4 Things You Didn’t Know About an Ectomycorrhizal Fungi. Number 3 Will Shock You (or Not)!

by AT

When talking about fungi, many people first think about mushrooms like the brown Portabellas that we use in cooking (which are actually just a matured version of the white mushrooms). But wait, there’s more! Besides mushrooms, there are other types of fungi. For example, there are fungi that actually form a symbiotic relationship with plants! Like a cat and its owner, symbiosis involves two different species doing good things for each other despite not needing each other. Some of these symbiotic fungi associate with plant roots and are called ectomycorrhizal fungi. In these relationships, the ectomycorrhizal fungi scavenge for nutrients and share these nutrients with their hosts in exchange for carbon fixed by plant photosynthesis.⁶ With that, here are five things you didn’t know (to be honest, you probably didn’t know it even existed) about an ectomycorrhizal fungi called Cenococcum geophilum (C. geophilum).

Fig 1. See that black stuff? That’s Cenococcum geophilum on
root tip. The white scale bar is 200 micrometers long.¹   

1. C. geophilum had several other names before. Talk about an identity crisis…

       Although C. geophilum is the official name for the species, it has historically been called other names such as Lycoperdon graniforme and Cenococcum graniforme.³ It was first named Lycoperdon graniforme by James Sowerby in 1800. In 1825, Elias Fries introduced the genus name of Cenococcum, replacing Lycoperdon. Several years later, the name C. geophilum was introduced, however, it was still interchangeable with Cenococcum graniforme for many years before C. geophilum was established as the official name. Finally.

2. Got trees? C. geophilum can form symbiotic relationships with many different hosts in different places.

            C. geophilum can pretty much grow anywhere. Other common ectomycorrhizal usually associate with just one plant host, but C. geophilum is known to associate with any plant that is capable of hosting ectomycorrhizal fungi. However, it is most commonly found in temperate forests.⁷ You can generally find C. geophilum growing on the roots of various pine, oak, birch, willow, and aspen trees all over Europe and North America. Also, it is commonly found as far north as the tundra of northern Alaska and as far south as Florida.⁷ Wet or dry soils, this fungus can take it all. Under conditions that aren’t looking too good, C. geophilum can form sclerotia, which are large masses of hardened mycelium that are resistant to harsh environmental conditions.³ In C. geophilum, the sclerotia are known to survive for several years. When there are more sunshine and rainbows, the sclerotia germinate to reestablish fungal communities. With such an ability to grow in different regions, it would be no surprise to find this fungus in other areas around the world like the tropics. In fact, it’s been found in Puerto Rico!⁷ Look no further for the fungal jack-of-all-trades.

3. C. geophilum could be very important to establishing forests. Stunning, tree-mendous, forests.

            Because C. geophilum is a very common ectomycorrhizal fungus, it has also been well studied since its discovery in 1800. An interesting recent discovery was how the production of melanin, a complex dark polymer, in the cell walls of hyphae helps the fungus resist dry conditions.² If an ectomycorrhizal fungus is resistant to drought conditions, then this resistance probably benefits the survival of the host tree as well. As an example, if the ectomycorrhizal fungus dies during a drought, the tree can survive, but it essentially becomes widowed. Then, the poor tree will need to establish a new relationship with an ectomycorrhizal fungus to obtain the nutrients provided by the previous symbiotic relationship. Otherwise, the tree can’t get enough water, and it could die too. Even if it found a new symbiotic partner, the partner may not provide the same nutrients in equal amounts. When forests are just getting established, this change could have bigger impacts because young trees cannot process as much water compared to older trees. Having drought-resistant fungi in the first place is probably better for both the plant and the fungus, because the plant will not have to find a new friend, and the fungus doesn’t have to die. So as soon as California gets some rain, planting some trees with C. geophilum might help the trees tolerate drought better.

