, 58°C for 90 s, 72°C for 80 s; a final elongation step at 72°C for 10 min. After PCR, the amplification products (pools of PCR: 2 × 50µl) were purified by using illustra GFX PCR DNA and Gel Band Purification Kit (GE Healthcare Life Sciences, Velizy-Villacoublay, France) following manufacturer's guidelines. Then, DNA concentration of PCR products were quantified by using a Qubit fluorometer (Qubit Fluorometric quantitation, Invitrogen) and the Qubit dsDNA HS Assay Kit. PCR product concentration was adjusted to 10ng/µl and subjected to paired-end Illumina MiSeq sequencing (2×300 bp) by Molecular Research LP (MR DNA, TX, USA). The 18S rRNA gene from the AM fungal inoculum has been amplified with the primers AML1 and AML2 according [START_REF] Lee | Improved PCR primers for the detection and identification of arbuscular mycorrhizal fungi[END_REF] and sequenced (Genoscreen, Lille, France). The sequence has been submitted to the NCBI database under accession number MH571752.

Bioinformatic data processing

MiSeq Illumina sequencing data were analysed by using Mothur software according the standard operating procedure (http://www.mothur.org/wiki/MiSeq_SOP) proposed in [START_REF] Kozich | Development of a dual-index sequencing strategy and curation pipeline for analyzing amplicon sequence data on the MiSeq Illumina sequencing platform[END_REF], except that only forward reads were analysed because of the length of PCR products not suitable for paired reads and of a higher quality of forwards reads compared to reverse reads. All sequences were depleted of barcodes and primers and a quality cutoff of Q30 was selected. The sequences < 150 bp or with ambiguous base calls or with homopolymer runs exceeding 8bp were removed. A pre-clustering step [START_REF] Huse | Ironing out the wrinkles in the rare biosphere through improved OTU clustering[END_REF]) was also performed to remove sequences still likely due to illumina sequencing errors. Chimera were checked by Uchime [START_REF] Edgar | UCHIME improves sensitivity and speed of chimera detection[END_REF] implemented in Mothur software because it showed improved performance over the Chimera Slayer algorithm [START_REF] Schloss | Reducing the Effects of PCR Amplification and Sequencing Artifacts on 16S rRNA-Based Studies[END_REF]. All sequences were first classified by using classify.seqs and a SILVA-compatible alignment database (Eukarya) to remove all no Glomeromycota sequences. Secondly, a preliminary clustering of sequences in OTUs with a 3 % divergence threshold was performed by using dist.seqs and cluster commands in Mothur, and all singleton OTUs were removed. The representative sequences of each OTU were then compared with a broader nucleotide database (Genbank database, BLASTN program) (http://www.ncbi.nlm.nih.gov/genbank), and all OTUs for which the representative sequence presented a similarity score < 95 % (100 % coverage) with the reference sequences were excluded of the data set. The number of sequences between each sample was then normalized with sub.sample command. This subsampling step allows reducing the number of spurious OTUs and is widely used to obtain robust estimation of alpha and beta diversity [START_REF] Gihring | Massively parallel rRNA gene sequencing exacerbates the potential for biased community diversity comparisons due to variable library sizes[END_REF]. Finally, taxonomic affiliation of OTUs was done using classify.otu and the Glomeromycota-based 18S rDNA sequence database from [START_REF] Krüger | Phylogenetic reference data for systematics and phylotaxonomy of arbuscular mycorrhizal fungi from phylum to species level[END_REF]. The taxonomic affiliation of OTUs was considered significantly robust for a given taxonomic level when the confidence threshold was superior to 50 % (https://rdp.cme.msu.edu/wiki/index.php/Classifier_Help). Raw data are available under the BioPproject ID PRJNA479949 (https://www.ncbi.nlm.nih.gov/bioproject).

Statistics

The AMF percentage colonization data were (arcsine x) 1/2 transformed to achieve homogeneity of variances. Means among all treatments (jujube cultivars, AM fungal inoculation or not, RP fertilization or not) were compared with three-way analysis of variance (ANOVA) followed by Tukey's HSD (Honestly significant differences (P < 0.05) using XLSTAT software (version 2010, Addinsoft). Diversity (Shannon, inverse Simpson [1/D], coverage), richness (number of OTUs, Chao) and evenness indexes (Shannon index-based measure) were estimated. The sequencing effort was evaluated by using Boneh calculator [START_REF] Boneh | Estimating the prediction function and the number of unseen species in sampling with replacement[END_REF]) implemented in Mothur. All indexes were compared among all treatments using R version 3.3.1 [START_REF] Core | R: A Language and Environment for Statistical Computing[END_REF]) by threeway ANOVA followed by post-hoc Tukey test, as implemented in aov() and TukeyHSD() functions. AM fungal community membership among treatments (jujube cultivars, inoculation or not) was assessed using the venn.diagram() function from the R package VennDiagram version 1.6.17 [START_REF] Chen | The physiological basis of containerised tree seedling 'transplant shock': a review[END_REF]). The differences in the AM fungal community structures among all treatments were based on the Bray-Curtis dissimilarity matrix and assessed using non-parametric permutational multivariate analysis of variance (PERMANOVA) as implemented in the adonis() function from the R package vegan version 2.4-3 [START_REF] Oksanen | vegan: Community Ecology Package. R package version 2.4-1[END_REF]. Multivariate dispersion was estimated for each treatment using the betadisper() function and permutest() as it can affect PERMANOVA results. The significance of AM fungal OTUs with respect to the jujube cultivar or the jujube status (inoculated or not, fertilized or not) was determined using the indicator value (IndVal) index, as implemented in multipatt() function from the R package indicspecies [START_REF] De Cáceres | Associations between species and groups of sites: indices and statistical inference[END_REF]. Two different probabilities were calculated, i.e. A (specificity), representing the probability of a sample to be defined by a group (i.e., jujube cultivar, AM inoculation status, fertilization status), given that the OTU has been detected, and B (sensitivity) representing the probability of finding the OTU in different samples characterized by a given group. Only the OTUs present in more than half of samples for a given group are considered, i.e. B superior to 0.5. Table transformations in R were performed with the tidyverse packages version 1.1.1 [START_REF] Wickham | Tidyverse: Easily Install and Load[END_REF].

