Silicophytoliths and silicon studies by field assays in mollic epipedons of the southeastern Pampean Plains, Argentina

Silicon is the second most abundant element in the earth's crust. It is essential for the normal development and growth of plants, and plays a key role in the physical, chemical and biological soil properties. Silicon is important in the formation of inorganic matrix and supporting structures, which in turn condition the availability and mobilization of basic elements,such as C, 0 , P, Al, and trace elements. Amorphous silica biomineralizations (silicophytoliths) constitute a significant source of silicon to the soil-plant-atmosphere system, as they dissolve faster than silicate minerals. However, their role in agronomic aspects related to the loss of physical, chemical and biological fertility is still poorly documented. Research on the importance of silicon nutrition in order to promote plant growth has been reported in many countries, but not in Argentina. Given the negative effects that the intense agricultural activity has been causing on soils of the Pampean Plain, this work aimed at evaluating the silicophytoliths and silicon contribution in natural and experimental soils sowed with two varieties of wheat (Aviso and Baguette), and with the application of solid (Silfix) or liquid (Quicksoil) silicon fertilizers . The content of silicophytoliths (% dry weight) in wheat was determined by calcination, and the content of SiO2 in soil solutions was determined through UV-Vis spectrophotometry by the silicomolybdate method. Wheat plants ( Triticum aestivum) produced 27 Kg silicophytoliths.ha-1 in the vegetative stage, and 738 Kg silicophytoliths.ha-1 in the maturity stage. Media values of silicon in soil solutions varied from 1100 μmol/L in natural soils, to 722 μmol /L in plots with solid silicon fertilizer and 635 μmol/L in plots with liquid silicon fertilizer. These results, showing a substantial Si content decrease in cultivated soils, are important in order to advance into the knowledge of inputs and losses of silicon in agro-ecosystems. Specially, given the increase of the production of some crops that are not commonly producers of silicophytoliths/ silicon (like soybean) in the Pampean Plain of Argentina. The Argentinian perspectives on agriculture application of silicon fertilizers and silicon enhancement of crops quality were also discussed. This work was supported by the Agencia Nacional de Promoci6n Cientifica y Tecnol6gica, Ministerio de Ciencia y Tecnica (PICT 1583-2013) and Universidad Nacional de Mar del Plata (EXA 741 / 15)

Silicophytoliths and taphonomy in Cenozoic pedostratigraphic sequences of the Pampean Plain, Argentina

Grasslands and savannas occupy one forth of the total surface of South America continent, and within it, the Pampean plain region, located in the central area of eastern Argentina, covers an area of 1,200,000 km2. The dominant soils are Mollisolls generally deep, developed from well-drained loessic parental material and characterized by a silty-loam texture. Pampean Plains is one of the most fertile regions of the world. Intense agricultural activities are carried out there and this, in turn, has strongly modified the native plant communities, especially grasslands. Depending on the environmental and pedological conditions, silicophytoliths are affected by diverse taphonomical processes, both in natural and anthropic environments. They can be preserved, dissolved or fragmented, and also be transported by different agents (wind, water, animals and people). Other taphonomical aspects also important to evaluate are the methodologies used in silicophytolith studies, from soil sampling to studies at a submicroscopic level. There are several current methodologies and the work is essentially done at a very detailed resolution level, which could lead to interpretation errors if the environmental or paleoenvironmental context of the study material is unknown or not clearly stated. The study area is located in regional geomorphological units from Pampean Plain, Argentina, and integrated profiles representative of typical pedoestratigraphic sequences were analyzed. Silicophytoliths were analyzed as part of the whole mineralogy of the soil samples and morphologies were described under optical and scanning electron microscopes. The results show high amounts of silicophytoliths which have been affected by various physical and chemical alteration and/or by taphonomic processes of different types and degrees of intensity. The percentage and number of silicophytoliths per gram of soil vary. In superficial horizons (O, A), the percentage ranged between 10-65%, with 11.000.000-30.000.000 phytoliths per gram of soil (n/g.s). In subsuperficial horizons (AC, B, BC) between 2-6% and 1.000.000-5.000.000 silicophytoliths n/g.s were observed. The percentage of silicophytoliths in loessic parent material (C) ranges between 0.4-2%, with 500.000-2.000.000 n/g.s. In paleosols, percentages range between 1-8%, and the number of silicophytoliths per gram of soils were 1.500.000-8.000.000. Silica and silicophytolith biomass content per ha of soil varied according C biomass, in the pedostratigraphic Cenozoic sequences from Pampean plains. Our data show that the content of silicophytoliths decreases between 50 and 95% from superficial to subsuperficial soil horizons due to pedological processes. The comprehension of the physico-chemical degradation and transference processes within silicophytolith-plant-soil-environment system is essential in order to evaluate the role of taphonomical processes in the biogeochemical cycle of silicon. Finally, it is proposed that the displacement of native grasslands may be bio-physico-chemically balanced by the introduction of crops, in relation to the silicon cycle, since they are also important silicophytolith producers in the SE Pampean agroecosystems. Acknowledgments: This work was supported by PICT 1583/2013 AGENCIA and EXA 741/15-UNMDP

