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Regional and Microenvironmental Scale Characterization of the Zostera muelleri Seagrass Microbiome.

ABSTRACT: Seagrasses are globally distributed marine plants that represent an extremely valuable component of coastal ecosystems. Like terrestrial plants, seagrass productivity and health are likely to be strongly governed by the structure and function of the seagrass microbiome, which will be distributed across a number of discrete microenvironments within the plant, including the phyllosphere, the endosphere and the rhizosphere, all different in physical and chemical conditions. Here we examined patterns in the composition of the microbiome of the seagrass Zostera muelleri, within six plant-associated microenvironments sampled across four different coastal locations in New South Wales, Australia. Amplicon sequencing approaches were used to characterize the diversity and composition of bacterial, microalgal, and fungal microbiomes and ultimately identify "core microbiome" members that were conserved across sampling microenvironments. Discrete populations of bacteria, microalgae and fungi were observed within specific seagrass microenvironments, including the leaves and roots and rhizomes, with "core" taxa found to persist within these microenvironments across geographically disparate sampling sites. Bacterial, microalgal and fungal community profiles were most strongly governed by intrinsic features of the different seagrass microenvironments, whereby microscale differences in community composition were greater than the differences observed between sampling regions. However, our results showed differing strengths of microbial preferences at the plant scale, since this microenvironmental variability was more pronounced for bacteria than it was for microalgae and fungi, suggesting more specific interactions between the bacterial consortia and the seagrass host, and potentially implying a highly specialized coupling between seagrass and bacterial metabolism and ecology. Due to their persistence within a given seagrass microenvironment, across geographically discrete sampling locations, we propose that the identified "core" microbiome members likely play key roles in seagrass physiology as well as the ecology and biogeochemistry of seagrass habitats.

SUBMITTER: Hurtado-McCormick V

PROVIDER: S-EPMC6527750 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Seagrasses are marine ecosystem engineers that are currently declining in abundance at an alarming rate due to both natural and anthropogenic disturbances in ecological niches. Despite reports on the morphological and physiological adaptations of seagrasses to extreme environments, little is known of the molecular mechanisms underlying photo-acclimation, and/or tolerance in these marine plants. This study applies the two-dimensional isoelectric focusing (2D-IEF) proteomics approach to identify photo-acclimation/tolerance proteins in the marine seagrass Zostera muelleri. For this, Z. muelleri was exposed for 10 days in laboratory mesocosms to saturating (control, 200 ?mol photons m-2 s-1), super-saturating (SSL, 600 ?mol photons m-2 s-1), and limited light (LL, 20 ?mol photons m-2 s-1) irradiance conditions. Using LC-MS/MS analysis, 93 and 40 protein spots were differentially regulated under SSL and LL conditions, respectively, when compared to the control. In contrast to the LL condition, Z. muelleri robustly tolerated super-saturation light than control conditions, evidenced by their higher relative maximum electron transport rate and minimum saturating irradiance values. Proteomic analyses revealed up-regulation and/or appearances of proteins belonging to the Calvin-Benson and Krebs cycle, glycolysis, the glycine cleavage system of photorespiration, and the antioxidant system. These proteins, together with those from the inter-connected glutamate-proline-GABA pathway, shaped Z. muelleri photosynthesis and growth under SSL conditions. In contrast, the LL condition negatively impacted the metabolic activities of Z. muelleri by down-regulating key metabolic enzymes for photosynthesis and the metabolism of carbohydrates and amino acids, which is consistent with the observation with lower photosynthetic performance under LL condition. This study provides novel insights into the underlying molecular photo-acclimation mechanisms in Z. muelleri, in addition to identifying protein-based biomarkers that could be used as early indicators to detect acute/chronic light stress in seagrasses to monitor seagrass health.

Project description:Macrofauna are important contributors to estuarine ecosystem services within and outside of seagrass beds. Here we documented the natural recolonisation of a temperate seagrass (Zostera muelleri) community over 15 years in an urban estuary (Waitemata Harbour, North Island, New Zealand). We also investigated the change in macrofaunal communities in relation to seagrass cover over time, from transition from bare sandflat to seagrass. Colonisation by seagrass was associated with an increase in macrofaunal species diversity (from an average of 32 species per core in 2001 to 46 species per core in 2015) and abundance (from 482 to 2273 individuals per core), as well as an increase in sediment mud (from 4.09% to 12.37%) and organic matter content (from 0.90% to 1.41%). The most abundant species within both seagrass and adjacent unvegetated sandflat were similar, the polychaetes Heteromastus filiformis, Aricidea sp., and Prionospio aucklandica, and the amphipod Paracalliope novizealandiae. The difference in macrofaunal community structure between seagrass and unvegetated sandflat was primarily associated with higher abundance of P. novizealandiae and lower abundance of Pseudopolydora sp. in seagrass. A successional effect was observed in macrofaunal communities over the 15 years following seagrass expansion, primarily associated with an increase in the abundance of Aricidea sp., H. filiformis, and P. novizealandiae, and a reduction in the abundance of the bivalve Linucula hartvigiana. This study is the first to document long-term changes in seagrass and their associated communities during a natural recolonisation event, providing insight into timeframes required both for the regrowth of a seagrass meadow from initial colonisation of individual patches, as well as the trajectories and timeframes of change from a sandflat to a seagrass-associated macrofaunal community. This research enhances our understanding of how changes in seagrass distributions due to seagrass loss or restoration may affect macrofaunal community composition and ultimately ecosystem function.

Project description:Understanding how multiple environmental stressors interact to affect seagrass health (measured as morphological and physiological responses) is important for responding to global declines in seagrass populations. We investigated the interactive effects of temperature stress (24, 27, 30 and 32°C) and shading stress (75, 50, 25 and 0% shade treatments) on the seagrass Zostera muelleri over a 3-month period in laboratory mesocosms. Z. muelleri is widely distributed throughout the temperate and tropical waters of south and east coasts of Australia, and is regarded as a regionally significant species. Optimal growth was observed at 27°C, whereas rapid loss of living shoots and leaf mass occurred at 32°C. We found no difference in the concentration of photosynthetic pigments among temperature treatments by the end of the experiment; however, up-regulation of photoprotective pigments was observed at 30°C. Greater levels of shade resulting in high photochemical efficiencies, while elevated irradiance suppressed effective quantum yield (?F/FM'). Chlorophyll fluorescence fast induction curves (FIC) revealed that the J step amplitude was significantly higher in the 0% shade treatment after 8 weeks, indicating a closure of PSII reaction centres, which likely contributed to the decline in ?F/FM' and photoinhibition under higher irradiance. Effective quantum yield of PSII (?F/FM') declined steadily in 32°C treatments, indicating thermal damage. Higher temperatures (30°C) resulted in reduced above-ground biomass ratio and smaller leaves, while reduced light led to a reduction in leaf and shoot density, above-ground biomass ratio, shoot biomass and an increase in leaf senescence. Surprisingly, light and temperature had few interactive effects on seagrass health, even though these two stressors had strong effects on seagrass health when tested in isolation. In summary, these results demonstrate that populations of Z. muelleri in south-eastern Australia are sensitive to small chronic temperature increases and light decreases that are predicted under future climate change scenarios.

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Regional and Microenvironmental Scale Characterization of the Zostera muelleri Seagrass Microbiome.

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