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Front. Microbiol. | doi: 10.3389/fmicb.2017.02293

Resource legacies of organic and conventional management differentiate soil microbial carbon use

  • 1Department of Soil Science, University of Saskatchewan, Canada
  • 2Department of Microbiology and Immunology, University of British Columbia, Canada
  • 3Saskatoon Research Centre, Agriculture and Agri-Food Canada (AAFC), Canada

Long-term contrasts in agricultural management can shift soil resource availability with potential consequences to microbial carbon (C) use efficiency (CUE) and the fate of C in soils. Isothermal calorimetry was combined with 13C-labelled glucose stable isotope probing (SIP) of 16S rRNA genes to test the hypothesis that organically managed soils would support microbial communities with greater thermodynamic efficiency compared to conventional soils due to a legacy of lower resource availability and a resultant shift towards communities supportive of more oligotrophic taxa. Resource availability was greater in conventionally managed soils, with 3.5 times higher available phosphorus, 5% more nitrate, and 36% more dissolved organic C. The two management systems harbored distinct glucose-utilizing populations of Proteobacteria and Actinobacteria, with a higher Proteobacteria:Actinobacteria ratio (2.4 vs. 0.7) in conventional soils. Organically managed soils also harbored notable activity of Firmicutes. Thermodynamic efficiency indices were similar between soils, indicating that glucose was metabolized at similar energetic cost. However, differentially abundant glucose utilizers in organically managed soils were positively correlated with soil organic matter (SOM) priming and negatively correlated to soil nutrient and carbon availability, respiration, and heat production. These correlation patterns were strongly reversed in the conventionally managed soils indicating clear differentiation of microbial functioning related to soil resource availability. Fresh C addition caused proportionally more priming of SOM decomposition (57 vs. 51%) in organically managed soils likely due to mineralization of organic nutrients to satisfy microbial demands during glucose utilization in these more resource deprived soils. The additional heat released from SOM oxidation may explain the similar community level thermodynamic efficiencies between management systems. Restoring fertility to soils with a legacy of nutrient limitation requires a balanced supply of both nutrients and energy to protect stable soil organic matter from microbial degradation. These results highlight the need to consider managing C for the energy it provides to ‎critical biological processes that underpin soil health.

Keywords: Thermodynamics, carbon use efficiency, microbial community composition, 13C-DNA-SIP, priming effect, Organic Agriculture, Calorimetry

Received: 11 Sep 2017; Accepted: 06 Nov 2017.

Edited by:

Alain F. Plante, University of Pennsylvania, United States

Reviewed by:

Chao LIANG, University of Wisconsin-Madison, United States
Mallory Choudoir, University of Colorado Boulder, United States
Kevin M. Geyer, University of New Hampshire, United States  

Copyright: © 2017 Arcand, Levy-Booth and Helgason. 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) or licensor 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: Dr. Bobbi L. Helgason, Agriculture and Agri-Food Canada (AAFC), Saskatoon Research Centre, 107 Science Place, Ottawa, S7N 0X2, Saskatchewan, Canada, Bobbi.Helgason@AGR.GC.CA