Results

Tree nursery -Growth, mineral nutrition and mycorrhizal colonization of jujube trees

Tree growth and nutrition of both cultivars were significantly improved by mycorrhizal inoculation with Rhizophagus irregularis IR27 (Table 1), with relatively stronger effects on the Gola cultivar compared to the Tasset cultivar. By contrast, fertilization with rock phosphate (RP) showed no effect on tree growth and nutrition, excepted regarding N nutrition for Gola cultivar, and no additional effect was observed when mycorrhizal inoculation was combined with RP fertilization compared to mycorrhizal inoculation only. A similar percentage of mycorrhizal infection was observed for both Tasset and Gola cultivars, reaching 65.8 % to 68.9 %, respectively. However, RP fertilization significantly decreased the mycorrhizal infection of both cultivars (Table 1).

Field monitoring -Survival, growth and mycorrhizal colonization of jujube trees

Beneficial effects (tree height and collar diameter) of mycorrhizal inoculation were observed on both jujube cultivars preliminary subjected to different mycorrhiza-based engineering strategies in tree nursery (mycorrhizal inoculation combined or not with RP fertilization), until the 13 months after outplanting. As observed in tree nursery, jujubes only fertilized with RP showed characteristics similar to controls during time.

Three months after planting, the rate of survival did not differ significantly between inoculated and non-inoculated plants, ranging from 75 % to 96 %. After 8 and 13 months, there was a significant increase in the rate of survival mediated by the mycorrhizal inoculation and mycorrhizal-fertilized treatments, notably for Tasset. The 13-month-old non-inoculated jujube trees showed low percentage of survival, 41.6 % and 45.8 % for Gola and Tasset respectively, whereas these percentage reach more than 70 % for the 13-month-old inoculated jujube trees, 70.8 % and 75 % for Gola and Tasset, respectively (Table 2). The height of jujube trees was the only parameter significantly different between 13-month-old inoculated jujube Gola (> 80 cm) and Tasset (< 75 cm) cultivars. In the mycorrhizal treatments, the highest values for height (81.2 cm) and collar diameter (24.8 mm) were recorded for Gola.

The estimation of height and diameter evolution during 13 months after transplanting showed a stability of nursery-driven impacts, with substantial higher rates (slope value of linear regression) notably for the height of inoculated trees (Fig. S1).

Mycorrhizal colonization was observed at 13 months after transplanting in jujubes roots.

Colonization levels were higher for all inoculated treatments of Gola (59.8 % inoculated and 50 % inoculated-fertilized) and Tasset (56.4 % inoculated and 46.4 % inoculated-fertilized) compared to non-inoculated controls and fertilized treatments (Table 2).

Field monitoring -Composition of the jujube root-associated AM fungal community

Overall, 285,783 sequences (forward reads) with a median length of 241 bp passed the initial quality assessment. Then, 166,737 sequences were retrieved after alignment denoising step, removal of chimera, non Glomeromycota sequences and singletons. In order to perform reliable comparison among samples, a normalization of sequence number was applied (number of sequence per sample set to 2,351), leading to a subset of 70,530 sequences. The clustering of final data revealed 239 AM fungal OTUs detected in a total of 30 composite root samples. The majority of AM fungal OTUs belonged to Glomeraceae (94 % of total reads, 178 OTUs) (Table S1), and few OTUS to Diversisporaceae (3 %, 31 OTUs), Paraglomeraceae (2 %, 11 OTUs), Gigasporaceae (0.5 %, 8 OTUs), Acaulosporaceae (0.06 %, 6 OTUs), Geosiphonaceae (0.01 %, 3 OTUs), Claroideoglomeraceae (< 0.01 %, 1 OTU) and Pacisporaceae (<0.01 %, 1 OTUs). Glomeraceae OTUs belonged to Sclerocystis (28 % of Glomeraceae reads), Rhizophagus (27 %), Glomeraceae related to Glomus sensu lato (22 %), Glomus sensu stricto (20 %), and in a lesser extent to Septoglomus (4 %), Funneliformis (0.4 %) and unclassified Glomeraceae (0.02 %).

