U.S. Department of Energy, Office of Science

Program for Ecosystem Research

Research Project   Interactive effects of elevated carbon dioxide and ozone on the mycorrhizal symbiosis

Principal investigator:   R. Michael Miller

AM fungus ecto fungus

Mycorrhizal fungi (top: AM; bottom: ecto).

Project goal

Understand how mycorrhizal fungi respond to changes in host partitioning of assimilated carbohydrates and soil nutrients resulting from changing atmospheric CO2 and O3 concentrations.

Ecosystems being studied

The belowground observations of this project are being conducted in both a forest system and a crop system.

The forest system involves constructed stands of (a) the pioneer species trembling aspen (Populus tremuloides), (b) a mixture of aspen and another pioneer species paper birch (Betula papyrifera), and (c) a mixture of aspen and the late successional species sugar maple (Acer saccharum). The research is part of the DOE Rhinelander, Wisconsin, FACE [free-air CO2 enrichment] experiment.

The crop system is a soybean crop in central Illinois (i.e., the SoyFace experiment).

Results

A significant positive relationship existed between aspen whole-tree biomass and the amount of root-associated mycorrhizal fungi (AMF + ECM, r^2 = 0.80, P < 0.0001). Other significant positive relationships occurred between mycorrhizal biomass and fine root biomass (r^2 = 0.87, P < 0.0001) and between mycorrhizal biomass and leaf biomass (r^2 = 0.69, P < 0.0001).

The relationship between mycorrhizal biomass and tree biomass was influenced by treatment. When the amount of root-associated mycorrhizal biomass was corrected for tree size, the slope of the relationship between mycorrhizal biomass and tree size was greater for elevated ozone-fumigated plants than for ambient air, elevated carbon dioxide, and the combination of elevated ozone and elevated carbon dioxide treatments.

With respect to the growth of extramatrical mycelium of ECM and AMF in the soil surrounding aspen trees (quantified using mesh hyphal in-growth bags, in conjunction with phospholipids for separating ECM from AMF) it was found that the combined elevated ozone plus elevated carbon dioxide treatments increased ERM with time (harvest date: P < 0.0001, slope 1.007 +/- 0.002 microg cm^-3 d^-1) for aspen. The amount of ERM declined for aspen grown in elevated ozone but not grown in the combination of elevated ozone and elevated carbon dioxide treatments (P < 0.0044).

Why this is important

Project findings from the DOE Rhinelander FACE experiment indicate that growth of mycorrhizal fungi is influenced by host production, although their partitioning of biomass is differentially affected by the carbon dioxide and ozone treatments. The strong treatment effect for elevated carbon dioxide by elevated ozone fumigation indicates that current models of carbon partitioning in plantes may not explain the growth and partitioning of photosynthate to mycorrhizal fungi. The consequences of lower production of extramatrical mycorrhizal mycelium for hosts grown under elevated ozone indicates a potential for lower nutrient scavenging resulting in a reduction in nutrient content in the host tissue and host plant. The lower production also indicates a significant reduction in mycorrhizal inputs to the soil carbon pool with elevated ozone concentration.

results chart results chart

Relationship between mycorrhizal fungal colonization and mycorrhizal biomass (top) and aspen FACE extraradicle mycelia (ERM) in-growth bag study (bottom).

Methods

The effect of host carbon partitioning on the production of lipid energy reserves of the mycorrhizal fungi is being investigated as an indicator of the state of the fungus (and potentially the state of the symbiosis) to the imposed treatments of elevated carbo dioxide and elevated ozone concentration, singly and in combination. Observations are facilitated through the use of recently identified phospholipid and neutral lipid fatty acid markers, ergosterol, and the use of mesh mycelial in-growth bags.

A state-of-the-science open air exposure system is being used to examine the effects of elevated carbon dioxide (537 ppm) and 1.5 x ambient ozone (each relative to ambient air) on growth, productivity, trophic interactions, and numerous ecosystem processes in constructed northern hardwood stands. More information on the forest experiment is available at the Rhinelander FACE experiment website.

A state-of-the-science open air exposure system is being used to examine the effects of elevated carbon dioxide (550 ppm) and 1.5 x ambient ozone (each relative to ambient air) on growth, productivity, and numerous ecosystem processes in a soybean crop. More information on the soybean experiment is available at the SoyFACE website.

Personnel

R. Michael Miller, Argonne National Laboratory

Victoria Allison, Argonne National Laboratory

Roser Matamala, Argonne National Laboratory

Funding period:   January 2002 to present