Plant and soil phytolith analysis of a relictual community of Butia yatay in temperate-humid savannas (Entre Ríos, Argentina)

Abstract

Although palms are recognized as a plant group of tropical and sub-tropical ecosystems, in South America they can also be found in temperate savannas under certain conditions. Therefore, since these plants have been widely used as palaeoindicators in warm and humid climates, it is important to know what phytolith contribution these plants have made in temperate environments. El Palmar National Park (Argentina) protects the largest remnant of savanna palm, Butia yatay (Mart.) Becc., one of the southernmost palm communities in the continent. This modern analogue study assessed the variability of silica phytoliths in 15 selected species of plants, 20 mulch samples (organic horizon) and 60 soil samples that were collected in all the plant communities selected for this study: dense palm trees (DPT), shrubbery with isolated tall palms (SIP), psammophile steppe (PS) and humid psammophile steppe (HPS). Our results show that grasses exhibit the most diverse forms. Palms, sedges and dicots can be distinguished by the different proportions of several diagnostic morphotypes. Palm tree communities can be characterized based on a presence a high proportion of globular echinate and trapeziform sinuate/oblong phytoliths. Psammophile steppes have a high proportion of bilobate, polylobate and cross phytoliths and a low presence of globular echinate. Humid psammophile steppes show a high presence of bilobate, cross and dicot phytoliths with a low proportion of trapeziform sinuate/oblong phytoliths and an absence of globular echinate morphotypes. The ratio of palm to grass phytoliths allowed us to obtain differences between the palm groves, psammophile steppe and humid psammophile steppe ecosystems. These analyses can then be used to determine this type of ecosystem in temperate humid savannas. Phytolith assemblages provide an important record for the characterization of the plant-soil system and production-incorporation system in mixed communities as a tool in the construction of palm trees paleoenvironments.