The native jujube root-associated AM fungal (untreated jujube trees) was composed of 85 (Gola) to 98 (Tasset) OTUs, with 80 % of sequences related to 15 known genera and 20 % only to Glomeraceae with uncertain position (unclassified Glomeraceae and Glomus sensu lato) (Table S2). A core AM fungal sub-community of 47 OTUs (93.4 % of sequences) (Fig. 1) was largely dominated by Glomeraceae, whose 26 % Sclerocystis, 18 % Rhizophagus, 28 % Glomus sensu stricto, 21 % Glomus sensu lato, 6 % Septoglomus and < 1 % Funneliformis (Fig. 1, Table S2). The cultivar Tasset presented the most diverse AM fungal community (Table 3), with a significant association of eight OTUs related to Redeckera, Rhizophagus and Glomus sensu stricto (Table S2). Three OTUs related to Glomus sensu stricto were significantly associated with the Gola cultivar but with a relatively low specificity (A < 0.7) (Table S2).

Field monitoring -Impact of ecological engineering strategies on the jujube rootassociated AM fungal community

A robust diversity coverage was obtained for the AM fungal community associated with both jujube cultivars, independently of jujube status (inoculated or not, fertilized or not), reaching more than 99 %, and with Boneh estimates evaluated to less than seven OTUs (Table 3). After 13 months, AM fungal inoculation (P < 0.001) and the type of cultivar (P < 0.05) had significant effect on AM fungal community richness, whereas RP fertilization (P < 0.05) mostly impacted AM fungal community diversity (Table 3). However, results revealed a fertilization effect on AM fungal community richness (P < 0.01) and diversity (P < 0.05) highly dependent on AM fungal inoculation. No impact of ecological engineering strategies was observed on the evenness of AM fungal communities, but a relatively, low evenness was revealed, ranging from 0.4 to 0.6. Globally, mycorrhizal inoculation and RP fertilization negatively impacted AM fungal richness and diversity, with the most significant impact observed for the local jujube cultivar Tasset when inoculated with R. irregularis IR 27. The use of RP fertilization in combination to mycorrhizal inoculation did not show a significant impact on AM fungal community richness and diversity compared to single treatments (inoculation or fertilization). Association analysis between each OTU and jujube cultivars or jujube status (inoculated or not, fertilized or not) revealed high significant associations for two OTUs related to Rhizophagus and Glomus sensu lato with the Tasset cultivar, independently of jujube status (Table 4), suggesting their stability through treatments.

Fertilization status was characterized by the association with Glomeraceae OTUs, one with fertilized jujube trees and two with non-fertilize jujube trees independently of jujube cultivars and inoculation status (Table 4).

As observed for AM fungal community richness and diversity, jujube inoculation with R. irregularis IR27 appeared as the most significant treatment (P = 0.011) affecting the AM fungal community structure of jujube trees on the field (Table 5). Nevertheless, the type of cultivar and the RP fertilization significantly affected the inoculation impact on AM fungal community structure (P = 0.019). The analysis of AM fungal community membership among inoculated and non-inoculated jujube trees for the both cultivars Tasset and Gola (Fig. S2) revealed a predominant core AM fungal sub-community (97 % of sequences) composed of 26 OTUs, as well as rare 23 OTUs (0.1 %) only detected in jujube trees inoculated with R. irregularis IR27, and rare 66 OTUS (0.3 %) only in non-inoculated jujube trees. AM fungal inoculation of jujube trees negatively impacted (P < 0.05) the abundance of eight OTUs belonging to Cetraspora (OTU_31), Gigaspora (OTU_25), Glomus (OTU_07, OTU_39), Redeckera (OTU_08, OTU_34), Rhizophagus (OTU_04) and Paraglomus (OTU_12) for the Tasset cultivar, and eight OTUs belonging to Glomus sensu stricto (OTU_07, OTU_09, OTU_78), Glomus sensu lato (OTU_15, OTU_20), Redeckera (OTU_16, OTU_41), Rhizophagus (OTU_29) for the Gola cultivar (Fig. 2). However, two OTUs belonging to Rhizophagus (OTU_02, OTU_14) were positively impacted for the Gola cultivar (Fig. 2). It has to be noted that the comparison between the 18S rRNA gene sequence from the AM fungal inoculum and the representative sequence of each OTU revealed 100 % similarity with one the most dominant OTUs, i.e. OTU_2 related to R. irregularis (Table S1). Association analysis (Table 4) emphasized the global negative impact for five of these OTUs belonging to Glomeraceae and Gigasporaceae, independently of jujube cultivar and fertilization status.

Discussion

The improvement of plant growth through ecological engineering strategies, notably using mycorrhizal inoculants, constitute a sustainable approach for increased food security and ecosystem conservation [START_REF] Rodriguez | The role of community and population ecology in applying mycorrhizal fungi for improved food security[END_REF][START_REF] Hart | Fungal inoculants in the field: Is the reward greater than the risk?[END_REF]). However, their long-term efficiency on field and their impact on native microbial communities remain critical issues for their adoption by national authorities and integration by end-users in agricultural and environmental practices. In this study, the efficiency and sustainability of two types of mycorrhiza-based ecological engineering strategies on jujubes were assessed from nursery to field.

