Assistant Professor McGill University, Quebec, Canada
Background/Question/Methods
Fungal biomass can be a considerable input to soil organic carbon (SOC), and a large portion of fungal biomass accumulates in the relatively more persistent mineral-associated organic carbon (MAOC). Arbuscular mycorrhiza fungi (AMF) have life-history traits conserved at the family level, yet how AMF traits and trait diversity relate to SOC accumulation and loss is unclear. AMF in the Gigasporaceae family act as competitors with higher investment in extraradical hyphae and slow growth rates. Glomeraceae exhibit ruderal or r-strategist traits, prioritizing fast growth and hyphal turnover. We examined how AMF communities representing different traits and trait diversity impact hyphal contributions to SOC and MAOC, decomposition, and hyphal biomass chemistry. We grew Sudan grass in a greenhouse with: 1) five species in the AMF family Gigasporaceae representing competitor traits, 2) five species in the fast-growing Glomeraceae family representing ruderal traits, or 3) a mixed community of all ten species representing trait diversity. Sudan grass was grown with 13C-CO2 for 12.5 weeks to label AMF biomass, then root-free soils were incubated for one month to allow for decomposition. We then quantified hyphal contributions to total SOC and MAOC before and after incubation, characterized the hyphal molecular chemistry and quantified plant phosphorus content.
Results/Conclusions
The Glomeraceae and Gigasporaceae communities decreased total SOC by 15% and 14% respectively after the one-month incubation (p < 0.05) but there was no change to MAOC concentrations. Net SOC losses were likely caused by AMF priming saprotrophic communities. Despite net SOC losses, hyphal C from all 3 AMF communities contributed an average 2.5 mg of fungal C to new SOC formation. Notably, only the Glomeraceae community contributed to MAOC (0.12% of total MAOC) before the incubation (p < 0.05). After one month of incubation, both the Glomeraceae and mixed trait communities contributed to MAOC (1 and 0.75 mg g- respectively). We expected that which communities contribute to MAOC and the lack of effect Gigasporaceae might be related to divergent hyphal chemistry influencing fungal decomposition and thus movement into MAOC. However, preliminary results from pyrolysis-GC/MS do not support this. Total plant phosphorus was the best predictor of fungal SOC formation, with the Glomeraceae and mixed communities increasing plant phosphorus uptake most. Given that AMF family abundances are subject to environmental selection pressures (e.g., disturbance, plant communities, phosphorus availability), this study helps inform how selection for community trait dominance or trait diversity at the family-level may impact SOC accumulation and loss.