Phytolith Assemblages and Systematic Associations in Grassland Species of the South-Eastern Pampean Plains, Argentina

• Background and Aims Phytolith descriptions of South American plant species are scarce. This knowledge is crucial for the interpretation of the fossil phytolith record of a region. In this study phytolith assemblages and systematic relationships of the main grasses and Asteraceae species of Paspalum quadrifarium grassland are described

Biomineralizaciones de sílice en Celtis tala¹ (Celtidaceae) Silica biomineralizations in Celtis tala (Celtidaceae)

Se estudió la asociación fitolítica de Celtis tala Planchon, su composición química y variabilidad morfológica, analizándose por separado los morfotipos presentes en hoja, tallo y fruto. La asociación fitolítica de Celtis tala está compuesta principalmente por cistolitos, fitolitos poliédricos articulados con paredes y/o lumen celular silicificados, y fitolitos de contorno irregular, superficie rugosa y lumen celular silicificado. Los análisis de EDAX y las observaciones al microscopio permitieron corroborar la presencia de biomineralizaciones de sílice y calcio en hoja, tallo y fruto. Además se detectaron otros elementos, como Mg, Al, K, P, Fe y S en algunos fitolitos. En particular, este trabajo revela la presencia de sílice como un componente fundamental en la estructura de los cistolitos en esta especie, apoyando los resultados obtenidos por otros autores para cistolitos en otras especies relacionadas. La presencia de un elemento mucho menos lábil que el carbonato de calcio, permite que estas estructuras luego de la descomposición de la materia orgánica, puedan permanecer durante más tiempo sin alterarse en el suelo, constituyendo importantes elementos indicadores de la presencia de Celtis tala en el registro fósil.The phytolith assemblage of Celtis tala, its chemical composition and variability were studied. Leave, stem and fruit phytolith morphologies were analyzed with the purpose of establishing the contribution of each organ. The results showed that cystolith types, articulated poliedric (with wall and lumen silicified) and irregular, rugose poliedric phytoliths were the main morphologies present in Celtis tala phytolith assemblage. Silicon and calcium biomineralizations were detected by EDAX analysis and microscope observations in leave, stem and fruit. Other elements, such as Mg, Al, K, P, Fe and S, were also detected by EDAX analysis in some phytoliths. The presence of silicon as an important structural cystolith component is detected in this study and supports the results obtained by other researchers for other species. The silicon cystolith constitution allows a long- term permanence of this morphology in sediment, and makes it an important Celtis tala indicator in fossil assemblages

Early silicification of leaves and roots of seedlings of a panicoid grass grown under different conditions: anatomical relation and structural role

• Grasses accumulate high amounts of silica deposits in tissues of all their organs, especiallyat mature stage. However, when and under which conditions do grass seedlings begin to produce these silica deposits and their relation with anatomy and developmentis little known. Here we investigated the silicification process in the first leavesand roots of seedlings of Bothriochloa laguroides grown in different substrate and Sitreatments. • The distribution and content of silica deposits in the organs of the seedlings grownunder different conditions were analyzed through staining techniques and SEM-EDAXanalyses. • Leaf silica deposits were accumulated 3–4 days after the first leaf emergence, alsounder low silica solution (0.17–0.2 mM). Their location was mainly restricted to shortcostal cells from basal sectors, and scarcely in trichomes and xylem at tips. Silica contentin leaves increased with the age of the seedlings. Roots presented dome-shaped silica aggregates, between 4–12 lm of diameter, located in the inner tangential wall ofendodermal cells and similar to those produced at maturity. • Silicification begins early in the first photosynthetic leaf, and silica distribution isopposite to that found in mature plants, mainly restricted to basal sectors, probablyacting as a reinforcing element. The fast incorporation of solid amorphous silica inleaves and roots, may be useful for farm applications in species that are Si-fertilize

Estabilidad, morfología y rugosidad de agregados de argiudoles típicos sometidos a distintos usos: su rol como indicadores de calidad física en suelos de la provincia de Buenos Aires, Argentina Stability, morphology and roughness of aggregates of typical argiudolls under diferent types of land uses: their role as indicators of soils physical quality in Buenos Aires province, Argentina

