The disappearance of the hidden helpers: Decreased abundance of mycorrhizal fungi found in urban environments

       Unfortunately, many people have a negative opinion, or a general indifference, towards fungi. They infect and lessen the yield of wheat. People believe that every other mushroom in the wild is deadly or poisonous. Even the edible mushrooms are slimy and gross in texture. Most individuals’ favorite interaction with fungi is kicking the unsightly mushrooms on their lawns as a kid. While often overlooked, fungi play a variety of different roles and are often crucial to a functioning ecosystem. Fungi can be parasites, attacking the weakened defenses of animals and plants; decomposers, taking dead material, breaking it down, and making nutrients available to microorganisms and plants; mycorrhizal, associating with plant roots  -- mostly trees -- and exchanging nutrients in a mutually beneficial relationship. These are only a few examples of how the important fungi are to the ecosystem. Fungi are an underappreciated and vital part of many functioning ecosystems in varying locations.

Another part of ecology that deserves more attention is urban environments which are ever increasing in today’s world. They are alive with organisms from trees lining the street to raccoons scurrying around at night. While more and more people are studying the ecology of these ecosystems, much more work needs to be done for this rapidly growing ecosystem.

In a recent study, Bainard, Klironomos, & Gordon (2011) sought to compare the abundance and  diversity of mycorrhizal fungi in urban versus rural areas. Past research has shown a decrease in mycorrhizal fungi abundance in urban areas in comparison to rural areas in some habitats such as deserts (Stabler et. al. 2001). Bainard, Klironomos, & Gordon (2011) continued this research by studying 26 different species of trees in southern Ontario. In order to measure the abundance of mycorrhizal fungi, the researchers took soil cores from underneath the trees and looked for ectomycorrhizal fungi at the tips of roots. The researchers also stained and examined small sections of roots in the soil cores for microscopic arbuscular mycorrhizal fungi. Bainard, Klironomos, &  Gordon (2011) found that while all trees in both environments have mycorrhizal fungi, trees from urban areas statistically have significantly less than their rural counterparts (Fig. 1). 

Fig. 3 All 26 tree species average mycorrhizal associations in rural versus urban environments. Asterisks indicate a significant difference between urban and rural environment bars below them (p=0.05) (Bainard, Klironomos, & Gordon, 2011).

Bainard, Klironomos, & Gordon (2011) stress the need to study more about what causes this decrease in abundance — theories include increased disturbance, fragmentation, and pollution -- and what can be done to increase the abundance of mycorrhizal in order to have healthier trees in urban settings.

Bainard, Klironomos, & Gordon’s (2011) study is important because some of the mushrooms we recently sampled as part of a Grinnell South Campus mushroom survey have  mycorrhizal associations with trees. Figure 2 shows Xerocomus ferrugineus, a mycorrhizal bolete similar to some of those found on the east side of the South Campus dorms. 

Figure 2. Xerocomus ferrugineus is a mycorrhizal bolete that associates with conifers and hardwoods throughout northern Europe and North America. (Kuo, 2016)

         These fungi are important for the health of trees that add beauty to our campus. We know from studies like Bainard, Klironomos, & Gordon’s (2011) that fungi are not as prevalent in urban environments and they have several theories for why this is. We are trying to  discern where the fungi are present in urban areas, such as the less disturbed areas on the east side of South Campus. Then, we can try to replicate these conditions to allow fungi to thrive throughout the campus. Therefore, we should have healthier trees and lawns that we cherish so much thanks to decomposing and mycorrhizal fungi making nutrients more accessible.

References

Bainard, L. D., Klironomos, J. N., & Gordon, A. M. (2011). The mycorrhizal status and colonization of 26 tree species growing in urban and rural environments. Mycorrhiza, 21(2), 91-96.

Kuo, M. (2016). Xerocomus ferrugineus. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/xerocomus_ferrugineus.html

Stabler LB, Martin CA, & Stutz JC (2001) Effect of urban expansion on arbuscular mycorrhizal fungal mediation of landscape tree growth. J Arboric 27:193–202