Natalia L. Borrelli

Calcium Biomineralizations Associated with Bioclastic Deposits in Coastal Pedostratigraphic Sequences of the Southeastern Pampean Plain, Argentina

The biomineralization process is genetically controlled, and it is the result of the metabolic activity of different organisms . Microorganisms , plants and animals produce calcium biomineralizations , calcium oxalates and carbonates being the most representative. The Quaternary pedosedimentary sequences of the southeastern coast of Buenos Aires province evolved from bioclastic and loess sediments, reworked by water and/or wind action . Calcium biomineralizations play an important role in the development of soils and contribute to differentiate sedimentary levels affected by pedogenesis . This work aims to characterize calcium biomineralizations in bioclastic , loessic and fluvio-eolian pedosedimentary sequences , typical of coastal environments of the southeastern Buenos Aires province . Modal soil profiles were defined in pedosedimentary sequences of the fluvio-eolian and coastal plains , in which disturbed and undisturbed samples were analyzed. Samples were analyzed at different scales of resolution: mesoscopic , microscopic and submicroscopic , using optical microscopy and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) . Organic matter content , pH , particle size distribution , mineralogy and calcium content were also quantified. Three geopedological units were differentiated in a sequence developed on loess mantle deposits: dunes and interdunes , coastal lagoon/paleo-coastal lagoon and shell ridges . In soils with incipient development, calcium biomineralizations are scarce, mainly associated with isolated bioclasts . In soils with more pedological development , bioclasts are affected by bioerosion through microorganism action (fungi and algae ), and subsequently calcium re-precipitated as secondary oxalates and carbonates (biomineralizations ). These biomineralizations also weakly add or bind skeletal components , incorporating themselves into the matrix of soils and sediments . The type and diversity of calcium biomineralizations increase directly in relation with time and pedogenetic evolution ; so, these biomineralizations have been determinant in the origin, evolution and resistance to natural and anthropic degradation of the late Quaternary pedosedimentary sequences of southeastern Buenos Aires province , Argentina .

Calcium Oxalate Crystals in Plant Communities of the Southeast of the Pampean Plain, Argentina

Calcium oxalate crystals (COC) are one of the most prevalent and widely distributed biomineralizations in plants. The aim of this work is to analyze and compare the data previously reported about the presence and production of COC in leaves of plant species from forests, wetlands, and agroecosystems of the southeast of the Pampean Plain. Diaphanization, clearing of tissues with 50% sodium hypochlorite, and cross sectioning of the leaves were realized. The material was mounted with gelatin–glycerin, and COC were identified and described with optical, polarization, and scanning electron microscopes. Crystal size and density were calculated. Calcification mainly occurred in leaf mesophyll. In terrestrial species, crystals were closely associated with vascular bundles, while in aquatic species, they were associated with aerenchyma. Druses, prisms, and raphides were observed in the leaves of all species analyzed. Average crystal size was smaller in terrestrial species than aquatic ones (12 and 80 μm, respectively), but average crystal density was higher (246 and 23 crystals/mm2, respectively). These different patterns in COC production and distribution may be related to taxonomical characteristics, the types of cells where crystals precipitate, their function, and the differential transpiration rates, among other factors.