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Abstract
Recent microbiome research has shown that soil fertility, plant-associated microbiome, and crop production can be affected by abiotic environmental parameters. The effect of aridity gradient on rhizosphere-soil (rhizosphere) and endosphere-root (endosphere) prokaryotic structure and diversity associated with cacti remain poorly investigated and understood. In the current study, next-generation sequencing approaches were used to characterize the diversity and composition of bacteria and archaea associated with the rhizosphere and endosphere of Opuntia ficus-indica spineless cacti in four bioclimatic zones (humid, semi-arid, upper-arid, and lower-arid) in Tunisia. Our findings showed that bacterial and archaeal cactus microbiomes changed in inside and outside roots and along the aridity gradient. Plant compartment and aridity gradient were the influencing factors on the differentiation of microbial communities in rhizosphere and endosphere samples. The co-occurrence correlations between increased and decreased OTUs in rhizosphere and endosphere samples and soil parameters were determined according to the aridity gradient. Blastococcus, Geodermatophilus, Pseudonocardia, Promicromonospora, and Sphingomonas were identified as prevailing hubs and were considered as specific biomarkers taxa, which could play a crucial role on the aridity stress. Overall, our findings highlighted the prominence of the climatic aridity gradient on the equilibrium and diversity of microbial community composition in the rhizosphere and endosphere of cactus.
Highlights
Semi-arid and arid zones occupy nearly 40% of the world’s terrestrial surface and are the most vulnerable to climate changes (Schlaepfer et al, 2017; Canter, 2018)
Fe3+, K+, total soil phosphorus (TP), and capacity exchange cation (CEC) concentrations and the% of humidity and total organic carbon (TOC) decreased while the Ca2+ concentration increased concomitantly with the aridity gradient (HSD Tukey test p < 0.05; Supplementary Table S1). pH and the total nitrogen were comparable in all bioclimatic zones (HSD Tukey test p < 0.05; Supplementary Table S1)
Firmicutes and Betaproteobacteria decreased in the rhizosphere; Cyanobacteria and Deltaproteobacteria in endosphere
Summary
Semi-arid and arid zones occupy nearly 40% of the world’s terrestrial surface and are the most vulnerable to climate changes (Schlaepfer et al, 2017; Canter, 2018). Prominent among these adaptations is the Crassulacean acid metabolism (CAM), a water-efficient type of photosynthesis, which allows plants to fix carbon dioxide through the night and prevent water loss during the day (Nobel, 2010) Their morphologies are characterized by succulent bodies, thick epidermis of cladodes covered with spines, and shallow and extensive root systems that enable cacti to exploit scarce rainfall and high temperatures. Cactus endophytic plant growth-promoting bacteria (PGPR) are known to facilitate plant growth by promoting production of phytohormones (auxins, gibberelins, cytokinins, and ethylene), diazotrophic fixation of nitrogen, and solubilization of phosphate They enhance the plant’s tolerance to various stresses, such as high salinity, drought, metal toxicity, pesticide load, and activity against a broad spectrum of phytopathogens (Puente et al, 2009a; Lopez et al, 2011; Kavamura et al, 2013). Two rhizobacteria related to the genus Bacillus were isolated from Brazilian cacti exhibiting plant growth-promotion abilities under drought conditions (Kavamura et al, 2013)
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