Composition and superposition of alluvial deposits drive macro-biological soil engineering and organic matter dynamics in floodplains
Author(s)
Sebag, D.
Turberg, P.
Guenat, C.
Adatte, T.
Schlaepfer, R.
Date issued
August 2019
In
Geoderma
No
355
From page
113899
To page
113910
Reviewed by peer
1
Abstract
Soil structure formation in alluvial soils is a fundamental process in near-natural floodplains. A stable soil
structure is essential for many ecosystem services and helps to prevent river bank erosion. Plants and earthworms
are successful soil engineering organisms that improve the soil structural stability through the incorporation
of mineral and organic matter into soil aggregates. However, the heterogeneous succession of different
textured mineral and buried organic matter layers could impede the development of a stable soil structure.
Our study aims at improving the current understanding of soil structure formation and organic matter dynamics
in near natural alluvial soils. We investigate the effects of soil engineering organisms, the composition, and the
superimposition of different alluvial deposits on the structuration patterns, the aggregate stability, and organic
matter dynamics in in vitro soil columns, representing sediment deposition processes in alluvial soils. Two
successions of three different deposits, silt–buried litter–sand, and the inverse, were set up in mesocosms and
allocated to four different treatments, i.e. plants, earthworms, plants+earthworms, and a control. X-ray
computed tomography was used to identify structuration patterns generated by ecosystem engineers, i.e. plant
root galleries and earthworm tunnels. Organic matter dynamics in macro-aggregates were investigated by Rock-
Eval pyrolysis. Plant roots only extended in the top layers, whereas earthworms preferentially selected the buried
litter and the silt layers. Soil structural stability measured via water stable aggregates (%WSA) increased in the
presence of plants and in aggregates recovered from the buried litter layer. Organic matter dynamics were
controlled by a complex interplay between the type of engineer, the composition (silt, sand, buried litter) and the
succession of the deposits in the mesocosm. Our results indicate that the progress and efficiency of soil structure
formation in alluvial soils strongly depends on the textural sequences of alluvial deposits.
structure is essential for many ecosystem services and helps to prevent river bank erosion. Plants and earthworms
are successful soil engineering organisms that improve the soil structural stability through the incorporation
of mineral and organic matter into soil aggregates. However, the heterogeneous succession of different
textured mineral and buried organic matter layers could impede the development of a stable soil structure.
Our study aims at improving the current understanding of soil structure formation and organic matter dynamics
in near natural alluvial soils. We investigate the effects of soil engineering organisms, the composition, and the
superimposition of different alluvial deposits on the structuration patterns, the aggregate stability, and organic
matter dynamics in in vitro soil columns, representing sediment deposition processes in alluvial soils. Two
successions of three different deposits, silt–buried litter–sand, and the inverse, were set up in mesocosms and
allocated to four different treatments, i.e. plants, earthworms, plants+earthworms, and a control. X-ray
computed tomography was used to identify structuration patterns generated by ecosystem engineers, i.e. plant
root galleries and earthworm tunnels. Organic matter dynamics in macro-aggregates were investigated by Rock-
Eval pyrolysis. Plant roots only extended in the top layers, whereas earthworms preferentially selected the buried
litter and the silt layers. Soil structural stability measured via water stable aggregates (%WSA) increased in the
presence of plants and in aggregates recovered from the buried litter layer. Organic matter dynamics were
controlled by a complex interplay between the type of engineer, the composition (silt, sand, buried litter) and the
succession of the deposits in the mesocosm. Our results indicate that the progress and efficiency of soil structure
formation in alluvial soils strongly depends on the textural sequences of alluvial deposits.
Publication type
journal article
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