Fungi are chief decomposers in our soils, breaking down organic matter through enzymes and carrying out a crucial role in biogeochemical cycles and the nutrient cycle
The utilization of mushrooms by humans
The human use of mushrooms as food and for food preparation has a far-reaching history, as they have been utilized to manufacture bread, wine, and beer for millennia. Since antiquity, the Saccharomyces cerevisiae, a single-celled fungal microorganism and yeast species, has been employed in baking, brewing, and winemaking. The Aspergillus oryzae, a filamentous fungus and mold known as kōji-kin, has been a chief ingredient of soy sauce for centuries as the condiment in its current form traces back to the ancient China of the Western Han dynasty about 2,200 years ago. According to researchers from the Institute for Russian and Eurasian Studies of Uppsala University, in Sweden in the early twenty-first century, mushroom-foraging has become a popular pastime among urban Swedes (Svanberg & Lindh, 2019). Fungi are one of the components of soil microbial communities, where they provide key ecosystem functions and services acting as mycorrhizal mutualists, decomposers, and pathogens. «Fungi are unique in terms of living organisms in that they have their own kingdom. In physical terms, fungi are a group of cells that look like tangled threads. These organisms can be unicellular too. Yeasts are fungi, and they’re made of a single cell. But the majority of fungi are threat-like organisms. They create this group of threads called the mycelium, which can inhabit different ecosystems like soils, deserts, forests, and even deep-sea sediments», explains Adriana L. Romero-Olivares Ph.D., assistant professor at the Department of Biology of the New Mexico State University. «Some mycelia produce mushrooms, while most fungal species do not present them. Mushrooms are called the fruiting body, as they are the body that carries the spores of the mycelium. In that sense, mushrooms are like fruits. Whenever the plant is ready to reproduce, it creates like a fruit, and inside it there are the seeds. Once those seeds are dispersed, another tree can grow. Fungi function in a similar way. They have spores, and the sole purpose of the mushroom is to bear them so that they can be dispersed and the mycelium can continue to live».
Lampoon review: soil organic carbon (SOC)
The carbon stored in global soils’ organic matter represents a portion of the carbon in most terrestrial ecosystems. Mycorrhiza is the symbiotic association between Mycorrhizal fungi and green plant roots. Mycorrhizal associations are crucial to soil chemistry, plant nutrition, and soil biology. On the boreal forested islands in Sweden, roots and Mycorrhizal fungi hold between fifty and seventy percent of the total soil carbon stored in the leaf litter and soil. A 2016 study conducted in 2014 in the Shendong coal mining subsidence area has shown that Arbuscular mycorrhizal fungi can be beneficial to ecosystems as they enhance soil carbon sequestration in the coalfields.
Mushrooms: a sensitive bioindicators of radioactive contamination
Due to their ability to store various radioactive elements from their surrounding environment, mushrooms are sensitive bioindicators of radioactive contamination. Mushrooms have been known for accumulating significant amounts of heavy metals. Researchers from the Gdańsk University of Technology and the Maria Curie-Sklodowska University have analyzed for a 2021 study several species of edible and inedible forest mushrooms from various Polish regions. They found that due to the accumulation of heavy metals, some forest mushrooms could pose a threat to the consumers of wild mushrooms in the area.
Through the analysis of about 34,500 dated herbarium records recorded between 1940 and 2006 and the monthly precipitation and temperature variables data, a 2008 study carried out by researchers from the University of Oslo, the Norwegian University of Life Sciences, and the Norwegian Veterinary Institute has shown that the increasing temperatures during autumn and the winter months have caused a significant delay of mushrooms’ fruiting time in Norway. European researchers from Norway, Austria, the UK, Switzerland, and Poland have analyzed 746,297 dated and geo-referenced mushroom records of 486 autumnal fruiting species from 1970 to 2007. Their analysis highlighted that the warmer climate had prolonged the mushroom season during those four decades, with the mean annual day of fruiting being delayed in the analyzed countries. As the planet’s temperature increases, fungal communities are being affected in a manner that impacts the soil carbon process. Scientists from the University of California and the Ensenada Center for Scientific Research and Higher Education have discovered through soil metatranscriptomics that when subjected to long-term experimental warming and associated drying, the fungi allocate their resources to cell metabolic maintenance rather than decomposition, causing an ecological tradeoff that can affect the ecosystem-scale carbon dynamics.
