How does sonication affect the mineral and organic constituents of soil aggregates?—A review

Abstract

Application of ultrasound to disperse soil aggregates has been critical in enabling researchers to separate and analyze aggregate building blocks that include organic and mineral particles as well as mineral associated organic matter. But the forces generated in the process may also alter the dispersion products and, thus, potentially interfere with the interpretation of experimental results. This review summarizes present knowledge on experimental conditions that may lead to physical damage and chemical modifications of aggregate building blocks. The energy level at which physical disintegration of organic particles could be detected was as low as 60 J mL -1 . Physical damage of sand-and silt-sized mineral particles was observed to commence at energy levels exceeding 700 J cm -3 . No evidence was found for the disintegration of particles within the clay-size fraction of soils even though studies analyzing pure minerals such as kaolinite revealed particle breakage after application of energy amounts > 12,000 J cm -3 . Here we outline a strategy to minimize artifacts such as physical damage of mineral or organic particles resulting from ultrasonication by adopting a stepwise dispersion protocol involving successively higher energy levels, accompanied by a sequential separation of organic and mineral compounds.

The nature of organic carbon in density-fractionated sediments in the Sacramento-San Joaquin River Delta (California)

“…Golchin et al, 1994;Cerli et al, 2012;Kaiser and Berhe, 2014). The fractionation scheme we and others have used for sediments is less energetic or disruptive (at least in the latter stages) than commonly used for soils and these methodological contrasts need to be considered when comparing results.…”

“…Mineral-rich/organicpoor soils and sediments typically have densities over the range of ∼ 2.4-2.9 g cm −3 ; mineral-poor/organic-rich soils and sediments have densities between ∼ 1.0 and 1.5 g cm −3 (Adams, 1973;Rühlmann et al, 2006). Density fractionation has been widely used on soils to elucidate mechanisms of how organic matter is physically and chemically associated with minerals and to estimate stability, residence and turnover times of organic matter (e.g., Golchin et al, 1994;Hedges and Oades, 1997;Baldock and Skjemstad, 2000;Baisden et al, 2002a;Sollins et al, 2006;Rühlmann et al, 2006;Crow et al, 2007;Castanha et al, 2008;Trumbore, 2009;Cerli et al, 2012;Kaiser and Berhe, 2014). The chemistry, stable and radiocarbon isotopic compositions, and turnover times for isolated fractions is particularly dependent on methodology.…”

Enzymatic biofilm digestion in soil aggregates facilitates the release of particulate organic matter by sonication

“…It is used for studying reduction of aggregate size (Imeson and Vis, 1984) as well as detachment of occluded POC (Golchin et al, 1994). Kaiser and Berhe (2014) reviewed 15 studies using ultrasonication of soil aggregates in consideration of its destructiveness to the soil mineral matrix and occluded POM. They found destruction of POM at applied energy levels > 60 J mL −1 , destruction of sand-sized primary particles at > 710 J mL −1 and of smaller mineral particles at even higher energy levels.…”

“…The method combines a modified enzymatic pretreatment (Böckelmann et al, 2003) with α-glucosidase, β-galactosidase, DNAse and lipase, a determination of the DNA ratio of sessile to suspended cells after enzymatic treatment and an ultrasonication of soil aggregates followed by density fractionation and soil organic carbon (SOC) measurement (Kaiser and Berhe, 2014). The ultrasonication/density fractionation separates SOC into three operational solid fractions: non-occluded free light fraction SOC (fLF-SOC), aggregate-embedded occluded light fraction SOC (oLF-SOC) and colloidal as well as (macro)molecular SOC, which is not detachable from mineral surfaces by the chosen fractionation method and subsumed under heavy fraction (HF-SOC) (Kaiser and Berhe, 2014).…”

“…The ultrasonication/density fractionation separates SOC into three operational solid fractions: non-occluded free light fraction SOC (fLF-SOC), aggregate-embedded occluded light fraction SOC (oLF-SOC) and colloidal as well as (macro)molecular SOC, which is not detachable from mineral surfaces by the chosen fractionation method and subsumed under heavy fraction (HF-SOC) (Kaiser and Berhe, 2014).…”