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Root silicification of grasses and crops from Pampean region and its relevance on silica and silicophytolith content of soils.
Encuentro; 10 International meeting on phytolith research; 2016
Root tissues of grasses and dicots can accumulate amorphous silica. Particularly inPoaceae family, silica can be restricted to the endodermis, spread throughout all tissues ordeposited into intercellular spaces. The aim of the present study were 1) to analyze thesilica content in typical grasses and crops (soybean, maize, wheat) from Pampean region,Argentina; 2) to evaluate the potential input of silica and silicophytoliths from roots to soilsin natural and cultivated areas. Roots from eight typical pampean grasses and three cropswere collected from eld. Also, soil samples, including the roots developed within them, werecollected every 10 cm along the proles from natural and cultivated areas. They were driedand weighted, and the relative contribution of roots to total weight was calculated. Rootsilicophytoliths were extracted following a calcination technique and the content was calcu-lated as percentage of dry weight. Silicophytolith morphologies were described under lightmicroscope, according previous literature. Silicophytolith content ranged between 4-11% inpampean grasses and between 0.8-4.20% in crops. Bothriochloa laguroides and Sorghastrumpellitum produce silica aggregates in endodermal walls; while the rest of the grasses producesilicications of endodermal walls and xylem. In crops, silica is deposited in xylem, endoder-mal cells and epidermal cells. In soils, the abundance of roots was higher at the rst 10 cm.In this section the roots represented the 0.39% of the weight of natural soils and 0.03% ofcultivated soils. Towards the base to the proles the values ranged between 0.0013-0.023%and 0.002-0.001%, in natural and cultivated soils, respectively. Considering a 15% (meanvalue) of silica content of roots obtained from soils, the total silicophytolith input from rootsto soils was 0.0585 gr per 100 gr of soil (at rst 10 cm) and between 0.000195-0.00345 grper 100 gr of soil (10-60 cm) in the natural area. Instead, in crop area, where silica in rootswas 11%, the mean value of silica input was 0.0033 gr per 100 gr of soil (rst 10cm) and0.00011-0.00022 gr per 100 gr of soil (10-60cm). The main morphologies found in soil rootswere silicied xylem and elongate phytoliths, similar to those found in roots from Pooideaegrasses and crops. The results obtained in this study revealed that 1) silicophytolith produc-tion in roots from pampean grasses and crops is abundant; 2) the morphologies found arecoincident with previous studies in relation to Poaceae; 3) the input of silica and silicophy-toliths from roots to soils may be more relevant in natural than in cultivated areas, due tothe higher development of roots but also due to the higher production of silicophytoliths innative grasses. Since the root silicophytolith morphologies seem to be more labile than themorphologies produced by other grass organs, it may be possible that they have a strongestinuence on silica cycle in soils, due to a higher/faster dissolution rate; and also it maycontribute to preservation of soil aggregates, due to the role that silica has on soil structure.