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Grass phytoliths analysis from natural grasslands in the SE Pampean region (Argentina): a preliminary study.
Moscu, Rusia
Otro; 5th International Meeting of Phytolith Research; 2004
In SE of Buenos Aires province, the pampas plains are interrupted by a rocky formation, the Tandilia and Ventana systems. These rocky areas disable the intensive agricultural activities, dominant in surrounding croplands, allowing natural flora growth. At present the “pajonal” of Paspalum quadrifarium and the “flechillar” of Stipa and Piptochaetium spp, represent the main native communities growing on these areas, but their Quaternary distributions are unknown in the region. Phytolith assemblage study of these communities represents a valuable tool for the understanding of the grassland history of pampas plains. In this preliminary study we described the phytolith assemblage of the main grass species for each community, linking them with the systematic groups of the family, and identifying the phytoliths that possess systematic and diagnostic importance. Phytoliths were extracted from leaves of six grasses: Paspalum quadrifarium Lam. (Panicoideae), Bothriochloa laguroides (D.C.) Pilger (Panicoideae), Bromus unioloides Humboldt, Bondpland et Kunth (Pooideae), Piptochaetium medium (Speg.) M. A. Torres (Stipoideae), Stipa papposa Nees (Stipoideae) y Vulpia dertonensis (All.) Gola (Pooideae), following Laboureau calcination methodology. Four hundred phytoliths per slide were counted and identified with a classification system that contemplates isolated and articulate forms. Multivariate analysis (Cluster and PCA) of these species phytolith assemblages were carried out, applying product – moment correlation and average Manhattan distance coefficients. The results showed that isolated and articulated short shank, convex ends panicoid dumbbells, thick crosses and rectangular smooth phytoliths (less than 35 ìm long) were the main Paspalum quadrifarium phytolith morphologies. Isolated and articulated short shank, straight - concave ends panicoid dumbbells were the most abundant in Bothriochloa laguroides phytolith assemblage, while isolated and articulated rectangular crenate phytoliths were the most frequent in Bromus unioloides. Short cells phytoliths were very frequent in Piptochaetium medium and Stipa papposa phytolith assemblages, mainly short shank, convex ends Stipa type dumbbells. Rondel shaped (truncated cones) were also very frequent in Stipa papposa phytolith assemblage. Cluster analysis results for species data showed three groups conformed by Bothriochloa – Paspalum, Stipa – Piptochaetium and Vulpia – Bromus, which resemble the taxonomy affinities of these species. PCA analysis results showed a strong Stipa – Piptochaetium grouping, clearly separated of the other species. Vulpia dertonensis was nearer to the Stipa - Piptochaetium group than to Bromus unioloides. Paspalum quadrifarium and Bothriochloa laguroides were the most distant of the groups. The main characters that differentiated the groups were articulated short cells phytoliths, rectangular crenate phytoliths, thick crosses, short shank panicoid dumbbells, Stipa type dumbbells and rondel shaped.