Soil moisture drives differences in the diversity and trophic complexity of high Arctic tundra soils.

The Arctic soil communities play a vital role in stabilizing and decomposing soil carbon, which affects the global carbon cycling. Studying the food web structure is critical for understanding biotic interactions and the functioning of these ecosystems. Here, we studied the trophic relationships of (microscopic) soil biota of two different Arctic spots in Ny-Ålesund, Svalbard, within a natural soil moisture gradient by combining DNA analysis with stable isotopes as trophic tracers. The results of our study suggested that the soil moisture strongly influenced the diversity of soil biota, with the wetter soil, having a higher organic matter content, hosting a more diverse community. Based on a Bayesian mixing model, the community of wet soil formed a more complex food web, in which bacterivorous and detritivorous pathways were important in supplying carbon and energy to the upper trophic levels. In contrast, the drier soil showed a less diverse community, lower trophic complexity, with the green food web (via unicellular green algae and gatherer organisms) playing a more important role in channelling energy to higher trophic levels. These findings are important to better understand the soil communities inhabiting the Arctic, and for predicting how the ecosystem will respond to the forthcoming changes in precipitation regimes.

Marine Vertebrates Impact the Bacterial Community Composition and Food Webs of Antarctic Microbial Mats.

The biological activity of marine vertebrates represents an input of nutrients for Antarctic terrestrial biota, with relevant consequences for the entire ecosystem. Even though microbial mats assemble most of the biological diversity of the non-marine Antarctica, the effects of the local macrofauna on these microecosystems remain understudied. Using 16S rRNA gene sequencing, 13C and 15N stable isotopes, and by characterizing the P and N-derived nutrient levels, we evaluated the effects of penguins and other marine vertebrates on four microbial mats located along the Antarctic Peninsula. Our results show that P concentrations, C/N and N/P ratios, and δ15N values of "penguin-impacted" microbial mats were significantly higher than values obtained for "macrofauna-free" sample. Nutrients derived from penguin colonies and other marine vertebrates altered the trophic interactions of communities within microbial mats, as well as the relative abundance and trophic position of meiofaunal groups. Twenty-nine bacterial families from eight different phyla significantly changed with the presence of penguins, with inorganic nitrogen (NH4 + and NO3 -) and δ15N appearing as key factors in driving bacterial community composition. An apparent change in richness, diversity, and dominance of prokaryotes was also related to penguin-derived nutrients, affecting N utilization strategies of microbial mats and relating oligotrophic systems to communities with a higher metabolic versatility. The interdisciplinary approach of this study makes these results advance our understanding of interactions and composition of communities inhabiting microbial mats from Antarctica, revealing how they are deeply associated with marine animals.

Ubiquity of dominant cyanobacterial taxa along glacier retreat in the Antarctic Peninsula.

Cyanobacteria are key organisms in the Antarctic ecosystem, but the primary succession of its communities in recently deglaciated soils remains poorly understood. In this study, we surveyed the primary succession of cyanobacterial communities with an in-depth Next Generation Sequencing approach in three Antarctic recently glacier forefields. Despite the similar physicochemical characteristics of the soils, we did not find a common pattern in the distribution of the cyanobacterial communities at the finest level of taxonomic resolution. However, the metabarcoding analysis revealed a common community of 14 cyanobacterial identical sequences in all the studied soils, whose lineages were not restricted to polar or alpine biotopes. These ASVs comprised a relative abundance within the cyanobacterial community of 51.5%-81.7% among the three locations and were also found in two cyanobacterial mats from the Antarctic Peninsula. Our results suggest that (micro)biotic interactions act as a key driver of the community composition and dynamics of Cyanobacteria during the early stages of succession in recently deglaciated soils of Antarctica. A few common genera might play a key role in the ecosystem, due to its ubiquitous presence not only in these soils but also in microbial mats, conforming probably the most widely disperse and dominant single genotypes in Antarctic soils.

Heterogeneity of Microbial Communities in Soils From the Antarctic Peninsula Region.

