Project description:The association with photosymbiotic algae is crucial for the proliferation of many coral reef organisms, but increases their sensitivity to environmental changes. Large benthic foraminifera (LBF) are a diverse group of carbonate producers harboring algal photosymbionts. They act as key ecological engineers and are widely used as bioindicators. As in corals, elevated temperatures and light intensities are known to induce bleaching in LBF, but the combined effects of ocean acidification and warming remain unclear. To shed light into the adaptive physiology of LBF, we linked the assessment of the holobiont and photosymbiont physiological condition (mortality, growth, coloration, and chlorophyll a) to a bottom-up proteomics approach that allows the examination of cellular responses of host and symbionts simultaneously. In a two-months experiment, we exposed Amphistegina lobifera to the combined effects of ocean acidification (400, 1000 and 2800 ppm pCO2) and warming (28-control and 31°C). More than 1,000 proteins were identified by label-free mass spectrometry-based whole proteome analysis and assigned to the host or photosymbionts. Photopigment concentrations declined in response to elevated pCO2, visible by discoloration. These indicate the reduction of photosymbiont densities under ocean acidification, despite the fertilizing effects suggested for high inorganic carbon availability, and imply metabolic adjustments. Increases of proteolytic proteins suggest active host regulation of photosymbiont density in order to maintain homeostasis with its algal photosymbionts. Growth rates, however, were unaffected by elevated pCO2 levels at control temperatures, but high pCO2 levels (2800 ppm, pH 7.52) combined with thermal stress (31°C) impaired growth, though mortality and shell dissolution was negligible. While growth was unaffected by intermediate pCO2 levels (1000 ppm, pH 7.98) combined with ocean warming, this treatment induced the most distinct proteome responses. These include the regulation of ion transporters and host cytoplasmic proteins that likely abet calcification under ocean acidification. This study reveals a highly complex cellular response in both the host and the photosymbiont, which appears to facilitate a high resilience potential of A. lobifera to end of the century ocean conditions. Nevertheless, our results imply that when pCO2 levels rise above 1000 ppm during persistent ocean warming or extreme heating events these adaptive mechanisms become disrupted.

Project description:Because of severe abiotic limitations, Antarctic soils represent simplified ecosystems, where microorganisms are the principle drivers of nutrient cycling. This relative simplicity makes these ecosystems particularly vulnerable to perturbations, like global warming, and the Antarctic Peninsula is among the most rapidly warming regions on the planet. However, the consequences of the ongoing warming of Antarctica on microorganisms and the processes they mediate are unknown. Here, using 16S rRNA gene pyrosequencing and qPCR, we report a number of highly consistent changes in microbial community structure and abundance across very disparate sub-Antarctic and Antarctic environments following three years of experimental field warming (+ 0.5-2°C). Specifically, we found significant increases in the abundance of fungi and bacteria and in the Alphaproteobacteria-to-Acidobacteria ratio. These alterations were linked to a significant increase in soil respiration. Furthermore, the shifts toward generalist or opportunistic bacterial communities following warming weakened the linkage between bacterial diversity and functional diversity. Warming also increased the abundance of some organisms related to the N-cycle, detected as an increase in the relative abundance of nitrogenase genes via GeoChip microarray analyses. Our results demonstrate that soil microorganisms across a range of sub-Antarctic and Antarctic environments can respond consistently and rapidly to increasing temperatures, thereby potentially disrupting soil functioning. We conducted in situ warming experiments for three years using open-top chambers (OTCs) at one sub-Antarctic (Falkland Islands, 52ºS) and two Antarctic locations (Signy and Anchorage Islands, 60ºS and 67ºS respectively) (see Supplementary Fig. 1 for a map). OTCs increased annual soil temperature by an average of 0.8°C (at a depth of 5 cm), resulting in 8-43% increase in positive-degree days annually and a decrease in freeze-thaw cycle frequency by an average of 15 cycles per year (8). At each location, we included densely vegetated and bare fell-field soils in the experimental design for a total of six environments. Densely vegetated and bare environments represent two contrasting environments for Antarctic soil microorganisms, with large differences in terms of C and N inputs to soils. Massively parallel pyrosequencing (Roche 454 GS FLX Titanium) of 16S rRNA gene amplicons was used to follow bacterial diversity and community composition [GenBank Accession Numbers: HM641909-HM744649], and functional gene microarrays (GeoChip 2.0)(11) were used to assess changes in functional gene distribution. Bacterial and fungal communities were also quantified using real-time PCR.

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