Phytolith transport in soil: a laboratory study on intact soil cores

Abstract

Column experiments on phytolith transport were conducted to assess the partial contributions of water percolation and earthworm activity to phytolith transport in loamy and sandy soils. Six intact cores of a loamy sandy Haplic Cambisol and nine cores of a silty loamy Stagnic Luvisol were excavated. With the Luvisol, three treatments were perfomed: a percolation treatment with periodic irrigation, but without earthworms, a percolation and earthworm treatment with periodic irrigation and earthworms (Aporrectodea caliginosa) and a control. The Cambisol cores did not contain earthworms and hence only percolation and control treatments were tested. The phytoliths of common reed (Phragmites australis) were labelled with the fluorescent dye fluorescein isothiocyanate and applied to the soil surface of each core. Except for the control treatment, 3600 mm of water was applied over 6 months. In the Cambisol, the weighted mean transport distance of phytoliths was significantly greater with percolation (2.2 ± 0.1 cm) than in the control (0.9 ± 0.3 cm), indicating that water percolation is a driving mechanism of phytolith transport. In the Luvisol, the difference in mean transport depth between control and percolation treatments (1.0 ± 0.2 and 1.5 ± 0.3 cm) was not significant. The earthworms did not affect the mean transport distance of phytoliths in the Luvisol, but the phytolith concentrations in the leachates were significantly greater and their size distribution did not change with soil depth as observed in the percolation treatment without earthworms. Further studies are required to quantify the effect of earthworms on phytolith transport.

Silicon pools in human impacted soils of temperate zones

“…In the “reference” situation the temperate landscape is dominated by deciduous climax forests. These systems show tight recycling of Si in the soil‐plant system [ Sommer et al , ; Cornelis et al , ], and dissolved Si in soil water can be taken up by plants and/or incorporated in clays [ Cornelis et al , , , ; Vandevenne et al , ]—“stage 1.” Biogenic Si (in litter) does not form a long‐term pool in our soils, and this is in line with other studies from temperate zones where a sharp drop in BSi and/or phytoliths is observed at the transition between organic and mineral horizons [ Barão et al , ; Fishkis et al , ]. Deforestation and land use cultivation with moderate to complete removal of biomass will then decrease BSi stocks in soils, in particular when not compensated by Si fertilizers.…”

“…Biogenic Si (in litter) does not form a long-term pool in our soils, and this is in line with other studies from temperate zones where a sharp drop in BSi and/or phytoliths is observed at the transition between organic and mineral horizons [Barão et al, 2014;Fishkis et al, 2010]. Deforestation and land use cultivation with moderate to complete removal of biomass will then decrease BSi stocks in soils, in particular when not compensated by Si fertilizers.…”

Modern soil phytolith assemblages used as proxies for Paleoscape reconstruction on the south coast of South Africa

“…Low phytolith concentration in very coarse soils or in very active bioturbation soils has also been shown to be the result of phytolith translocation (e.g. Fiskish et al, 2010). These authors showed size dependence on phytolith percolation by water, with phytoliths with a size diameter of 5μm being the most susceptible to move downward In our study, if phytolith translocation had occurred in our samples with low number of phytoliths (limestone fynbos, coastal thicket, strandveld vegetation types) then we would expect to not see small morphotypes, such as GSSC rondels and saddles or spheroids psilates and rugulates, what is not the case.…”

Diatom percolation through soils: a proof of concept laboratory experiment

“…For instance, transport of bacteria and colloids in soils is widely documented for dimensions up to 10 µm (McKay et al ., ; Jacobsen et al ., ; Semenov et al ., ; Wang et al ., ). On the other hand, percolation of phytolith and nematodes (dimensions spanning from <5 up to 500 µm) through soil columns is found negligible or null (Planchon et al ., ; Fishkis et al ., , ).…”