Beneficial effects of mycorrhizal inoculation on jujube trees from nursery to field

The current nursery results emphasized the AM-mediated plant benefits previously observed on different jujube cultivars or provenances [START_REF] Guissou | Responses of Parkia biglobosa (Jacq.) Benth., Tamarindus indica L. and Ziziphus mauritiana Lam. to arbuscular mycorrhizal fungi in a phosphorus-deficient sandy soil[END_REF][START_REF] Guissou | Effect of of arbuscular mycorrhizae on growth and mineral nutrition of greenhouse propagated fruit trees from diverse geographic provenances[END_REF][START_REF] Sidibé | The use of mycorrhizal inoculation in the domestication of Ziziphus mauritiana and Tamarindus indica in Mali (West Africa)[END_REF][START_REF] Thioye | Growth response of different species of Ziziphus to inoculation with arbuscular mycorrhizal fungi[END_REF]) in terms of growth and nutrient uptake (N, P, K). In addition, a higher P assimilation from RP of jujubes when inoculated by R. irregularis IR27 was confirmed compared to non-inoculated jujubes [START_REF] Bâ | Mobilization of rock phosphates by soil microorganisms associated with Zizyphus mauritiana Lam. and Vigna unguiculata (L.) Walp[END_REF]). Nevertheless, no significant benefit was obtained when RP fertilization was used combined with mycorrhizal inoculation in comparison to mycorrhizal inoculation alone, as observed in [START_REF] Bâ | Mycorhization contrôlée et fertilisation phosphatée: Application à la domestication du jujubier[END_REF]. Some authors argue that mycorrhizal inoculation can be considered as a substitute of P fertilization in tree nursery management [START_REF] Smith | Mycorrhizal Symbiosis[END_REF]. In addition, RP fertilization negatively affected R. irregularis IR27 root colonization, which may suggest a non-optimum P-supply in the nursery conditions [START_REF] Liu | Arbuscular mycorrhizal fungi in soil and roots respond differently to phosphorus inputs in an intensively managed calcareous agricultural soil[END_REF]. The significance of increased P assimilation from RP through mycorrhiza has been already showed as unclear [START_REF] Antunes | Can the arbuscular mycorrhizal fungus Glomus intraradices actively mobilize P from rock phosphates?[END_REF], probably depending of biotic (mycorrhizal strain × host plant) and abiotic (soil or substrat P contents, provenance of RP) characteristics, and the duration of plant cultures [START_REF] Bâ | Mycorhization contrôlée et fertilisation phosphatée: Application à la domestication du jujubier[END_REF][START_REF] Antunes | Can the arbuscular mycorrhizal fungus Glomus intraradices actively mobilize P from rock phosphates?[END_REF][START_REF] Khan | Plant growth promotion by phosphate solubilizing fungi -current perspective[END_REF]). The mycorrhizal-mediated jujube nutritional benefit may explain the enhanced jujube growth performance, but non-nutritional benefits should also be investigated to fully decipher mycorrhizal-mediated plant fitness, notably on field [START_REF] Delavaux | Beyond nutrients: a metaanalysis of the diverse effects of arbuscular mycorrhizal fungi on plants and soils[END_REF][START_REF] Lekberg | Integrating physiological, community, and evolutionary perspectives on the arbuscular mycorrhizal symbiosis[END_REF].

The beneficial effects of mycorrhiza-based ecological engineering strategies used in nursery on jujube cultivars and their durability was evaluated on a field site characterized by degraded and arid conditions. The impacts of mycorrhizal inoculation in degraded or desertified landscapes are expected to be highly significant because of low soil mycorrhizal potential [START_REF] Hart | Fungal inoculants in the field: Is the reward greater than the risk?[END_REF], confirmed by current results. Consequently, a better establishment and growth of jujube trees were expected as for other plants in similar harsh conditions [START_REF] Requena | Assessment of natural mycorrhizal potential in a desertified semiarid ecosystem[END_REF][START_REF] Estaun | AM inoculation as a biological tool to improve plant revegetation of a disturbed soil with Rosmarinus officinalis under semi-arid conditions[END_REF][START_REF] Duponnois | The mycorrhizal fungus Glomus intraradices and rock phosphate amendment influence plant growth and microbial activity in the rhizosphere of Acacia holosericea[END_REF]Bilgo et al. 2012). The most significant plant benefit was the rate of survival, which constitutes the primary target in horticulture, especially in such harsh environmental conditions as the ones encountered in the pan-African Great Green Wall (GGW) experimental sites. The benefit of mycorrhizal inoculation on jujube height was still significant after 13 months following outplanting but not on collar diameter. However, more plant parameters should be investigated in long term to fully evaluate the sustainability of mycorrhizal inoculation effects. A higher colonization rate was still observed between inoculated and non-inoculated jujubes in the 13-month-old orchard, but the differences observed in nursery between inoculated jujube seedlings with or without RP fertilization had disappeared likely due to native AM colonization. A two year-long field monitoring [START_REF] Pellegrino | Establishment, persistence and effectiveness of arbuscular mycorrhizal fungal inoculants in the field revealed using molecular genetic tracing and measurement of yield components[END_REF] previously demonstrated the link between an increase colonization rate and yield increases, but a meta-analysis based on inoculation surveys between 1998 and 2003 confirmed this relationship for only 23 % of study sites [START_REF] Lekberg | Is plant performance limited by abundance of arbuscular mycorrhizal fungi? A meta-analysis of studies published between 1988 and 2003[END_REF]. In addition, the benefit on field has to be put in perspective since jujube heights between untreated and treated (inoculation and/or fertilization) trees were different when transplanting. The monitoring of height-based or diameter-based growth rate tends to show a relative stability of pre-treatments in nursery, but more robust assessment of growth rates taking a higher number of plant parameters are needed. The better field survival of inoculated jujubes is evidently due to seedling status improvements (higher mycorrhizal infection rate, nutrition) in nursery and potentially to a residual effect of the AM inoculated strain.

