Palynomorphs in Holocene sediments from a paleolagoon in the coastal plain of extreme southern Brazil

Acta Botanica Brasilica 28(2): 165-175. 2014. Palynomorphs in Holocene sediments from a paleolagoon in the coastal plain of extreme southern Brazil Ebráilon Masetto1 and Maria Luisa Lorscheitter1,2 Received: 7 July, 2013. Accepted: 10 October, 2013 ABSTRACT This paper presents the results of a qualitative palynological analysis of a 140 cm-thick section of Holocene sediments from a paleolagoon, representing the last 2600 years, taken from an outcrop at Hermenegildo Beach (33°42’S; 53°18’W), located in the municipality of Santa Vitória do Palmar, in the state of Rio Grande do Sul, Brazil. Samples were treated with hydrochloric acid, hydrofluoric acid and potassium hydroxide, after which they were subjected to acetolysis and mounted on glycerin-coated slides for light microscopy analysis. Among the 48 palynomorphs identified were 25 fungi, eight algae, three bryophytes, and 12 pteridophytes. Brief descriptions and illustrations of each palynomorph are presented, together with ecological data from the organism of origin when possible. Our findings will serve as reference material for paleoenvironmental studies in the coastal plain of southern Brazil. Key words: palynomorph descriptions, paleolagoon, Holocene, southern coastal plain, Rio Grande do Sul Introduction Materials and methods Little is known about sea-level oscillations and their effects on climate and vegetation dynamics in the southern coastal plain in the state of Rio Grande do Sul, Brazil, despite the contribution that such oscillations have made to shaping the current landscape of the region. Studies of plant succession can expand the understanding of the historic climate and vegetation dynamics responsible for the existing phytogeographic patterns. Palynological analysis of Quaternary sediment profiles with the associated chronological context is of great importance to plant succession studies because it elucidates vegetation changes over time. Archived catalogs are fundamental to the correct identification of palynomorphs in sediments. Few palynomorph descriptions exist for use in paleoenvironmental studies of the > 600 km-long coastal plain of Rio Grande do Sul, the southernmost Brazilian state (Lorscheitter 1988, 1989; Neves & Lorscheitter 1992, 1995a; Neves & Bauermann 2003, 2004; Roth & Lorscheitter 2013), and there are no palynological references for the extreme southern portion of the region. The purpose of the present study was to document the palynology of coastal plain sediments from the extreme south of Rio Grande do Sul, representing the last 2600 years, as reference material for paleoenvironmental research. We provide taxonomic descriptions and photomicrographs, as well as ecological information about the organism of origin when possible. A 140 cm-thick sediment profile of a paleolagoon was obtained from a Holocene outcrop at Hermenegildo Beach (33°42’S; 53°18’W), located in the municipality of Santa Vitória do Palmar, in the state of Rio Grande do Sul, in the coastal plain in the extreme south of Brazil (Fig. 1). Twenty-eight samples were taken at 5-cm intervals. Each was collected in an 8-cm3 box, directly from the vertical slope. The radiocarbon date at the base of the profile was determined by Beta Analytic Inc. (Miami, FL, USA). The samples were treated by hydrochloric acid, hydrofluoric acid and potassium hydroxide, after which they were subjected to acetolysis and filtered through a net with a 250μm mesh (Faegri & Iversen 1989). The samples were mounted on glycerin-coated slides (Salgado-Labouriau 1973; Faegri & Iversen 1989) and examined under light microscopy (DIAPAN; Leica Microsystems, Wetzlar, Germany). We counted a minimum of 300 pollen grains per sample. In parallel counts, we identified spores and other palynomorphs, which were monitored by saturation curves. Photomicrographs were taken using a digital camera (DFC295; Leica Microsystems) connected to the microscope. Botanical identification was based on the reference collection of the Palynology Laboratory of the Department of Botany at the Federal University of Rio Grande do Sul, located in the city of Porto Alegre, and on descriptions in the literature (Van Geel 1978; Hooghiemstra 1984; Barnett 1 2 Universidade Federal do Rio Grande do Sul, Instituto de Biociências, Departamento de Botânica. Porto Alegre, RS, Brazil Author for correspondence: Ebráilon Masetto and Maria Luisa Lorscheitter Figure 1. A. State of Rio Grande do Sul, in southern Brazil; B. Location of Hermenegildo Beach; C. Hermenegildo Beach and the Holocene paleolagoon outcrop studied, composed of dark-clay organic sediments covered by transgressive sands. & Hunter 1987; Lorscheitter 1989; Tryon & Lugardon 1990; Neves & Lorscheitter 1992; Lorscheitter et al. 1998, 1999, 2005; Leal & Lorscheitter 2006; Leonhardt & Lorscheitter 2007; Roth & Lorscheitter 2008; Scherer & Lorscheitter 2008; Spalding & Lorscheitter 2009). Taxonomic treatment was based on Chase & Reveal (2009), Pirani & Prado (2012) and electronic databases: Index Fungorum (2013), Algaebase (2013) and MOBOT (2013). The word “type” was used when precise identification was not possible, following Berglund (1986). When identification was not possible, the material was separated by number to permit future identification. The palynological description of each taxon is briefly presented, with nomenclature based on Punt et al. (2007) and Tryon & Lugardon (1990). In some cases, it was not possible to measure the polar axis of the grains due to their fixed position. Where possible, ecological data for the organisms of origin are included in order to facilitate future paleoenvironmental studies. 166 Results and discussion The radiocarbon date at the base of the Hermenegildo Beach sediment profile was 2590 ± 60 years BP, indicating that the study sequence represented the last 2600 years. A total of 48 taxa were identified in the sequence: 25 fungi, eight algae, three bryophytes and 12 pteridophytes. Fungi Phylum: Glomeromycota Class: Glomeromycetes Order: Glomerales Family: Glomeraceae 1. Glomus Tul. & C. Tul. Fig. 2 Spheroidal, yellow and smooth-walled chlamydospore, always connected to coenocytic hyphae. Diameter: ca. 22 μm. Acta bot. bras. 28(2): 165-175. 2014. Palynomorphs in Holocene sediments from a paleolagoon in the coastal plain of extreme southern Brazil Note: The genus was reported for the Quaternary in Rio Grande do Sul under the former names Rhizophagites Rosendahl (Lorscheitter 1989) and Rhizophagus Dang (Neves & Lorscheitter 1992; Neves & Bauermann 2003). Ecological data: Glomus is the most common genus of arbuscular fungi in mycorrhizal associations with the roots of many vascular plants (Schübler et al. 2001). Phylum: Ascomycota Class: Dothideomycetes Order: Pleosporales Family: Tetraplosphaeriaceae 2. Tetraplosphaeria tetraploa (Scheuer) Kaz. Tanaka & K. Hiray. Fig. 3 Conidia multicellular, elongated, dark brown, verrucate, with four divergent septate appendages. Long axis (wit (...truncated)