It is widely known that biodiversity is declining worldwide due to anthropogenic forces like climate change and habitat loss. The ramifications for ecosystem integrity are massive, and the challenge of stopping this downward slide is equally daunting. This decline is found across groups, from plants to birds to fungi, and is especially true in urban areas because of the transformation of previously available habitat. Often inconspicuous and sometimes seen as insignificant, fungi in fact play an important role in many ecosystems. They decompose dead organic matter and return nutrients like nitrogen to the environment that would otherwise stay locked in those dead organisms. There the nutrients can be used by plants and animals. They also form symbiotic relationships with plants and can behave as indicator species. Their population decline needs to be investigated to better understand how and why it is occurring and improve management practices.
Abrego et al. (2020) takes an innovative approach to quantifying this decline. They investigated fungal diversity in urban and natural areas, using DNA analysis of soil samples and aerial spore samples to assess the prevalence, number, specialization, and composition of different species. They sampled plots within larger areas representing urban and natural areas, in both the core of these areas and their edges, in or near five different Finnish cities. Measuring in multiple cities allowed the researchers to track how communities changed over larger distances than just those shown in the example areas below.
Figure 1. Image from Abrego et al. (2020) demonstrating the sampling points and the techniques used to sample from the air and soil. The tool at the top is a cyclone sampler, used for collecting aerial mushroom spores.
What’s interesting in what they found is that there wasn’t an overall difference in the total number of species between urban and natural areas. There were, however, more species per sample in the natural areas even though the overall number was the same. They also found many more natural specialist mushrooms than urban ones, and more in the air than the soil- both of generalists and specialists. Surprisingly, the air samples indicated a larger drop in diversity and abundance between natural and urban habitats than the soil samples. The researchers had thought that it would be the soil samples that would show lower abundance in urban habitats because of limited dispersal relative to wind-born spores. Instead of being homogenous over large areas, aerial fungal communities demonstrate a structure based on location.
Figure 2. Image from the article visualizing their results. S represents the predicted species richness per sample, while the colors represent the specializations of the fungi identified. Specialists were defined as species more than 10 times more prevalent in one habitat than another.
These distribution patterns are certainly influenced by management practices within these areas, a question we are currently studying in an urban ecology project on the Grinnell College Campus. We’re looking at how gradients of management across campus influence the presence of dead wood and the saprotrophic fungi that colonize it. Our study should provide insight into how our management practices influence habitat availability and population distribution for these important organisms.
These results symbolize the reduction in diversity that is happening across taxa and emphasize the need to conserve and protect natural areas. Fungi are important as decomposers and plant symbionts. They must be taken into consideration in any conservation planning to preserve the integrity of existing ecosystems and the future functioning of the planet.
Citation
Abrego, N., Crosier, B., Somervuo, P., Ivanova, N., Abrahamyan, A., Abdi, A., Hämäläinen, K., Junninen, K., Maunula, M., Purhonen, J., & Ovaskainen, O. (2020). Fungal communities decline with urbanization—more in air than in soil. The ISME Journal, 14(11), 2806–2815. https://doi.org/10.1038/s41396-020-0732-1
What an intriguing approach to studying fungal populations, and useful for analyzing fungal diversity over large areas. For your study, I'll be interested in seeing how you've characterized "management gradients" on campus. Perhaps you'll be able to speak to how different management practices can promote favorable fungal diversity.
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