Field environmental impacts of mycorrhizal inoculation on native AM fungal biodiversity

The range and sustainability of AM fungal-mediated plant benefits (biomass, yield, survival) are the most obvious concerns for end-users [START_REF] Berruti | Arbuscular Mycorrhizal Fungi as Natural Biofertilizers: Let's Benefit from Past Successes[END_REF]), but the environmental impacts of AM fungal inoculant introduction in agroecosystems remains a critical issue.

Three levels of environmental impacts were categorized [START_REF] Rodriguez | The role of community and population ecology in applying mycorrhizal fungi for improved food security[END_REF], (i) alteration of composition and structure of native AM fungal population and/or community, (ii) exchange of genetic material with native AM fungal population and/or community, and (iii) persistence and/or spread of AM fungal inoculants, increasing consequently the first two impacts.

The native AM fungal community in jujube roots was targeted because considered as the symbiotically AM fungal community [START_REF] Chagnon | Is root DNA a reliable proxy to assess arbuscular mycorrhizal community structure?[END_REF][START_REF] Hart | Navigating the labyrinth: a guide to sequencebased, community ecology of arbuscular mycorrhizal fungi[END_REF], and differs significantly from the soil (spore and extraradical mycelia) compartment [START_REF] Varela-Cervero | The composition of arbuscular mycorrhizal fungal communities differs among the roots, spores and extraradical mycelia associated with five Mediterranean plant species[END_REF]. Although over-interpretations were suggested in experimental designs using mycorrhizal-free plants as controls [START_REF] Hart | Fungal inoculants in the field: Is the reward greater than the risk?[END_REF]), the differences in mycorrhizal infectivity between inoculated and non-inoculated jujube trees may indicate a higher colonization of R. irregularis IR27 compared to the native AM fungal community because of a priority effect due to pre-colonization of jujube roots in the nursery [START_REF] Verbruggen | Mycorrhizal fungal establishment in agricultural soils: factors determining inoculation success[END_REF][START_REF] Werner | Order of arrival structures arbuscular mycorrhizal colonization of plants[END_REF]. This hypothesis is emphasized by the predominance of OTU_2 in roots of inoculated jujube trees, especially for the Gola cultivar. Indeed, this OTU may indicate the persistence and abundance of R. irregularis IR27 since their 18S rRNA gene fragment presented 100 % similarity. It has been demonstrated that the persistence and abundance of an AM fungal strain could be promoted by the presence of other AM fungal species [START_REF] Hart | Hiding in a crowd-does diversity facilitate persistence of a low-quality fungal partner in the mycorrhizal symbiosis?[END_REF], even if this AM fungal strain was not the most efficient one.

However, more informative methods should be used, notably because of the limited resolution of 18S rRNA gene to distinguish certain AM fungal species [START_REF] Hart | Navigating the labyrinth: a guide to sequencebased, community ecology of arbuscular mycorrhizal fungi[END_REF]. The new advances in population genomic analysis (Savary et al. 2017) should be determinant to evaluate not only the persistence of R. irregularis-based inocula but their spread, a major environmental impact poorly investigated [START_REF] Rodriguez | The role of community and population ecology in applying mycorrhizal fungi for improved food security[END_REF][START_REF] Hart | Fungal inoculants in the field: Is the reward greater than the risk?[END_REF]Janouskova et al. 2017). A second hypothesis may be the positive effect of R. irregularis IR27 pre-colonization on the native AM fungal community colonization [START_REF] Rodriguez | The role of community and population ecology in applying mycorrhizal fungi for improved food security[END_REF][START_REF] Werner | Order of arrival structures arbuscular mycorrhizal colonization of plants[END_REF]. Beneficial interactions between AM fungal inocula and the native AM fungal community have been suggested for field trials with Olea europaea in semiarid, degraded land [START_REF] Alguacil | A molecular approach to ascertain the success of "in situ" AM fungi inoculation in the revegetation of a semiarid, degraded land[END_REF].

