title: Disentangling interactions between microbial communities and roots in deep subsoil.
abstract: Soils, paleosols and terrestrial sediments serve as archives for studying climate change, and represent important terrestrial carbon pools. Archive functioning relies on the chronological integrity of the respective units. Incorporation of younger organic matter (OM) e.g. by plant roots and associated microorganisms into deep subsoil and underlying soil parent material may reduce reliability of paleoenvironmental records and stability of buried OM. Long-term effects of sedimentary characteristics and deep rooting on deep subsoil microbial communities remain largely unknown. We characterized fossil and living microbial communities based on molecular markers in a Central European Late Pleistocene loess-paleosol sequence containing recent and ancient roots with ages of several millenia. The molecular approach, comprising free and phospholipid fatty acids (FAs), core and intact polar glycerol dialkyl glycerol tetraethers (GDGTs), as well as 16S rRNA genes from bacterial DNA, revealed the presence of living microorganisms along the sequence, with bacterial community composition comparable to that of modern topsoils. Up to 88% redundancy between bacterial genetic fingerprint and molecular signature of fossil microorganisms suggested a time-integrated signal of the molecular markers accumulated over a time span potentially lasting from sedimentation over one or more rooting phases until today. Free FAs, core GDGTs and DNA, considered as remains of fossil microorganisms, corresponded with ancient and recent root quantities, whereas phospholipid FAs and intact polar GDGTs, presumably derived from living microorganisms, correlated only with living roots. The biogeochemical and ecological disequilibrium induced by postsedimentary rooting may entail long-term microbial processes like OM mineralization, which may continue even millenia after the lifetime of the root. Deep roots and their fossil remains have been observed in various terrestrial settings, and roots as well as associated microorganisms cause both, OM incorporation and mineralization. Therefore, these findings are crucial for improved understanding of OM dynamics and carbon sequestration potential in deep subsoils.
authors.affiliation: Department of Geography, University of Zurich, Winterthurerstrasse 190, 8057 Zürich, Switzerland. Electronic address: mgocke@uni-bonn.de.
authors.forename: Martina I
authors.initials: MI
authors.lastname: Gocke
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7619, METIS, 75005 Paris, France. Electronic address: arnaud.huguet@upmc.fr.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Huguet
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UMR 7619, METIS, 75005 Paris, France. Electronic address: sylvie.derenne@upmc.fr.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Derenne
authors.affiliation: Leibniz Center for Agricultural Landscape Research, Landscape Biogeochemistry, Eberswalder Straße 84, 15374 Müncheberg, Germany. Electronic address: steffen.kolb@zalf.de.
authors.forename: Steffen
authors.initials: S
authors.lastname: Kolb
authors.affiliation: Department of Agricultural Soil Science, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany. Electronic address: dippold@gwdg.de.
authors.forename: Michaela A
authors.initials: MA
authors.lastname: Dippold
authors.affiliation: Department of Geography, University of Zurich, Winterthurerstrasse 190, 8057 Zürich, Switzerland. Electronic address: guido.wiesenberg@geo.uzh.ch.
authors.forename: Guido L B
authors.initials: GLB
authors.lastname: Wiesenberg
mesh_terms: D001419:Bacteria; D057965:Carbon Sequestration; D057231:Climate Change; D004987:Ethers / Q000032:analysis; D005580:Fossils; D005858:Germany; D010743:Phospholipids / Q000032:analysis; D018517:Plant Roots / Q000254:growth & development* / Q000382:microbiology; D012336:RNA, Ribosomal, 16S / Q000032:analysis; D015203:Reproducibility of Results; D012987:Soil; D012988:Soil Microbiology
chemical_list: D004987:Ethers; D010743:Phospholipids; D012336:RNA, Ribosomal, 16S; D012987:Soil
keywords: Biopore; Microbial hotspot; Molecular marker; Paleoenvironmental archive; Rhizosphere; Terrestrial sediment