Shiitake happens! Fungi grow faster when lightning strikes
Japanese researchers are closing in on understanding why electrical storms have a positive influence on the growth of some fungi. Koichi Takaki from Iwate University in Japan and colleagues have shown that artificial lightning strikes do not have to directly hit shiitake mushroom cultivation beds to promote their growth. Now they are developing technology to use electric stimulation in the production of the mushrooms, which are popular in many east Asian cuisines (J. Phys. D: Appl. Phys. 53 204002).
Shiitake mushrooms are grown in hardwood logs in a process that takes around a year. First, branching vegetative filaments called hyphae are grown in the logs, which are kept in beds. Farmers then submerge the logs in water for one or two days and then beat the logs mechanically. When this is done skilfully, it disrupts the interlinking hyphae, moving the shiitake into its reproductive phase of growth that produces the desirable mushroom caps.
Atmospheric electricity has long been known to boost the growth of living things, including plants, insects and rats – even if the electric storm is located miles away. Takaki’s team had previously increased Shiitake yield by running a direct current through the log, but in the latest work focussed on the effect of indirect lightning strikes on growth. They first submersed the logs for 24 hours in water and then arranged them 3 m away from electrodes of an impulse voltage generator. In an electrical storm a cloud generates three or four strikes on average, so the team programmed the same number of sparks to sequentially discharge between electrodes.
Compared to a control set of logs sitting 12 m away from the strikes, the team found that they could collect twice as many mushrooms that had a top more than 50 mm in diameter. Logs that were exposed to daily sets of lightning strikes for a week produced an even higher yield than those only exposed to one set of strikes. “The large current from a lightning strike causes temperature to quickly rise from room temperature to about 10,000 °C,” explains Takaki. “This quick rise in temperature rapidly increases the volume of the air producing a shock wave that propagates to, and then vibrates inside the log to stimulate fruiting body formation.” The team is working to adapt their equipment for deployment in the fungiculture industry.
Louisa Cockbill