Wood decay fungi obtain resources by secreting enzymes to break down complex carbohydrates such as lignin, cellulose, and chitin, and absorb the resulting products to fuel fungal processes such as growth and reproduction. Over the past 30 years, fungal sexual reproduction, or fruiting, has demonstrated phenological shifts related to earlier springs and warmer falls corresponding to changing climate. Whether shifts in fungal fruiting phenology might indicate similar changes in the timing of fungal resource acquisition is unclear. We set out to determine how closely fungal fruiting phenology is linked to the more cryptic phenology of fungal decay enzyme activity. We performed monthly surveys of fungal fruiting bodies for 3 years at the Smithsonian Environmental Research Center in Edgewater, MD, and paired these with sampling of wood substrates for extracellular enzyme activity. We targeted 3 cellulose degrading enzymes, 1 chitin degrading enzyme, and 2 suites of lignin degrading enzymes in our assays. The distribution of fruiting abundances was compared with the distribution of enzyme activity potentials to look for coordination in the timing of reproductive and resource acquisition activities in fungal communities.
Fruiting fungal communities showed distinct seasonal turnover between spring (April-June), summer (July-September), fall (October-December), and winter (January-March). Overall fruiting abundances remained relatively high through the fall until daily low temperatures, averaged over a two week sliding window, fell below freezing. Overall peak fruiting abundances occurred in the fall each year, although the timing varied slightly from year to year. All three cellulose degrading enzymes showed peak activity in late spring, whereas chitinase activity peaked in mid to late summer. The offset between the peak activity of these enzymes might indicate a shift in fungal foraging for resources from woody carbohydrates to fungal biomass recycling in the later summer, corresponding with a turnover in fungal fruiting communities. There was no discernible seasonal pattern in oxidase or peroxidase production. Overall, our findings suggest that while coordination occurs between fruiting and hydrolytic enzyme production, maximum decay potential precedes maximum fruiting.