Microbial planktonic communities as environmental indicators in a Tierra del Fuego peat bog

MATALONI, G.

České Budějovice

Conferencia; 6th International Conference on Polar and Alpine Microbiology; 2015

International Arctic Science Committee, Scientific Committee for Antarctic Research

Peatlands are key ecosystems which store 30% of all C in the soil and 10% of the total freshwater volume on Earth. Only a small proportion of these wetlands are located in the Southern Hemisphere; and opposedly to their Northern Hemisphere counterparts, their ecology and diversity has been poorly studied. The insular Province of Tierra del Fuego (Argentina) encompasses a vast area of pristine peatlands (ca. 27000 km2), many of which occupyglacial valleys between the Andean ridges, are typically dome-shaped and ombrotrophic (fed only by precipitation) and host many small pools. At Rancho Hambre peat bog, we aimed at investigating the influence of climatic, topographic and morphometric features on the abiotic environment of the pools, and how this shaped the structure and dynamics of planktonic communities.Eight samplings were carried out in October, December, February and April 2008-2010 in five pools representing distinct morphometric features. An automatic weather station was located in the area. Abiotic features (water temperature, conductivity, pH, transparency, dissolved oxygen, total hardness, DOC, total N and P, NO3-N, NH4-N and PO4-P) were measured. Abundance and biovolume of heterotrophic bacteria (HB) and flagellates (HF), picophytoplankton (PP) nano+microphytoplankton, ciliates and mesozooplankton were measured on quantitativesamples. Also, species richness, taxonomic composition and diversity were analyzed on qualitative samples ofnano+microphytoplankton, ciliates and mesozooplankton (Quiroga et al. 2013). In 2012, the molecular diversity of the prokaryotes and the smaller eukaryotes of these same  pools were studied by means of high-throughput sequencing (Quiroga et al. 2015, Lara et al. 2015).Topographic variations resulted in a low hydrological connectivity, which largely accounted for the strong environmental differences found among pools. These could be classified into ombrotrophic (softer, more acidic) and minerotrophic. Their morphometry played a key role by modulating seasonal changes in water temperature and hydrological stability. In spring, the structures of the planktonic communities were similar, whilst in late summer there were significant differences in the abundance and biomass of the different trophic compartments among small, shallow water bodies and large ones. Results of a canonical correspondence analysis ascribed theseto pool size-driven patterns of water temperature variation (Quiroga et al. 2013).Analysis of the taxonomic composition of the microphytoplankton and ciliates coincided in low values for Jaccard index among pools. Despite such differences, phytoplankton of minerotrophic pools was typically richer in desmids, diatoms and Chlorophytes, while that of ombrotrophic oneswas richer in cyanobacteria. These communities underwent paralell structure changes over time. Community composition of the smallest size fraction was studied using GUniFraC and separated minerotrophic and ombrotrophic sites (Lara et al. 2015). The 5% best indicators for bothenvironments were searched using an IndVal analysis. Among these, autotrophic taxa were more common in minerotrophic environments, whereas mixotrophic taxa represented best ombrotrophic water bodies.Bacterioplankton communities were diverse (72% of rare sequences) yet widely dominated by only 10 OTUs belonging to the Proteobacteria, Actinobacteria, Bacteroidetes and Verrucomicrobia, which represented 53% of sequences. PERMANOVA analyses showed that community structure was largely explained by differences in hydrological connectivity, pH and nutrient status (ombro/minerotrophic pools) (Quiroga et al. 2015).The results pertaining all studied communities revealed a strong underlying pattern supporting thecharacterization of pools according to their size and minero/ombrotrophic character. Overall differences in the structure of trophic compartments became more evident with the onset of the growth season. Remarkably, molecular diversity spatial patterns for both small-sized eukaryotes and prokaryotes coincided with those detected for larger planktonic communities studied by traditional morphology-based taxonomy. In general, ombrotrophic pools showed significantly poorer communities, suggesting stronger environmental filtering operating in these pools.