Abstract
Marine sediments are important sites for global biogeochemical cycling, mediated by macrofauna and microalgae. However, it is the microorganisms that drive these key processes. There is strong evidence that coastal benthic habitats will be affected by changing environmental variables (rising temperature, elevated CO2), and research has generally focused on the impact on macrofaunal biodiversity and ecosystem services. Despite their importance, there is less understanding of how microbial community assemblages will respond to environmental changes. In this study, a manipulative mesocosm experiment was employed, using next-generation sequencing to assess changes in microbial communities under future environmental change scenarios. Illumina sequencing generated over 11 million 16S rRNA gene sequences (using a primer set biased toward bacteria) and revealed Bacteroidetes and Proteobacteria dominated the total bacterial community of sediment samples. In this study, the sequencing coverage and depth revealed clear changes in species abundance within some phyla. Bacterial community composition was correlated with simulated environmental conditions, and species level community composition was significantly influenced by the mean temperature of the environmental regime (p = 0.002), but not by variation in CO2 or diurnal temperature variation. Species level changes with increasing mean temperature corresponded with changes in NH4 concentration, suggesting there is no functional redundancy in microbial communities for nitrogen cycling. Marine coastal biogeochemical cycling under future environmental conditions is likely to be driven by changes in nutrient availability as a direct result of microbial activity.
Highlights
Marine sediments play a vital role in global biogeochemical cycling, in terms of carbon, nitrogen and oxygen dynamics (Glud, 2008)
The dissimilarity matrix generated for the Unifrac metric was utilized for non-metric multidimensional scaling (NMDS) analysis to visualize the sequence data with respect to the environmental variables including; mean temperature (Figure 3), CO2 treatment and temperature fluctuation (Figure S4)
From both the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) tree grouping (Figure 2) and NMDS plots, a strong mean temperature effect on species-level bacterial community composition was observed, as reflected by sample grouping in relation to mean temperature (6, 12, and 18◦C)
Summary
Marine sediments play a vital role in global biogeochemical cycling, in terms of carbon, nitrogen and oxygen dynamics (Glud, 2008). The predicted global climate change scenarios (IPCC, 2014) will result in marine sediments being subjected to many environmental pressures, e.g., increasing mean temperature, greater temperature fluctuation, and increasing CO2 levels (ocean acidification: OA) (Doney et al, 2009; Dossena et al, 2012). Biogeochemical cycling within sediments, and at the sediment water interface, varies with sediment type (Aldridge et al, 2017; Hicks et al, 2017a), and this is reflected in the different microbial communities (Currie et al, 2017; Kitidis et al, 2017). Considering the contribution of benthic microbes to ecosystem services (Bell et al, 2005), biogeochemical cycling (Dyksma et al, 2016), it is vital that we understand how microbial population dynamics are likely to shift under future climate change scenarios, and how this may affect ecosystem service provision
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