Rhizosheath microbial community assembly of sympatric desert speargrasses is independent of the plant host

Abstract

BackgroundThe rhizosheath-root system is an adaptive trait of sandy-desert speargrasses in response to unfavourable moisture and nutritional conditions. Under the deserts’ polyextreme conditions, plants interact with edaphic microorganisms that positively affect their fitness and resistance. However, the trophic simplicity and environmental harshness of desert ecosystems have previously been shown to strongly influence soil microbial community assembly. We hypothesize that sand-driven ecological filtering constrains the microbial recruitment processes in the speargrass rhizosheath-root niche, prevailing over the plant-induced selection.MethodsBacterial and fungal communities from the rhizosheath-root compartments (endosphere root tissues, rhizosheath and rhizosphere) of three Namib Desert speargrass species (Stipagrostis sabulicola, S. seelyae and Cladoraphis spinosa) along with bulk sand have been studied to test our hypothesis. To minimize the variability determined by edaphic and climatic factors, plants living in a single dune were studied. We assessed the role of plant species vs the sandy substrate on the recruitment and selection, phylogenetic diversity and co-occurrence microbial networks of the rhizosheath-root system microbial communities.ResultsMicroorganisms associated with the speargrass rhizosheath-root system were recruited from the surrounding bulk sand population and were significantly enriched in the rhizosheath compartments (105 and 104 of bacterial 16S rRNA and fungal ITS copies per gram of sand to up to 108 and 107 copies per gram, respectively). Furthermore, each rhizosheath-root system compartment hosted a specific microbial community demonstrating strong niche-partitioning. The rhizosheath-root systems of the three speargrass species studied were dominated by desert-adapted Actinobacteria and Alphaproteobacteria (e.g. Lechevalieria, Streptomyces and Microvirga) as well as saprophytic Ascomycota fungi (e.g. Curvularia, Aspergillus and Thielavia). Our results clearly showed a random phylogenetic turnover of rhizosheath-root system associated microbial communities, independent of the plant species, where stochastic factors drive neutral assembly. Co-occurrence network analyses also indicated that the bacterial and fungal community members of the rhizosheath-root systems established a higher number of interactions than those in the barren bulk sand, suggesting that the former are more stable and functional than the latter.ConclusionOur study demonstrates that the rhizosheath-root system microbial communities of desert dune speargrasses are stochastically assembled and host-independent. This finding supports the concept that the selection determined by the desert sand prevails over that imposed by the genotype of the different plant species.Electronic supplementary materialThe online version of this article (10.1186/s40168-018-0597-y) contains supplementary material, which is available to authorized users.

Microbiome Dynamics Associated With the Atacama Flowering Desert

“…The other two clusters appeared much more site-specific and were dominant. This general picture of the organization and distribution of microbial consortia highlights the strong effect of the desert habitat over the soil-and rhizosphere-microbiome, coherently with Marasco et al (2018). However, the bacterial cluster appears to be consistently associated to C. longiscapa: the site-independent enrichment of this cluster in the rhizosphere further supports this conclusion.…”

“…During the rainy year, C. longiscapa recruits and selects through sugar-rich exudates, amino acids and organic acids specific microorganisms (Marasco et al, 2018), which could favor its development under different aridity conditions, in addition to repel others. Consistent with previous studies of arid environments, Ascomycota (fungi), Proteobacteria and Bacteroidetes (prokaryotes) were the most abundant phylum in the active rhizosphere (Maestre et al, 2015;Hassani et al, 2018).…”

Testing the Two-Step Model of Plant Root Microbiome Acquisition Under Multiple Plant Species and Soil Sources

“…However, previous reports show a larger diversity in rhizospheres than in soils comparing different biomes ( Thompson et al, 2017 ). Marasco et al (2018) found a higher 16S rRNA copies (qPCR) in the rhizosphere and rhizosheath than soil, of three species of dune colonizing speargrasses ( Stipagrostis sabulicola, S. seelyae, and Cladoraphis spinosa ). The larger rhizosphere and rhizoheath suggest an increase in microbial abundance and activity in these plants influenced microniches compared to soils.…”

Longevity of Chinese Chestnut Correlates with Stable Root Microbiomes

“…Mantel test was used to analyse the correlation between two matrices, which were the dissimilarity matrix of bacterial communities (Bray-Curtis) and the distance matrix of tree ages. The occurrence of increasing delta tree age patterns in all 3 compartments has been tested using the linear regression between the dissimilarity of bacterial communities (Bray-Curtis) and the tree age differences (25), see supplementary table 3 and 4.…”