Quantification of distinct phytolith pools in a perhydrated Andosol

Silicon (Si) is the second most abundant element of the earth crust. The Si cycle strongly depends on the bio-cycling of Si by plants. Plants roots absorb the dissolved silicon (DSi) present in the soil solution and accumulate it into amorphous silica bodies called phytoliths (PhSi). Once plant debris return to soil, PhSi may constitute an important silica pool in soil. PhSi strongly contributes to the DSi pool; especially in desilicated weathered soils. To understand the soil-plant Si cycle it is thus primordial to quantify the PhSi pool in the soil. However, quantification methods are still not very well defined especially in soils in which pedogenic amorphous silica pools are abundant. The studied soil comes from the Basse-Terre island in Guadeloupe (16°N, 61°W). MAP is 4270 mm. The soil is a perhydrated Andosol with high organic matter content and secondary minerals typical of Andosol. DRX analyses allowed to identify pyroxene and plagioclase as the main primary minerals while halloysite and gibbsite are the main crystalline secondary minerals. Volcanic glasses are absent in the studied soil. Allophane and imogolite content is 8.0 % and ferrihydrite content is 2.6%