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Front. Microbiol. | doi: 10.3389/fmicb.2019.00926

Roots Mediate the Effects of Snowpack Decline on Soil Bacteria, Fungi, and Nitrogen Cycling in a Northern Hardwood Forest

 Patrick O. Sorensen1, 2*, Jennifer M. Bhatnagar2, Lynn Christenson3, Jorge Duran4,  Timothy Fahey5,  Melany Fisk6, Adrien C. Finzi2,  Peter Groffman7, Jennifer L. Morse8 and  Pamela Templer2
  • 1Lawrence Berkeley National Laboratory, United States
  • 2Boston University, United States
  • 3Vassar College, United States
  • 4University of Coimbra, Portugal
  • 5Cornell University, United States
  • 6Miami University, United States
  • 7The City University of New York, United States
  • 8Portland State University, United States

Rising winter air temperature will reduce snow depth and duration over the next century in northern hardwood forests. Reductions in snow depth may affect soil bacteria and fungi directly, but also affect soil microbes indirectly through effects of snowpack loss on plant roots. We incubated root exclusion and root ingrowth cores across a winter climate-elevation gradient in a northern hardwood forest for 29 months to identify direct (i.e. winter snow-mediated) and indirect (i.e. root-mediated) effects of winter snowpack decline on soil bacterial and fungal communities, as well as on potential nitrification and net N mineralization rates. Both winter snowpack decline and root exclusion increased bacterial richness and phylogenetic diversity. Variation in bacterial community composition was best explained by differences in winter snow depth or soil frost across elevation. Root ingrowth had a positive effect on the relative abundance of several bacterial taxonomic orders (e.g. Acidobacterales and Actinomycetales). Nominally saprotrophic (e.g. Saccharomycetales and Mucorales) or mycorrhizal (e.g. Helotiales, Russalales, Thelephorales) fungal taxonomic orders were also affected by both root ingrowth and snow depth variation. However, when grouped together, the relative abundance of saprotrophic fungi, arbuscular mycorrhizal fungi, and ectomycorrhizal fungi were not affected by root ingrowth or snow depth, suggesting that traits in addition to carbon acquisition strategy will mediate fungal community responses to snowpack decline in northern hardwood forests. Potential soil nitrification rates were positively related to ammonia-oxidizing bacteria and archaea abundance (e.g. Nitrospirales, Nitrosomondales, Nitrosphaerales). Rates of N mineralization were positively and negatively correlated with ectomycorrhizal and saprotrophic fungi, respectively, and these relationships were mediated by root exclusion. The results from this study suggest that a declining winter snowpack and its effect on plant roots each have direct effects on the diversity and abundance of soil bacteria and fungal communities that interact to determine rates of soil N cycling in northern hardwood forests.

Keywords: elevation gradient, Plant Roots, Soil N cycle, Snowpack, Soil bacteria and fungi

Received: 06 Dec 2018; Accepted: 11 Apr 2019.

Edited by:

Maria A. Niklińska, Jagiellonian University, Poland

Reviewed by:

Christopher Blackwood, Kent State University, United States
Zachary B. Freedman, West Virginia University, United States  

Copyright: © 2019 Sorensen, Bhatnagar, Christenson, Duran, Fahey, Fisk, Finzi, Groffman, Morse and Templer. 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: Dr. Patrick O. Sorensen, Lawrence Berkeley National Laboratory, Berkeley, California, United States, posorensen@lbl.gov