Unique arbuscular mycorrhizal fungal communities uncovered in date palm plantations and surrounding desert habitats of Southern Arabia

Abstract

The main objective of this study was to shed light on the previously unknown arbuscular mycorrhizal fungal (AMF) communities in Southern Arabia. We explored AMF communities in two date palm (Phoenix dactylifera) plantations and the natural vegetation of their surrounding arid habitats. The plantations were managed traditionally in an oasis and according to conventional guidelines at an experimental station. Based on spore morphotyping, the AMF communities under the date palms appeared to be quite diverse at both plantations and more similar to each other than to the communities under the ruderal plant, Polygala erioptera, growing at the experimental station on the dry strip between the palm trees, and to the communities uncovered under the native vegetation (Zygophyllum hamiense, Salvadora persica, Prosopis cineraria, inter-plant area) of adjacent undisturbed arid habitat. AMF spore abundance and species richness were higher under date palms than under the ruderal and native plants. Sampling in a remote sand dune area under Heliotropium kotschyi yielded only two AMF morphospecies and only after trap culturing. Overall, 25 AMF morphospecies were detected encompassing all study habitats. Eighteen belonged to the genus Glomus including four undescribed species. Glomus sinuosum, a species typically found in undisturbed habitats, was the most frequently occurring morphospecies under the date palms. Using molecular tools, it was also found as a phylogenetic taxon associated with date palm roots. These roots were associated with nine phylogenetic taxa, among them eight from Glomus group A, but the majority could not be assigned to known morphospecies or to environmental sequences in public databases. Some phylogenetic taxa seemed to be site specific. Despite the use of group-specific primers and efficient trapping systems with a bait plant consortium, surprisingly, two of the globally most frequently found species, Glomus intraradices and Glomus mosseae, were not detected neither as phylogenetic taxa in the date palm roots nor as spores under the date palms, the intermediate ruderal plant, or the surrounding natural vegetation. The results highlight the uniqueness of AMF communities inhabiting these diverse habitats exposed to the harsh climatic conditions of Southern Arabia.

Fig. 1

Simplified map of Southern Arabia showing main geographical features of the area (modified from Preusser et al. 2002) including the sampling sites. The four sites are an oasis (filled triangle), an experimental station (empty triangle), an undisturbed habitat (filled circle), and sand dunes (empty circle)

Fig. 2

Plants studied in the different habitats of Southern Arabia: a date palm (Phoenix dactylifera), b P. erioptera, c Z. hamiense, d S. persica, e P. cineraria, and f H. kotschyi

Fig. 3

Dendrogram of cluster analysis based on the similarity of AMF morphospecies community composition across the host plants in all studied habitats. Two main clades were formed suggesting that AMF communities associated with date palm in the two plantations have different composition than that of vegetation in the undisturbed habitat (inter-plant area, S. persica, P. cineraria, and Z. hamiense), the disturbed area of the experimental station (P. erioptera), and the sand dunes (H. kotschyi). The group average clustering method and the squared Euclidean distance metric were used

Fig. 4

Comparison of the effect of plant species in different study habitats on a AMF spore abundance in the field, b AMF species richness in the field and the trap cultures, and c the infection potential. Values are reported as means (±SD). Non-significant differences between the means are indicated by similar letters above their error bars

Fig. 5

The relationship between a the infection potential and field spore abundance (r = 0.676, P = 0.0001) and b the infection potential and species richness (r = 0.729, P = 0.0001)

Fig. 6

Phylogenetic tree of sequences obtained in this study from the date palms in the oasis plantation (OA) in 2006 and the experimental station (ES) in 2004 and 2006 and sequences from public databases. Sequences obtained in the present study are shown in boldface and are labeled with the database accession number (e.g., GQ406077), the plantation (e.g., oasis OA), the root sample replicate (e.g., 1), RFLP pattern (e.g., A), and the sampling year. The tree was obtained by neighbor-joining analysis of 308 characters from the 18S rDNA. The numbers above the branches are neighbor-joining bootstrap values from 1,000 replications. The tree was rooted using Paraglomus occultum. Note: S. castanea, S. gregaria, and S. fulgida were all recently renamed R. castanea, R. gregaria, and R. fulgida, respectively (Oehl et al. 2008); Kuklospora colombiana is the former Entrophospora colombiana (Sieverding and Oehl 2006); Ambispora appendicula is the former Archaeospora leptoticha (Spain et al. ; Walker 2008)