Heike Bucking, a South Dakota State University plant science professor, leads a team digging into the world of soil mycorrhizal fungi.

Approximately 65% of land plant species form relationships with arbuscular mycorrhizal fungi, sharing carbohydrates with fungi that colonize their roots, according to Bucking.

In exchange, these fungi provide plants with nitrogen and phosphorus as well as the trace elements of copper and zinc.

Additionally, these fungi appear to protect plants from environmental stresses, such as drought, salinity and heavy metals, and diseases. “All the stresses that a plant can potentially be exposed to are generally improved by mycorrhizal interactions,” she says.

“We think these fungi can increase the biomass production of bioenergy crops and the yield of food crops, and do so in a more sustainable and environmentally friendly way.”

Her research has been supported by the National Science Foundation, South Dakota Wheat Commission, Sun Grant Initiative, South Dakota Soybean Research and Promotion Council, the U.S. Department of Energy Joint Genome Initiative and the USDA National Institute of Food and Agriculture through the South Dakota Agricultural Experiment Station. This work involves collaboration with researchers at the Vrije University in Amsterdam and the University of British Columbia as well as Agricultural Experiment Station researchers. Five doctoral students, two master’s students and three undergraduates work on this research.

The challenge is to figure out which fungi will most benefit specific crops and under which environmental conditions, Bucking says.

Their research has shown that although a host plant is colonized by multiple fungal species simultaneously, the plant knows exactly where certain benefits are coming from.

“The host plant can distinguish between good and bad fungal behavior and allocates resources accordingly,” she says.

The host plant transfers anywhere from 4% to 20% of its photosynthetically fixed carbon to mycorrhizal fungi.

These fungi also form common mycorrhizal networks that give them access to multiple hosts. The research showed that when host plants were shaded, and thus decreased their carbohydrate allocation, fungi responded by reducing their nutrient share.

“Despite depending on their hosts for reproduction, fungal partners can thereby retain their bargaining power,” she says.

In addition, Bucking and her collaborators have found that some fungi are more cooperative than others. For example, they evaluated the relationship between alfalfa and 31 different isolates of 10 arbuscular mycorrhizal fungal species. They then classified the fungal isolates as high-, medium- or low-performance isolates. The researchers found that high-performance isolates increased the biomass and nutrient uptake of alfalfa by more than 170%, while the low-performance ones did not have any effect on growth.

However, those that benefit one crop may not provide the same nutrients or benefits to another crop species. “Even different isolates of one fungal species can behave differently,” she says.

Researchers have much to learn about the complex relationship between host plants and mycorrhizal fungi, Bucking says. “To maximize the nutritional benefits for the host — particularly food and bioenergy crops — we need to better understand how nutrient transport is regulated and controlled.”

Once scientists unravel the secrets of this ancient relationship, you may be able to seed the appropriate fungi on a particular crop, thus reducing fertilizer needs.

Source: SDSU