Long-term nitrogen fertilization inhibits carbon and nitrogen loss during late-stage fungal necromass decomposition depending on necromass chemistry
DeLancey, L. C., C. R. See, K. Heckman, P. G. Kennedy and S. E. Hobbie. 2025.
Abstract
1. Fungal necromass is increasingly recognized as a key component of soil carbon
(C) and nitrogen (N) cycling. However, how C and N loss from fungal necromass
during decomposition is impacted by global change factors such as anthropogenic
N addition and changes to soil C supply (e.g. via changing root exudation and
rhizosphere priming) remains unclear and understudied relative to plant tissues.
2. To address these gaps, we conducted a year-long decomposition experiment with
four species of fungal necromass incubated across four forested sites in plots
that had received inorganic N and/or labile C fertilization for two decades in
Minnesota, USA.
3. We found that necromass chemistry was the primary driver of C and N loss from
fungal necromass as well as the response to fertilization. Specifically, N addition
suppressed late-stage decomposition, but this effect was weaker in melanin-rich necromass, contrary to the hypothesis based on plant litter dynamics that N
addition should suppress the decomposition of more complex organic molecules.
Labile C addition had no effect on either the early or late stages of necromass
decomposition.
4. Nitrogen release from necromass also varied among species, with N-poor
necromass having lower N release after controlling for differences in mass loss
via regression. The relatively minor effects of N fertilization on the proportion
of initial necromass N released suggest that N demand by decomposers is the
primary control on N loss during fungal necromass decomposition.
5. Synthesis. Together, our results stress the importance of the afterlife effects
of fungal chemical composition to forest soil C and N cycles. Further, they
demonstrate that C and N release from this critical pool can be reduced by
ongoing anthropogenic N addition.
Key Words
carbon addition, decomposition, fertilization, FTIR, fungal necromass, global change ecology, nitrogen addition, nitrogen release
