Soil organic matter formation in the Byers Peninsula, Maritime Antarctica: origin and biochemical composition
Authors:   , Silva Jônatas Pedro da 
Published: June 2023

The knowledge about the dynamics of soil organic matter (SOM) in Antarctica is fundamental to better understand the functioning of terrestrial ecosystems and to analyze the possible impacts of global climate change. Despite this, information on SOM in Maritime Antarctica is still incipient. Thus, we aimed to: i) analyze the elemental and biochemical constitution of the SOM; ii) calculate the soil C and N stocks; iii) perform the dating of the C present in the soils of the Byers Peninsula, Maritime Antarctica; iv) evaluate the soil microbial composition and activity, and; v) identify possible formation routes of the SOM present in the Antarctic biome. The Byers Peninsula with about 60 km 2 - is the largest ice-free area in Maritime Antarctica. It is designated a Specially Protected Antarctic Area (ASPA N° 126) due to its identification as a habitat of global importance, since it hosts breeding colonies of several birds and intense occupation of elephant seals. It is also considered the most important limnological site in the region and the most vulnerable to human interference. Thirteen soil profiles were opened and classified to represent vegetational, geological, geomorphological diversity and distance from the Rotche Dome glacier. The profiles were described and classified according to Soil Taxonomy and World Reference Base for Soil Resources (WRB). Samples were collected from all horizons for chemical and physical characterization. Vegetation material surrounding the profiles was also collected. The characterization of the SOM was done by physical fractionation, determining the POM and MAOM fractions. From these, the determination of the contents of C, N, C/N ratio and the isotopic signatures of δ 13 C and δ 15 N was made, as well as in the collected vegetal materials. In order to biochemically characterize the SOM present in these fractions and the vegetation, thermochemolysis analysis was performed with identification of the compounds by GC/MS to analyze whether there is a correlation between the composition of these vegetables and the biochemical composition of the SOM. Nuclear magnetic resonance spectroscopy ( 13 C NMR CP/MAS) analysis was also performed in order to characterize the SOM at the molecular level and to identify the abundance of functional groups present in it. The C dating by the 14 C method was also performed to assess whether there is a correlation of this with glacier retreat. To understand the microbiological activity present in the Antarctic soils and its relationship with SOM and soil attributes, DNA was extracted from selected samples for identification of the organisms. The high diversity of biotic and abiotic factors acting in Maritime Antarctica directly affects the accumulation, transformation, and stabilization of SOM. Due to the greater presence of ecological niches, greater plant diversity with the presence of vascular plants, and the marked action of avifauna, these factors differentiate the processes involved in the redistribution of SOM between Maritime and Continental Antarctica, in addition to the humidity factor (in the form of net precipitation) being a key factor in the most active humification processes in the soils studied. Keywords: Dynamics of soil organic matter. Elemental and biochemical composition. C and N stocks. Microbial composition. Formation routes of the SOM.