Characterizing the chemical changes in fungal necromass as it degrades, particularly over short time intervals (days to weeks), is critical to clearly understanding how this organic matter source contributes to various belowground carbon and nutrient pools. Using a range of chemical analyses, we assessed the degradation of four types of ectomycorrhizal fungal necromass from three species differing in biochemical composition. Samples were buried in a forest in Minnesota, USA and harvested at eight time points over a 90-day incubation period (1, 2, 4, 7, 14, 28, 60, 90 days). Three of the necromass types lost greater than 50% of their initial mass in the first seven days, but mass loss plateaued for all four types at later harvests, and after 90 days, none of the samples were completely degraded. Relative to undegraded necromass, degraded necromass consistently contained a lower relative abundance of aliphatic compounds and a higher relative abundance of carbohydrates, sterols, and aromatic compounds. For three of the four necromass types, nitrogen content was lower after 90 days of degradation and FTIR spectra revealed distinct peaks broadening from day 0 to day 90. While melanin content significantly slowed degradation within species, differences in degradation rates across species were more closely aligned with initial nitrogen content. Collectively, our results indicate that the rapid mass loss of dead fungal mycelium is accompanied by a wide range of changes in necromass chemistry, likely contributing to both short-term soil nutrient and longer-term carbon pools.
Bibliographical noteFunding Information:
Dr. Elizabeth Austin-Minor provided valuable input on an early version of this manuscript, and two anonymous reviewers also provided comments that significantly improved its quality. Field and laboratory support from Amanda Certano (University of Minnesota Twin Cities) and Julia Agnich (University of Minnesota Duluth) was indispensable. We thank the Cedar Creek Ecosystem Science Reserve for allowing us to use a plot of their land to perform the field degradation study. Funding for this study was provided by the University of Minnesota Duluth to K.M. Schreiner and NSF DEB Grant 1554375 to P.G. Kennedy.
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- Mycorrhizal fungi
- Necromass chemistry
- Soil organic matter