Few studies investigated in-depth the modifications of native AM fungal communities following mycorrhizal inoculations, contrary to the impact of fertilization [START_REF] Camenzind | Nitrogen and phosphorus additions impact arbuscular mycorrhizal abundance and molecular diversity in a tropical montane forest[END_REF][START_REF] Lin | Long-term balanced fertilization decreases arbuscular mycorrhizal fungal diversity in an arable soil in north China revealed by 454 pyrosequencing[END_REF][START_REF] Liu | Arbuscular mycorrhizal fungi in soil and roots respond differently to phosphorus inputs in an intensively managed calcareous agricultural soil[END_REF][START_REF] Peyret-Guzzon | Arbuscular mycorrhizal fungal communities and Rhizophagus irregularis populations shift in response to short-term ploughing and fertilisation in a buffer strip[END_REF][START_REF] Williams | Long-term agricultural fertilization alters arbuscular mycorrhizal fungal community composition and barley (Hordeum vulgare) mycorrhizal carbon and phosphorus exchange[END_REF]. Most of studies were based on low-throughput approaches and a limited number of community characteristics [START_REF] Pellegrino | Establishment, persistence and effectiveness of arbuscular mycorrhizal fungal inoculants in the field revealed using molecular genetic tracing and measurement of yield components[END_REF][START_REF] Jin | Impact of arbuscular mycorrhizal fungal inoculants on subsequent arbuscular mycorrhizal fungi colonization in pot-cultured field pea (Pisum sativum L.)[END_REF]. The dominance of Glomeraceae and its high frequency in the native AM fungal community of jujubes confirms the worldwide trend described by [START_REF] Davison | Global assessment of arbuscular mycorrhizal fungus diversity reveals very low endemism[END_REF]. These observations were hypothesized as a consequence of its ruderal life strategy (Chagnon et al. 2013), i.e. early productions of spores, high growth rates, higher intraradical host colonization, which is particularly adapted for early re-colonization of host plants in degraded environments such as the ones encountered on the route of the GGW. The preferentially intraradical host colonization of Glomeraceae members may explained their predominance inside roots compared to others AM fungal families such as Pacisporaceae / Paraglomeraceae and Diversisporaceae / Gigasporaceae, which allocate their biomass mainly to the spores and the extraradical mycelium (ERM) [START_REF] Goss | Functional Diversity of Mycorrhiza and Sustainable Agriculture -Management to Overcome Biotic and Abiotic Stresses[END_REF].

Glomeraceae members were also the main family allowing to differentiate the composition and response of native AM fungal community between both jujube cultivars, emphasizing the hypothesis that AM fungal species with a preferentially intraradical lifestyle are mostly affected by host characteristics [START_REF] Sosa-Hernández | Subsoil arbuscular mycorrhizal fungal communities in arable soil differ from those in topsoil[END_REF]. The native AM fungal community associated with jujube trees on the route of the GGW presented several particularities compared to the generally described AM fungal communities. First, Rhizophagus or Funneliformis or members of Glomus sensu lato generally constitute the most dominant genera in Glomeraceae in semiarid environments [START_REF] Yamato | Community of arbuscular mycorrhizal fungi in drought-resistant plants, Moringa spp., in semiarid regions in Madagascar and Uganda[END_REF][START_REF] Alguacil | Soil characteristics driving arbuscular mycorrhizal fungal communities in semiarid Mediterranean soils[END_REF]Torrecilas et al. 2012), but rarely Glomus sensu stricto or Sclerocystis as observed in the current study. Second, Paraglomeracae, a rare AM fungal family in AM fungal surveys [START_REF] Davison | Global assessment of arbuscular mycorrhizal fungus diversity reveals very low endemism[END_REF], was the third most abundant family detected inside the roots, even if its abundance level remained low compared to Glomeraceae. This genus has been described as preferentially detected in soil compared to roots and ERM [START_REF] Hempel | Differences in the species composition of arbuscular mycorrhizal fungi in spore, root and soil communities in a grassland ecosystem[END_REF][START_REF] Varela-Cervero | The composition of arbuscular mycorrhizal fungal communities differs among the roots, spores and extraradical mycelia associated with five Mediterranean plant species[END_REF], probably due to its life strategy (see above). An in-depth AM survey in tropical African ecosystems revealed for the first time a high predominance of Paraglomeraceae in grasslands and open areas highlighting the existence of ecological specificity of AM fungi [START_REF] Rodríguez-Echeverría | Arbuscular mycorrhizal fungi communities from tropical Africa reveal strong ecological structure[END_REF]).

An overall negative impact of the different treatments was observed on the native AM fungal community. The AM fungal richness was the characteristic the most affected by all treatments, notably inoculation. The pre-colonization of jujube roots in nursery by the exotic AM fungal strain was supposed to have a strong negative impact on the AM native fungal community colonization rate, but it was also supported by the persistence of the inoculum evidenced in the results (high level of OTU2). Richness is the main community characteristic assessed to monitor AM fungal community but a general trend remains difficult to define [START_REF] Antunes | Influence of commercial inoculation with Glomus intraradices on the structure and functioning of an AM fungal community from an agricultural site[END_REF][START_REF] Mummey | Arbuscular mycorrhizal fungi preinoculant identity determines community composition in roots[END_REF]Koch et al. 2011). For instance, whereas a negative impact was observed in the current study, a positive tendency had been observed in a 14-month-old olive orchard [START_REF] Alguacil | A molecular approach to ascertain the success of "in situ" AM fungi inoculation in the revegetation of a semiarid, degraded land[END_REF]. When considering the global AM fungal community structure, only inoculation had a significant impact, leading to a negative effect on abundance of few AM fungal OTUs. The importance to monitor multiple community characteristics appears essential, particularly given that it remains challenging to link a specific community characteristic to a beneficial or detrimental plant effect [START_REF] Rodriguez | The role of community and population ecology in applying mycorrhizal fungi for improved food security[END_REF].

