Veera Norros: Species of wood-inhabiting fungi display different reproductive and dispersal strategies—which is the winning strategy in changing environments?

In this new post, Finnish Senior Research Scientist, Veera Norros, present her latest work ‘Spore production monitoring reveals contrasting seasonal strategies and a trade-off between spore size and number in wood-inhabiting fungi’. She discusses the importance of season for fungi spore-production, the vulnerability of wood-dependant species, and the challenges to conciliate research and family.

About the paper

Habitat loss and climate change divide species into winners and losers. It is becoming clear that this is not random—there are certain traits that make species especially vulnerable to human-induced pressures. The ability to move from one area to another can be either an asset or a handicap—high mobility makes it possible for a species to reach isolated remnants of its habitat, but many of the moving individuals may die before finding a suitable site.

Fungi that decay wood are a keystone group in forest ecosystems, creating food and habitats for a whole society of other organisms, from beetles to birds. The dead wood community is greatly affected by intensive forestry which leaves little wood to be decayed. However, some species of wood-inhabiting fungi seem to suffer much more than others. We wondered, could this be caused by differences in their reproductive or dispersal capacities? This question has been difficult to answer due to our very incomplete understanding of life history processes in fungi.

In calm weather, you can sometimes see a “smoking” fungus – a cloud of spores emanating from the fruit body. This photo shows the common generalist polypore, Fomitopsis pinicola, at our study site, an old-growth forest in Central Finland (credit: Markus Sirkka)

Our goal in this study was to produce the first quantitative estimates of the total reproductive output in different species of wood-inhabiting fungi throughout the growing season. We were also interested in the timing of spore release, as model simulations have shown that spores produced during turbulent and windy conditions remain airborne much longer and are thus carried further.

Spore production was measured by allowing spores to settle on a piece of plastic foil pinned to the fruit body (here, Phellinus tremulae). Spores from the foils were then rinsed into a known volume of ethanol and their concentration in the suspension determined microscopically or using a particle counter (credit: Panu Halme)

About the research

We were intrigued to find that although the highest numbers of fruit bodies and species are found in the autumn—the “mushroom season”—many species with perennial fruit bodies produce most spores during the spring. Species with small spores produced more spores, but the total spore volume was surprisingly constant across species. We estimated that a fist-sized fruit body produces in one month a volume roughly equivalent to a match head, divided into millions or billions of spores depending on their size.

Spore size has also been linked to spore viability and many other species traits and responses. Taken together, these results seem to suggest that fungal life history strategies fall on an axis between two extremes. The first are species whose substrate is common but difficult to enter (such as live trees), requiring enough resources and thus large spores. This is contrasted with species specialized on patchy, short-lived substrates (such as a specific type of dead wood) which need a high number of small spores to make sure that at least some land at the right place at the right time.    

Paradoxically, it could be the specialized species with small spores that are less equipped to colonize distant habitats, and thus more prone be on the losing side in human-dominated landscapes. The small size makes it possible for them to cover their immediate surroundings with spores even when released into the still air of the forest floor. However, when transported higher into the atmosphere, their spores stay airborne too long and begin to lose viability due to harsh atmospheric conditions such as high UV radiation. The spore cloud also becomes very diluted in the atmosphere, making it unlikely to hit rare substrates far away from the source.

A figure from our study summarizing reported correlations between spore size and other traits in wood-inhabiting fungi. A hypothesis of two contrasting life history strategies is emerging from the patterns (credit: Veera Norros)

Many fundamental processes in the life of fungi are still unknown. For example, do the many animals living close to fungi also play a role in spore transport? During our field work, we noticed that some fungi, particularly the aspen-associated polypore, Phellinus tremulae, emit a strong, almost flowery odour when sporulating. Is this a by-product of metabolic processes or a signal for animals?

It will take time to unravel the mysterious life of fungi in all its detail, but the conservation of vulnerable species cannot wait. It is already clear that many wood-dependent species need more dead wood than is available in today’s production forests, and their survival currently depends on the remnants of more natural forests.

About the author

Veera Norros (credit: Ramon Küntzler-Norros)

Like many Finns, I grew up in a city but spent all my summers at a cottage by a lake surrounded by forest. To me, the natural world always felt more fundamentally real than anything built by humans. As a biology student, I was especially inspired by the early 2000s biodiversity-functioning research that showed how ecosystem processes depend on the diversity and traits of individual organisms. I think we urgently need a deeper understanding of the mechanisms and consequences of the biodiversity crisis we are responsible for.

In my current position as a Senior Research Scientist at the Finnish Environment Institute, I am particularly motivated by the possibility to work as a part of a multidisciplinary team to find science-based solutions for a more sustainable society. My main task is to apply mathematical models to study and predict how species and ecosystems respond to changing environments.

I am also the mother of three small children and often concerned about the difficulties many young scientists face when attempting to combine work and family. Even in a country like Finland—with an excellent public parental support system—many of us are only able to cope with the conflicting responsibilities thanks to our support networks of family and friends. Still, it has been encouraging to realize that there are many niches in the field of science for less linear career paths. For me, working for a governmental institute has offered an opportunity to do interesting and meaningful research in a collaborative environment.

Enjoyed the blogpost? Read the research here!

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