En los últimos diez años se observó un importante cambio en el uso de la tierra en la llanura pampeana, lo cual ha llevado a una marcada degradación de los suelos. El objetivo del trabajo fue evaluar la estabilidad, la morfología y la rugosidad de distintos tamaños de agregados como indicadores de calidad en Argiudoles Típicos del sudeste bonaerense sometidos a distintos usos de suelo y a distintas intensidades de manejo. Se trabajó con el epipedón mólico de parcelas con distinto uso de suelo: cultivadas, forestadas y naturales. Los resultados mostraron mayor estabilidad en los suelos no laboreados y en los forestados de más de treinta años. En los sitios cultivados y forestados se observaron agregados alargados, cuadrangulares y esféricos, mientras que en los sitios sin laboreo no se presentaron las formas esféricas. La rugosidad de los agregados fue mayor en los suelos sin laboreo, si bien ello varió con el tamaño de los agregados. La estabilidad, morfología y rugosidad de agregados demostraron ser buenos indicadores de calidad de suelos del SE bonaerense.During the last ten years, an important land use change took place in the Pampas region of Argentina. This change led to a significant soil degradation. This work aims to evaluate the stability, morphology and roughness of soil aggregates in soils under different land uses. The values found for each land use could serve as soil quality indicators in southeastern Buenos Aires. Samples were taken from mollic epipedons under cultivated, forest and natural soils. Results showed higher aggregate stability in virgin and forest soils than in cultivated soils. Aggregates were elongated, quadrangular and spherical in cultivated and forest soils. Aggregates from non-cultivated soils did not show the expected spherical forms; they also presented a high roughness although it varied across the different aggregate sizes. Soil aggregate stability, morphology and roughness were suitable indicators of soil quality in southeastern Pampas

Leaf and culm silicification of Pampas grass (Cortaderia selloana) developed on different soils from Pampean region, Argentina

Amorphous silica accumulation in grasses is widely described in numerous species; however, work done in relation to the factors affecting this accumulation in the tissues and different type of cells, is still incipient. Here, we analysed a perennial tussock grass, Cortaderia selloana (Schult. & Schult.f.) Asch. & Graebn. (Pampas grass), a native and widely spread species from South America, which is also considered an invasive plant in many regions of the world.Weanalysed the relation between silicification process, soil type and environment, and anatomical features. Silicophytolith content and distribution in plants was analysed through calcination and staining techniques and SEM-EDAX analyses. Silicophytolith content was higher in leaves (2.48–5.54% DW) than in culms (0.29–0.43% DW) and values were similar to other tussock grasses. A relationship between the habit of a grass species and the potential maximum content of amorphous silica is suggested. Plants grown in soils from modified environments with high silica content (Anthrosol and Tecnosol) produced a higher content of amorphous silica. In leaves, the distribution of silicified cells was conditioned by leaf xeromorphic features. Soil Si content and environmental conditions (radiation, disturbance) are more relevant in silicification process than phenological factors. Within leaves, the accumulation of amorphous silica is conditioned by anatomy and transpiration

Amorphous silica biomineralizations in Schoenoplectus californicus (Cyperaceae): their relation with maturation stage and silica availability

