Abstract
Cactaceae represents one of the most species-rich families of succulent plants native to arid and semi-arid ecosystems, yet the associations Cacti establish with microorganisms and the rules governing microbial community assembly remain poorly understood. We analyzed the composition, diversity, and factors influencing above- and below-ground bacterial, archaeal, and fungal communities associated with two native and sympatric Cacti species: Myrtillocactus geometrizans and Opuntia robusta. Phylogenetic profiling showed that the composition and assembly of microbial communities associated with Cacti were primarily influenced by the plant compartment; plant species, site, and season played only a minor role. Remarkably, bacterial, and archaeal diversity was higher in the phyllosphere than in the rhizosphere of Cacti, while the opposite was true for fungi. Semi-arid soils exhibited the highest levels of microbial diversity whereas the stem endosphere the lowest. Despite their taxonomic distance, M. geometrizans and O. robusta shared most microbial taxa in all analyzed compartments. Influence of the plant host did only play a larger role in the fungal communities of the stem endosphere. These results suggest that fungi establish specific interactions with their host plant inside the stem, whereas microbial communities in the other plant compartments may play similar functional roles in these two species. Biochemical and molecular characterization of seed-borne bacteria of Cacti supports the idea that these microbial symbionts may be vertically inherited and could promote plant growth and drought tolerance for the fitness of the Cacti holobiont. We envision this knowledge will help improve and sustain agriculture in arid and semi-arid regions of the world.
Highlights
Arid and semi-arid regions represent one third of the Earth’s land surface area (McGinnies, 1979; Peel et al, 2007)
In order to investigate the role of microorganisms associated with M. geometrizans and O. robusta, we focused on the seed-borne bacteria
In order to gain an overall picture of microbial community structure in Cacti, we first analyzed the distribution of measurable bacterial/archaeal and fungal OTUs by all the factors considered in the experimental design, namely season, site, Cacti species and plant compartment
Summary
Arid and semi-arid regions represent one third of the Earth’s land surface area (McGinnies, 1979; Peel et al, 2007) These ecosystems are characterized by their low water availability which restrains biological activity (Noy-Meir, 1973). Cactaceae are an extremely diverse family of plants; to date, around 2000 species have been identified, distributed from Southwest Canada to Southern Argentina (Bravo Hollis and Sheinvar, 1999) This rich family of succulent plants use the crassulacean acid metabolism (CAM) for photosynthesis, a biochemical strategy that allows them to fix carbon dioxide during the night and prevent water loss during the day (Nobel, 2003). This strategy, together with morphological changes such as a thin and superficial root systems (which enable water uptake in moisture-limiting conditions), and succulent bodies (used for water storage), have likely enabled their success in arid and semi-arid regions around the globe (Nobel, 2010)
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