Emulating global warming with greenhouses in Alaska
«My Ph.D. advisor, Kathleen Treseder, and her collaborators had set up a warming experiment in Alaska. There they were emulating global warming by setting up greenhouses in the forest in Alaska. The conditions present inside the greenhouses were supposed to emulate what will happen to the world in the following fifty to 100 years. We wanted to understand how the fungal community inside the greenhouses was affected by those conditions compared to the fungal community outside of them. We were interested in seeing the different aspects of the fungal community’s reaction and whether there were changes in their composition or metabolism. We wanted to see in general what was happening to the fungal community and how that related to carbon cycling. One of the reasons fungi are relevant is that they mediate the carbon cycle, and their state in the soil has direct implications for the emissions of carbon dioxide, a greenhouse gas. Fungi have the potential of making matters better or worse for climate change. That’s why we’re so interested in studying them. In the study’s site, I measured the decomposition happening inside the greenhouses and outside of them. The measurements showed that the decomposition was taking place at a slower rate inside the greenhouses. If there’s less decomposition, fewer nutrients are available for plants, insects, and other organisms. That’s because so many organisms depend on the process of decomposition, of which fungi carry out the majority. In Alaska, I took some soil samples and then extracted the RNA from the soil. By extracting RNA, one is able to see the gene expression of the fungi. Through that process, we found out that the fungi were experiencing severe stress. Inside the greenhouses, they were so stressed that they were producing a lot of stress tolerance genes and heat shock proteins, and they were investing all of their resources in staying alive, respiration, and keeping their metabolism going. As they were wasting all of their energy in doing these processes, there was none of it left to produce the enzymes that are responsible for decomposition». Dr.Romero-Olivares says.
The kingdom of fungi
«Conservation agencies are not investing in fungi. There are two reasons why that is happening. The first one is that we don’t have as good of a sense of how many fungi there are, compared with the plant community or the animal community. The other reason is that it’s challenging to persuade people to preserve something they cannot see. Some scientists are pushing towards conservation initiatives for fungi and mushrooms, and educating people on the value of the role that fungi play in our ecosystems is a way to start».
144,000 known species of Eukaryotic organisms such as rusts, smuts, mildews, yeasts, molds, and mushrooms constitute the kingdom of Fungi, which is part of the Eukaryota domain. This kingdom is made up of a diverse group of organisms. Fungi can be unicellular and multicellular. They are formed by filiform elements, called hyphae, that form the body called mycelium. Fungi are widely distributed on Earth and can be found free-living in soils or bodies of water, while other species build symbiotic or parasitic relationships with animals and plants. These heterotrophs acquire the nourishment they need through the absorption of dissolved molecules. This characteristic allows Fungi to be the chief decomposers in our planet’s ecosystems, breaking down organic matter with the enzymes they send out, carrying out a crucial role in the biogeochemical cycles of carbon (C), oxygen, (O), nitrogen (N), and phosphorus (P) and the nutrient cycle. Climate change and global warming are impacting fungi and changing their behavior, with extensive consequences for the ecosystems and the planet at large.
Adriana L. Romero-Olivares, Ph.D.
Soil microbiologist who works at the intersection of ecosystem ecology and evolution with an emphasis on fungi. Her overall research’s goal is to better understand and plan for the ecosystem-scale effects of global climate change. Originally from Mexico, Dr.Romero-Olivares received her PhD from the University of California Irvine.