Response of enchytraeid worm populations to different forms of nitrogen (ammonia, ammonium, and nitrate) deposition

The changes to ecosystems and ecosystem functioning induced by anthropogenic reactive nitrogen deposition continue to be studied in a range of habitats. In semi-natural habitats, these effects can be pronounced, often with negative impacts on the native flora. An experimental site established on an ombrotrophic bog provides a unique opportunity for the study of the effect of long-term simulated N deposition. The response of enchytraeid worms to different forms of nitrogen deposition (as ammonia, ammonium or nitrate) was assessed at this site, which has been receiving N treatments since 2002: previous studies on the site have shown that high N deposition (64 kg N ha-1 yr-1) has changed the above- ground vegetation. In this study, the below-ground response of enchytraeids to N treatment was shown to be dependent on site wetness. Under favourable site conditions, i.e. when the peat moisture content was high, enchytraeid abundance was negatively affected by N deposition in the form of ammonia or nitrate, whereas addition of ammonium, ammonium plus PK (=K2HPO4), and to a lesser extent, nitrate plus PK, appeared to increase enchytraeid abundance. However, when the bog was drier, enchytraeid numbers were similar across all treatments and appeared to be insensitive to N.