A guest post by Sarah Brown
When asked to think of fungi, you may picture the iconic red-and-white Amanita muscaria mushroom, or the rows of white oyster mushrooms in supermarket produce aisles. But the Kingdom Fungi includes a wide variety of diverse organisms that inhabit an equally diverse number of environments, from terrestrial environments to the deep sea, where scientists have only just begun to explore fungal diversity.
In the deep sea, marine fungi have been discovered in diverse environments, from seawater to sediments to hydrothermal vents. Fungi are even present in the Southern Ocean surrounding Antarctica, one of the most rapidly changing regions on Earth.
A sea change in the Southern Ocean’s ecosystem
Climate change has already had a profound impact on the Southern Ocean. Increases in atmospheric CO2 concentrations have resulted in increased oceanic CO2 absorption, leading to a drop in pH, and the ocean’s temperature is already increasing. Continued changes are expected to have effects on the Southern Ocean ecosystem. For example, changes in the productivity of phytoplankton – a large group of photosynthetic plant-like organisms that form the base of the food web – could have effects on the larger organisms that feed on them.
Unfortunately, we still don’t know how many other organisms in this ecosystem will respond to climate change, even though changes in the distribution or productivity of one organism could impact others. Such changes could also affect ecosystem functioning, or large-scale environmental processes maintained by the organisms within an ecosystem, such as the movement of elements like carbon and nitrogen through the environment. Fungi, for example, play an important role in the function of the Southern Ocean ecosystem as decomposers by recycling dead organisms and returning important nutrients to the environment for other organisms to use.
Despite the essential function that fungi provide in this environment, we don’t yet have a clear understanding of how environmental conditions, such as temperature, salinity, pH, and oxygen concentrations, determine the species and number of fungi present in Southern Ocean sediments. This makes it hard to tell how these fungi will respond as global ocean temperatures continue to rise and how changes to fungal communities could impact this ecosystem as a whole.
However, a recent study exploring Antarctic fungal communities may finally illuminate the response of deep-sea fungi to changing environmental conditions.
Shedding light on deep-sea fungi
In order to examine Antarctic fungal communities, a team of researchers collected sediment samples from two locations in the Ross Sea, part of the Southern Ocean off the coast of Antarctica. The two sampling sites experienced different temperature, salinity, and oxygen concentrations, allowing scientists to compare the impact of different environmental conditions on the fungi present. When researchers identified fungi at each site by examining their DNA, they found that the communities, much like the environmental conditions at each site, were distinct.
Using statistical analyses, the scientists concluded that these different environmental conditions played a large role in determining which fungi were present at each site, with temperature having the greatest effect. However, temperature, salinity, and oxygen concentrations aren’t the only environmental factors that could impact fungi.
While fungi on land decompose the remains of dead plants and animals, recent research indicates that the organic matter that deep-sea fungi consume is primarily the remains of phytoplankton that sink to the deep from the surface waters of the ocean. Differences in the amount of this organic matter could thus affect fungal populations, which won’t grow as large with less food – so the researchers needed to determine how much organic matter was reaching the seafloor from the ocean’s surface.
To do this, they measured concentrations of organic carbon and of different colors, called phytopigments, that are present in phytoplankton. Measuring concentrations of phytopigments, such as chlorophyll, that are present in the sediments can help determine how much of the organic matter produced by phytoplankton during photosynthesis reaches the deep sea. Organic carbon concentrations, on the other hand, were calculated from measurements of the major components present in organic matter – proteins, carbohydrates, and lipids – that make it to the sediments.
By examining the relationship between the number of fungi present and phytopigment and carbon concentrations, the team was able to determine that these factors explained the majority of differences in the number of fungi between the two sites. For example, the site with ten times the phytopigment and carbon concentrations also had significantly more fungi. This relationship indicates that the amount and species of fungi present in Southern Ocean sediments is strongly influenced by the quantity and quality of organic matter reaching the sediments.
Fungi, ecosystem functioning, and the future
As climate change continues to affect the Southern Ocean, changes in temperature and phytoplankton populations will potentially impact deep-sea fungal communities, changing the number and species of fungi present in the sediments. This could change how much organic matter is degraded, thus impacting ecosystem functioning by changing the flow of carbon and nutrients within this ecosystem and, consequently, affecting other organisms.
But fungi and other decomposers in the Antarctic are just one piece of the puzzle. Fungi aren’t the only organisms expected to respond to changes in temperature, and the combined effects of climate change on these organisms could have further impacts on ecosystem functioning. To save these vulnerable, high-latitude ecosystems from an uncertain future, we’ll need more information on how underexplored organisms may respond to climate change, as they collectively contribute to the well-being of the whole ecosystem.
Reference: Barone, G., Corinaldesi, C., Rastelli, E., Tangherlini, M., Varrella, S., Danovaro, R., & Dell’Anno, A. (2022). Local Environmental Conditions Promote High Turnover Diversity of Benthic Deep-Sea Fungi in the Ross Sea (Antarctica). Journal of Fungi, 8(1), 65.