In December 2019, the first cases of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were identified in the city of Wuhan, China. Since then, it has spread worldwide with new mutations being reported. The aim of the present study was to monitor the changes in genetic diversity and track non-synonymous substitutions (dN) that could be implicated in the fitness of SARS-CoV-2 and its spread in different regions between December 2019 and November 2020. We analyzed 2213 complete genomes from six geographical regions worldwide, which were downloaded from GenBank and GISAID databases. Although SARS-CoV-2 presented low genetic diversity, there has been an increase over time, with the presence of several hotspot mutations throughout its genome. We identified seven frequent mutations that resulted in dN substitutions. Two of them, C14408T>P323L and A23403G>D614G, located in the nsp12 and Spike protein, respectively, emerged early in the pandemic and showed a considerable increase in frequency over time. Two other mutations, A1163T>I120F in nsp2 and G22992A>S477N in the Spike protein, emerged recently and have spread in Oceania and Europe. There were associations of P323L, D614G, R203K and G204R substitutions with disease severity. Continuous molecular surveillance of SARS-CoV-2 will be necessary to detect and describe the transmission dynamics of new variants of the virus with clinical relevance. This information is important to improve programs to control the virus.

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In December 2019, the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in the province of Wuhan, China. Since then, it has spread worldwide with new mutations being reported. We performed genomic analysis to identify the changes in genetic diversity of SARS-CoV-2 between December 2019 and November 2020, and through molecular surveillance, we monitored the mutations that could be involved in viral fitness. We analyzed 2,213 complete genomes from 6 geographical regions worldwide, which were downloaded from GenBank and GISAID databases. Although SARS-CoV-2 presented low genetic diversity, there has been an increase over time, with the presence of several hotspot mutations throughout its genome. We identified 7 frequent mutations that resulted in non-synonymous substitutions (dN). Two of them, C14408T>P323L and A23403G>D614G, located in the nsp12 and Spike protein, respectively, emerged early in the pandemic and showed a considerable increase in frequency over time. Two other mutations, A1163T>I120F in nsp2 and G22992A>S477N in the Spike protein emerged recently and have spread in Oceania and Europe. Continuous molecular surveillance of SARS-CoV-2 will be necessary to detect and describe the transmission dynamics of new variants of the virus with clinical relevance. This information is important to improve programs to control the virus.

The Monte Azul archaeological site is located in the inter-Andean Aburrá Valley of the upper Medellín River in Colombia and it is dated from the Middle Ceramic period to the Republican period. In this study area, it is common to find evidence of disturbed soils that is related to ancient use and erosion. In Monte Azul, the pedogenesis is associated with the presence of fast-weathering eolian volcanic ash deposits, extreme acidity, low base saturation, strong leaching, high precipitation, and high temperature; hence, some of these tropical conditions are responsible for the low conservation of the archaeological record. Consequently, we used a geoarchaeological approach with paleoenvironmental, sedimentary, geochemical, and soil micromorphological proxies as integral units of analysis to understand site formation processes. Micromorphological and paleobotanical records indicate soil use dynamics and changes in paleoenvironmental conditions from humid conditions to small and persistent clearings around a domestic unit. This approach sheds light on the development of possible pre-Hispanic activity areas and cultivation techniques related to the ancient use of the Ferrería pottery style in the Central Mountain Range of Colombia.

Changes in soil structure can be monitored in undisturbed soil samples through the micromorphometric analysis of thin sections. In this methodology, it is common that individual images (three to ten repetitions) are used and that they cannot be related in different scales between soil components; in addition, although a minimum study area is established, its representativeness in the soil components is unknown. The objective of this study was to quantify the soil constituent (pores, aggregates, and roots) and to compare the values obtained from individual images versus high-resolution mosaics from a complete thin section. Unaltered samples were collected in three soils with different clay contents (Entisols, Inceptisols, and Vertisols) and presence of maize roots in the same phenological development stage (physiological maturity). Three thin sections of each soil (5 × 7 cm × 30 μm 1865 mm 2) were prepared and sequential images of 11.1× 7.4 mm (63 in total) were obtained at 2× magnification using a petrographic microscope and plane polarized light (PPL). The high-resolution mosaics (2.6 µm píxel-1) at a colour depth 24 bits (8 bits × 3 bands in standard RGB) were built using space operators; subsequently, three, five and ten images were randomly selected. The individual images and the mosaics were transformed by principal component analysis in ArcGis® and soil constituents were delimited according to their variances values. The results indicate that individual images are recommended only to quantify porosity or in homogeneous systems in structure and color, but not in heterogeneous systems where the data obtained show high variability. Even when the results are similar to those calculated in the mosaics, the dispersion of the data is high (variance 5 times greater than the mean) and with little representation. In contrast, high-resolution mosaics offer the total quantification of the thin section and soil components can be grouped into classes or categories to observe intra or inter relations in the soil system. In addition, the soil components can be related to different scales, for example macroaggregates and roots.

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<p>Several types of secondary carbonate accumulations have been reported, but some of them are not completely well defined in the field due to unclear nomenclature. This is the case of the “queras”, reported in several Loess-palaeosol sequences of the Ebro Valley, which have often been described as pseudomycelia. Micromorphologically, they are complex pedofeatures (including calcified root cells, infillings and hypocoatings of carbonates and a decarbonated zone), resulting from calcification/decalcification processess at a microscale. They are composed of a central channel (1-2 mm wide and 2-3 cm long) filled with biosparite crystals (Herrero et al., 1992). The study of these secondary carbonate bioaccumulations are important archives for climatic reconstructions in terrestrial environments and can be used for paleoenvironmental reconstructions. The aims of this research are the characterization (morphological, optical and isotopically) of the biocalcifications present in Loess-palaeosols sequences, OSL-dated, to determine the main factors that originate them and their possible use as a palaeoenvironmental proxy. We collected soil samples from seven profile of Loess-palaeosols where the presence of these biocalcifications was recorded. We isolated and manually cleaned complete fragments of queras to describe them and to determine their isotopic composition. For that purpose, we used the queras fraction (sieved fraction of bulk soil between 100-250 µm) removing the residues of micrite with a buffer solution and manually separating the quera fragments with the help of a stereoscope. Thin sections were made to analyse the micromorphology in a petrographic microscope and cathodoluminescence techniques to determine the origin of the calcite. The micromorphology of these biocalcifications is similar in most cases: they present the same number of rows around the central channel (4 to 5), and a decarbonated hypocoating around it, supporting the hypothesis that their origin is derived from the calcification of cells of the root tips as a strategy to acidify the soil surrounding to absorb nutrients. Under cathodoluminescence biosparite has a different behaviour than non-biological calcite crystals. The age of the queras was similar in most horizons and their formation is independent of the age of the loess deposit. The isotopic composition of δ<sup>13</sup>C correspond mainly to CAM plants and the temperatures of precipitation calculated correspond to a Mediterranean template climate (Cerling and Quade, 1993), implying that the biocalcifications developed in warm environments. Finally, we hope to gain some more certainty of their origin and formation processes from the ongoing analyses of DNA sequencing and pollen recording.</p>