Ice-free areas represent less than 1% of the Antarctic surface. However, climate change models predict a significant increase in temperatures in the coming decades, triggering a relevant reduction of the ice-covered surface. Microorganisms, adapted to the extreme and fluctuating conditions, are the dominant biota. In this article we analyze the diversity and composition of soil bacterial communities in 52 soil samples on three scales: (i) fine scale, where we compare the differences in the microbial community between top-stratum soils (0-2 cm) and deeper-stratum soils (5-10 cm) at the same sampling point; (ii) medium scale, in which we compare the composition of the microbial community of top-stratum soils from different sampling points within the same sampling location; and (iii) coarse scale, where we compare communities between comparable ecosystems located hundreds of kilometers apart along the Antarctic Peninsula. The results suggest that in ice-free soils exposed for longer periods of time (millennia) microbial communities are significantly different along the soil profiles. However, in recently (decades) deglaciated soils the communities are not different along the soil profile. Furthermore, the microbial communities found in soils at the different sampling locations show a high degree of heterogeneity, with a relevant proportion of unique amplicon sequence variants (ASV) that appeared mainly in low abundance, and only at a single sampling location. The Core90 community, defined as the ASVs shared by 90% of the soils from the 4 sampling locations, was composed of 26 ASVs, representing a small percentage of the total sequences. Nevertheless, the taxonomic composition of the Core80 (ASVs shared by 80% of sampling points per location) of the different sampling locations, was very similar, as they were mostly defined by 20 common taxa, representing up to 75.7% of the sequences of the Core80 communities, suggesting a greater homogeneity of soil bacterial taxa among distant locations.

Carbon Pathways Through the Food Web of a Microbial Mat From Byers Peninsula, Antarctica.

Microbial mats are complex communities that represent a large biomass fraction in non-marine Antarctic ecosystems. They confer structure to soils and constitute, by themselves, intricate microecosystems, where a great variety of microorganisms and microfauna contributes to the ecosystem functions. Although in recent years Antarctic microbial mats have been thoroughly investigated, trophic relationships within the communities remain unresolved. We therefore conducted a study of the trophic relationships of a microbial mat from Byers Peninsula, Antarctica, using DNA analysis and stable isotopes as trophic tracers. Our results suggested, based on a Bayesian mixing model, that at least four trophic levels are present within this microecosystem: primary producers (cyanobacteria and diatoms), primary consumers (rotifers and tardigrades), secondary consumers (nematodes) and decomposers (fungi). Nematodes would play a key role as top consumers of the community, connecting the two carbon inputs described into the system, as omnivores at the secondary trophic level. In addition, carbon pathways from primary trophic level to consumers take place quickly during the first 24 h after its incorporation in the primary producers, dispersing across all the trophic levels and reaching secondary consumers in less than 11 days. This suggests that, given the changing physical conditions and presumably short periods of activity, there is a fine temporal coupling among the organisms in the community, minimizing the redundancy in function performance among trophic levels.

Long-term outcomes and predictors of morbi-mortality according to age in stemi patients with multivessel disease: Impact of an incomplete revascularization.

BACKGROUND: Optimal management strategy for patients with ST-segment elevation myocardial infarction (STEMI) and multivessel disease (MVD) still remains unclear, especially in the elderly population. The aim of this study was to assess long-term outcomes and predictors of morbi-mortality according to age in patients with a STEMI and MVD. METHODS: We prospectively included 381 consecutive patients with a STEMI who underwent primary angioplasty and showed MVD in the angiogram. 111 (29.1%) patients were older than 75 (≥75) years and 270 (70.9%) were younger than 75 (<75) years. The co-primary outcomes were the incidence of all-cause mortality and major adverse cardiac events (MACE) during follow-up. RESULTS: During a median follow-up of 22 months, patients ≥75 years showed a higher incidence of all-cause mortality and MACE, as compared to younger patients. On multivariate analysis, incomplete revascularization (IR) was only an independent predictor of MACE (HR = 3.1, CI 95%:1.9-4.7; P = .02) in younger patients; whereas in the elderly group severely depressed ejection fraction was the unique independent predictor of MACE (HR = 2.7, CI 95%:1.5-4.8; P = .001). IR was not associated with the risk of all-cause mortality in any group. CONCLUSION: This study confirms the relevant prevalence of MVD in STEMI patients, as well as the difference in outcomes of an IR strategy between both age-groups, being only independently associated with MACE in younger patients. This finding supports that a routine complete revascularization (CR) strategy seems to be the best therapeutic option in younguer patients, whereas in the elderly population may not confer a clear clinical benefit during a long-term follow-up.