Conclusion

The current study constitutes an in-depth field investigation of mycorrhizal inoculation impact with an exotic isolate on native AM fungal community. Results clearly showed that ecological engineering strategies using R. irregularis significantly promote jujube performance (growth and nutrition) notably at very early stages in nursery, and highly improved the rate of survival on the field. In addition, a relative stability of nursery-driven plant benefits of inoculated jujube trees was observed. Nevertheless, the mycorrhizal field-observed benefits on jujube growth remain difficult to evaluate due to differences in jujube growth at outplanting. The comparison of a local (Tasset) and exotic (Gola) jujube cultivars pointed a potential higher persistence of AM fungal inoculum for the exotic and more limited disturbances of native AM fungal community. Results provide important insights to develop and improve the ecological management of jujube orchards on the route of the GGW (Senegal), but further investigations should be implemented to assess the long-term plant impact of such mycorrhiza-based ecological engineering strategies and to fully evaluate the persistence and spread of exotic mycorrhizal inocula versus native AM fungi. Further investigations are also required to evaluate the effect of inoculation with native AM fungi selected species or consortia of AM fungi. Understanding how introduced AM fungal strains interact and coexist with the native AM fungal community and whether this directly leads to changes in plant productivity is the key for an acceptation by stakeholders and national authorities of the use of AM fungi in agriculture, particularly in arid area where plant productivity sustainability is the major issue.

Funding

This study was supported by the Africa-Brazil-France tripartite research program entitled "Fight against desertification in Africa". Babacar Thioye received grants from the Institut de Recherche pour le Développement (IRD) and the Institut Sénégalais de Recherches Agricoles (ISRA). The block factor was not significant (P > 0.05)

Values in columns followed by the same letter do not differ significantly according to Tukey's HSD. Significant levels: *P < 0.05; **P < 0.01; ***P < 0.001; ns, not significant; Ri: Rhizophagus irregularis; RP: rock phosphate; Mycorrhizal infection was only assessed at 13 months after planting.

  followed by the same letter do not differ significantly according to Tukey's HSD. Significant levels: *P < 0.05; **P < 0.01; ***P < 0.001; ns, not significant. Ri: Rhizophagus irregularis IR27; RP: rock phosphate.

1

  PERMANOVA was based Bray-Curtis dissimilarity matrix and assessed using adonis() function (iterations = 9,999 permutations). '*' P < 0.05; ' ns ' P > 0.05. Multivariate dispersion was tested using the betadisper() and permutest() functions (iterations = 9,999 permutations; alpha = 0.05) revealing a significant homogeneity of group dispersions. df = degrees of freedom; SS = sum of squares; MS = mean sum of squares; F model = F statistics; R 2 = partial Rsquared.

Fig. 1 .

 1 Fig. 1. Comparison of AM fungal community membership (Venn diagram analysis) between non-inoculated jujube trees from the two cultivars Tasset and Gola. All sequences were clustered in OTUs (97 % similarity). For each Venn category, the number of OTU and the relative abundance (% of sequences) are indicated. Color pie charts represent the abundance of OTUs shared between the two cultivars and specific to each. "incertae sedis" represents OTUs related to Glomus sensu lato for which uncertain position in Glomeraceae has been described, and "unclassified" OTUs affiliated only to Glomeraceae level.

Fig. 2 .

 2 Fig. 2. Changes in abundance of AM fungal OTUs among inoculated and non-inoculated jujube Tasset and Gola cultivars. Only OTUs with significant differences (P < 0.05) are shown. Statistics were performed using Kruskal-Wallis' test. "Un. Glomeraceae" indicates affiliation to references belonging to Glomus sensu lato, for which uncertain position in Glomeraceae has been described.

Table 1

 1 Effect of Rhizophagus irregularis IR27 inoculation and rock phosphate fertilization on growth, mycorrhizal colonization and mineral nutrition of 4month-old jujube (Z. mauritiana) tree cultivars (Tasset, Gola) (tree nursery).

	Treatment	Height	Collar diameter	Total dry biomass	Mycorrhizal	N	P	K
		(cm)	(mm)	(g)	colonization (%)	(%)	(%)	(%)
	Gola	19.7 ± 2.3 c	2.8 ± 0.4 cd	1.4 ± 0.1 cd	0.0 d	1.3 ± 0.1 b	1.3 ± 0.7 d	08.4 ± 1.0 d
	Gola+RP	22.6 ± 4.4 c	3.2 ± 0.3 c	1.6 ± 0.1 c	0.0 d	2.4 ± 0.4 a	1.5 ± 0.6 cd	10.0 ± 2.0 bcd
	Gola+Ri	54.3 ± 8.6 a	4.8 ± 0.6 a	3.6 ± 0.5 a	68.9 ± 14.1 a	2.4 ± 0.2 a	2.7 ± 0.2 a	14.6 ± 0.9 a
	Gola+Ri+RP	50.2 ± 9.6 a	4.5 ± 0.4 ab	3.5 ± 0.5 a	51.4 ± 14.9 b	2.5 ± 0.4 a	2.6 ± 0.1 ab	14.3 ± 0.5 a
	Tasset	15.9 ± 2,4 d	2.5 ± 0.3 c	1.3 ± 0.1 d	0.0 d	1.3 ± 0.1 b	1.2 ± 0.1 d	09.4 ± 0.7 cd
	Tasset+RP	17.8 ± 4.0 cd	3.1 ± 0.4 c	1.3 ± 0.1 cd	0.0 d	1.6 ± 0.2 b	1.2 ± 0.2 d	08.7 ± 1.1 d
	Tasset+Ri	35.9 ± 6.9 b	4.1 ± 0.9 b	2.6 ± 0.4 b	65.8 ± 11.5 a	2.1 ± 0.0 a	2.1 ± 0.0 bc	11.0 ± 0.6 bc
	Tasset+Ri+RP	37.7 ± 7.5 b	4.1 ± 0.9 b	2.7 ± 0.5 b	38.7 ± 15.6 c	2.1 ± 0.1 a	2.3 ± 0.0 ab	11.3 ± 0.4 b
	All treatments
	Cultivar (C)	***	**	***	ns	**	*	**
	Inoculation (I)	***	***	***	***	***	***	***
	Fertilization (F)	ns	ns	ns	ns	**	ns	ns
	(C) × (I)	***	ns	***	ns	ns	ns	***
	(I) × (F)	ns	**	ns	ns	**	ns	ns