4. C. geophilum responds to different levels of Nitrogen, sometimes not very well.

            Like many other soil fungi, C. geophilum cannot fix free nitrogen from the air. It is able grow using ammonium (NH₄⁺), nitrate (NO₃^-), and amino acids as its nitrogen source, but it likes to utilize ammonium the most.⁷ But like work, too much available nitrogen can have a detrimental effect on the abundance of this fungus. In a 2008 study, researchers found that as nitrogen availability increases, C. geophilum becomes less common on the roots of red spruce trees.⁵ This decrease is not small; it drops from being present in 90% of the roots to about 50% when the nitrogen concentration in roots doubles. In the last century, human activity has doubled the amount of nitrogen deposited into the ground, which is expected to continue increasing.⁸ Things like fertilizers and manure really increase the amount of nitrogen in soils, and farming uses a whole lot of it. With this ever-increasing amount of nitrogen in the world’s soil, it is possible that C. geophilum will become less important in plant symbiosis. This is because the plant now has an easier time getting nitrogen without the help of C. geophilum. It’s like going to your friends’ house all the time to see their puppies, but then your significant other buys one for you instead. However, other fungi aren’t at a loss. When the nitrogen availability increases, the frequency of some other ectomycorrhizal fungi increases, but these other fungi are not as common as C. geophilum.⁵ For our Midwestern friends, think about how the ectomycorrhizal fungi in your front-yard tree will be affected when you decide to sprinkle that grass fertilizer onto your lawn. You may get end up with a beautiful yard, but C. geophilum is hurting from losing its friend.

            On a general level, nitrogen can also affect an ectomycorrhizal community. Another study found that the concentration of nitrogen in the soil also affects how fast different ectomycorrhizal fungi decompose when they die.⁴ For C. geophilum, the biomass decays about 35% in one month, which was less decomposition than the other ectomycorrhizal fungi that were tested. These other fungi also had a higher concentration of nitrogen in their tissues, possibly meaning that a higher tissue concentration of nitrogen resulted in a higher decomposition rate. However, an increased nitrogen availability didn’t really change the decomposition rate of C. geophilum. In fact, it actually decayed less than several other types of ectomycorrhizal fungi in the same amount of time. So even though C. geophilum gets left out of the symbiotic relationship when nitrogen levels increase, it sticks around when it dies, almost as if it wants to guilt the tree for leaving it behind.

There you have it: 5 things you didn’t know about C. geophilum! Do you think have learned a ton of new things? Take the quiz and find out how much you now love and understand C. geophilum! (Actually, there is no quiz.)

References

1. Cenococcum geophilum [homepage on the Internet]. Wikipedia. 2016 Nov 15 [cited 2016 Dec 5]. Available from: https://en.wikipedia.org/wiki/Cenococcum_geophilum.

2. Fernandez CW, Koide RT. The function of melanin in the ectomycorrhizal fungus cenococcum geophilum under water stress. Fungal Ecology. 2013; 6(6): 479-486.

3. Fernández-Toirán L, Águeda B. Fruitbodies of cenococcum geophilum. Mycotaxon. 2007; 100: 109-114.

4. Koide RT, Malcolm GM. N concentration controls decomposition rates of different strains of ectomycorrhizal fungi. Fungal Ecology. 2009; 2(4): 197-202.

5. Lilleskov EA, Wargo PM, Vogt KA, Vogt DJ. Mycorrhizal fungal community relationship to root nitrogen concentration over a regional atmospheric nitrogen deposition gradient in the northeastern USA. Canadian Journal of Forest Research. 2008; 38(5): 1260-1266.

6. Talbot J, Allison S, Treseder K. Decomposers in disguise: Mycorrhizal fungi as regulators of soil C dynamics in ecosystems under global change. Funct Ecol. 2008; 22(6): 955-963.

7. Trappe JM. Cenococcum graniforme--its distribution, ecology, mycorrhiza formation, and inherent variation. 1962.

8. Zak DR, Pregitzer KS, Burton AJ, Edwards IP, Kellner H. Microbial responses to a changing environment: Implications for the future functioning of terrestrial ecosystems. Fungal Ecology. 2011; 4(6): 386-395.