TY - JOUR

T1 - Legacy of rice roots as encoded in distinctive microsites of oxides, silicates, and organic matter

AU - Kölbl, Angelika

AU - Schweizer, Steffen A.

AU - Mueller, Carsten W.

AU - Höschen, Carmen

AU - Said-Pullicino, Daniel

AU - Romani, Marco

AU - Lugmeier, Johann

AU - Schlüter, Steffen

AU - Kögel-Knabner, Ingrid

N1 - Funding Information: The National Rice Research Centre is gratefully acknowledged for giving us the opportunity to work at the paddy field near Zeme (Mortara, Italy), for help during soil sampling, and for providing important information about the sampling area. The authors thank Peter Schad for his description of the soil profiles. We acknowledge B?rbel Angres and Monika Heilmeier for their analysis of basic soil parameters. Three anonymous reviewers are gratefully acknowledged for their suggestions which considerably improved the manuscript. Funding from the German Research Foundation (DFG) is acknowledged for the NanoSIMS instrument (KO 1035/38-1). Financial support for Steffen Schweizer is acknowledged from Deutsche Forschungsgemeinschaft within the framework of the research unit ?MAD Soil?Microaggregates: Formation and turnover of the structural building blocks of soils? (DFG RU 2179) through project KO 1035/48-1. We are grateful to the Deutsche Forschungsgemeinschaft (DFG) for their generous funding of the Research Unit FOR 995: Biogeochemistry of paddy soil evolution. Funding Information: Acknowledgments: The National Rice Research Centre is gratefully acknowledged for giving us the opportunity to work at the paddy field near Zeme (Mortara, Italy), for help during soil sampling, and for providing important information about the sampling area. The authors thank Peter Schad for his description of the soil profiles. We acknowledge Bärbel Angres and Monika Heilmeier for their analysis of basic soil parameters. Three anonymous reviewers are gratefully acknowledged for their suggestions which considerably improved the manuscript. Funding from the German Research Foundation (DFG) is acknowledged for the NanoSIMS instrument (KO 1035/38-1). Financial support for Steffen Schweizer is acknowledged from Deutsche Forschungsgemeinschaft within the framework of the research unit “MAD Soil—Microaggregates: Formation and turnover of the structural building blocks of soils” (DFG RU 2179) through project KO 1035/48-1. We are grateful to the Deutsche Forschungsgemeinschaft (DFG) for their generous funding of the Research Unit FOR 995: Biogeochemistry of paddy soil evolution. Publisher Copyright: © 2017 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2017/12

Y1 - 2017/12

N2 - Rice (Oryza sativa) is usually grown under flooded conditions, leading to anoxic periods in the soil. Rice plants transport oxygen via aerenchyma from the atmosphere to the roots. Driven by O2 release into the rhizosphere, radial gradients of ferric Fe and co-precipitated organic substances are formed. Our study aimed at elucidating the composition and spatial extension of those gradients. Air-dried soil aggregates from a paddy field were embedded in epoxy resin, cut, and polished to produce cross sections. Reflected-light microscopy was used to identify root channels. With nano-scale secondary ion mass spectrometry (NanoSIMS), we investigated transects from root channels into the soil matrix and detected12 C−,16 O−,12 C14 N−,28 Si−,27 Al16 O−, and56 Fe16 O− to distinguish between embedding resin, organic matter, oxides, and silicates. Image analyses reveal high occurrences of56 Fe16 O− within and in close proximity of oxide-encrusted root cells, followed by a thin layer with high occurrences of27 Al16 O− and12 C14 N− . In two of the three transects,28 Si− only occurs at distances larger than approximately 10 µm from the root surface. Thus, we can distinguish distinct zones: the inner zone is composed of oxide encrusted root cells and their fragments. A thin intermediate zone may occur around some roots and comprises (hydr)oxides and organic matter. This can be distinguished from a silicate-dominated outer zone, which reflects the transition from the rhizosphere to the bulk soil.

AB - Rice (Oryza sativa) is usually grown under flooded conditions, leading to anoxic periods in the soil. Rice plants transport oxygen via aerenchyma from the atmosphere to the roots. Driven by O2 release into the rhizosphere, radial gradients of ferric Fe and co-precipitated organic substances are formed. Our study aimed at elucidating the composition and spatial extension of those gradients. Air-dried soil aggregates from a paddy field were embedded in epoxy resin, cut, and polished to produce cross sections. Reflected-light microscopy was used to identify root channels. With nano-scale secondary ion mass spectrometry (NanoSIMS), we investigated transects from root channels into the soil matrix and detected12 C−,16 O−,12 C14 N−,28 Si−,27 Al16 O−, and56 Fe16 O− to distinguish between embedding resin, organic matter, oxides, and silicates. Image analyses reveal high occurrences of56 Fe16 O− within and in close proximity of oxide-encrusted root cells, followed by a thin layer with high occurrences of27 Al16 O− and12 C14 N− . In two of the three transects,28 Si− only occurs at distances larger than approximately 10 µm from the root surface. Thus, we can distinguish distinct zones: the inner zone is composed of oxide encrusted root cells and their fragments. A thin intermediate zone may occur around some roots and comprises (hydr)oxides and organic matter. This can be distinguished from a silicate-dominated outer zone, which reflects the transition from the rhizosphere to the bulk soil.

KW - Image analysis

KW - Iron plaque

KW - NanoSIMS

KW - Paddy soil

KW - Reflectance light microscopy

KW - Rhizosphere

KW - Scanning electron microscopy

UR - http://www.scopus.com/inward/record.url?scp=85043696081&partnerID=8YFLogxK

U2 - 10.3390/soils1010002

DO - 10.3390/soils1010002

M3 - Journal article

AN - SCOPUS:85043696081

VL - 1

JO - Soil Systems

JF - Soil Systems

SN - 2571-8789

IS - 1

M1 - 2

ER -