Archives For mycorrhizal fungi relationship with plants

Vanilla cookies, vanilla perfume, and everything vanilla swept through my nostrils at a scented display at last year’s Orchid Show. The sweet smell was a great way to show many visitors that vanilla comes from the fruits of the vanilla orchid (Vanilla planifolia).

PHOTO: Orchid pods on the farm have dates scribbled on them in permanent marker, to help estimate a harvest date.

What are the scribbles about? Orchid pods are dated to estimate how long the pods have been on the vine, possibly to determine a good time to harvest them.

As a docent at last year’s show, I was eager to show off the Garden’s vanilla plant (located in the Tropical Greenhouse next to the banana trees), because I knew that may visitors didn’t know that they had an orchid in their spice cabinet.

Currently, I am in the second year of my research of the vanilla orchid. Vanilla is an exciting plant to study because it grows as a vine with two different types of roots. These roots help vanilla grow as a vine (more precisely a hemiepiphyte) because terrestrial roots anchor it within the soil, and epiphytic roots anchor it to tree trunks. My last post, Vanilla inhabitants: The search for associated bacteria and fungi, showcased my ongoing experiment in Mexico. This included collecting roots from four different Mexican farms that had very different practices for how they grew the orchid. We know that vanilla orchids use their epiphytic roots for support, but what other functions do they perform? Do they also form symbiotic relationships with fungal partners to obtain nutrients and water, like terrestrial roots?

Monocultures—crops with genetically identical heritage—are common in vanilla cultivation.

PHOTO: Many vanilla plantations use man-made structures for the vining orchids. Here, an old tree provides support to this orchid.

Many vanilla plantations use man-made structures for the vining orchids. Here, an old tree provides support to this orchid.

The fungal partners of orchids, known as mycorrhizal fungi, help an orchid start its life by providing needed nutrients for its seeds to germinate. No orchids in the wild can germinate without one or more mycorrhizal fungi. As a scientist, my goal is to study the interactions that the vanilla orchid has with these fungi as they mature. This is important because most vanilla farms are monocultures—it is easier to obtain clones from cuttings of vanilla than to germinate them from seeds. This, however, creates serious problems, because farms that have low genetic diversity in their vanilla orchids can lose their entire crop if a disease (such as root rot caused by Fusarium) appears.

Prior reports based on classic techniques have documented two or three species of mycorrhizal fungi within vanilla roots. In addition to these mycorrhizal fungi, there are also fungal pathogens (fungi that cause disease) and fungal endophytes (fungi that seem to have a mutualistic relationship with the host) that colonize a vanilla’s root.

To further investigate the situation, I ran an experiment using the latest DNA technology—Next Generation Sequencing (NGS)—to document the communities of fungi within terrestrial and epiphytic vanilla roots.

As fungal endophytes take up nutrients from their host, the mycotoxins they produce reduce herbivory and susceptibility to pathogens.

PHOTO: A length of canopies shields the growing vanilla orchids from harsh direct sunlight.

A length of canopies shields the growing vanilla orchids from harsh direct sunlight.

I documented 142 species of fungi associated with vanilla roots from the four Mexican farms, with an average of nine fungi colonizing a single vanilla root at one time. Of these 142 species, 20 are likely mycorrhizal. I find that fascinating, because these mycorrhizal fungi were found within both root types and across all farms. It was also surprising to know that epiphytic roots have a similar diversity of mycorrhizal fungi as terrestrial roots even though the epiphytic roots were green and could photosynthesize and have been considered primarily as support structures.

My study also documented a high number of previously unreported species of fungal pathogens and fungal endophytes colonized the roots of vanilla plants. This means that if plants are unhealthy, fungal pathogens likely can quickly take over, because they are already present within the roots. Overall, vanilla roots have good and bad partners just like we do, but contain more beneficial fungi (fungal endophytes and mycorrhizal fungi) than previously believed. These beneficial fungi not only supply the plant with water and nutrients, but also help control fungal pathogens. Thus, they are essential for plant health.

This research is funded with support from Mexican collaborators as part of the SAGARPA-CONACYT-SNITT 2012-04-190442 Mexican Vanilla Project.

PHOTO: Vanilla planifolia (vanilla orchid) in bloom.

Learn more about the orchids in your kitchen cabinet with our Vanilla Infographic; read up on another edible orchid in A Sip of Salep. Stay tuned for more orchid research projects, amazing orchid displays, and fun facts on our blog. The Orchid Show opens February 13!


©2016 Chicago Botanic Garden and my.chicagobotanic.org

The Secret Society of Soil

Undercover Science

Julianne Beck —  December 21, 2015 — 4 Comments

When you lift a rock in your garden and glimpse earthworms and tiny insects hustling for cover, you’ve just encountered the celebrities of soil. We all know them on sight. The leggy, the skinny, the pale…the surprisingly fast.

Behind this fleeting moment are what may be considered the producers, editors, and set designers of the mysterious and complex world of soil—fungi. They often go unrecognized, simply because most of us can’t see them.