Table 2

 2 Effect of Rhizophagus irregularis IR27 inoculation and rock phosphate fertilization on growth, rate of survival and mycorrhizal colonization of jujube tree cultivars after transplanting.

	Treatment	3 months after planting		8 months after planting		13 months after planting
		Height	Collar	Rate of	Height	Collar	Rate of	Height	Collar	Rate of	Mycorrhizal
		(cm)	diameter	Survival	(cm)	diameter	Survival	(cm)	diameter	survival	colonization
			(mm)	(%)		(mm)	(%)		(mm)	(%)	(%)
	Gola	24.5±3.1 de	07.2±1.2 de	83.3±38.7 ab	29.1±3.3 cd	13.8±2.2 de	50.0±51.0 cd	38.5±8.7 d	17.9±1.8 bc	41.6±50.3 d	21.4±4.8 c
	Gola+RP	27.2±3.3 cd	08.0±1.6 cd	95.8±20.4 a	31.4±3.5 c	16.5±3.5 abcd 66.6±48.1 bc	39.2±3.8 d	21.8±2.0 ab	54.1±50.8 c	21.8±4.2 c
	Gola+Ri	59.9± 8.8 a	09.3±1.9 ab	91.6±28.2 ab	66.3±12.9 a	16.9±2.0 abc	83.3±38.0 ab	81.2±13.8 a	20.6±3.5 abc	70.8±46.4 ab	59.8±5.7 a
	Gola+Ri+RP	55.6±11.1 ab	10.2±1.8 a	95.8±20.0 a	63.4±9.8 a	19.3±4.9 a	91.6±28.2 a	79.5±11.1 ab	24.8±3.8 a	66.6±48.1 abc 50.0±8.1 ab
	Tasset	18.9±5.2 de	06.7±1.7 e	79.1±41.4 ab	22.7±3.4 d	13.1±1.2 bcde 62.5±49.4 bcd 34.6±3.5 d	18.1±1.6 bc	45.8±50.8 d	26.0±3.7 c
	Tasset+RP	20.4±6.9 e	07.2±1.8 de	75.0±44.2 b	26.1±6.7cd	12.8±2.1 e	41.6±50.3 d	37.6±4.6 d	15.3±1.3 c	41.6±50.3 d	21.0±4.7 c
	Tasset+Ri	40.1±6.8 bc	09.2±1.9 ab	91.6±28.2 ab	51.2±9.6 b	17.6±2.6 ab	83.3±38.0 ab	74.9±15.7 c	20.9±2.3 abc	75.0±44.2 a	56.4±7.3 ab
	Tasset+Ri+RP	42.1±11.2 bc	08.6±2.8 bc	83.3±38.0 ab	53.1±6.6 ab	16.7±2.4 cde	70.8±46.4 abc 77.2±38.3 abc 19.7±2.4 abc	62.5±49.4 bc	46.4±5.2 b

Table 3

 3 Effect of jujube cultivar, mycorrhizal inoculation and rock phosphate fertilization on richness, diversity and evenness of the jujube root-associated AM fungal community.

		Richness		Diversity	Evenness
	Treatment	Number of OTUs Chao	Shannon	Invsimpson	Shannoneven	Boneh	Coverage (%)

Table 5

 5 Impact of jujube cultivar, AM fungal inoculation and RP fertilization on the jujube rootassociated AM fungal community structure (field experiment).

	Treatments	df	SS	MS	F model R 2	P value 1
	Cultivar (C)	1	0.253	0.253	1.224	0.038	0.268 ns
	Inoculation (I)	1	0.563	0.563	2.726	0.084	0.011*
	Fertilization (F)	1	0.199	0.199	0.967	0.029	0.470 ns
	(C) × (I)	1	0.135	0.135	0.655	0.020	0.722 ns
	(C) × (F)	1	0.343	0.343	1.660	0.051	0.113 ns
	(I) × (F)	1	0.130	0.130	0.630	0.019	0.767 n
	(C) × (I) × (F)	1	0.496	0.496	2.400	0.074	0.019*
	Residuals	22	4.546	0.206		0.681
	Total	29	6.668			1

package indicspecies (De Cáceres and Legendre, 2009). 3 Statistics were obtained using 9,999 permutations. Significance code: '***' P<0.001; '**' P<0.01; '*' P<0.05. A and B correspond to specificity and sensibility. Only the OTUs present in more than half of samples for a given group are considered, i.e. B superior to 0.5. "Un. Glomeraceae" indicates affiliation to references belonging to Glomus sensu lato, for which uncertain position in Glomeraceae has been described.

between inoculated and non-inoculated jujube trees from the two cultivars Tasset and Gola.

Ri, R. irregularis IR27.