Mushrooms use convectively created airflows to disperse their spores

Abstract

Thousands of basidiomycete fungal species rely on mushroom spores to spread across landscapes. It has long been thought that spores depend on favorable winds for dispersal-that active control of spore dispersal by the parent fungus is limited to an impulse delivered to the spores to carry them clear of the gill surface. Here we show that evaporative cooling of the air surrounding the pileus creates convective airflows capable of carrying spores at speeds of centimeters per second. Convective cells can transport spores from gaps that may be only 1 cm high and lift spores 10 cm or more into the air. This work reveals how mushrooms tolerate and even benefit from crowding and explains their high water needs.ooted in a host organism or patch of habitat such as a dead log, tens of thousands of species of filamentous fungi rely on spores shed from mushrooms and passively carried by the wind to disperse to new hosts or habitat patches. A single basidiomycete mushroom is capable of releasing over 1 billion spores per day (1), but it is thought that the probability of any single spore establishing a new individual is very small (2, 3). Nevertheless in the sister phylum of the basidiomycete fungi, the Ascomycota, fungi face similarly low likelihoods of dispersing successfully, but spore ejection apparatuses are highly optimized to maximize spore range (4-6), suggestive of strong selection for adaptations that increase the potential for spore dispersal.Spores disperse from basidiomycete mushrooms in two phases (7): a powered phase, in which an initial impulse delivered to the spore by a surface tension catapult carries it clear of the gill or pore surface, followed by a passive phase in which the spore drops below the pileus and is carried away by whatever winds are present in the surrounding environment. The powered phase requires feats of engineering both in the mechanism of ejection (8-10) and in the spacing and orientation of the gills or pores (11,12). However, spore size is the only attribute whose influence on the passive phase of dispersal has been studied (13). Spores are typically less than 10 μm in size, so can be borne aloft by an upward wind of only 1 cm/s (11). Buller claimed that such wind speeds are usually attained beneath fruiting bodies in nature (11): Indeed, peak upward wind velocities under grass canopies are of order 0

Mushroom Emergence Detected by Combining Spore Trapping with Molecular Techniques

“…In theory, the initial phase of spore dispersal of some basidiomycete mushroom-forming species involves the discharge of basidiospores from the gill by a mechanism promoted by a droplet, also known as a Buller's drop (26), which is normally stimulated by the secretion of mannitol and other sugars (27). Then, convective airflows promoted by the pileus enhance the vertical movement of these spores, which may then reach dispersive winds (28). Finally, these spores may fall by gravity or rainfall events.…”

Terrestrial Macrofungal Diversity from the Tropical Dry Evergreen Biome of Southern India and Its Potential Role in Aerobiology

“…The role of macrofungi as a strong source of fungal spores in the atmosphere has been investigated using the Gaussian plume model (GPM) [44,45] for standard atmospheric conditions. Here, it is assumed that the source (a spore emission rate of 540 spores cm -2 s -1 [46]) is located 10 cm above the ground and that the spore concentrations were derived within a vicinity of 100 m and up to a height of 10 m (PM 10 sampling was performed at a height of 10 m in the same location during the same study period; however, the PM 10 results are not shown here).…”

“…To estimate the concentration, we set the following conditions: (i) the fruiting body height as 10 cm from the ground, (ii) an average spore size of 3 μm, (iii) an initial spore release rate of Q = 540 spores cm -2 s -1 [46], and (iv) an average wind speed of 1.79 m/s (the average wind speed observed during the sampling period). The following steps were conserved in the dispersal estimation: (i) estimating the settling velocity, V s , [45] (S1 Text); (ii) estimating the rate of convective airflow in terms of the gravity current, U g [46]; and (iii) estimating the presence of spores in terms of their concentration for a fixed height (10 m) using GPM [44].…”

“…The following steps were conserved in the dispersal estimation: (i) estimating the settling velocity, V s , [45] (S1 Text); (ii) estimating the rate of convective airflow in terms of the gravity current, U g [46]; and (iii) estimating the presence of spores in terms of their concentration for a fixed height (10 m) using GPM [44]. The settling velocity, V s , estimated for the average spores of 3 μm (the dominant size range of fungal spores observed on a global scale) [13,47–49], was incorporated in the gravity current estimations.…”

“…The settling velocity, V s , estimated for the average spores of 3 μm (the dominant size range of fungal spores observed on a global scale) [13,47–49], was incorporated in the gravity current estimations. For the gravity current estimations, we followed the steps reported by Dressaire et al, 2016 [46]. Furthermore, the spore dispersal estimations were derived from the ground level where the fungal spore source is assumed to be located.…”