Microscopic fungi that live in plants’ roots play a major role in the storage and release of carbon from the soil into the atmosphere, according to a University of Texas at Austin researcher and his colleagues at Boston University and the Smithsonian Tropical Research Institute. In a research letter published online this week in the Journal Nature the team reported that the role of these fungi is currently unaccounted for in global climate models.
Some Types Of Symbiotic Fungi Can Lead To 70 Percent More Carbon Stored In The Soil
“Natural fluxes of carbon between the land and atmosphere are enormous and play a crucial role in regulating the concentration of carbon dioxide in the atmosphere and, in turn, Earth’s climate,” says Colin Averill, lead author on the study and a student in the ecology, evolution and behavior graduate program in the lab of Christine Hawkes, associate professor in the Department of Integrative Biology Graduate Program in Ecology, Evolution and Behavior, at the University of Texas at Austin. The Hawkes lab addresses broad questions in plant, microbial, and ecosystem ecology that are important for understanding how communities and ecosystems will respond to plant invasions, altered climate, and other global changes. “This analysis clearly establishes that the different types of symbiotic fungi that colonize plant roots exert major control on the global carbon cycle, which has not been fully appreciated or demonstrated until now,” Mr. Averill notes.
A UT at Austin release notes that Soil contains more carbon than both the atmosphere and vegetation combined, so predictions about future climate depend on a solid understanding of how carbon cycles between the land and air. Plants remove carbon from the atmosphere during photosynthesis in the form of carbon dioxide. Eventually the plant dies, sheds leaves, or loses a branch or two, and that carbon is added to the soil. The carbon remains locked away in the soil until the remains of the plant decompose, when soil-dwelling microbes feast on the dead plant matter and other organic detritus. That releases carbon back into the air.
One of the limits that both the plants and the soil-dwelling microbes share is the availability of nitrogen, an essential nutrient for all life. Most plants have a symbiotic relationship with mycorrhizal fungi, which help extract nitrogen and nutrients from the soil and make that nitrogen available for the plants to use. Recent studies have suggested that plants and their fungi compete with the soil microbes for the nitrogen available in the soil and that this competition reduces decomposition in the soil.
“This research is not only relevant to models and predictions of future concentrations of atmospheric greenhouse gases, but also challenges the core foundation in modern biogeochemistry that climate exerts major control over soil carbon pools,” comments Adrien Finzi, co-investigator and professor of biology at Boston University.
The research letter, entitled “Mycorrhiza-mediated competition between plants and decomposers drives soil carbon storage, co-authored by Colin Averill, Benjamin L. Turner, and Adrien C. Finzi (Nature (2014) doi:10.1038/nature12901) was published online on 08 January 2014.
There are two major types of the symbiotic fungi, ecto- and ericoid mycorrhizal (EEM) fungi and arbuscular mycorrhizal (AM) fungi. EEM fungi produce nitrogen-degrading enzymes, which allows them to extract more nitrogen from the soil than the AM fungi extract.
Examining data from across the globe, Averill and his colleagues found that where plants partner with EEM fungi, the soil contains 70 percent more carbon per unit of nitrogen than in locales where AM fungi are the norm.
The EEM fungi allow the plants to compete with the microbes for available nitrogen, thus reducing the amount of decomposition and lowering the amount of carbon released back into the atmosphere.
The research letter’s abstract notes that soil contains more carbon than the atmosphere and vegetation combined, and understanding the mechanisms controlling the accumulation and stability of soil carbon is critical to predicting the Earth’s future climate.
The researchers observe that recent studies suggest decomposition of soil organic matter is often limited by nitrogen availability to microbes, and that plants, via their fungal symbionts, compete directly with free-living decomposers for nitrogen. Using global data sets, they show that soil in ecosystems dominated by EEM-associated plants contains 70% more carbon per unit nitrogen than soil in ecosystems dominated by arbuscular mycorrhizal (AM) fungi-associated plants. They observe that the effect of mycorrhizal type on soil carbon is independent of, and of far larger consequence than, the effects of net primary production, temperature, precipitation and soil clay content. Hence the effect of mycorrhizal type on soil carbon content holds at the global scale. This finding links the functional traits of mycorrhizal fungi to carbon storage at ecosystem-to-global scales, suggesting that plant–decomposer competition for nutrients exerts a fundamental control over the terrestrial carbon cycle.
“This study is showing that trees and decomposers are really connected via these mycorrhizal fungi, and you can’t make accurate predictions about future carbon cycling without thinking about how the two groups interact. We need to think of these systems holistically,” says Colin Averill in the UT release
The researchers found that this difference in carbon storage was independent of and had a much greater effect than other factors, including the amount of plant growth, temperature and rainfall.
Dr Finzi’s principal research field is factors regulating productivity and nutrient cycling in terrestrial ecosystems, and research in his lab largely focuses on biogeochemistry and global change in forest ecosystems. His research is primarily field based using observational and experimental approaches. He notes on his BU faculty page that he is particularly interested in how interspecific differences in resource uptake and loss affect the distribution of carbon and nitrogen in terrestrial ecosystems, and also in the interaction between microbial activity and forest dynamics. The unzip Lab’s research perspective is generally integrative, focusing on how the different components of an ecosystem (soils, microbes, plant species) interact with the physical environment to affect biogeochemical cycling.
Dr. Finzi also observes that human activity is transforming the basic function of the terrestrial biosphere at an accelerating rate, noting that fossil fuel combustion is increasing the concentration of carbon dioxide in the atmosphere, and that fixation of atmospheric N by humans now exceeds the rate of non-anthropogenic N fixation, with changes in land use and the introduction of invasive species that will have legacy effects on carbon storage and biogeochemical cycling that last for decades.
University of Texas at Austin
Smithsonian Tropical Research Institute
University of Texas at Austin
Smithsonian Tropical Research Institute