Micronutrient transfer from saprotrophic fungi to decaying wood and its impact on the activity of nitrogen-fixing bacteria.

Deadwood contributes to nutrient cycling, and its decomposition is hindered by low nutrient concentrations. Fungi can transfer nutrients from the surrounding soil to support metabolic activity and the enzymes involved in decomposition. However, evidence of elemental transfer is limited to a few elements. The extent and factors underpinning micronutrient transfer to deadwood by fungi remain elusive. We hypothesized that fungal elemental transfer to deadwood is influenced by the type of rot, and by the elemental composition of organic materials with which fungi are in contact. Because nutrient limitation can affect the entire microbiome, fungal elemental transfer could profoundly influence the activity of the microbial community inhabiting deadwood. Molybdenum availability is known to limit biological nitrogen fixation in deadwood. We explored the role of micronutrient transfer (molybdenum), on biological nitrogen fixation. Experiments were conducted in microcosms using wood disks of black spruce trees in contact with three types of organic materials common in boreal forest floors. Results show that fungi transfer many elements to deadwood, but transfers were species-specific with no effect of rot type. The transfer of Mo was associated with increased BNF in one species, highlighting that fungal nutrient transfer can affect important microbial metabolic pathways in deadwood.