Too much of a good thing? Inorganic nitrogen (N) inhibits moss-associated N2 fixation but organic N can promote it

Moss-associated nitrogen (N2) fixation is one of the main inputs new N in pristine ecosystems that are characterized by low availability. Previous studies have shown N2 inhibited inorganic (IN) inputs, but if mosses similarly affected organic (ON) remains unknown. Here, we assessed two dominant boreal forests (Pleurozium schreberi and Sphagnum capillifolium) response to different levels N, simulating realistic (up 4 kg ha−1 year−1) extreme addition rates 20 IN (ammonium nitrate) ON (alanine urea). We also can recover from additions. In scenario, was increasing NH4NO3 additions P. not S. capillifolium, alanine urea stimulated both moss species. contrast, additions, species all forms. Nitrogen more sensitive than capillifolium higher recovery phase after compared These results demonstrate less highlight importance considering forms species-specific responses when estimating impact on ecosystem functions such as moss-associated fixation.