Abstract

It is well established that application of biochar to soils can promote soil fertility, which ultimately may enhance plant growth. While many mechanisms have been proposed to explain this, one specific mechanism, the "microbial refugia hypothesis," suggests that biochar may provide physical protection for soil microbe from soil microfauna that otherwise exert top-down control on microbial biomass and activity. We tested the microbial refugia hypothesis by incubating two boreal soils with and without biochar derived from a wood mixture of boreal tree species (Picea abies and Pinus sylvestris), and with and without soil nematodes. We measured phospholipid fatty acids (PLFA) as a relative measure of microbial biomass, and several variables indicative of microbial activity, including extractable nutrient concentrations (NH4+, NO3-, and PO4-), heterotrophic N-2-fixation, and soil respiration. Contrary to our expectations, we found that biochar by itself did not stimulate microbial biomass or activity. Furthermore, we found that nematode addition to soil stimulated rather than depressed the biomass of several bacterial PLFA groups. Finally, interactive effects between the nematode treatment and biochar never worked in a way that supported the microbial refugia hypothesis. Our findings suggest that a typical boreal biochar applied to boreal soils may not have the same stimulatory effect on microbial biomass and activity that has been shown in some other ecosystems, and that enhanced plant growth in response to biochar addition sometimes observed in boreal environments is likely due to other mechanisms, such as direct nutrient supply from biochar or amelioration of soil pH.

Keywords

biochar; boreal forest; carbon sequestration; microbial activity; microbial biomass; microbial refugia; soil microfauna; top-down control

Published in

GCB Bioenergy
2022, Volume: 14, number: 8, pages: 972-988
Publisher: WILEY

SLU Authors

• Pingree, Melissa

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Kardol, Paul

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Nilsson Hegethorn, Marie-Charlotte

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Wardle, David

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    
  • Nanyang Technological University (NTU)

• Maaroufi, Nadia

  • Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences
    
  • University of Bern

• Gundale, Michael

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

Associated SLU-program

SLU Plant Protection Network
SLU Forest Damage Center


UKÄ Subject classification

Forest Science


Publication identifier

DOI: https://doi.org/10.1111/gcbb.12978

Permanent link to this page (URI)

https://res.slu.se/id/publ/118232