SILICOPHYTOLITHS IN DIFFERENT GROWTH STAGES OF SOYBEAN PLANTS FROM PAMPEAN REGION, ARGENTINA.

BENVENUTO, MARIA LAURA; OSTERRIETH, MARGARITA; FERNÁNDEZ HONAINE, MARIANA

Encuentro; 9th International Meeting on Phytolith Research; 2014

In the last years, the intensification of land use by agriculture caused negative effects on the soils of the Pampean region. These effects can be reflected in their physical, chemical and biological properties. In order to understand how this agricultural practices affect the terrestrial silicon cycle, we determined: 1) the amount of amorphous silica biomineralizations (silicophytoliths) incorporated in different organs of soybean plants (N=9) during 3 growth stages: (V1) first set of unfolded trifoliolate leaves; (R1) plants with at least one flower on any node; and (R7) one normal pod on the main stem has reached its mature pod color; 2) the production of silicophytoliths in early stages of development in plants grown under different silica (SiO2) concentrations. The silica content and the extraction of silicophytoliths were subjected to the calcination technique sensu Labouriau (1983). To carry out the first objective, several complete specimens of soybean were collected from three plots located in the southeast of the province of Buenos Aires, Argentina. The rest of the plants were grown during only 6 days in river sand, under conditions of light and temperature controlled, and concentrations of SiO2 varying from 0.1 mM (value of the substratum) to 0.6 mM and 1.9 mM. The results of silica content allowed to estimate an increase of silica (gr.Sio2/m2) from V1 = 0.26 to R7 = 8.85 in the soybean crop. This was reflected in a significant increase in the production of silicophytoliths and in the percentage of dry weight of SiO2 in leaves (from V1 = 0.7 to R7 = 3). The silicophytolith production was not significant different in plants grown at different concentrations of SiO2. In the ashes obtained from cotyledons, only tabular morphologies were observed. The EDAX analysis performed on leaves and cotyledons in plants of 6 days grown showed values of Wt% lower (0.60-2.06 and 0.35-1.1, respectively) than those detected in leaves silicophytoliths in the R7 stage (34.54 Wt% ). These results contribute to the knowledge of the rate of incorporation of silicon / amorphous silica in plants and their contribution to the soils under different agricultural practices.