Fungi may determine the future of soil carbon

Posted By News On January 8, 2014 - 6:30pm
Fungi may determine the future of soil carbon

When scientists discuss global change, they often focus on the amount of carbon in the atmosphere and vegetation. But soil contains more carbon than air and plants combined. This means that even a minor change in soil carbon could have major implications for the Earth's atmosphere and climate. New research by Smithsonian Tropical Research Institute scientist Benjamin Turner and colleagues points to an unexpected driver of soil carbon content: fungi.

"This finding puts soil biology at the front and center of the debate about the factors that drive soil carbon storage," said Turner, who collaborated with researchers at the University of Texas at Austin and Boston University.

Previous studies considered soil degradation, climate and plant productivity to be the most important regulators of soil carbon content. However, findings published this week in Nature by researchers including Turner suggest that soil biology plays a greater role. Some types of symbiotic fungi can lead to 70 percent more carbon in the soil. The role of these fungi is currently not considered in global climate models.

The majority of plants team up with fungi, exchanging plant carbon for soil nutrients supplied by the fungus. These mutually beneficial relationships can be broadly grouped into three major categories: arbuscular mycorrhizas AM, ectomycorrhizas, and ericoid mycorrhizas. The AM symbiosis is most common, occurring in approximately 85 percent of plant families, while ecto- and ericoid mycorrhizas EEM occur in a few common families.

After an exhaustive number of model runs on data from more than 200 soil profiles from around the globe, the authors found that soils supporting EEM plant communities contained 70 percent more carbon per unit nitrogen than soils supporting AM-dominated plant communities. The effect is significant at the global scale, because it is independent of biomass accumulation, temperature, precipitation and soil clay content.

Fungi, in association with tree roots, may play an important role in storing carbon in soil.

(Photo Credit: STRI Archives)

The marked difference in soil carbon levels between AM and EEM ecosystems is due to the way the two kinds of mycorrhizal fungi acquire nutrients. EEM fungi produce enzymes that allow them to access organic forms of nitrogen, which are not available to AM fungi. By depleting nitrogen from the soil organic matter, EEM fungi limit the activity of the microorganisms that break down dead organic matter and return the carbon to the atmosphere. AM ecosystems impose fewer restrictions on the growth of carbon-consuming microbes.

"This study shows that trees and decomposers are really connected via these mycorrhizal fungi, and that you can't accurately predict future carbon cycling without thinking about how the two groups interact," said Colin Averill, the study's lead author, currently a graduate student at UT Austin. "We need to think of these systems holistically."

Turner said the study provides strong evidence to support a theory published in 2011 by researchers in the United Kingdom and New Zealand. The results suggest any widespread shift in the species composition of forests could change the amount of carbon stored in soil, with consequences for atmospheric carbon dioxide concentrations.

"These findings will help to refine Earth-system models and promote debate on the extent to which soil microbes influence the global carbon cycle," said Turner.

Very interesting findings in this article! In addition to the soil biota's role in globabl climate cycles (change), I beleive the soil's role in the hydrologic cycle is a major factor in gloabal climate cycles. Whenever water cannot infiltrate into the soil (because of hardsurfacing or degraded soil health) it runs off, when it runs off it increases streamflow velocities causing rapid rises in water (flooding in some cases), incresed streambank erosion (more sedimentation downstream), and the list of implications could go on and on. This is leading to the extremes in our hydrologic cycle, extreme drought or extreme precipitation events, because the system is "getting to fast"> We need to slow it back down with sotring more water in the soil. If anyone has any scholarly information related to this, I would love to see it shared. Unhealthy soils are found all over - urban/developed areas and agricultural lands. Many progressive farmers are starting to address soil health and realizing the benefits of it.

There is an interesting recent article concerning the relation between in soil degradation and its hydrologic influences in a forested area of western Kenya: Recha, Lehmann, Walter, Pell, Verchot and Johnson in American Meteorological Society's Earth Interactions vol. 16, Issue13 (Dec. 2012), 'Stream Discharge in Tropical Headwater Catchments as a Result of Forest Clearing and Soil Degradation'. The principles and mechanisms are very similar in less-tropical areas also, but insufficient attention is being paid to researching how best to use hydrologic and agronomic principles in planning land uses and their management for prevention, minimisation and/or control of floods and erosion. There is much researched evidence of how catchments degrade, but not yet enough in-field research and implementation to know how best to use this knowledge to reverse the degradation processes and restore the land's potentials for acceptance and provision of water and plants, and to sustain the improvements into the future.