Mushroom Spores: How They Travel Through Air

Mushrooms have developed a variety of methods to disperse their spores, which are launched at high speeds and can travel great distances. The spores are carried by wind currents and can remain in the atmosphere for days, weeks, or even months. The timing of spore release is critical for survival, with spores released at night travelling for hours, and those released during the day lingering for days. The distance travelled by spores also depends on the species of mushroom, with some species achieving discharge distances of a few tenths of a meter. Some mushrooms, such as Sclerotinia, release thousands of spores simultaneously, forming a plume that creates its own wind, allowing the spores to travel even farther.

The role of mushroom spores in rainfall

Mushrooms release millions of tons of spores into the atmosphere every year. These spores are discharged from the gills of mushrooms by the rapid displacement of a droplet of fluid on the cell surface. This fluid is called Buller's drop and is formed by the condensation of water on the spore surface, stimulated by the secretion of mannitol and other hygroscopic sugars.

The Buller's drop evaporates once the spore is airborne, but environmental electron microscopy has shown that droplets reform on spores in humid air. These droplets then act as giant cloud condensation nuclei (CCN), which are essential for raindrop formation. CCN are surfaces on which water vapour condenses, eventually forming rain.

Hygroscopic basidiospores, which are classed as large aerosol particles, are particularly effective as CCN. They aid the coalescence of smaller droplets to form precipitation-sized drops. This process may be especially important in ecosystems with large populations of ectomycorrhizal and saprotrophic basidiomycetes, such as tropical forests.

Research into the role of mushroom spores in rainfall has heightened interest in the global significance of fungi and raised concerns about the sustainability of forests dependent on heavy precipitation. It has also led to a better understanding of how mushrooms tolerate and benefit from crowding, as well as their high water needs.

How mushroom spores travel through the air

Mushroom spores are discharged from gills by the rapid displacement of a droplet of fluid on the cell surface. This droplet is formed by the condensation of water on the spore surface, stimulated by the secretion of mannitol and other hygroscopic sugars. The fluid is carried with the spore during discharge but evaporates once the spore is airborne. Mushrooms use convectively created airflows to disperse their spores.

Mushroom spore dispersal is a two-phase process: the active ejection of spores clear of the gill surface by surface tension catapults, followed by a passive phase in which the spores are carried by the winds present beneath the mushroom cap. Water vapor loss creates slow airflows that carry spores out from under the mushroom cap and into the air. Convective cells can transport spores from gaps that may be only 1 cm high and lift spores 10 cm or more into the air.

The timing of fungal spore release dictates survival during atmospheric transport. Spores released at night are likely to travel for hours, while spores released during the day may linger for days. Drivers are stronger in lower, warmer latitudes. Because spores in the open atmosphere are likely to die from prolonged exposure to light and air, the timing of spore release will impact survival.

Millions of tons of fungal spores are dispersed in the atmosphere every year. These living cells, along with plant spores and pollen grains, may act as nuclei for the condensation of water in clouds. Basidiospores released by mushrooms form a significant proportion of these aerosols, particularly above tropical forests.

The impact of mushroom spores on human health

Mushrooms are the fungal fruiting body, typically comprising a stem and a cap with gills on the underside. The gills of the mushroom produce spores, which aid in the propagation of the fungus. Millions of tons of these fungal spores are dispersed in the atmosphere every year. The spores are discharged from the gills by a catapult mechanism powered by the rapid movement of a drop of fluid over the spore surface. This fluid is carried with the basidiospores after discharge but evaporates once the spore is airborne.

In addition to ingestion, exposure to mushroom spores through inhalation can also have potential health implications. Certain individuals who are predisposed to specific diseases may experience adverse health effects when inhaling fungal spores. This includes people who produce specific IgE to fungal antigens, those with respiratory conditions susceptible to irritants, and immunocompromised patients susceptible to infections.

Furthermore, research has suggested a link between exposure to environmental fungi and the development of respiratory diseases such as asthma. Early exposure to dampness or fungi may contribute to the development of asthma and increased asthma morbidity, particularly in young children. Outdoor exposure to high concentrations of spores, such as during thunderstorms, can trigger asthma attacks in susceptible individuals.

Overall, the impact of mushroom spores on human health varies depending on the mode of exposure and individual susceptibility. While toxic mushroom ingestion can lead to severe health consequences, exposure to mushroom spores in the air may primarily affect individuals with specific predispositions or respiratory conditions.

The life cycle of mushrooms and spores

Mushrooms are a type of fungus, not plants. They are like the 'fruit' of fungi. Similar to how a tree produces fruits, the fungi produce mushrooms. Mushrooms produce and release spores from the gills that are located underneath the mushroom cap. Each mushroom is capable of producing hundreds of thousands of spores that can travel beyond the limits of the parent mushroom. These spores are discharged from gills by the rapid displacement of a droplet of fluid on the cell surface. This droplet is formed by the condensation of water on the spore surface stimulated by the secretion of mannitol and other hygroscopic sugars. The fluid is carried with the spore during discharge but evaporates once the spore is airborne.

The spore phase can be thought of as both the beginning and end of a mushroom's life. A mature mushroom will almost immediately begin to decompose after releasing its spores. However, mushroom spores also represent the new life for the next generation of mushrooms. Once spores settle on a favourable surface, they begin to divide and produce hyphae. Hyphae are structures that a fungus uses to gather nutrients and energy, as well as grow further. They look like long, thin strings that spread out through a growing medium. Once hyphae begin to form a larger colony, we refer to it as mycelium. Mycelium can be thought of as the web-like root system of the fungus.

When the hyphae of one spore meet the hyphae of another spore, they combine to produce fertile mycelium. During this stage of growth, mycelium expands at an exponential rate. The mushroom channels all its energy and nutrients to develop the fruit body, which will then produce spores. The fruit body releases spores into the environment for propagation. The spores are dispersed in airflow around the mushroom cap. Convective cells can transport spores from gaps and lift them into the air.

The impact of land use and climate change on outdoor airborne fungal spores

Millions of tons of fungal spores are dispersed in the atmosphere every year. These spores are discharged from the gill surfaces by a catapult mechanism and are dispersed in airflow around the mushroom cap. Mushrooms also use convectively created airflows to disperse their spores. The active ejection of spores is followed by a passive phase where the spores are carried by the winds present beneath the mushroom cap. This passive phase is also under the control of the fungus, which uses water vapour loss to create slow airflows that carry spores out from under the mushroom cap.

Outdoor airborne fungal spores are associated with allergies and allergic diseases. A systematic review of outdoor fungal seasonality in Europe found that allergenic spores of Alternaria and Cladosporium were the focus of most studies. These allergenic spores exceeded clinical thresholds in nearly all locations, with median peak concentrations of 665 and 18,827 per m3, respectively.

The main factors associated with fungal seasonality are meteorological variables such as temperature, precipitation, and relative humidity. Land use is another important factor, particularly proximity to agricultural and coastal areas. While correlations between increased season length and decreased annual spore concentrations with increasing average temperatures have been reported, the number of such studies is too small to make definitive conclusions.

Further studies are required to establish clinical thresholds and provide daily spore concentrations for a wider range of fungal taxa over long-term sampling periods. This will enable a more conclusive analysis of the effect of climate change on fungal spore seasonality and any associated changes in clinically relevant exposures.

Frequently asked questions