Above and below-ground bacterial communities shift in seagrass beds with warmer temperatures

Current rates of ocean warming are predicted to exacerbate ongoing declines in seagrass populations. Above-ground responses of seagrass to increasing temperatures have been studied from a direct physiological perspective while indirect effects, including changes to microbially-mediated below-ground processes, remain poorly understood. To test potential effects of increased temperature on seagrass growth and associated microbial communities, we sampled seagrass beds experiencing ambient and elevated water temperatures at Lake Macquarie, Australia. Sites with warmer water were associated with a plume from a power station discharge channel with temperatures analogous to conditions predicted by 2100 under current rates of ocean warming (+3°C). The microbial community composition in both sediments and leaf tissues varied significantly between warm and ambient water temperatures with higher relative abundances of putative sulphate-reducing bacteria such as Desulfocapsaceae, Desulfobulbaceae and Desulfosarcinaceae in sedimentary communities in warm water. Above-ground biomass and seagrass growth rates were greater at warm sites while below-ground biomass and detrital decomposition rates showed no difference suggesting potential buffering of temperature effects below-ground. These findings suggest a 3°C rise in temperate regions is unlikely to induce mortality in seagrass however, it may shift microbial communities towards more homogenous structure and composition

Single-Turnover Variable Chlorophyll Fluorescence as a Tool for Assessing Phytoplankton Photosynthesis and Primary Productivity: Opportunities, Caveats and Recommendations

Phytoplankton photosynthetic physiology can be investigated through single-turnover variable chlorophyll fluorescence (ST-ChlF) approaches, which carry unique potential to autonomously collect data at high spatial and temporal resolution. Over the past decades, significant progress has been made in the development and application of ST-ChlF methods in aquatic ecosystems, and in the interpretation of the resulting observations. At the same time, however, an increasing number of sensor types, sampling protocols, and data processing algorithms have created confusion and uncertainty among potential users, with a growing divergence of practice among different research groups. In this review, we assist the existing and upcoming user community by providing an overview of current approaches and consensus recommendations for the use of ST-ChlF measurements to examine in-situ phytoplankton productivity and photo-physiology. We argue that a consistency of practice and adherence to basic operational and quality control standards is critical to ensuring data inter-comparability. Large datasets of inter-comparable and globally coherent ST-ChlF observations hold the potential to reveal large-scale patterns and trends in phytoplankton photo-physiology, photosynthetic rates and bottom-up controls on primary productivity. As such, they hold great potential to provide invaluable physiological observations on the scales relevant for the development and validation of ecosystem models and remote sensing algorithms

Differential temperature adaptation in marine Synechococcus lineages: ecological distribution, molecular and physiological acclimation mechanisms

Thesis by publication.Includes bibliographical references.1. Introduction -- 2. Effects of low temperature on tropical and temperate isolates of marine Synechococcus -- 3. Growth physiology and cellular responses of marine Synechococcus isolates to high temperature -- 4. Seasonal variation in the marine cyanobacterial community in Sydney Harbour estuary and the influence of temperature on community structure -- 5. Microbial primary producers of Oceania: molecular characterisation of prokaryotic and eukariotic communities across a range of habitats -- 6. Impact of DNA damaging agents on genome-wide transcriptional profiles in two marine Synechococcus species -- 7. Conclusions and future directions -- Appendix.Marine picocyanobacteria are abundant photosynthetic prokaryotes contributing significantly to global primary production and nutrient cycling. The genus Synechococcus is ubiquitous in the marine environment. Their habitat ranges from the polar regions to the equator and mesotrophic to oligotrophic environments. Such a widespread occurrence across a broad array of environmental conditions is facilitated by the diverse genetic complement of lineages of Synechococcus.This work explores the influence of temperature on the lineages of Synechococcus which occupy different temperature niches. Responses and acclimation strategies employed by individual lineages were examined with gene expression analyses including global cellular proteomics and transcriptomics. Comparisons of growth physiology at different temperature conditions provide evidence for the specific temperature preferences of lineages. This is the first study to compare temperature acclimation responses across multiple lineages of marine Synechococcus. The acclimation responses to temperature involved the light harvesting complex, photosynthesis, membrane fluidity and protein synthesis with distinct differences between lineages.This is the first study to determine the composition and structure of the Synechococcus community across different temperature regimes in regions around Australia were studied using various phylogenetic markers. Distinctive spatial and temporal partitioning of lineages is observed with temperature as a potential key factor shaping the population. Other co-varying factors such as nutrients and mixing were also determined to influence the partitioning of lineages.This work provides insights into temperature acclimation and the distinct niche preferences of marine Synechococcus lineages. The differences in their distribution, growth and acclimation suggest that changes in temperature regimes can significantly alter Synechococcus community structure. Culture based studies in addition to environmental distribution provide valuable information for predictive models. As significant contributors to primary production and biogeochemical cycling, it is important to understand the influence of temperature and other factors on their diversity and distribution for better monitoring of ecosystem health.Mode of access: World wide web1 online resource (xxi, 192 pages) illustations, map

A user guide for the application of single turnover active chlorophyll fluorescence for phytoplankton productivity measurements

This document represents the collective efforts of SCOR Working Group 156, ‘Active Chlorophyll Fluorescence for Autonomous Measurements of Global Marine Primary Productivity’. The group was established in 2019, bringing together researchers and instrument manufacturers from 10 countries and 5 continents, with the goal of developing standards of best practice for the application of single turnover active chlorophyll fluorescence (ST-ChlF) to examine phytoplankton productivity. We focused our efforts on single turnover methods, which are most commonly used in phytoplankton research, while recognizing that other approaches, including Pulse Amplitude Modulation (PAM) fluorescence techniques, are also employed with macro-algae, corals and terrestrial plants. Over the past two years, our group has worked to build consensus around best practice for the collection, analysis and archiving of ST-ChlF data from a variety of aquatic environments. We aim to facilitate wide-spread use of ST-ChlF methods by the international research community, and have thus far focused our work on several key activities outlined in the Working Group’s terms of reference