Abstract
Abstract. Land use change (deforestation) has several negative consequences for the soil system. It is known to increase erosion rates, which affect the distribution of elements in soils. In this context, the crucial nutrient Si has received little attention, especially in a tropical context. Therefore, we studied the effect of land conversion and erosion intensity on the biogenic silica pools in a subtropical soil in the south of Brazil. Biogenic silica (BSi) was determined using a novel alkaline continuous extraction where Si ∕ Al ratios of the fractions extracted are used to distinguish BSi and other soluble fractions: Si ∕ Al > 5 for the biogenic AlkExSi (alkaline-extractable Si) and Si ∕ Al < 5 for the non-biogenic AlkExSi. Our study shows that deforestation can rapidly (< 50 years) deplete the biogenic AlkExSi pool in soils depending on the slope of the study site (10–53 %), with faster depletion in steeper sites. We show that higher erosion in steeper sites implies increased accumulation of biogenic Si in deposition zones near the bottom of the slope, where rapid burial can cause removal of BSi from biologically active zones. Our study highlights the interaction of erosion strength and land use for BSi redistribution and depletion in a soil toposequence, with implications for basin-scale Si cycling.
Highlights
The terrestrial Si cycle has received increased attention in the past two decades
Our study shows that deforestation can rapidly (< 50 years) deplete the biogenic AlkExSi pool in soils depending on the slope of the study site (10–53 %), with faster depletion in steeper sites
There is a decrease in AlkExSi pools from forest to cropland
Summary
The terrestrial Si cycle has received increased attention in the past two decades. Multiple studies show its complexity, with a strong interaction among primary lithology and weathering, biotic Si uptake, the formation of secondary pedogenic phases and environmental controls such as precipitation, temperature and hydrology (Struyf and Conley, 2012). Lithology controls the primary source of Si through the weathering of silicate minerals of the bedrock (Drever, 1994). This process provides Si to the soil solution in the form of monosilicic acid (H4SiO4), referred to as dissolved silicon (DSi). This DSi is taken up by plants and is resupplied to the soil in the form of relatively soluble (compared to crystalline silicates) biogenic silicates (BSi) upon plant die-off, usually in the form of phytoliths (plant silica bodies) (Piperno, 2006). During soil formation, the DSi released to the soil solution through the dissolution of lithogenic and biogenic
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