Turnover of dead fungal mycelia (i.e., fungal necromass) potentially represents a large input of carbon into soil organic matter pools. Despite this potential, we have a limited understanding of controls on fungal necromass decay and how they overlap with drivers of plant litter decomposition, namely substrate quality and soil nutrient status. We aimed to test if necromass decay rates differ between arbuscular (AM) and ectomycorrhizal (EcM) dominated forest stands (differing in a number of edaphic factors) and between two fungal species differing in their melanin and nitrogen concentrations. We hypothesized that necromass decay rates would be fastest for high quality litters (i.e., tissues with low melanin and high [N]) decaying in soils with abundant N availability (AM dominated stands), and that litter quality would be a stronger determinant of decay rates than soil environment.
Fourteen 20 x 20m plots, seven AM and seven EcM (associated trees were >85% of basal area) were utilized in a deciduous hardwood forest in south-central Indiana. In July of 2017, litterbags containing necromass from either Mortierella elongata (high quality) or Meliniomyces bicolor (low quality) were incubated for two week, one month and three month intervals. Percent mass remaining in litterbags was determined after each incubation period.
Results/Conclusions
Necromass decomposition differed significantly over time and between species. In support of our hypothesis, M. elongata decomposed more quickly in both AM and EcM dominated plots. During the first two incubation periods, the remaining mass of M. bicolor was double that of M. elongata (P<.01). After three months in the field, mass loss did not differ between species (P=.48). There was a significant effect of mycorrhizal association on percent mass remaining (P=.02; overall, decomposition was slightly faster in AM dominated plots (P=.02). The species by mycorrhizal association interaction term was not significant, meaning that individual species decomposed at a similar rate in AM and EcM plots. Faster initial decomposition of M. elongata was likely due to higher concentrations of nitrogen and lower concentrations of melanin compared to M. bicolor. Similar mass loss between species after three months is indicative of a rapid initial phase of decomposition followed by a slower phase. Our results show that substrate quality may be more important in predicting decay of fungal necromass than decay environment. These data add to our growing understanding of the controls on decomposition of fungal mycelia.