Skip to main content
SLU publication database (SLUpub)
Research article - Peer-reviewed, 2022

Exploring the Role of Cryptic Nitrogen Fixers in Terrestrial Ecosystems: A Frontier in Nitrogen Cycling Research

Cleveland, Cory C.; Reis, Carla R. G.; Perakis, Steven S.; Dynarski, Katherine A.; Batterman, Sarah A.; Crews, Timothy E.; Gei, Maga; Gundale, Michael J.; Menge, Duncan N. L.; Peoples, Mark B.; Reed, Sasha C.; Salmon, Verity G.; Soper, Fiona M.; Taylor, Benton N.; Turner, Monica G.; Wurzburger, Nina


Biological nitrogen fixation represents the largest natural flux of new nitrogen (N) into terrestrial ecosystems, providing a critical N source to support net primary productivity of both natural and agricultural systems. When they are common, symbiotic associations between plants and bacteria can add more than 100 kg N ha(-1) y(-1) to ecosystems. Yet, these associations are uncommon in many terrestrial ecosystems. In most cases, N inputs derive from more cryptic sources, including mutualistic and/or free-living microorganisms in soil, plant litter, decomposing roots and wood, lichens, insects, and mosses, among others. Unfortunately, large gaps remain in the understanding of cryptic N fixation. We conducted a literature review to explore rates, patterns, and controls of cryptic N fixation in both unmanaged and agricultural ecosystems. Our analysis indicates that, as is common with N fixation, rates are highly variable across most cryptic niches, with N inputs in any particular cryptic niche ranging from near zero to more than 20 kg ha(-1) y(-1). Such large variation underscores the need for more comprehensive measurements of N fixation by organisms not in symbiotic relationships with vascular plants in terrestrial ecosystems, as well as identifying the factors that govern cryptic N fixation rates. We highlight several challenges, opportunities, and priorities in this important research area, and we propose a conceptual model that posits an interacting hierarchy of biophysical and biogeochemical controls over N fixation that should generate valuable new hypotheses and research.


agriculture; asymbiotic; free-living; global change; N-2 fixation; nitrogen cycle; symbiotic; terrestrial ecosystems

Published in

2022, Volume: 25, number: 8, pages: 1653-1669
Publisher: SPRINGER

    Associated SLU-program

    SLU Plant Protection Network
    SLU Forest Damage Center

    UKÄ Subject classification


    Publication Identifiers


    Permanent link to this page (URI)