MANGANESE LIMITATION AS A MECHANISM FOR REDUCED DECOMPOSITION IN SOILS UNDER LONG-TERM ATMOSPHERIC NITROGEN DEPOSITION

Long-term atmospheric nitrogen (N) deposition has been shown to reduce leaf litter and lignin decomposition in forest soils, leading to an accumulation of soil carbon. Reduced decomposition has been accompanied by altered structure and function of fungal communities, the primary decomposers in forest ecosystems; however, a mechanistic understanding of fungal responses to chronic N enrichment is lacking. A reduction in soil and litter manganese (Mn) concentrations under N enrichment (i.e., Mn limitation) may explain these observations, because Mn is a cofactor and regulator of lignin-decay enzymes produced by fungi. We conducted a 6-month incubation study to evaluate the effect of Mn availability on decomposition dynamics in chronically N-enriched soils. We measured ligninolytic enzyme activities, mass loss and lignin (% change) in litter, and characterized the whole litter fungal community by ITS2 metabarcoding. We show a significant positive correlation between Mn availability and ligninolytic enzyme activities in litter. In addition, we demonstrate an increase in the relative abundance of ‘weak’ decomposers (e.g., yeasts) under long-term N enrichment, and a reversal of this response with Mn amendment. Our results suggest that higher Mn availability may promote fungal communities better adapted to decompose lignin. We conclude that Mn limitation plays an important role in decomposition dynamics under long-term atmospheric N deposition and may represent a mechanism that explains reduced decomposition and soil C accumulation under this global change factor