The factors involved on the silicification process in Cyperaceae are scarcely known. In this study we analyse the effect of maturation stage and silica availability on the production of amorphous silica biomineralizations in culms of Schoenoplectus californicus. Young and senescent culms were collected from ponds with different silica availability. Two complementary methodologies (calcination and staining techniques), light and scanning electron microscopy and EDS were applied for amorphous silica analyses in plants. Quantitative data were analysed by Kruskal-Wallis and a two-way ANOVA tests. There were no significant differences between silica content of culms collected in ponds with different silica availability. Instead, silica content in senescent culms was higher than in young culms (F=91.43, P<0.01). Young culms only produce cone-shaped amorphous silica bodies, located in epidermal cells overlying sclerenchyma. Senescent culms produce a higher diversity of silicified cells, such as epidermal, stellate (aerenchyma) and parenchymatic cells. Silicification process in S. californicus is clearly affected by age and may act as a mechanism of structural resistance improvement. Some cells became silicified very early in the development and others may be silicified at a later stage depending on wall characteristics or rate of transpiration.Biomineralizaciones de sílice amorfo en Schoenoplectus californicus (Cyperaceae): su relación con el estado de maduración y la disponibilidad de sílice. Los factores involucrados en el proceso de silicificación en Cyperaceae son poco conocidos. En este estudio se analiza el efecto del estado de maduración y la disponibilidad de sílice en la producción de biomineralizaciones de sílice amorfo en tallos de Schoenoplectus californicus. Tallos jóvenes y senescentes fueron recolectados de lagunas con diferente disponibilidad de sílice. Dos técnicas complementarias (calcinación y tinción), microscopía óptica y electrónica y EDAX fueron aplicados para el análisis en las plantas. Los datos cuantitativos fueron analizados por tests de Kruskal-Wallis y ANOVA de dos vías. No hubo lagunas con diferente disponibilidad de sílice. En cambio, el contenido en tallos senescentes fue mayor que en los jóvenes (F=91,43; P<0,01). Los tallos jóvenes solo producen cuerpos silíceos cónicos, localizados en células epidérmicas asociadas al esclerénquima. En los tallos senescentes se silicifican una mayor diversidad de células, como las epidérmicas, del aerénquima y esclerénquima. El proceso de silicificación en S. californicus está claramente afectado por la edad y mejoraría la resistencia estructural. Algunas células se silicifican tempranamente, mientras que en otras depende de las características de la pared celular y/o de la tasa de transpiraciónFil: Fernández Honaine, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mar del Plata. Instituto de Investigaciones Marinas y Costeras; Argentina; Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina;Fil: Borrelli, Natalia Lorena. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mar del Plata. Instituto de Investigaciones Marinas y Costeras; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina;Fil: Osterrieth, Margarita Luisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mar del Plata. Instituto de Investigaciones Marinas y Costeras; Argentina; Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario; Argentina;Fil: del Río, Laura Sombra. Universidad Nacional de la Plata. Facultad de Ingeniería. Departamento de Ciencias Básicas; Argentina; Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario; Argentina; Unidad Académica Mar del Plata. Universidad Tecnológica Nacional; Argentina

Microartrópodos como indicadores de disturbio antrópico en entisoles del área recreativa de Miramar, Argentina Microarthropods as indicators of anthropic disturbance in entisols in a recreational area of Miramar, Argentina

En áreas recreativas el tránsito humano provoca alteraciones en el horizonte superficial del suelo, destruyendo parte o la totalidad de éste, reduciendo la porosidad y modificando el microambiente edáfico. La mesofauna edáfica, por habitar principalmente en los horizontes superficiales del suelo, resulta ser un buen indicador de este impacto antrópico. Se evaluó la distribución de ácaros oribátidos y colémbolos de suelo frente al impacto del tránsito humano en el área recreativa del Vivero Dunícola "Florentino Ameghino" de Miramar, Buenos Aires, Argentina. Se consideraron tres zonas de impacto: máximo, medio y mínimo. Se extrajeron los microartrópodos y se determinaron hasta nivel de especie colémbolos y oribátidos. Se calculó riqueza específica, diversidad y paridad por sitio y horizonte. Se realizó un análisis de correspondencia y se elaboró un índice de impacto teniendo en cuenta los diferentes horizontes y la frecuencia de especies. Se hallaron 29 especies de ácaros oribátidos y 19 especies de colémbolos. La diversidad (H´) fue significativamente diferente entre los sitios de máximo y de mínimo impacto. El análisis factorial de correspondencia definió tres grupos de acuerdo al grado de alteración de los horizontes superficiales y las características pedológicas (horizonte orgánico o mineral). El índice de impacto (II M) en la zona de mayor tránsito fue II M=9 mientras que en la de mínimo impacto fue II M<1. Los resultados demostraron que la comunidad de microartrópodos considerada resultó ser un buen indicador de impacto antrópico y adecuada para bioevaluar el estado del área estudiada.<br>Human trampling in recreational areas causes alterations in the soil surface horizon, partially or totally disrupting soil structure, reducing porosity and modifying the edaphic microenvironment. Soil mesofauna, is a good indicator of this human impact since it inhabits mainly soil surface horizons. We evaluated the changes in edaphic oribatid mite (Acari) and springtail (Collembola) communities sufferering from the impact of human trampling in the recreational area of Vivero Dunícola "Florentino Ameghino" Miramar, in the Province of Buenos Aires, Argentina. Three impact areas were considered: maximum, medium and minimum. Collembola and oribatid were determined to species level. Species richness, diversity and parity by site and horizon were calculated. A correspondence analysis was carried out and an impact index elaborated taking into account the different horizons and species frequencies. Twenty-nine species of oribatid mites and 19 species of Collembola were found. Diversity (H´) was significantly different between the maximum and minimum impact sites. Factorial Correspondence Analysis defined three groups in terms of degree of alteration of the surfacel horizon and pedological characteristics (organic or mineral horizons). The value of the impact index (II M) in the maximum trampling area was II M=9 while in that of minimum impact it was II M < 1. The results support the usefulness of the microarthropod community as an indicator of human impact and their suitability for bioevaluating the state of the study area