Mobilisation of Al, Fe, and DOM from topsoil during simulated early Podzol development and subsequent DOM adsorption on model minerals

Abstract

Podzols are characterised by mobilisation of metals, particularly Al and Fe, and dissolved organic matter (DOM) in topsoil horizons, and by immobilisation in subsoil horizons. We mimicked element mobilisation during early podzolisation by irrigating the AE horizon of a Dystric Arenosol with acetic acid at different flow velocities and applying flow interruptions to study rate-limited release in experiments with soil cylinders. We used eluates in batch experiments with goethite and Al-saturated montmorillonite to investigate DOM reactivity towards minerals. Both the flow velocity and flow interruptions affected element release, pointing to chemical non-equilibrium of release and to particles, containing Fe and OM mobilised at larger flow velocity, characteristic of heavy rain or snowmelt. Based on chemical extractions, the source of mobilised Al and Fe, the vast majority of which was complexed by DOM, was no oxide phase, but rather organic. Rate limitation also affected the composition of DOM released. Carboxyl and phenolic species were the most important species adsorbed by both minerals. However, DOM composition affected the extent of DOM adsorption on goethite more distinctly than that on montmorillonite. Our findings evidence that the intensity of soil percolation affects quantitative and qualitative element release during early podzolisation and adsorptive DOM retention in subsoil horizons.

Understanding the Adaptive Mechanisms of Plants to Enhance Phosphorus Use Efficiency on Podzolic Soils in Boreal Agroecosystems

“…Unique characteristics of podzolic soils, such as increased acidity, higher exchangeable Al 3+ and Fe 2+ content, lower cation exchange, and water retention capacity result in higher P retention capacity and low soil P concentration (<0.01 mg P L −1 ), typical in boreal agroecosystems (Pierzynski et al, 2005 ; Paul et al, 2011 ). Under natural conditions, the podzolization process facilitates leaching of cations such as Al 3+ , Fe 2+ , and Ca 2+ , dissolved organic matter, and chelates from organic layers or eluviated profiles that accumulated in illuviated profiles (Paul et al, 2011 ; Grand and Lavkulich, 2013 ; Krettek and Rennert, 2021 ). However, most agricultural podzolic soils have lost the organic and eluviated profile or a small proportion is mixed with illuviated B horizon rich in Al and Fe minerals during initial or successive soil preparation (Paul et al, 2011 ).…”

Distribution of Al, Fe, Si, and DOC between size fractions mobilised from topsoil horizons with progressing degree of podzolisation

“…2). Preferential flow responsible for the concentration patterns should be of minor importance in the extremely sandy soils, as previously discussed 12 . Concentrations after the first interruption exceeded those of the first flush and were partially very high, for instance c(Fe) > 70 mg L −1 (Fig.…”

“…Furthermore, there was no significant effect of the degree of podzolisation on the total element concentrations. First flush is a common feature of element release in the initial phase of column experiments, pointing to mobilisation of particles or rate-limited desorption or dissolution 12,31,32 . Non-equilibrium release became more evident after the longer interruption of irrigation after 10 pv eluted, and to smaller extent after the shorter irrigation after 20 pv eluted (Fig.…”

“…This was particularly the case with data from experiments with the least podzolised soils (P1, P2), while the points representing the most podzolised soils (P4, P5) plotted away from the equilibrium lines. X-ray amorphous soil constituents, which may include SROAS, were dissolved in a laboratory podzolisation experiment with the A horizon of P1 12 . According to previous studies 17,19,46,47 , undersaturation with respect to SROAS is a common feature of the soil www.nature.com/scientificreports/…”

Complementary effects of sorption and biochemical processing of dissolved organic matter for emerging structure formation controlled by soil texture

“…Although the depth of the direct influence by roots is limited to the extension of the root system, percolating DOM from upper soil horizons can transfer OC into much deeper soil regions. This depth migration is dependent of the water flow in the vadose zone and OC retention at mineral surfaces (Krettek & Rennert, 2021; McCarthy, 2005; Merdy et al., 2021), implying that soil texture can have a major influence on OC mobility.…”