PHOTO: Otidea decomposer.

Otidea, a decomposer

Fortunately, new technologies are helping experts, like Chicago Botanic Garden scientist Louise Egerton-Warburton, Ph.D., get a better look at fungi than ever before, and discover vital information.

“One of the problems we have with soil science is that you can’t see into it so you really depend on a lot of techniques and methods to work out what’s happening,” explained Dr. Egerton-Warburton, associate conservation scientist in soil and microbial ecology. 

In the last year, she has used high-throughput sequencing (also termed Next Generation Sequencing) to identify more than 120 species of mycorrhizal fungi in a single plant community. In contrast, previous reports suggested there were, at most, about 55 mycorrhizal species in a plant community. These tiny heroes are microscopic organisms that attach themselves to plant roots, for example, to carry out critical functions that support all life on earth. They are essential for the well-being of more than 85 percent of all plants, including those in your garden.

Mycorrhizal fungi are fungi that have a symbiotic relationship with roots of a vascular plant; from the Greek for “fungus” and “root.”

PHOTO: White mushrooms.

Mushrooms are the above-ground fruiting body of fungi.

If climate change results in more intense rainfall and drought—as is predicted by climate change scientists—mycorrhizal fungi will also play an important role in processing varied levels of water in the soil.

Egerton-Warburton has just returned from November field work in the Yucatán peninsula of Mexico, where she has been testing the responses of mycorrhizal fungi to changes in rainfall and soil moisture, especially to drought. Will fungi be able to keep pace? Will they be able to survive? What does that mean for other plant life? “Fungi are really good indicators of any environmental problems. So they are more likely to show the effects of any environmental stress before the plants will,” she said.

Each type of fungi also has a specific role, according to Egerton-Warburton, with some specialized to take up nutrients from the soil, while others cooperate to complete a function, such as fully decomposing a leaf.  A lot of fungi are needed to keep the system working. “You get 110 yards of fungal material in every teaspoon of soil,” she explained.

Aside from breaking down deceased plant material, fungi play a key role in many plant-soil interactions and the redistribution of resources in an ecosystem. They filter water that runs into the ground, cleaning it before it hits the bottom aquifers and drains out into rivers. Also, in the top few inches of soil, many fungi are respiring, along with their earthworm and other living counterparts, helping to filter gases and air that move through the system. Of growing interest, is also the fact that fungi could have a major role in soil carbon sequestration.

Soil carbon sequestration is the process of transferring carbon dioxide from the atmosphere into the soil in a form that is not immediately reemitted.

PHOTO: Leucocoprinus fungi.

Leucocoprinus fungi

For the past four years, Egerton-Warburton and colleagues at Northwestern University have been working to better understand the flow of carbon through fungal communities that results in long-term soil carbon sequestration. Soil’s capacity to store carbon is a reason for hope and a potential way to mitigate climate change. According to Egerton-Warburton, soil is known to hold three times more carbon than plants and trees above ground. “Maybe there are other ways we can manage the systems and enhance that capacity in the soil,” she said.

The study has required a lot of ‘getting to know you’, as the researchers first sought to identify each type of fungi involved in the process of carbon sequestration. As plant parts above ground are faced with absorbing and converting larger and larger amounts of carbon dioxide from our atmosphere into sugars, and sending it down into their roots, the more beneficial it will be to have a healthy suite of fungi waiting to receive it, use it, and move it along for future long-term storage.

Part of this equation has been to understand which fungi benefit from the increasing supply of sugar. Previous work by Egerton-Warburton has shown that mycorrhizal fungi respond to increases in atmospheric carbon dioxide by producing large quantities of hyphae, a fine root-like structure, in the soil. This is because increases in atmospheric carbon dioxide allow a plant to produce more sugars during photosynthesis, and these sugars are shunted below ground for use by roots and their mycorrhizal fungi. At the other end of the equation are saprophytic and decomposer fungi, waiting to break down the new hyphae.

Recent work in the Dixon Prairie has used the high throughput sequencing and chemical fingerprinting to identify the fungi involved in this decomposition phase. Once that is resolved, they will be able to better understand how the fungi interact and balance the cycle carbon through specific pathways of activity.

Learn more about soil science in the winter 2015-16 issue of Keep Growing, pages 28-30.

PHOTO: Louise Egerton-Warburton.

Louise Egerton-Warburton at work in the soil lab

The more the merrier, when it comes to fungi, and when it comes to people who are willing to help them endure, said Egerton-Warburton. The scientist often works with students who are interested in careers in the field, but encourages additional people to consider this critical line of work. “There’s a real need for soil ecologists in the country,” she said.

The good news is that the future story of fungi is one we can all help to script. Gardeners, she advised, can pay attention to the type of mulch they use in their garden, and plant lots of native species that will naturally enrich the function of that wonderful world that holds us up.


©2015 Chicago Botanic Garden and my.chicagobotanic.org