Tree Friendly Beneficial Soil Microbes: Inoculations and Occurrences

Summary: Jeffrey O. Dawson of the University of Illinois at Urbana-Champaign discusses inoculations and occurrences of tree friendly beneficial soil microbes.

mycorrhizal fungi encircle white spruces (Picea glauca): USDA Forest Service-Northeastern Area/USDA Forest Service/Bugwood.org,, CC BY 3.0 United States, via Forestry Images

Actinorhizal and rhizobial bacteria and ectomycorrhizal and endomycorrhizal fungi are tree friendly beneficial soil microbes, according to Things Arborists Should Know about Soil Microbes in the February 2013 issue of Arborist News.

Jeffrey O. Dawson, Forest Biology professor emeritus in the University of Illinois' Department of Natural Resources and Environmental Sciences at Urbana-Champaign, broaches bacterial and fungal symbionts. Symbionts construct "mutually defensive partnerships" whereby host tree roots exchange along- or in-root shelter and excess photosynthetic sugars for bodyguard services and soluble nitrogen and phosphorus. Inaccessible or unavailable phosphorus diminishes chemical energy transfer and use by plant cells in older, leached soils of Australia and of sandy coastal southeastern United States.

Nitrogen, like phosphorus, "macronutrient that soils commonly lack, worldwide," exerts similar impacts upon plant growth as the "essential component of amino acids, proteins [and] nucleic acids."

Arbuscular mycorrhizal fungi (AMF), also known as endomycorrhizae, form symbiotic associations with "broader host ranges" on "more plant species than any other type of mycorrhizal fungi."

Endomycorrhizal infections give "tree-like" looks to the "microscopic hyphal clusters that form inside the outer cells of young tree roots" penetrated, but not killed, by AMF. Tree friendly beneficial soil microbes, such as endomycorrhizal fungi, hasten "little if any change in external root morphology" whereas ectomycorrhizal fungi (EMF) have hyphae-filled fungal mantles. Dense hyphal mantles extending from root exteriors "out into soil some distance" impede root intrusion by "harmful soil bacteria and fungi" and increase root-fungal absorptive surfaces.

EMF-hosting beeches, birches, cedars, cherries, chestnuts, Douglas-firs, firs, hawthorns, hazels, hemlocks, hickories, hornbeams, larches, lindens, oaks, pines, spruces and walnuts join AMF-/EMF-hosting eucalypts, poplars and willows.

Ectomycorrhizal fungi, endomycorrhizal fungi and filamentous actinomycetes called actinorhizal bacteria keep casuarina tree roots healthy with soluble nitrogen, even in mine spoils and fill-and-rubble urban soils.

Nitrogen-fixing nodules formed by actinorhizal bacteria to convert atmospherically inert nitrogen gas to ammonia let alders supplement AMF- and EMF-hosting root intakes of nitrogen and phosphorus. Rhizobial bacteria manage high-profile nitrogen-fixing since actinorhizal bacteria nodulate 24 genera in eight families, including autumn and Russian olives, bayberries, bog and wax myrtles and Ceanothus. Rhizobial bacteria nodulate temperate and tropical tree legume members of the bean and pea family, including acacias, black locusts, New Mexico locusts and Siberian pea shrubs. They offer no nitrogen-fixing services as tree friendly beneficial microbes to temperate honey locusts, Kentucky coffee trees, redbuds or yellowwoods even though redbuds may be EMF-hosted.

Feedback mechanisms in host plants prevent symbiotic uptakes when soils provide roots with sufficient amounts of moisture and of such essential elements as nitrogen and phosphorus.

Tree friendly beneficial soil microbes such as some actinorhizal bacterial strains qualify as natural occurrences while other strains quit being present in locations without host plants. Inoculation represents an option when actinorhizal, mycorrhizal and rhizobial plants relocate beyond native ranges, such as Australian casuarinas in Florida and Californian radiata pines in Chile. Inoculations and occurrences of actinorhizal bacteria, ectomycorrhizal fungi, endomycorrhizal fungi and rhizobial bacterial salvage alluvial deposits and debris from landslides, mining, riparian bars, tsunamis and volcanoes.

Inoculation tends to be successful when "biological, physical, and chemical properties of a given soil" treat the biological, chemical and physical needs of hosts and symbionts.

Douglas fir (Pseudotsuga menziesii subsp. menziesii) root with ectomycorrhizae (Corinarius sp.), in Corvallis, Benton County, west central Oregon: B. Zak/USDA Forest Service, Public Domain, via Wikimedia Commons

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

mycorrhizal fungi encircle white spruces (Picea glauca): USDA Forest Service-Northeastern Area/USDA Forest Service/Bugwood.org,, CC BY 3.0 United States, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=1396184

Douglas fir (Pseudotsuga menziesii subsp. menziesii) root with ectomycorrhizae (Cortinarius sp.), Corvallis, Benton County, west central Oregon: B. Zak/USDA Forest Service, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Ectomycorrhizae002.jpg

For further information:

Dawson, Jeffrey O. February 2013. "Things Arborists Should Know about Soil Microbes." Arborist News 22(1): 14-20.
Available @ http://viewer.epaperflip.com/Viewer.aspx?docid=2e673a77-9270-4a84-b4d5-a2a400bb6926#?page=14

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

Marriner, Derdriu. 15 December 2012. “Healthy Urban Tree Root Crown Balances: Soil Properties, Soil Volumes.” Earth and Space News. Saturday.
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