26The epiphytic vascular flora is scarce and facultative in semiarid Mediterranean 27 ecosystems, thus covering diverse taxonomic groups. However, differently to terrestrial 28 conditions, little is known about the factors driving mycorrhizal communities in 29 epiphytic environments. Here, we investigated the arbuscular mycorrhizal fungi (AMF) 30 harboured by 31 plant species occurring in the trunks of Phoenix dactylifera. We 31 wanted to ascertain if host identity and plant functional traits shape mycorrhizal 32 communities. Specifically, we tested the plant life-cycle (perennial versus annual), the 33 plant life-form (herbaceous versus woody), the plant origin (exotic versus native) and 34 the plant species. 35 The roots were examined by molecular and phylogenetic analysis of AMF community. 36 The plant affiliation to species strongly influenced the AMF assemblages. Plant life-37 form and plant life-cycle also shaped AMF interactions. The AMF community differed 38 between annual and perennial species and higher AMF richness was detected in 39 perennial plants. The indicator species analysis revealed three Operational Taxonomic 40 Units belonging to the Glomeraceae, associated with annual species. However, the 41 epiphytic plants associated with AMF irrespective of whether they were native or not, 42 probably because here no functional differences derive from plant origin. 43 44 IMPORTANCE 45 Arbuscular mycorrhizal (AM) symbiosis has a decisive role in plant nutrient and water 46 uptake by plants, with particular importance in stressful environments. Under semiarid 47 conditions, the facultative epiphytic flora should cope with harsh conditions. While 48 numerous studies have been conducted on factors driving terrestrial AM assemblages, 49 3 the epiphytic environment remains unexplored. We offer new insights into composition 50 of AM communities as shaped by epiphytic plant host identity and functional traits. 51 52 53 54 Keywords: Facultative epiphytes; arbuscular mycorrhizal fungi; diversity; SSU rDNA; 55 semiarid ecosystems; 56 57 58 59Epiphytic habitats are considered as extreme plant environments due to the large fluxes 60 of temperature and low water and nutrient availability they are subjected to. In these 61 conditions, symbiotic associations such as mycorrhizal symbiosis could be crucial 62 because of their widely demonstrated role in plant nutrient and water uptake in 63 terrestrial habits, with particular importance in stressful environments (38).
64Furthermore, the availability of compatible and suitable mycorrhizal fungi might be a 65 key factor constraining the development and distribution of epiphytic plants and vice 66 versa.
67In semiarid Mediterranean ecosystems the epiphytic vascular flora is scarce and 68 facultative or accidental, mainly occurring on the trunks of certain palm species. Here, 69 the microhabitat conditions that originate in the cut leaves formed by the pruning of 70 dead or old leaves allow water and debris accumulation, which enables occasional plant 71 establ...