Epiphytes influence the transformation of nitrogen in coniferous forest canopies.

The transformation of atmospherically-deposited nitrogen (N) by coniferous forest canopies has primarily been attributed to epiphytic lichens, despite microbes being present on leaf surfaces. We examined the relative contribution of live foliage with its epiphytic microbes and epiphytic lichen on N transformations in black spruce canopies. The epiphytic microbes and live foliage intercepted 27% of rainwater, 72% of incident nitrite + nitrate, and 63% of incident ammonium, while enriching throughfall with organic N by 52%. Epiphytic lichens on dead lower branches intercepted 60% of rainwater and depleted absolute amounts of inorganic and organic N, even though solute concentration increased as water passed through the lichens. Relationships were found between the number of colony forming units of epiphytic fungi and the depletion and enrichment of different forms of N in throughfall. Intensive forest management practices could result in the canopy being a net sink for N as a result of higher lichen biomass. [ABSTRACT FROM AUTHOR]