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Front. Environ. Sci. | doi: 10.3389/fenvs.2018.00140

Root exudates induce soil macroaggregation facilitated by fungi in subsoil

  • 1Technische Universität München, Germany
  • 2V V Dokuchaeva Soil Institute, Russian Academy of Agricultural Sciences, Russia
  • 3Joint Institute for Nuclear Research, Russia
  • 4Georg-August-Universität Göttingen, Germany
  • 5Institute for Advanced Study, Technical University of Munich, Germany

Subsoils are known to harbor large amounts of soil organic carbon (SOC) and may represent key global carbon (C) sinks given appropriate management. Although rhizodeposition is a major input pathway of organic matter to subsoils, little knowledge exists on C dynamics, particularly stabilization mechanisms, such as soil aggregation, in the rhizosphere of different soil depths. The aim of this study was to investigate the influence of natural and elevated root exudation on C allocation and aggregation in the topsoil and subsoil of a mature European beech (Fagus sylvatica L.) forest. We experimentally added model root exudates to soil at two different concentrations using artificial roots and analyzed how these affect SOC, nitrogen, microbial community composition, and size distribution of water-stable aggregates. Based on the experimental data, a mathematical model was developed to describe the spatial distribution of the formation of soil aggregates and their binding strength. Our results demonstrate that greater exudate additions affect the microbial community composition in favor of fungi which promote the formation of macroaggregates. This effect was most pronounced in the C-poor subsoil, where macroaggregation increased by 86 % and SOC content by 10 %. Our modeling exercise reproduced the observed increase in subsoil SOC at high exudate additions. We conclude that elevated root exudation has the potential to increase biotic macroaggregation and thus the C sink strength in the rhizosphere of forest subsoils.

Keywords: soil depth, rhizosphere, Aggregate fractionation, artificial roots, microbial community composition, Aggregation model, Soil Organic Carbon

Received: 03 Sep 2018; Accepted: 02 Nov 2018.

Edited by:

Hannes Schmidt, Universität Wien, Austria

Reviewed by:

Lukas Van Zwieten, New South Wales Department of Primary Industries, Australia
Paul Hallett, University of Aberdeen, United Kingdom  

Copyright: © 2018 Baumert, Vasilyeva, Vladimirov, Meier, Kögel-Knabner and Mueller. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Ms. Vera L. Baumert, Technische Universität München, Munich, Germany, vera.baumert@wzw.tum.de