Diurnal temperature fluctuation inhibits the growth of an Antarctic fungus.

The surface temperatures of Antarctic soils and bryophyte colonies can fluctuate from close to freezing point to approximately 20 °C under clear skies around solar noon during midsummer. However, whether diurnally fluctuating temperatures influence the growth and metabolic activities of fungi inhabiting these substrates remains unknown. Here, 10 isolates of Pseudogymnoascus roseus, an ascomycete that is widespread in Antarctica, were exposed in vitro to temperatures fluctuating daily from 2 °C to 15-24 °C. Relative to controls incubated at the constant mean temperature of each treatment, temperatures fluctuating from 2 °C to ≥18 °C inhibited the growth of all isolates by 10-51% at 24 h and 48 h, and by up to 79% for individual isolates. Over a period of 21 days, all fluctuating temperature treatments reduced mean growth rates by between 3% and 48%, but had few effects on specific β-glucosidase activity, a proxy measure for metabolic activity. It is concluded that temperatures fluctuating diurnally to ≥18 °C during summer in mesic Antarctic soils and bryophyte colonies, exacerbated by the occurrence of climate-change associated heatwaves, are likely to inhibit the growth of P. roseus and perhaps also other ecologically important fungi.