Abstract
Rhizosphere bacterial community structures and their determining drivers have been studied in a variety of marine and freshwater ecosystems for a range of plant species. However, there is still limited information about the influence of habitat on microbial communities in seagrass beds. This study aimed to determine which factors (habitat and plant species) have crucial roles on the rhizospheric bacteria associated with two tropical seagrass species (Thalassia hemprichii and Enhalus acoroides) that are dominant at Xincun Bay and Tanmen Harbor in Hainan Island, South China. Using Illumina HiSeq sequencing, we observed substantial differences in the bacterial richness, diversity, and relative abundances of taxa between the two habitats, which were characterized differently in sediment type and nutrient status. Rhizospheric bacteria from sandy sediment at the eutrophic Xincun Bay were dominated by Desulfobacteraceae and Helicobacteraceae, which are primarily involved in sulfate cycling, whereas rhizosphere microbes from the reef flat at oligotrophic Tanmen Harbor were dominated by Vibrionaceae and Woeseiaceae, which may play important roles in nitrogen and carbon fixing. Additionally, we speculated that host-specific effects of these two seagrass species may be covered under nutrient-rich conditions and in mixed community patches, emphasizing the importance of the nutrient status of the sediment and vegetation composition of the patches. In addition, our study confirmed that Proteobacteria was more adapted to the rhizosphere environment than to low-carbon conditions that occurred in bulk sediment, which was primarily dominated by well-known fermentative bacteria in the phylum Firmicutes.
Highlights
Sediment, especially the rhizosphere of plants, is a complex and heterogeneous hotspot inhabited by various microorganisms (Wei et al, 2017). Lennon and Jones (2011) noted that the physicochemical properties of the soil, together with plant species, dominated which members of microorganisms can grow and thrive
Dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) concentrations in pore water at Xincun Bay (322.8 ± 135.7 and 8.5 ± 6.1 μmol/L, respectively) were much higher than those observed for the Tanmen Harbor sediment (90.9 ± 42.1 and 0.4 ± 0.6 μmol/L, respectively)
Both DIN and DIP contents were much higher in vegetated sediment than those measured in bare sediments (Table 1)
Summary
Especially the rhizosphere of plants, is a complex and heterogeneous hotspot inhabited by various microorganisms (Wei et al, 2017). Lennon and Jones (2011) noted that the physicochemical properties of the soil, together with plant species, dominated which members of microorganisms can grow and thrive. Other studies have demonstrated that the host plant and sediment are both major factors affecting community structure under natural conditions (Berg and Smalla, 2009; Tkacz et al, 2015). Sediment can override the plant effects on rhizosphere microorganisms, it is unclear which sediment properties (i.e., pH, texture, and nutrient status) contribute to this phenomenon (Nunan et al, 2005; Veresoglou et al, 2011). Singh et al (2007) suggested that rhizosphere bacterial communities are influenced by similar environmental factors, indicating that different plant species do not select specific microbial populations in their rhizospheres. Veresoglou et al (2011) revealed that nutrient fertilization of soil may mask the ability of plant species to shape their own rhizosphere microbial community
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